Wind shear on Gyro with HS

[PTKay]

Gentlemen,

I would be happy to clear a dispute from Australia.

First a quote of a post by Birdy
(forget the spelling, read it to the end, please):

I am going to stick my head on the block with this one.
To Mitch,Paul,Tom, Dick and Harry,to an extent i agree with you on H.stabs.
But,and a big BUT,i don't beleave they stabelise in all conditions!!!
If you close your eyes and imagine a machine flying in strong,even gusty HORISONTAL winds it is easy to see the stab would have a canceling efect on drag variations on the airframe in horisontal gusts.
Now throw in some extreme virtical gusts,on a windy or still day and my minds eye can clearly see how the stab WILL pitch the matchine.
A 2500 fpm up draught=around 50kmh,up.So if you are cruising at 60-70kmh,it is a severe chang in AOA on the airfame,including the stab.[such up draughts and stronger are comone in arid oz,winter or summer.]A strong up draught has miniscule afecte on a machines pitch with no
stab,sure the horisontal gusts do pitch it a bit,but no way near as much as the virticle ones with a stab fitted.I know which ones i would rarther contend with.
PLEASE,close your eyes and try to see were i am coming from befor you shoot me down in flames,remember,i am a simple cow grower,i confuse easly with long winded explenations and technical jargon.[dont worry,i'm not a front verander pilot ether,i can see it in my minds eye and feel it in my cheeks up there]
I feel better now.


For me Birdy is right !

On a fixed wing such an up wind-shear changes the AoA dramatically and leads to immediate stall, so the HS function to pitch the craft down immediately decreases the AoA and prevents stall.

BUT: 1. Gyro cannot stall, this dramatic change of the rotor AoA means noting, just
more lift !
2. The change of gyro pitch does NOT change the rotor AoA, (if the stick is not
fixed to the dashboard...) like on the fixed wing.

So the only effect is swinging the cabin under the rotor !!!

What I am scared of, is that in an extreme case a long, tall tail can hit the blades !!!!

The centrifugal forces on the rotor will keep it flat, and the tail will be pushed
up against the baldes. PLEASE, correct me if I am wrong !

Of course this is a case described by Birdy, big HS on a gyro with no cabin.
Then the vertical Center of Drag from below is far behind the CoG and
we have high pitching moment.
If the area of the cabin and HS, as seen from below, are symmetric against the
CoG than there is no problem.

So, maybe not HS, CLT but the "harmony" as described by Mr. Magni and Greg Gremminger is what counts.

Big, long cabin (tandem) has to be balanced with big, long HS.

Short, no cabin gyro needs no HS.

For short, no cabin gyro long, big HS is DEADLY in an up wind-shear.

I know, nobody here has the cash to do wind tunel tests,
but maybe there is an objective way to settle this dispute
in a civilized way.

Please.

PTKay

[PTKay]

Ctnd.

Of course, such a strong DOWN wind-shear will unload the rotor regardless of HS anyway. Swinging the frame under the rotor won't help
also in this case, I suppose....

Please, comment....

PTKay

[gyromike]

On a fixed wing such an up wind-shear changes the AoA dramatically and leads to immediate stall, so the HS function to pitch the craft down immediately decreases the AoA and prevents stall.

BUT: 1. Gyro cannot stall, this dramatic change of the rotor AoA means noting, just
more lift !
2. The change of gyro pitch does NOT change the rotor AoA, (if the stick is not
fixed to the dashboard...) like on the fixed wing.

So the only effect is swinging the cabin under the rotor !!!

What I am scared of, is that in an extreme case a long, tall tail can hit the blades !!!!

The centrifugal forces on the rotor will keep it flat, and the tail will be pushed
up against the baldes. PLEASE, correct me if I am wrong !



If this situation were to occur in flight, why would the Disc AOA remain the same?

If the aircraft is trimmed out in cruise, and an updraft were to hit it and cause the frame to pitch nose-down, a cyclic input to the blades would occur because the Disc is 'connected' by the trim spring. The tension on the spring would be relaxed allowing the Disc AOA to change to match the attitude of the airframe. It would be no different than if you had a firm grip on the rotor while the pitch-down occured. Even if you didn't move the stick relative to the frame, the disc would still see a cyclic input until the frame stopped rotating.

Let the frame pitch back up, and the reverse would happen. The trim spring tension would increase, applying a nose-up cyclic input.

I can't see an updraft occuring that would be so violent as to pitch the tail up into the rotors...unless you are flying over active volcanos.

[PTKay]

Mike,

thanks for the explaination.

Birdy is not flying over volcanos, but over Australian desert.

It is -5C in the night and + 50C day. So the thermals must be really strong !

Anyway, maybe the rotor will not hit the tail, but the frame will be shaken anyway.

So this is maybe, what for Birdy is "instability" ?

PTKay

[Spaced]

PTKay, thanx for posting a question I was about to ask.
I have been trying to follow this debate, not sure how Im going though.
Asuming that the gyro has the thrust line higher than the vertical CG, neglecting the cabin for a moment, then there would be a nose down moment. Say you correct for this moment with a neg angle on the H stab.
How could this be any less stable than a CLT Gyro. Providing there is sufficient down force on the stab, the moment of the gyro shoud be stable. If you had a CLT gyro with a Hstb set at zero incedence, then surely the gyro would hunt in pitch slightly due to the lower loading on the stab?
Say you get a gust from the front, you woudl get a pitch down moment from the gyro due to the increased airflow over the stab, and the same would apply for the CLT gyro.
Say you get a gust from behind, you would get a pitch up moment due to the reduced airflow over the hstab, the same would be true for the CLT gyro.
Now the up draught/ down draft issue. If hit by an up draft the AOA of the stab would increase, creating a nose down moment, same for CLT. And the opposite would be true for the down draft.
So I guess what Im asking is is there any difference between the two?
It seems to me that as long as there is a stab there with the correct AOA, then there isnt much difference.
Please correct me if Im wrong.

[Doug Riley]

One of the principal purposes of the HS is precisely to make the nose swing into the relative wind. If you hit an updraft, the nose SHOULD pitch down to maintain your prior angle of attack. In a downdraft, the nose should pitch up.

In a gyro with an adequate HS, you should hold the stick still when hitting an updraft. If you do, the spindle will tip forward and the rotor experience a cyclic pitch input and will itself tip forward within a rev or two (that is, a fraction of a second). This helps to maintain the rotor's angle of attack and greatly reduces "ballooning" from thermals. Hold it still in a downdraft and the gyro will do a similar self-correction.

(By holding the stick still and allowing the HS to do its work, you're momentarily converting your direct-tilt control system back to Cierva's original control system. It used a non-tilting rotor head. Cyclic pitch commands were given to the rotor by tilting the whole body of the machine with airplane-style elevators and ailerons.
The old-time Cierva system had some real virtues; among them was the fact that control over the position of the fuselage was not lost in a zero-G event.)

When a rotor hits a gyro's tail in flight, it's not just a matter of the tail having swung up too fast. Instead, what has occurred is retreating-blade stall -- uncontrolled flapping -- caused by loss of RRPM, a very large, rapid cyclic input, or both.

[birdy]

PTKay,Spaced,and anyone else interested!! :)
I'v just read a few pages on this forum and it don't sound no different to the ozzy one.

Alot of oppinions from alot of people,from all parts of the world........FLYING GYROS FOR DIFFERENT REASONS.

I'll repeat my favoret saying....horses for courses.

Different purpouses DEMAND different designes.

I read somewere in this forum "stability dosn't compromise manoverability",sorry, I disagree,I'v flown with and without stablisers on both my single and two seaters,in all typs of weather and I prefer to fly without.
This is only my preferance.
Maybe it's something to do with rarely exceeding 200',not having much option in what weather I fly in,where I fly in it or what I do below 200'.

I NEED manouverability,for the safty of my own neck.

This hole stability argument here in oz started when I first used this computer a mounth ago.
I read alot of oppinions from certain people on what should be the"STANDARD FOR GYRO DESIGEN."This did'nt bother me,but the next 3 words got my blood boiling."ENFORCED BY AUTHORITY".

What I'v been trying to do here is get people to appreciate there is no single gyro desigen that will suit all purposes.
I'll never tell anyone how to build or fly any machine or when to or when not to fly.

I also wont be told by someone who dosn't know me,know what I do or in what type of machine I do it in.

I am not a blind sheep,happily following the leader,simply because he THINKS he knows what is good for me.If,on the other hand ,he has been here and done this for longer than I,then I would listen.


It may appear I don't like irrelivant authority.......your right,I don't.

I am a bit embarrased that my name poped up a few times on this forum,but I appreciate people taking an interest in my point of veiw.

[PTKay]

Birdy,

sorry for citing your opinion on this forum without asking you for permission.

But as you probably noticed on your other forum, I found your arguments very convincing and wanted to get some feedback form the Yankee Gyro World.

It seems, it worked well.

Gald to see you also here on this forum.

Kepp posting also here and give them some of your stories.

PTKay

[Udi]

Birdy is making some very interesting arguments. His main argument is that a horizontal stabilizer makes a gyroplane less maneuverable, and maneuverability is on top of his list of priorities.

I believe that Birdy is technically correct. A horizontal stabilizer adds dynamic stability, which, by definition, is resisting changes in pitch. I think it makes sense that a gyroplane without a stab will maneuver more quickly in pitch than an identical gyro with an effective stab. The stab dampens pitch movements and, for most people, this is a good thing.

The stab also adds static pitch stability. Note that I said, "adds"... A gyroplane with a stable rotor and an offset gimbal rotor head is already statically stable when flown hands off. The problem with a no-stab gyro is that the airframe is not stabilized. This is mostly a problem for people who have not mastered such gyroplanes, AND for people who fly gyroplanes in which a high thrust line offset is making an otherwise stable gyro, unstable (this is mouthful).

In a gyro with no stab, the inexperienced pilot has a hard time keeping track of what the rotor is doing. The horizontal stab is the link that connects the gyro airframe - thus the pilot frame of reference - with the relative wind - the direction in which gyro is going.

In other words - in a gyro with no stab, the pilot flies the rotor. In a gyro with an effective stab, the pilot flies the airframe, just like a fixed wing airplane.

In a gyro with no stab, airframe pitch changes are secondary - they happen some time AFTER the rotor has made a change in the direction of the flight. This is the root cause of PIO.

In a gyro with no stab, airframe pitch angle is a direct result of the location of the rotor thrust vector (RTV). Aerodynamic forces have almost no bearing on the angle of the airframe. In a stabbed gyro, airframe pitch angle is determined by both the relative wind (just like a weathercock), and by the location of the RTV. This weathercocking reaction of the airframe to directional changes is telling the pilot that a directional change has happened - without delay. Thus, no PIO.

Mr. Birdy, I agree that no one should force you or anyone else to fly with a stab. In the US, gyroplanes are mostly built as experimental aircraft and every builder has the final say on how to build it.

HOWEVER - poor gyroplane design has been the number one cause of death among gyroplane pilots. By poor design I mean a high engine thrust line offset, and no stab.

Making a gyroplane CLT is the first step in making it more stable (by removing the de-stabilizing effect of the high thrust line). And a stab is making the gyroplane even safer for pilots who have not mastered the "fly the rotor" piloting technique, which you apparently have.

Thanks for giving us your valuable point of view!

Udi-

[Gordon Gibson]

"However, poor gyroplane design has been the number one cause of deaths among gyro pilots"

Well said Udi, this ties in with another post I made, this is IMHO perhaps the single biggest factor inhibiting the growth of our movement.

CLT and effective HS's. Way to go.
Gordon Gibson.

[Greg Mitchell]

Gentlemen,

I posted this for Sonnyj on the OZ forum, 17th March, 2004. comments please.

G'Day Sonnyj,

CENTER LINE THRUST....CLT.....wherein the design configuration of a gyroplane places the Thrustline on the Vertical Centre of Gravity and ideally has the Center of Drag on the same line. In otherwords, to achieve CLT, I believe you need to get Thrust and Drag coaxial and on the Vertical CofG.

It is said by many in the gyro fraternity that if your thrustline is plus or minus 5cms from the CofG then you have a CLT craft.

CLT designs are said to reduce pilot work load and provide more stability than the more traditional Benson style gyros and others that have a more radically high thrustline.

Persons in the CLT Camp vary in the final analysis of what CLT is.

There has been an attempt to remove the PPO event from occurring and as a result there are those who suggest you need to have thrustline on or below the CofG in order to achieve this.

Much debate continues with respect to CLT and the different design fixes required to achieve Power, Airspeed and G-Load Stability. Test processes have been developed to determine static and dynamic stability for gyroplanes. The suggestion is, that an adequate Horizontal Stabiliser will need to be part of the design configuration. Here in lays one of the sticking points, at what angle of incidence and whether to place the HS in or out of propblast.

A slightly high thrustline "CLT" has different design fixes to one that has the thrustline just under the CofG. Personally, I think there are several divisions within the CLT debate, but efforts to build craft with smaller offsets of thrustline to CofG, in my opinion, is the here and now and future of gyroplane design.

I'm a 'Newbie', so take everything I say in that light. I hope this helps Sonny. Still waiting to hear from Keith re Ply blades project.

Great to have you on this forum,

I don't presume to tell Birdy how to muster his cattle or what type of machine he should be flying.
As a 'newbie' I have it in my head that the use of the word 'ADEQUATE' when referring to HS's implies a HS of the correct size for said craft. Am I correct in assuming that an 'adequate' HS will weathercock craft at the required rate and amount due to its size and placement.......as opposed to say a HS which is undersized to do the job required........and further, if the HS is to Big could this be what Birdy is referring to. I have read about HS's, that the bigger, the better.

In 'bad air' as Birdy calls it out in Central Australia with an oversized HS, I can almost visualize what he's talking about with respect to large thermal up drafts and gusts, possibly causing the tail to have too much over-riding contol of the fuselage.

Udi's post was very helpfull.

Regards,

Mitch

[Mike Jackson]

Udi -

Your description of gyro stability is one of the best reviews I've read. I might add that in para 2 you describe dynamic stability and in para 3 you mention static stability. By strict definition, static stability is the initial resistance, or lack thereof, to a disturbance - pitch in this discussion.

Dynamic stability refers to how a system returns (or doesn't) to its original state after initial disturbance - often measured in terms of damping, frequencies, numbers of overshoots from equilibrium, etc.

How about giving us a little discussion on the offset gimbal.

Nice job.

Mike

[birdy]

Firstly PTKay,jobs cool mate,if I didn't want my oppinions quoted I wouldn't have posted them myself.

Udi,Giday,[Thanks for your understanding]
You said "a new pilot has trouble keeping track of what the rotors are doing."
Well bugger me!! you hit the nail on the head.[I like it when I can draw inteligent comments from inteligent people.It saves me saying it,not beeing understood,and shrugged off as just another simple cow grower.]Why can't the student keep track of the rotors????He was'nt taught to fly THEM.He was taught to fly the STABLE MACHINE.
Udi has stated one of my personal gripes,which I'v never mentioned for the reason above. []


We are all flying a ROTORCRAFT.
The controle of the rotor system,how it works,autorotation,lightness of control input and the RESPONSE LAG,should be the most important things drumed in to student pilots.
ESPESIALY the responce lag.
I reckon this is what brings most people in to PIO.
The first solo goes like this.....
Nerves are out of control
Sitting in your own machine,only you can bring it down after you leave the ground
You have just left the ground,you can't help be excited
You hit your first air disturbance,you react to correct the machine
This is the criticle point.You notice the machion dosn't respond,[instantly],so you correct with more input.
Now your first input takes effect,but your mind is racing and you think it is a responce to your second input.Now your second input takes effect,you respond with a sudden counter-correction[your still nervous],the machine dosn't respond instantly,so you give it more,and so on and so on.

PIO
In all the things I'v heard and read,I'v never heard of responce lag.No amount of stablizing gear will help this poor,panicking barsted.Only thorough instruction can save him from PIO.
Students should be told to FLY THE ROTOR,not the seat.
When it comes down to it,it matters little what the air-frame is doing,so long as the rotors are where they are ment to be.


Paul B. I hope you are reading ALL posts with an open mind,there are some inteligent and articulate people on this forum,not just simple cow growers.

Sorry if this post is a bit slow,I'm not the worlds fastest typer.

[Chuck Irby]

Bravo Greg and Birdy,

You guys are okay. I appreciate your posts, and you have made some good and interesting points. I am, as probably most of us are, really happy that you have joined us here. It's always good to have people with your credentials join us. We can learn from you, and hopefully you can learn from us. But don't get me wrong, I also appreciate the posts of Paul Bruty. Paul has been a real benefit to the forum and many of us individually.

However, even though I have only flown five different gyros, and I realize that there are a hundred other models that I haven't flown, I can not imagine a machine being more maneuvererable nor more stable than the one I am flying, the Dominator single. I also know that there are other machines that are as stable and as maneuvererable as the Dominator. Have you ever tried herding cattle with this type machine?

[Greg Mitchell]

Hello Chuck,

Paul is a friend, see previous post under " I give up." He has done what many around the world have been slow to do or not do at all.
He is a valuable asset to us all.

I look forward to the day when I can get the likes of Birdy and fellow cattle musters ie Miss Barbara Brown (over 3500 hours) to test fly the Monarch with G FORCE suspension. They all love their Soobs or rotax 912's and 914's and may have a problem comming down to a 582, least ways that's what Barbara told me. Nevertheless, it is folk like them who work gyro's for a living that I figure could give some excellent feedback on the Monarch.

There are a lot of Dominator/type craft down under and some excellent manufactures building similar one off machines. I personally believe that the introduction of Ernie's craft to the market place improved safety and the perceptions of gyro's all round the world.

Like I said previously Chuck I am very new to the sport and don't have much experience. I have recently finished 15 hours of official training, racked up six hour in a stabbed Raf prior to starting and have flown in two Rafs with stabs, another craft with high thrustline very low CofG with small pod, which I swore at last years Nationals that I would'nt go up in, but did.
I was surprised at how well it flew and how few stick imputs were required to fly it. Also had the pleasure to fly with Paul in his Hybrid Firebird, very impressive and far more user friendly than the Rafs I have flown. It was blowing thirty knots and most of the time it was all hands off.

It's good to be learning from you all.

Mitch.

[birdy]

Chuck,mate,this is the second time I typ this,I must have touched a wrong button and, POOF, the screen was bare,so I'll try again.

I don't have many credentials,I just fly a gyro,apparantly in an unorthidox way,in central oz.
This is the main reason I will always dissagree with Paul on some topics.He dosn't know what I do,or the conditions I do it in.Same as alot of ag gyro pilots in oz,and because he dosn't know he should'nt be telling any ag pilots what to fly or how to fly it.

I admire Paul for his pasion and enthusiasm for gyros and his quest for a stable machine.But some people don't need a stable machine,this is a point I have trouble getting through to him,he won't accept that things are different.
Paul holds you yanks in high regard here in oz,deservidly so too,you have the same objectives.
Am hoping you could explain to him the horses for courses motto,he won't listen to simple cow growers.He may listen to you.

If paul was'nt an instructer I would'nt give a sh.t what he did,but he is and I worry for the students who may want to fly in an "unorthidox" way.

When it comes to mustering Paul knows stuffall,and he should inform his students so.
If he wants to instruct in a limosioun with cruse control,the student should be aware that that is all he is capable of flying.To not make this clear to the student is very irisponsible.

[Udi]

Much debate continues with respect to CLT and the different design fixes required to achieve Power, Airspeed and G-Load Stability. Test processes have been developed to determine static and dynamic stability for gyroplanes. The suggestion is, that an adequate Horizontal Stabiliser will need to be part of the design configuration. Here in lays one of the sticking points, at what angle of incidence and whether to place the HS in or out of propblast.

A slightly high thrustline "CLT" has different design fixes to one that has the thrustline just under the CofG. Personally, I think there are several divisions within the CLT debate, but efforts to build craft with smaller offsets of thrustline to CofG, in my opinion, is the here and now and future of gyroplane design.
.
.
.
.
.

I don't presume to tell Birdy how to muster his cattle or what type of machine he should be flying.
As a 'newbie' I have it in my head that the use of the word 'ADEQUATE' when referring to HS's implies a HS of the correct size for said craft. Am I correct in assuming that an 'adequate' HS will weathercock craft at the required rate and amount due to its size and placement.......as opposed to say a HS which is undersized to do the job required........and further, if the HS is to Big could this be what Birdy is referring to. I have read about HS's, that the bigger, the better.

In 'bad air' as Birdy calls it out in Central Australia with an oversized HS, I can almost visualize what he's talking about with respect to large thermal up drafts and gusts, possibly causing the tail to have too much over-riding contol of the fuselage.



Mitch,

Arguing on how to design a stable gyroplane is like arguing which beer is best. You may like a Foster, and I like Corona. There is more than one way to skin a cat. The soon to be published LSA standard for gyroplanes does not tell manufacturers HOW to build a stable gyro. Rather, the standards describe some tests the gyro has to pass in order to prove it is stable. Fixed wing aircraft and helicopters have similar standards.

You can design a perfectly stable gyroplane that has a high thrust line, a low drag line and a stabilizer. Stab in the prop wash or not – it does not matter! At the end of the day, only a flight test can prove if a gyro is stable - as per some acceptable standards, or not. Let the designers to their job and let the test pilots give the verdict. But there must be some acceptable standards for gyroplane flight characteristics. All other aircraft have them, why not gyros?

The reaction of a stabbed gyro to vertical gusts is no different than the reaction of a fixed wing. All fixed wing aircraft are built to weathervane into the wind. This is the definition of stability – the return of the aircraft to its last trimmed condition. I have flown the Magni M-16 in a fairly blustery day. This gyro may have the largest stab out there. I can tell you it handled the gusts like a champ. I didn’t have to do a thing, the gyro simply corrected itself and kept a constant airspeed. I have also flown the AAI modified RAF in Arizona thermals in the summer – also a champ.

I can understand people like Birdy who are used to flying a stabless gyro in all weather conditions; a stabbed gyro would feel un-natural to them. But for new pilots, there is no reason for them to go through the long and risky learning curve Birdy had to go through to become proficient. They can have the benefit of better and safer designs.

Udi

[Udi]

Udi -

Your description of gyro stability is one of the best reviews I've read. I might add that in para 2 you describe dynamic stability and in para 3 you mention static stability. By strict definition, static stability is the initial resistance, or lack thereof, to a disturbance - pitch in this discussion.

Dynamic stability refers to how a system returns (or doesn't) to its original state after initial disturbance - often measured in terms of damping, frequencies, numbers of overshoots from equilibrium, etc.

How about giving us a little discussion on the offset gimbal.

Nice job.

Mike


Mike,

I didn't want to get too technical with regard to static and dynamic stability. The important points are that:

1. Without a stab, there is no dynamic stability, thus no damping. The only damping mechanism in a stabless gyro is the pilot, and an out of tune pilot may cause the oscillations to diverge. We call this a PIO.

2. Without a stab the pilot has no immediate feedback from the rotor. Birdy's description of a PIO progression is accurate. An effective stab makes this problem much smaller. Aerodynamic feedback.

Offset gimbal head. I wish I had a drawing. This mechanism is basically equivalent to a "CG in front of the center of lift" in a fixed wing aircraft. A higher G-force is forcing the rotor to pitch down and lower G-force is forcing the rotor to pitch up. Your typical G-force stability mechanism. There are two problems with this mechanism - one, it works only with a floating stick. Two, it has a limited range (due to cyclic stops). This is another good reason to stabilize the airframe.

Udi-

[birdy]

Udi,to your last paragragh,you are correct in my mind,so long as the student UNDERSTANDS what will happen if he is unlucky enough to get caught in rough weather.
BTW,It wasn't a risky learning curve,I was lucky enough to be trained in a similar machine to the one I bought.I was taught to fly the rotors.

Lucky me ay.

[Greg Mitchell]

Udi,

Dr Houston's report re; thrustlines being no more than 5cms plus or minus. I find this to be a dilema. Greg Grimminger theories suggest thrustline needs to be above CofG with neg angle of attack HS. And you and others seem to agree with this, (if I am wrong, I apologise), BUT many in the CLT Camp (and you do talk the CLT thing), suggest the thrustline needs to be on or just below the CofG. Dominator, SparrowHawk, Butterfly/Monarch. I ommit the Aussie craft simply because I don't have enough detail/specs to comment on them, though I would think that Owen Dulls and Murray Barkers craft designs may fall into this group also. I don't know.

Anyway, there is a bloody big spectrum there in that plus or minus figure. 2" or 2 1/2" doesn't seem like a hugh range, but when we look at all the variables, your CLT and my CLT are definitely different. You could help us all out by telling us who you think is most correct given this CLT thing seems to present more questions than answers.

The guys who are looking to get thrustline on or below are trying to remove the PPO effect given rotors are unloaded for whatever reason.
Whilst Greg and the PRA seemed to espouse CLT sometime ago, there appears to have been a very definite shift by Greg and perhaps the PRA toward this Airspeed, Power and G-Load Stability only being attainable with slightly high thrustline and Neg angle of attack HS.

This may account for some of the rank and file clubs in the US wanting to distance themselves from the PRA. Greg makes a powerfull arguement, intelligent and articulate. BUT is he right, or simply trying to justify a high thrustline product??? Everyone, manufacturing or distributing craft will claim there's is the way to go. And yet I am fighting this temptation with respect to the Butterfly/Monarch. I don't want to sell them, they should do that on their own merit, proof is in the testing.....RIGHT.

Thanks Paul,

This I posted recently on OZ forum. I am aware of the great work done by many to get a set of tests in place to assess static and dynamic stability. I agree the testing will verify. I'm really looking at the attempts of those designers who have endeavoured to eliminate a PPO event, primarily occuring on high thrustline low CofG craft. Udi I have read much of Greg Grimmingers material and have communicated with him also. He has been of great assistance to me. So when Greg says you need a slightly high thrustline with a neg angle of attack HS in order to be Airspeed, Power and G-Load stablility, I wonder where that leaves all the rest.

Udi, could you help me fully understand the HS adequacy issue.
The Magni has a lot of frontal plate surface area and needs a much larger HS to have the craft weathercock. But it is a balance is it not?
In other words, if you placed a HS which was very large on a open frame single seater, isn't it possible that it could be too effective in a wind shear situation???

I have flown in a gyro which had a very high thrustline very low CofG and drag and I was surprised at just how comfortable it was, requiring very few stick imputs. However, I'm not certain that it would pass the stability tests and it would PPO in a heartbeat given the right/wrong set of circumstances. I don't know if I call that stable.

I am all for safer, more user friendly craft with HS's.

regards

Mitch

[stuart]

I'm not familiar with the argument for a high trust line/neg incidence HS mentioned in this thread by Greg Mitchell; what is the trust of it? Thanks, stuart

[rehler]

Mitch,

I'm with you. I have also read Greg's article in PRA Rotorcraft magazine, and it sound very logical (to have a little high thrust line along with negative HS pitch). But I am concerned that he may be trying to justify his Magni product. In the past Chuck Beaty seemed to clearly explain how real CLT is best. At lease we know that high thrust -vs- CG is not good.

I have just rebuilt my gyro to get exact center line thrust with me and 1/2 full fuel. It took a lot of time and work. Now, I am not sure it was the right thing to do.

I guess until this is sorted out I'll just test fly it as is and later if I find that a little high thrust is better I can raise my engine up a 1/2" or so.

I would really like to know what is the very best - Zero, up 1/4", up 1", etc.?

[raghu]

Birdy is making some very interesting arguments. His main argument is that a horizontal stabilizer makes a gyroplane less maneuverable, and maneuverability is on top of his list of priorities.

I believe that Birdy is technically correct. A horizontal stabilizer adds dynamic stability, which, by definition, is resisting changes in pitch. I think it makes sense that a gyroplane without a stab will maneuver more quickly in pitch than an identical gyro with an effective stab. The stab dampens pitch movements and, for most people, this is a good thing.

Udi-



Udi and birdy,
I am afraid your conception of stability and maneverability is incorrect. Here is why:

The rate of pitch change or roll change of the airframe is of little concern when we talk of “maneuverability” ( particularly in a gyro). When we say we need more “maneuverability” what we are trying to say is we what to able to change an aircrafts flight path from one state to another rapidly. For example, from straight and level to a steady climb, or from straight flight to a turn. This is what a pilots needs to save his neck or as Birdy put more eloquently *$#@! .

The only way to change the flight path is by applying a force at the CG (Newtons first law). This force would need to be upward for a pullup, and side ways to make a turn. This force in a gyro is provided by the rotor, while in the case of an airplane by the wing.

Now here is why most of the misconception vis-à-vis stability and "maneuverability" comes in. In a FW airplane the only way to get the wing to provide the extra force to change the flight path ( i.e. changing the lift) is by pitching or rolling the airframe. So before one can change the flight path you have to pitch or roll the airplane. And as we are all aware stability abhors pitch or roll digressions and impedes them, thus taking longer to apply the force needed for path change.

In a gyro, things are a little different. The rotor provides the force and we have complete control in vectoring it in pitch and roll. While the pitching of the airframe will and can be used to augment the vectoring we do not really need it, all the vectoring we need can be provided by moving the cyclic control ( the limits of +-9 degrees is well over what you need in all flight regimes- the extra margin is really for getting the rotor to flying speed during take-off). Of course the rotor will not respond instantly, but the rate of change is independent of gyro stability- it depends on the rotor MOI and lift/drag coefficients. Bottom line, making the airframe of a gyro stable by putting a HS or in any other way has no effect on the "maneuverability". Note, strictly speaking what I have described as "maneuverability' is really is agility.

Cheers
Raghu..

[pwendell]

Raghu,

You made the point I was about to, just let me put in slightly different language.

As far as I understand it, in a Gyro we are always 'flying the rotor'. The airframe can affect the rotor's position only by means of the trim spring, friction in the cyclic, and the pilot's hand, if he/she is holding the stick firmly. A dynamically stable airframe is one whose attitude changes will follow changes in rotor position, albeit with some finite delay. A statically stable airframe is one that does not depend on rotor thrust to balance the other static forces that are being exerted on it, and will, as a result, remain in a stable attitude even when rotor thrust is removed.

If these summaries are true then a statically stable airframe should have no effect on the maneuverability of the gyro -- static airframe stability has on effect on the rotor. It should also follow that a dynamically stable airframe will only limit maneuverability to the extent that the lag in its response with respect to the rotor is transmitted to the rotor, primarily through cyclic friction (as in the Magni gyroplanes) or through the pilot's firm grip. With minimal cyclic friction and a light touch, the dynamically stable airframe should only have a significant affect on gyroplane maneuverability when it lags behind the rotor so much that it takes up all available cyclic travel.

If all of this is true, and my understanding may very well be flawed, then a stable airframe in and of itself, need have little or no affect on maneuverability. Other design features such as the amount of friction in the cyclic and the rate of attitude change of the airframe with respect to the rotor, along with piloting skill and technique, e.g. hamfistedness, will determine the degree to which the airframe's attitude affects the rotor.

[mceagle]

Gidday fellas

I do believe that a stable airframe does have an effect on gyroplane maneuverability - it improves it.
If the gyro airframe is always pointing directly into the relative airflow, then the joystick is always in the mean position giving you maximum deflection in any direction. In some cases it may not take much movement to initiate the maneuver but it takes double the control movement to pull out.
Gyroplanes rarely fly perfectly balanced because of load and power considerations so it is definately an advantage to have the maximum control displacement available to you. It is very common to see a gyroplane operating close to one of its control limits and without a stabilized airframe there is little on no margin for error.

[birdy]

Now we are getting to the guts of my argument.

I appreciate all responces,and points of view,but I still say H.stabs do impead manoverability/agility or whatever you whant to call it.

Please,keep your minds open,and try to understand were I'm coming from.I know I have difficulty putting my thoughts on the screen,but I'll have a go.

Firstly,I NEED manouverability,not only to do the job but also for the safty of my neck.
I do 99% of flying below tow hundred,most of the tight turning at both high and low speeds is 10/20' above tree top or the ground.To do this stuff safly you NEED a machine that is suited.I'v flowen both with and without stabs,I know the difference in the handeling characteristics ,and when you turn down wind with only 20' between your ass and the deck,you need 100% control of the rotor.What you don't need is a stab interfering by applying extra work load on your control.
When you are at 300',it dosn't matter if a down draught steals 50' from you,it dose matter at 20'.

The gyro airframe is hanging like a pendulum from the rotor bearing bolt.When you are doing a 180 degree turn,with a 90 degree bank on the rotors,the mast is paralell to the ground.The centrifical force will keep the COM pulling directly opposit the lift. which is paralell to the ground.Because you are holding back stick and on full power,you are, in effect,in a steep climb situation,only horisontally.
The difference between climbing horisontaly and virticaly is that centrifical force replaces gravity ,and in a steady virtical climb,there is 0G,in a tight turn you have positive G.To hold +G in a climb would have you doing a loop.A 360 degree turn with90 degree bank is only a horisontal loop in respect to the rotor discs attatude.

Now,anything that prevents the airframe from swinging freely around the outside of a 90 degree bank is going to increase the diamiter of the turn circle.[Impead manoverability]

A steep,continous turn is the same as continualy initiating a climb,:ie,a loop,now, we all know what happens when we pull back on the stick,the nose INITIALY wants to swing up,but the H stab prevents this swing going too far.
When you pull back stick at 90 degrees to the ground,you WANT the nose to swing up,to be able follow the rotors freely.
Remember,you are 20' from the ground,turning down wind,you are dropping,you are allready on full power,you have two options.Ether streighten back in to the wind and gain a few more feet alt or increase the load on the rotors thereby stopping the sink.You can only take the first option if there isn't a tree in the way.

Have used this technique many times to evade the ground,and I can tell you,the slight impeadence to manouverability that is caused by the H stab would have been enough to bring me unstuck.

[Chuck Irby]

Ken Rehler, please keep us posted re the results of your tests. This should prove to be of real interest to many.

[Chuck Irby]

Birdy, Mate,

After carefully reading your last post, I have to admit that you drive a very hard bargain. What you have stated, rather eloquently in fact, actually makes sense to me. I can definitely see that there could be times when a horizontal stab could keep you from maneuvering as you might have the need to do.

In addition, I can visualize a time, especially when 15 to 20 feet above the deck, that a down draft could put you on the deck sooner with a horizontal stab than without one.

Birdy, please post a picture of your machine and describe what you have for an engine, gear box and reduction ratio, prop and blades.

[RHerron]

Birdy,

There is no loss of response with the addition of a proper tail on a gyro. If you have flown a gyro for a long time without proper stabilization, you have mentally adjusted to the overly-sensitive, over-shooting machine and are quite content with it.
That doesn't make it safe for someone else. I too learned in stabless gyros and lived to tell about it.
I wouldn't go back to that on a bet.
What you have experienced when you installed a tail was that the machine did what it SHOULD instead of what you were used to.
I challenge you (or anyone else) to prove that there is any difference in response time when you add a stabilzer.
You said yourself that the pilot "flys the rotor". That doesn't change.
When you change the angle of rotor incidence, the craft responds, tail or no. The huge difference is that the aircraft now ONLY responds to the pilot's exact command and is not overruled by an unstable airframe. The actual response is quicker with a tail, ie., no lag, no over-shoot.
It is easily perceived as "less responsive" when you are used to flying from an unstable platform. Been there, done that and won't go back. What you have is a "touchy" aircraft that would quickly kill a newbie. Fly it if you like...but don't claim it is better.
When I first started testing my aircraft I had a very highly respected person in PRA warn me that an updraft would "blow the tail into the rotor".
Just a little more study into the physics of this and that thought will disappear.
Doug, I still have a machine with aerodynamic controls. I couldn't sell the idea to anyone initially but now I see new interest. That "no loss in low "G" was my theme.
They fly really nice with this type of control and as I've preached all along, are more forgiving. The downside is very lowspeed flight without engine power... The controls become mushy but funtional. With engine power on, all is good.
BTW I am talking about a gyro with 20 square feet of horizontal tail surface mounted on a 10 ft. arm.

[Udi]

Mitch and Ken,

I do not believe that a high thrust line is a requirement for having a positive airspeed stable gyroplane. I have heard Greg’s arguments a few times and, with all due respect for Greg, I do not accept these arguments. Greg's argument is (and I hope I am doing it justice) that a negative pitched stab is required in order to have an airspeed stable gyroplane. And in order to have a negative pitched stab, you also want to have a slightly high thrust line, so that the high thrust line nose down pitching moment cancels out the negative stab nose up pitching moment, which is a by product of the prop blast hitting the stab.

I don't agree with this argument simply because the gyroplane’s teetering rotor is providing plenty of airspeed stability. The airframe does not have to be airspeed stable. The airframe may be airspeed neutral. A stable teetering rotor has a very strong airspeed stability, and that is taking care of the whole gyro.

Also, even if you had a CLT machine and you wanted the stab to have a negative angle of incidence. What's the problem?

Now I said before the proof is in the pudding. Take the Sparrow Hawk for example. This gyro is a true CLT, with a zero angled stab. I have flown the SH up to 100 mph, and I can tell you it is as stable as the Magni. I am not a test pilot, but Jim Mayfield has plenty of hard data to support my armature observations.

Please don’t get me wrong. I think the Magni gyros are excellent machines. I have flown the M-16 with Greg, and I was thoroughly impressed. I think this is a very refined machine. I like the Magnis, and I like Greg. However, I believe the Magni would have flown just as well with a true CLT configuration and no angled stab. One great thing about the Magni gyro is the fact that they are a low profile machine and yet so stable.

From a stability point of view, I don’t think it really matters if you have a CLT machine, or a HTL machine with an adequately pitched stab, as long as the sum of all the moments about the CG is small relative to the power of the stab. A large and effective stab will stabilize machines that are not exactly CLT. I don't know how many inches or centimeters of offset are acceptable - only flight-testing can tell.

From a PPO point of view, I would want the sum of all the moments about the CG to be zero or slightly nose up. This will ensure the gyro is not pitching in the wrong direction in the event of rotor thrust loss.

Mitch, you've asked what is the optimum sized stab, and can a stab be too large. I guess what you meant was, can a too large stab make a gyro unsafe under certain conditions. I think the answer is no. Look at the early Autogiros. They had a huge tail volume. Ron Herron is the authority on Autogiros and he can probably give a better insight into this question, but I don't believe they had such a problem.

I think the stab should be large enough to make the gyro statically and dynamically stable. Period. Just like any other aircraft.

Udi
p.s. - now I see that Ron has already responded above - duh...

[birdy]

Chuck,I'll see what I can do for the photo,that's the wifes domaine.

Herron,thanks for a constructive reply,but I never said that I would expect a newbe to fly a machine like mine,I know it si twitchy on controls,which is the way I need it to be.Also I'v never argued against stabs,CLT or anything eles the general gyro scene sees as a safty issue,what I'v always said,will always say espesialy here in oz is that these issues don't always apply to AG pilots.We don't need stability.
Your term,"over shooting machine" describes what I'v been trying to say for ages,and yes ,it is just what I need for what I do.

I also have no need to prove anything to anyone,I'm not selling anything.I have proved it to myself,and i'm the only one who flys my machine.

What I mean by "fly the rotor" is it matters not what the machine is doing,only the rotors .When you are working close to the ground,in strong turbulance,the machine is tossed around in yaw and pitch,this tossing around [Which is exaggerated if a stab is fitted] is applying extra inputs to the rotors ,which I don't need.In this situation I fly almost free stick,applying inputs only when I want to chang.



Please,everyone,I'm not telling anyone that I am right,only right for MY application.

Alot of people underestimate the ability of the gyro,but when one learns to fly it to its pertentual,you realise lust how manuverable ,controlable and stable it can be.

Why eles would I use one for what I do.

[Udi]

Raghu,

I think your comment is correct only within the limits of your assumptions. Your main assumption was that we never have to use the cyclic all the way to the stops. I think that in Birdy's case, this assumption is incorrect.

The main difference between a sharp pitching maneuver with a stabbed gyro and one without a stab is that, in a stabbed gyro, the stab is resisting the RTV pitching moment about the CG. In a stab-less gyro, only the airframe MOI is resisting the RTV pitching moment.

For example - lets say I am entering a sharp turn and pull the stick all the way back to the stops, and hold it there. In a stab-less gyro, the RTV, having moved a few good inches in front of the CG, is spinning the gyro airframe quickly nose up (i.e. into the turn). Since I am holding the stick all the way back, the quickly pitching gyro is feeding back into the cyclic, accelerating the rate of turn.

Now, in a stabbed gyro, the stab is resisting the RTV pitching moment both due to static and damping moments. The rate of turn will thus be slower.

Although I don't recommend for anyone to fly a stab-less gyro, I have to agree with Birdy's argument that a stab may make a gyro less agile for some people.

Udi-

[birdy]

I have a simple request,
whenever you use abbreviations [PPO,CLT and such],could you please identify what the mean.
I,along with alot of newbes have no idea what you are saying.

Udi,what is,RTV and MOI.[While I appreciat and agree with your comments,I dout I have ridden the left or right stops while flying,but have been on the back stop plenty of times.]

[birdy]

I stuffed that up.

Anyway,as I was saying,while I don't ride the stops in flight,I probably would be closer than most.But because I don't fly a stab,the inputs are not very big.I only iniciate the turn with the stick,and because the machine can swing freely,the movement of the machine means I don't have to put in large stick movements to get a large responce.

Dose that make any sence?????????????

[Greg Mitchell]

Birdy,

RTV.....Rotor thrust vector.

MOI.....Moment of inertia.

Mitch.

[Greg Mitchell]

Udi, Ken,

For me Udi your last couple of posts have been spot on, I agree. I have communicated with Jim Mayfield and thankfully he took the time to respond on more than one occassion. I am sure the likes of the Sparrowhawk, Butterfly/Monarch are pretty much on the money.

Your explanation of the CG getting ahead of the RTV, feeding back and thereby further accelerating the process was very clear and easy to visualise.

Like Ken, I am just trying to see what works best in most situations and given the current thinking from those that do design and build gyros, I really like what I see happening .....moving forward.
Let us know how she flys Ken with the changes you have made.

Regards,

Mitch.

[Aussie_Paul]

Does anyone have access to putting the "Glossary of terms" that Greg G. was formulating, onto this forum?

Aussie Paul.

[MGman]

Paul - Greg Gremminger has posted a good set of definitions on the mangi web site
http://www.magnigyro.com/USA/features.htm

Dave Bohler

[MGman]

Sorry - my fingers got twisted - that's the magni site

Dave B

[Aussie_Paul]

Click on this link Birdy.


http://www.magnigyro.com/USA/feature_articles/GyroTerms.pdf

Aussie Paul.

[birdy]

Gees Paul,that's what I call information overload. ???

Bit too much for my meager brain power to absorb,gess I'll just have to keep refering back to that looooong list. :-[

[Greg Mitchell]

Birdman,

That site of Greg's is the one I mentioned with all the excellent articles. Really helpful in getting your head around all the concepts and tech talk.
Greg is always happy to answer emails and discuss gyros. You might raise the HS wind shear stuff with Greg and see where he's at with it.

Cheers.

Mitch

[Spaced]

birdy, do you know what the thrust line on your machine is like.
ie, when you apply power and fix the stick which way does she pitch?
Just thought this might help with the discussion.

[birdy]

Spaceman,can't say for sure,up a little I reckon,I'll have to take notice when I go for my next blap.
My thrust line LOOKS high,middle of me back I'd say.
But I don't reckon it's not to high because I know it dosn't nose over when power is increased,but I'll check anyway and let you know.
Probably not tomorow because we have water problems here at the moment,and me cows water supply comes before anything.

BTW,I finished the suspension on the RAF today,feels good on the ground.

[gyrogreg]

(Sorry ‘bout the length of this post – I’ll s-plit it up into a c0uple of posts – read through it if you like!)

Boy, what a wonderful thread! I am so happy to see more and more people presenting such learned and thoughtful explanations to help the gyro community learn about flying safer. Only when we can improve the safety record of gyros will the industry truly grow to its full potential. There is safety in knowledge and understanding, and many of you contributing so wisely to these forums are influencing the saving of lives and safe growth of this sport we love.

I’d like to make some comments – mostly reinforcement of the points I see so eloquently made above in this thread:

Maneuverability is not affected by stability of the gyro. That is what is so beautiful and unique about gyros – they do not have the maneuverability compromises of a fixed-wing, but they can have at least, or even much more stability than a fixed-wing!!! An additional point as to why a well stabilized gyro can be more maneuverable is that the airframe provides a reliable and precise reference from which the pilot can make his/her maneuvering inputs. In a well stabilized gyro, the airframe tracks nearly perfectly with the flight path and provides the pilot with a very accurate and precise reference from which to make a precise maneuver.

Maneuverability IS affected by the MOIs of the airframe and rotor – larger and longer gyros may have less maneuverability and even more stability – but even for those, maneuverability is exceptional for aircraft of that size.

For a well “harmonized” stable gyro in normal flight, there is no requirement for the pilot to do anything to counter outside disturbances such as wind gusts – even the largest vertical wind gusts! The reason for this is that the gyro inherently and automatically and without need for pilot input or intervention, can do exactly the right thing to correct for that disturbance. That means the pilot does not have to react or do anything to counteract an external, “uncommanded” disturbance – the stable gyro does it all!! That means the pilot uses the cyclic control only for his/her “commanded” maneuver inputs. And those cyclic “commanded” inputs have the advantage of a very accurate and precise airframe reference with which to make those maneuver inputs – the airframe is ALWAYS tracking and pointing exactly in the direction the aircraft is moving in the air! This is for WELL stabilized gyroplanes only!

(One small caveat to the pilot does not have to do anything to correct for an “uncommanded” disturbance – when close to the ground, such as in a landing flare, when it is not desirable for the aircraft’s automatic disturbance reaction to drive you to the ground – the pilot will have to override the aircraft’s inherent stable response to avoid touching the ground and to accomplish a nice soft touchdown even in gusty winds. But, the pilot’s cyclic control is probably 5-10 times more effective at controlling the aircraft’s flight path than any wind transient is – because the pilot can directly and immediately re-vector the rotor through the very powerful cyclic control – this is a real beauty of gyros – the pilot has much more control power than any outside disturbance can produce!)

[gyrogreg]

I grant Udi the argument that the rotor may provide some of the static pitch (airspeed and g-load) stability that a down-loaded HS can provide. However, I think it is very possible that a poorly configured HS – one that is forced to provide a lot of statically destabilizing up-lift, can override those stabilizing properties of the rotor and even of the offset gimble. But, that can only be known by testing the final result. So, it may be that the rotor stability characteristics can provide the static stabilities that would not be otherwise provided by a down lifting HS. The SH seems to be verification of this concept – and I agree that is good – any gyro that is stable is good, no matter how that stability is achieved! But let me suggest there are possibly some other rotor issues also that might enter into the whole static stability equation. Rotor blades that do not have enough reflex have a tendency to create negative static airspeed stability – the faster you go the more the stick pulls forward to want to go faster. Some of the first couple of Dragon Wing rotors had this scary effect – I know I had a pair of them which I bought from Carl Schneider, who sold them because he did not like that characteristic! Ernie very quickly corrected that condition and my several other Dragon Wing blades had very good flight and stability qualities. So Udi, I grant you argument that CLT with no HS download can still be statically stable – with a lot of other qualifications! Final flight testing tells the total results!

One of my reasonings for desiring a slightly high prop thrustline and the resultant “balancing” HS download is that this can be “tuned” to provide good “Power Stability”. Poor power stability can offset the cyclic stick movement range and can cause the airframe pitch (and trimmed airspeed) to change quickly and radically with sudden power changes – such as a thrust stoppage. This can make landing power adjustments difficult for the less experienced, but, of more concern with very low prop thrustlines, it can cause a rapid nose drop upon power stoppage, possibly resulting in pilot over-reaction (start of PIO) or even, if severe enough an immediate buntover or precession stall! A very low prop thrustline forces the nose artificially high – a very good thing to do for g-load stability. But, this nose-high attitude forces a large up-lift of the HS at the same time – static airspeed destabilizing! That is not so bad, in fact that is a very pleasant and stable aircraft to fly in that condition – and good with gusts! But, upon a sudden power loss, the nose immediately begins to pitch down from the loss of nose-up prop thrust, AND from the up-lift on the HS. If the pilot does not exercise proficient reaction, the nose will continue to pitch down until the HS reaches a down-lift AOA. But, this condition for a level HS and no prop thrust is with the CG passing to the rear of the RTV at the same time. That puts the g-load stability negative – with the rotor thrust decreasing rapidly – the possible start of a progressive buntover!

I’m not badmouthing any particular machine configuration – again the proof is in the flight test results! To avoid such issues completely, the machine flight test should verify that the gyro provides all three static stabilities – G-load, Airspeed, and Power static stabilities! If flight test confirms there are issues or deficiencies in any of these stability factors, that should be considered in the limitations within which you fly that gyro! (G-load stability over the full flight envelope is probably the most important characteristic – this is what can readily lead to a buntover)

I have always commended the Dominator style, low prop thrustline for great improvements in gyroplane stability and safety. I’m not at all saying any gyro is unsafe – and Ernie Boyett should rightfully receive the credit for probably saving the most number of lives in the gyroplane sport of anyone else. His influence and demonstrated stability improvements with the Dominator have tremendously influenced the growing understanding of the important safety issue of stability. For any gyro configuration, I am only encouraging knowledge of these stability and aerodynamic issues so that the pilot may know and understand the limits of his/her machine and the limts of the pilot’s proficiency in that machine!

[gyrogreg]

For you technical glutton types, here’s another perspective on the various static stability requirements. A good control system – for anything, such as a remote control crane system – is designed with several “feedback loops” to provide precise control of the device or system. Engineers will provide the control system with “harmonized” feedback loops for POSITION, RATE and ACCELERATION. By harmonizing these feedback loops, a very precise and stable control can be accomplished. This means it moves a quickly as possible to the new “commanded” position – using the position, rate of movement (velocity) and change-of-rate (acceleration) feedback to provide the quickest, and most precise response. A control loop that only has position as the feedback loop may not be very quick, or overly quick with a lot of oscillation or searching for the proper point. The second and third order feedback loops of velocity and acceleration help to overcome the delays and control complications of friction, inertia, etc.!

The pitch control of a gyro is no different – it is a control system with feedback loops! Stick position provides the POSITION (first order) feedback loop – the rotor tries to settle out on the new position of the spindle. The HS provides the VELOCITY (second order) feedback loop – the closer the airframe (and spindle) get to the desired airspeed (airframe and rotor attitude), the less powerfully the HS drives the attitude to that desired attitude. G-load stability (pitching of the airframe due to its vertical acceleration) is the ACCELERATION (third order) feedback loop. Just as in an engineered remote crane control system, these three feedback loops can be harmonized to provide the most precise and quick and stable (not oscillating and not overshooting) response to gyroplane cyclic inputs (both wind disturbance – un-commanded, and “commanded” pilot inputs!) To not have either or both airspeed or g-load stability suffers a less responsive and less accurate and possibly oscillating and over-shooting control system for the gyro. It may not be necessary to have all three feedback loops, but, well “harmonized” three orders of control feedback loops can provide exceptional controllability in a gyro!

[gyrogreg]

The ASTM standards that are being developed for the U.S. LSA rules (and available for use by other “authorities”) does require these three orders of static stability – and a minimal degree of dynamic stability. These criteria have proven over the years in other aircraft to provide control characteristics that are readily learned and safe for the normal (“standard”) human pilot. These rules or standards do not necessarily apply to you. They apply to manufacturers who might wish to sell gyroplanes under the advantages of meeting an accepted “standard”. In most countries, you are free to fly any machine you want. You may elect to fly a machine that is totally unstable, or only stable to some degree. But, we are hoping that this new gyroplane standard influences even those who don’t want to be regulated, but do want to be safe, by providing guidelines for certain safety issues in gyroplanes. Even within these “standards”, the manufacturer and you have flexibility to provide perhaps lighter, and more nimble gyros, heavier and more care-free flight characteristics, etc. – whatever they think their competitive nitch is. These three orders of stability control characteristics can be “harmonized” in many different ways to create the control “feel” that particular customers might desire. People who have flown both the Magni and the SH say they do “feel” different, even though they may both as equally meet the stability requirements of the standard! Even gyros that meet the stability of the criteria in the standard can spread over a wide range of control feel and maneuverability. For instance, all stable gyros will provide some cyclic stick resistance to extreme pilot commands, but rotors can be designed with lighter sticks and quicker responses, while still allowing the gyro to meet the required stability characteristics. Others, such as Magni and SH may choose to provide very heavy stick “feel” that might appeal to pilots who are more comfortable with a machine that helps prevent inadvertent over-control.

[gyrogreg]

Glossary of Gyro Terms: Right now the best place to get this may be on the Magni Website. It has also been posted on some of the conference forums, but I’ve lost track of where. It has also been posted on the PRA website, but that website is currently undergoing a revamp, and the Glossary is not currently linked on that site. The glossary was developed by a number of contributors for the purpose of improving communication and knowledge and understanding of technical and training issues among the gyro community – promotion of safety in knowledge! This is not intended to be a Magni document, but we make it available on our website because we have access to that medium. Please feel free to publish or distribute the glossary in any medium you would like.

[gyrogreg]

Promoting Magni. I am always cognizant that many might think my technical articles are intended to be self-serving as a Magni promoter. I try not to do that. The Magni gyros are too expensive for me to have a real financial stake in their promotion. I utilize the Magni as a demonstration tool to show what a gyroplane can be designed to do – stability and control, maneuverability ,and safety-wise. I try to refrain from promoting only Magni configuration and characteristics. But, the Magni gives us a “standard” against which to compare other gyro characteristics – and to verify alternative concepts and theories. There may be even higher “standards” achievable! So, I maintain that there may be a large number of configurations that can be designed to meet the desired safe stability characteristics – certainly the SH and Magni are very different configurations, but they both meet the stability criteria of the gyroplane ASTM standard! But, in the interest of true knowledge, and not voodoo “cookbook” sweeping solutions, I feel I must present the full technical picture when misleading misconceptions tend to favor one configuration at the discouragement of other perfectly acceptable configurations. Perhaps there are configuration favorites and alternatives, but “popular” and simplified conceptions should not limit the many alternative configurations probably available for gyros! I sometimes wish I could completely avoid discussing specific configuration issues – thrustlines, HSs, etc.) but to prevent a misleading and incomplete knowledge base and “cookbook” solutions, I feel we sometimes need to present the full engineering issues involved in designing to stability criteria. I don’t say one or the other configuration cannot meet the stability criteria, I simply point out that you can’t eliminate one configuration type because it does not fit a popular “cookbook” solution. And, to rely on some popular “cookbook” solutions, might indeed encourage false confidences in recognizing limitations of you and your gyro! The Magni, I think, provides all of us with the verification that other alternatives may be just as valid as some other combination of the popular “cookbook” solutions.

Everyone, keep up doing the good work of spreading knowledge – knowledge and recognizing limitations is the foundation of making good decisions and safe flying!

[quadrirotor]

we can always be inspired by Magni! ;)

here is the Spanish version!...

http://www.elaaviacion.com/

[raghu]

Raghu,

I think your comment is correct only within the limits of your assumptions. Your main assumption was that we never have to use the cyclic all the way to the stops. I think that in Birdy's case, this assumption is incorrect.

The main difference between a sharp pitching maneuver with a stabbed gyro and one without a stab is that, in a stabbed gyro, the stab is resisting the RTV pitching moment about the CG. In a stab-less gyro, only the airframe MOI is resisting the RTV pitching moment.

For example - lets say I am entering a sharp turn and pull the stick all the way back to the stops, and hold it there. In a stab-less gyro, the RTV, having moved a few good inches in front of the CG, is spinning the gyro airframe quickly nose up (i.e. into the turn). Since I am holding the stick all the way back, the quickly pitching gyro is feeding back into the cyclic, accelerating the rate of turn.

Now, in a stabbed gyro, the stab is resisting the RTV pitching moment both due to static and damping moments. The rate of turn will thus be slower.

Although I don't recommend for anyone to fly a stab-less gyro, I have to agree with Birdy's argument that a stab may make a gyro less agile for some people.

Udi-


Udi,
Couple of things to clarify the control situation:

Firstly, when you for move the cyclic two things happen: 1) the rotor speeds/slows down , 2) and the RTV moves fore/aft. It turns out 1) dominates over 2). In a non HS gyro the gyro will start to climb/decend before the pitching motion really starts building up. That is why you see the lag in control in a non HS gyro. The HS tries to align with the direction of motion thus reacting with less lag. The control power of the rotor is quite low, also as the airframe starts to accelerate the lagging behind of the rotor causes it to damp the pitching motion ( this damping is of the same order as the pitching motion)

secondly, when the gyro starts to climb/decend the AOA of the rotor decreases/increases thus reducing the force needed for the rapid maneuver. In an HS equipped gyro the AOA of the rotor is maintained resulting in a much faster maneuver.

Finally, we need to keep in perspective the real potential of the force a rotor can provide to change the path of the gyro ( i.e. make more agile). The rotor RPM needs to speed up to provide this extra force- there is a delay in this and at best we are looking at around 2.5 G's (nothing compare to a fixed wing), well within the limit of the cyclic tavel. Needless to say, this margin is a lot lot less in terms of negative maneuvers.

Now, to the extreme turn example you give. Ironically a HS will allow for a more coordinated and rapid turn, as it will try to align with the relative wind resulting from the turn and pulls the gyro to the inside a turn - think of an hypothetical 90 degree turn- it is HS that will act as a VS (vertical stabilizer) in coordinating the turn; in shallower turns both the HS and VS will provide this function.

[birdy]

Raghu,I don't think you understand what I meant when I first started this manouverability/stability aument.

The 90degree bank I was refering to goes like this.

You are cruising at close to max speed,close to the ground.[10/20']
You want to go in the opposit direction as soon as possible.
The best way I'v found to do this goes like so.
You first have to shed airspeed,by cutting power,pulling hard back AND right,you effectively put the machine in to a virtical decent,horisontally.
you are now traveling,mains first,mast parallel to the ground,and slowing down fast.This also eccelerates the rotors[G force].
As you near 0 ground speed,you level the disc,GENTLY increase power,kick right rudder and straighten the machine in to the direction you just came.
The stored energy in the rotors is starting to whind off,but if done correctly,you are actualy climbing in an inertia hover.you are now positioned to go back the way you came,in very short time,with next to no turn circle.

To be able to do moves like this in rough conditions,whether up wind,down wind or cross wind,you need to have TOTAL control you don't any stabilising surfaces applying any corrective inputs.

When you are in the horisontal/virtical decent situation,a stab will try to push the nose down,not what I need in that situation.

As I'v said before in this forum,I do some unorthidox things,so I need an unorthidox machine.

BTW,kids,don't try this at home,it takes alot of practice,and I'm certainly not saying this is what everyone wants to do.

[Aussie_Paul]

I guess Birdy that because you have never experienced a truly pitch stable gyroplane (that is what you said) you cannot make a comparison. You do not have the experience in both a pitch stable and pitch unstable gyroplanes.

You only know how to fly a pitch unstable gyroplane, that is all. I commend you for being able to do that, but most of us have been there and done that, only to be pleasantly surprised when we finally flew a pitch stable gyroplane that will do your job even better than you can now, in your current gyroplanes.

When you follow this forum for a number of years you will gradually be convinced, though that will only happen if you want to learn!!!! That is your decision.

Aerodynamics and physics do not care whether you are a mustering pilot or not. Those principles cannot be changed at whim to suit your or my particular needs.

I have no doubt that if I were a good a pilot as you, that I would leave you wanting way behind with my pitch stable gyroplane. Because I am not, I guess that we will never know.

Although, I think that the current group of gyroplane knowledgeable people would know the result.

Aussie Paul.

[Greg Mitchell]

Gentlemen,

I'd like to thank Greg Grimminger for his informative posts, as always Greg you talk that tech stuff in a way that newbies like myself can understand and learn from, you've been a big help to me over the last eighteen months with the ongoing learning process. Thanks Mate.

Paul,

I reckon Birdy knows his stabless Gyro is unstable. That's what he says he needs to work with. And I'm going to take a walk on a slippery path here. If I understand Birdy correctly, he is indicating that when he puts his gyro into a 90 degree attitude tight turn, he does not want any up lift on a HS keeping the nose from whipping around in the arc of the turn, or slowing the rate of that manuevour.

What would be interesting would be if Birdy were to try this manuevour at ALTITUDE, yes Birdman, ALTITUDE, well at least enough altitude to maintain a safe margin for recovery, test with a HS fitted to your trusty steed. A comparison. I couldn't see why there would be any odjections to such a comparative test, after all if it is done at around 250' theoretically it should be safer using a HS???

BIRDMAN,

You have tested with and without on your Rosco machine, Yeah? Could you have a go at this. I know, I know I did say 250', perhaps you could adjust that slightly to suit your comfort level. :o 8)

Regards,

Mitch

[Chuck Irby]

Aussie Paul made a good point in his post, i.e., Birdy can't really compare his unstable machine with one that is stable. I have only two hours in a machine without a HS. However, I will never forget how the unstable machine felt. I, for one, would never want to go back to the machine without a HS.

If Birdy has never flown anything with a HS and he is content with his machine as it is, the chances are that he wouldn't even want to try anything else, and I can understand him feeling as he does. To each his own.

However, I do believe that if Birdy took the time to learn to fly, or really get the feel for a HS machine comparable to the one has, especially one with centerline thrust, that he would be pleasantly surprised.

[Greg Mitchell]

G'Day Chuck,

I understand Birdy has flowen his Rosco craft with and with out HS's and prefers to work cattle without one. I believe he owns a Raf2000 also which has an aftermarket stab fitted.

My Butterfly and Birdy's stabless craft are worlds apart. Birdy has indicated to me he likes the look of the Butterfly/Monarch.

They way I read Birdy's posts here and on the OZ forum is that for MUSTERING Cattle, his stabless Rosco, works best for him.

Chuck I agree that if we could get Birdy mustering in your beautiful craft (by the way I downloaded them all, Thanks) or similar ie Close to CLT types with HS's we may be plesantly surprised. I think ??

Cheer Chuck,

Mitch

[gyrogreg]

I’d like to comment on Birdy’s theory that he can make that sharp, high-G turn better in his stabless gyro. In the interest of technical understanding, but at the risk of blasphemy --- I think Birdy’s turn might be easier for him to make without a HS for possibly two reasons. Both of these reasons provide Birdy a lot less cyclic stick forces to make that 90 degree turn. I present the following as just thought theories, so, don’t take these as proven:

If Birdy’s turn, or hard nose-up pitch is sharp enough, he may indeed experience essentially a vertical descent in the horizontal plane. A HS in this situation MIGHT require more cyclic stick aft force to overcome the tendency of the HS to pitch the nose down.

For the same turn, in a gyro that does not have powerful HS to hold the CG forward of the RTV (as the RTV moves forward as a result of the aft cyclic stick), the nose-up G-force of the aft CG will assist Birdy in applying aft cyclic pressure to get through the turn.

A stable gyro can create cyclic stick resistance to the pilot forcing the gyro in sharp, high G maneuvers. A pilot should never make overly rapid and strong cyclic stick movements – especially an inexperienced pilot, and especially in the nose-down direction! It is certainly possible for a pilot to learn (program his brain computer, burn the brain synapses) through lots of experience in that machine, to master the control responses to fly even a highly unstable machine. (I am always fascinated by the things that athletes and others can learn to do – ride unicycles, work on trapezes, ride skate boards, skate, twirl and ski jump!) So pilots very experienced in THEIR gyro, such as Birdy in his particular gyro, may be able to use his learned skills to the advantage of much reduced and even momentarily reversed stick forces to master the kind of maneuvering he needs to do – with less stick force and physical work.

As an example of this, I note that Magni gyros, being very stable, present a strong cyclic stick force resistance to severe stick movements. This force feedback increases at higher airspeeds where severe stick movements are much less desirable – because smaller stick movements are much more effective at higher airspeeds. But, even the Magni can make those hard and sharp 90 degree turns (you ought to see the Italians fly these!), but it takes strong arm muscles to make that happen. In other words, I don’t think Birdy would be able to muster very long if he had to work the cyclic that hard for his work.

My point is, I think I can see Birdy’s point in terms of the physical work it would take to continuously perform such maneuvers for long periods in a stabilized machine. And, Birdy’s learned skills allow him to fly his unstable machine probably safely!

Finally. I want to admit that my proposed theories DOES NOT take into account the much more complex dynamic rotor issues that Udi points out! Perhaps those issues could shoot holes in my theories above! Please don’t take my comments as proven, and please don’t take this as any encouragement that your gyro should not have a HS. The resistance to pilot over-control of a stable gyro is a very important element to safer flying for the less experience gyro pilots. IMHO all gyro pilots, except maybe those who have already mastered the stability of their particular gyro, should fly stable gyros – and that probably means a gyro with a HS! Even Birdy would probably have initial difficulties maneuvering and stabilizing a gyro that had different stability (dynamic and static) characteristics (pitching rates, damping rates, inertial effects, etc.) than the one he is familiar with flying. In fact, that is partially the reason he probably would not like flying a more stable gyro – his present skills and reactions don’t work exactly and would have to be re-learned!

Look at this another way: Birdy has probably trained his brain (autopilot computer) to be a very effective stabilizer for HIS unstable aircraft. This is much the same as the stabilizing computer on a very unstable modern jet fighter. The main difference I suggest is that stable gyro is just as maneuverable as the unstable one (for similar weights and inertias), but the programmed computer (Birdy’s brain) stabilizes the inherently unstable gyro to allow him to fly those maneuvers with less physical strength and work!

I am always reluctant to offer specific configuration theories and preferences. But, it is fun to join in those debates. But, in the end, stability and control cannot be precisely determined by configuration or “paper” theories – especially considering the rotor dynamics that Udi likes to point out! The final result can only be measured by flight testing.

[PTKay]

I am really really satisfied with the quality of this discussion I was able to stirr up with my post. Thank you all, this is a great qauality leap against the "mud fight" on the other forum (nothing against it, it has it's great value) in the direction of reasonable dispute.

It is really amazing that a Polish "newbee" brings guys from US and blokes form Oz to argue across the Date Line.

And I am learning....

PTKay

[Udi]

PTKay - you're not the only Polish around here... Both my parents were born in Poland.

Greg - I apologize if my theoretical discussions make your work, explaining gyroplane aerodynamics, more complicated. Just like you, I want to improve my understanding and help everyone else learn in the process. I am very interested in your control feedback theory (being an engineer myself), and I believe we can refine them further by taking into account some additional rotor feedback mechanisms. This should probably wait for another discussion, or off line.

Regarding Birdy's situation and the discussion on gyroplane agility stab vs. no stab - I think that some folks here have not read Birdy's posts carefully enough. If you read his posts carefully enough, you will see that the maneuvers Birdy is describing cannot be done with a gyroplane that has an effective stab on it. It does not matter that stabbed gyros can do some things better than non-stabbed gyros. This is irrelevant for this particular discussion.

Look, we are not talking about stability. We are not talking about making coordinated turns. We are not talking about making gyros fly like airplanes. The flying that Birdy is doing is radical in terms of gyroplane maneuverability. Birdy may be utilizing his gyroplane as a ROTORCRAFT, better than anyone else here. The maneuvers that Birdy is describing in this thread are taking full advantage of the aircraft, without limiting the airframe directional heading.

Lets face it. When you have a horizontal stabilizer, you fly the aircraft just like an airplane. In essence, you are flying forward, relative to the wind, all the time. The HS doesn't allow vertical assent or vertical descent at high airspeeds. Thus, a HS makes a gyroplane less of a 3-D rotorcraft than it could be.

Although I don't think I will ever fly gyroplanes without a horizontal stabilizer, I do envy Birdy's skills in flying gyroplanes.

Udi-

[raghu]

The HS doesn't allow vertical assent or vertical descent at high airspeeds. Thus, a HS makes a gyroplane less of a 3-D rotorcraft than it could be.
Udi-


Udi,
can you elaborate on this ? A vertical descent/ascent by definition involves zero horizontal speed. Not sure what high speed or low speed has to do with it. You can equally perform this maneuver when you are going fast or slow.

If you are at high speed and you pull the stick abrubtly, you will first ballone up and the HS will nose up a little, and then as you slow down you will begin to descend and this time the HS will cause a little nose down ( nb. both these nose ups and downs are not divergent they will reach equilibrium). When you you reach a zero velocity (horizontal) the HS would be stalled but will provide some up force ( essentially drag) which will result in a little nose down ( just enough nose down so that the RTV fore movement will balance the moment caused by the HS.

[Doug Riley]

"The HS makes the rotorcraft less 3-D." That's a bit over the top. Modern helicopters all have HS's, including the hot combat rigs. I don't think their designers were shooting for something "less 3D" than it might be.

Compare this to fixed-wing fighters. Some ARE deliberately designed to be pitch-unstable, to add maneuverability. I doubt that professional helo engineers are, as a group, more stupid than professional jet-fighter engineers.

With or without a HS, a gyro with direct cyclic pitch control is NOT like a fixed-wing plane. In a FW plane, we can't tilt the wings directly. We tilt the body of the craft using the elevators. The wings are rigidly bolted on, so they follow the body. There's a rigid, one-to-one relationship between what the body does and what the wings do. A Cierva with fixed spindle and elevators works almost (not quite) the same way as a FW plane, in the sense that the body leads.

In a direct-cyclic gyro/helo, we tip only the rotor. The body follows along as best it can. The HS helps it follow better: quicker and more reliably. We want the body to follow the rotor -- not only because it confuses pilots when it doesn't, but also because the trim spring and control stops are attached to the body. Moreover, control friction and the pilot's grip on the stick mean that motions of the body are to some extent fed to the rotor. Having the body whipping about in a delayedmanner and uncoordinated with the rotor's motion is messy and can be dangerous.

The maneuver that Birdy wants to be able to do will require more control pressure and movement with a HS, no question. It should be possible all the same. The HS will stall in such a "vertical" maneuver, but it still produces a stabilizing force when stalled. It will still try to get the fuselage pointed in the direction the machine is travelling... which is not what you want in order to rev the rotor up. A controllable HS, with an interlink between the HS and the stick (going back partly to the Cierva system) would probably help. Cierva himself proposed such a dual system.

[Udi]

I may be way off base with this, Raghu, and I am doing a lot of hypothesizing. But let me try and explain what I meant.

As long as a horizontal stabilizer is keeping the airframe pointing into the wind, the maximum rotor disc AOA (in pitch) is limited by the stops. Think about flying at 80 mph, entering a 90 degree bank, and pulling the stick all the way back. The rotor disc AOA will remain pretty constant throughout the turn, as long as the HS has enough power to keep the airframe pointed into the relative wind. The cyclic pitch range determines the AOA. Is that correct?

Do the same maneuver with a stab-less gyro. The initial disc AOA will be the same and, yes, there will be a delay in the time the airframe will start pitching up (into the turn) compared to the stabbed gyro. But once the airframe radial speed (which is determined by the RTV x moment arm) has exceeded the stabbed gyro radial speed (which is determined by the disc AOA making a big circle in the sky), the rotor disc AOA will get larger and larger. Obviously, the rotors will accelerate at a certain rate, and the G forces will be limited. But I don't see any reason why the rotor disc AOA cannot reach 90 degrees if the maneuver is done fast enough.

This is all hypothetical, and I don't know what it reasonably achievable, but if the rotor has reached a 90 degrees AOA and the gyro is still advancing at 40 mph, than you may call this a high speed vertical descent.

If I understand Birdy's description correctly, this is exactly the maneuver he is performing to turn quickly 180 degrees around a point.

Udi-
p.s. I should probably mention again that I am not trying to argue for flying without a stab. I am just trying to understand what kind of crazy maneuvers may be possible only without a stab. I have no intention of ever trying it, and I would not recommend anyone else to. HS is good, and I personally will always fly in stable machines This discussion, from my point of view, is purely theoretical.

[birdy]

Gyrogreg
Doug
UDI
PTKay
Chuck
And my mate Mitch.
Thank you all for READING and UNDERSTANDING where I'm coming from.As the six of you can see my point,this dosn't mean it is for everyone,but you are OPENMINDED enough to understand something compleatly foreign to some.Again,thankyou.
I'll rest my case.


To Raghu and oz paul,please try to see my point,these other blokes can,they know its not for everyone but the can see the need for some to have an unstable gyro.

BTW,I know my machines are far from perfect,but they are the ones I have,while I'v improved the performance of both,there is always room for more improvments.

[Gordon Gibson]

Birdy!! he da man!! ;D
No seriously, Birdy is obviously a highly accomplished operator.
I have seen for myself how those Aussie cattle mustering pilots handle their gyros, it is truly a thing to behold.

But it is not for most of us already flying gyros and it is certainly not for the newbie guys who want to have a go at our wonderful recreational passtime. We need gyros to be more user-friendly for low time pilots if we are to arrest the decline in the gyro movement.

Birdy is super-human. He is doing a job that is vital to the cattle industry in Australia but his machine has the prop pushing way higher than the VCG. And he has no HS. This works fine for Birdy, in his particular application.

Thanks, Gordon Gibson.

Cheap flying is not necessarily safe. Safe flying is not necessarily cheap.

[Chuck Irby]

Well stated Gordon.

It's a real pleasure to have you, the Birdman, Mitch and Paul all from that part of the world here with us on this wonderful forum that has been so graciously provided to us all by Mr. T.

The fact that we can all share with each other about the best sport ever enjoyed by anyone, makes me wish that it was economically feasible for me to take my machine to New Zealand and fly with you all over your beautiful island, then go to Australia and do the same with Aussie Paul, Birdy, and Mitch. (I would love to help Birdy muster his cattle.)

Oh well, I guess I had better wake up now and stop my dreaming.

[mceagle]

I think I might be misunderstanding something here. I presume that we are talking about doing a 180 degree turn with a bank angle of 90 degrees. The rotor thrust vector cannot normally change in relation to the C of G without joystick input. Lets assume that the gyroplane is balanced correctly and the RTV is just behind the C of G. As the "G" forces increase, the nose of the gyro is being pulled away from the turn, and only muscled effort with the joystick can resist that tendency (until the pilot runs out of back stick). If that same gyro has an effective H/S set a couple of degrees neg. then it would resist the tendancy of the nose to drop (swing away from the turn) and in effect help the pilot to keep the nose into the turn by taking some of the load from the joystick. In fact the pilot should not be able to run out of stick travel.

Talking about vertical gusts, my feeling is that airframe pitching should be worse without a H/S because of the frontal surface area ahead of the C of M with no balancing surface area behind the C of G. (especially with a large pod). If uncomfortable pitching is felt when a H/S is fitted then it is because either the gyro is out of balance or there are other aerodynamic forces trying to override the H/S. In either case, the uncomfortable feeling was just the H/S trying (in vain) to do its job of stabilizing the airframe.
I would compare it to fitting power steering to an earlier model car to correct a wandering problem. If anything, the power steering would amplify the problem and make it appear worse. However the power steering was not at fault because it was being overpowered by some other previous fault.

If there is one thing you need for survival in a gyroplane in all conditions it is for the tail feathers to have enough power to overrule any other force that is thrown at it, either in pitch or yaw.

[Aussie_Paul]

Tim, I was having similar thoughts today. I applaud Birdy for his ability to fly his unstable machine in the application that he does.

I have been thinking about Greg’s scenario that might be an explanation. Remember Greg said might. All the other posts were about stability.

I tend to agree with your thoughts on the 180-degree turn, BUT for the sake of the exercise lets say that Greg is correct. Out of all the flying done mustering it must only be a very small percentage of the overall time in these 180-degree change of direction at a bank angle of 90 degrees.

This means that Birdy is fighting the machine (of course Birdy does not know this because he has addmitted to never flying truly pitch stable gyroplane) for lets say at a guess of 99% of the time, because he has no stability to help him when he is not in that 90 degree bank.I can appreciate that Birdy does not know, as I was in his same boots a few years ago.

I refer to my previous post where I said that,

I have no doubt that if I were a good a pilot as you, that I would leave you wanting way behind with my pitch stable gyroplane. Because I am not, I guess that we will never know.

The only time that Birdy would have less work to do is in the, small% of his flying, 90-degree bank scenario. All the rest of the time I would be having a rest compared to Birdy with his pitch unstable gyroplane. At the end of the day I would not have used anywhere near the energy to do the same job for the day.

Aussie Paul.

[birdy]

Paul, you keep goi'n on about "work load in an unstable machine".
Well bugger me,I must be superman!!!

Just an example off the top of me head.

Late spring last year,we were on to the last mob of cattle we had to brand,we had been hard at it for the last 2 mounths straight.
There was two paddocks to be mustered,[one is 550squ km,the other 350.].It was going to take 2 days to muster each padd in to a smaller holding padd.
Day one,9 hours,calm conditions.
Day 2,3,and 4 it blew like a bastered the hole time.Hot,thermally northerly dust storm.the dust was so thick I had trouble to see the cattle on the ground,only 100' below and 100 yards away.[not to mention the cattle were pretty pissed in these conditions also]
The groung crew,driving 4wd bullcatchers, coulds not see any better.[when ideling along behind the mod,they had to go in reverse so the radiators on the vehicles could get some air flow from the howling tail wind,to prevent boiling.]

Total air time for the 4 days,37.5 hours.Was I stuffed,no ,I reckon I could have gon a couple of rounds with Mike Tyson.[mabey not that good]

But then,I suppose you haven't done this sort of thing ,so you are talk'n from an ignorant's point of view.
Take it from someone who has done it Paul,it ain't that hard.

[Chuck Irby]

Hello Birdy, Mate,

In my post above, I stated that "I would love to help Birdy muster his cattle". However, after your last post, I would have to pick the good weather days.

Birdy, what do you mean by "stuffed"?

Also, "it ain't that hard" to you because you've done it, and done it, and done it. Right, Mate? Anyone, who hasn't done it, would be ignorant. Also, it sounds to me that you are one hellofa pilot, Birdy.

[StanFoster]

Birdy: I would love to see some cattle roundup pictures. There just is something about Australia and gyrocopters with me. I never will forget seeing "The Road Warrior". I watched and watched that gyro in that movie...I could not believe that thing. I had to have one and it wasnt but a few months I had one.

I never will forget the look on my dads face..who is a seasoned pilot...when he came out into the barn with me sitting in my Bensen doing the hang test. I swear the look on his face would not have been much worse if I would have been hanging in the barn :P.

Here is a very, very poor quality picture of me hovering above the numbers in high winds back in 1985.

[birdy]

Chuck,as I'v said on the oz forum,I'm not blow'n no trumpit,just stating facts.
Stuffed in oz means,burn't out,rooted,shagged,knoked up,worn out or just plain tyred.

Ignorance is one point i'v been trying to get Paul to see.No-one can be blamed for ignorance,but your an idiot to argue when you are.

I'll have to admit to lying on most of my posts, when I say "I", I realy mean my subconsios. Most of the time mustering,the last thing I'm thinking of is flying,most thinking is taken up on the job I'm doing,ie:what the cattle are doing,what they are going to do,what are the idiot staff NOT doing,where's my fuel dump,how much fuel have I got left,will we get the job done befor sundown,I need a piss or just singing my faveret song to myself.
This dosn't leave much room in my small mind to think of flying.

Also,I'm not the bosting type,I'v aquired the skills from nessesity,these machines have saved me countless thousands over the years,the more I use them for more and more different jobs,the more I save.
So obviosly I get plenty of practice in all conditions ,doing all typs of jobs.If I an't any good by now I ought to give it away.

An't I the lucky bastered,doi'n the job I love with the machine I love in the country I grew up in and would'nt swap for all the money in the world.

[Chuck Irby]

Thank you Birdy,

As an observer, I don't see that Paul is trying to put you down, or trying to get you to fly with a HS. By the same token, I don't see that you are trying to get Paul to switch to flying a machine without a HS. You are both strong willed blokes who just want to show that you are right.

Well, I believe that you are both right. The stabless machine works well for you in mustering cattle, and you probably prefer a good stable machine for cross country flights. I'll bet that you guys could really enjoy a tall, cool one together.

[PTKay]

This gets really frustrating.

Birdy has declared on the Aus forum "I rest my Case" and as it seems, his statement on this forum, few posts ago, was exactly in this mood....

But NO, Paul is still trying to dig in this hole, where it seems that most of us came to a conclusion satisfying everybody.

"Horses for courses". "Live and let live" or whatever you wish to call it...

I am slowly getting the feeling it is not about the matter, but about and EGO, a big EGO...

Birdy, I think you will not come around posting or e-mailing to us the video of your mystering job....

PTKay

[Greg Mitchell]

G'Day Gentlemen,

I've read the stuff about having enough horizontal tail to counter the plate surface up front so as to track the relative air ect, and just as people point out the down side to any stabless gyro, for some reason I still have it in my head, that it may be a really large HS, on a long moment arm, might possibly be too reactive to windshear effects.
Example being single place, open frame gyro with hugh HS, massive thermally updraft, disc tilts back and tail pushes up hard and fast......???? Is this possible?

Regards

Mitch

[Aussie_Paul]

Birdy you posted, "But then, I suppose you haven't done this sort of thing ,so you are talk'n from an ignorant's point of view.
Take it from someone who has done it Paul,it ain't that hard."

Of course it aint that hard when you can do it. Riding a unicycle is not that hard when the person can do it.

I may be partly ignorant of mustering, but I am certainly not ignorant with flying unstable machines hard and also having had students trying to kill me in my unstable trainers.

I do know the sort of flying you do, as I grew up with stock, and once again I admire you for the skill that you use in your everyday job.

On the other hand you would have to say that you are ignorant of pitch stable gyroplanes. As you said you have never flown one.

I used to have to use many more skills training than I do today, Why? Due entirely to the unstable training machines I once used.

By the way, none of this is a slight at you. I just happen to disagree with some of your thinking. You keep pushing this "special flying" that you do that requires an unstable gyroplane. So far there has been no definite consensus that this is correct, only "might" be. As I said your comments have made us all, me included, to think deeper to see if it is a possibility, and I thank you for doing that.

I am looking forward to seeing the suspension that you have developed for your Raf.

From your local knowledge of the Alice area, would you say it would be better for me to go north or south of the control zone around the Alice Springs Airport?

Regards, Aussie Paul.

[PTKay]

Greg,

heve a look at the beginnig of this topic, this is exactly what my doubt was....

In the meantime you have already 5 pages to read about it ;-)


PTKay

[PTKay]

Greg,

sorry, before I posted my last text it became 6 pages....

And Paul is obviously not giving up the opporunity to have the "last word" in this dispute.....

I give up posting here, anyway, it was very infomative for me and helped me a lot, but now I am just fed up... to put it straight.

PTKay

[Aussie_Paul]

Paul, I just want to understand. A major problem of mine.

Anyway, one thing that there is no doubt about, and that is Birdy and I will be having a cold one or two or three or four over Easter.

Ain't the right Birdy?

Anyway no more posting on this topic if thats what everyone wants.

Aussie Paul.

[gyroman]

Has anyone watched the dominator video? There are several scenes in it in which the pilot whips the machine around 180 degrees really fast, I believe he was flying the dom without the pod. I'm sure that guy could "muster" some cattle. Birdy if that's the type of flying you do without even thinking about it then my hats off to ya.

[gyrogreg]

There have been several comments that a HS on a gyro could be too big! Except for structural or hangar fit reasons, I’m not sure this is true.

I say this because we know that the Little Wing HS is huge – volume-wise. My experience with the Magni also suggests the very large HS has no real drawbacks. Here is what I have reasoned from my experience with the Magni.

Statically, we have always been saying that the HS must be in “balance” with the offset prop thrust – reacting to propwash. And that the HS must be in “balance” with the other aerodynamic moments acting on the airframe – HS reacting to free airstream! I believe this is absolutely true and the way these static “balance” of moments must be understood from a stability design standpoint.

But, in the case of a very large HS, this “balance” is accomplished simply by the HS assuring that the airframe is ALWAYS nearly perfectly aligned with the free-airstream – no matter what the prop wash is and no matter how strong or weak the airstream is. When the airframe can be aligned perfectly with the free airstream, the aircraft acts essentially like a fixed-wing where the CG is steadily “fixed” relative to the rotor lift vector – except for some short transitional dynamic affects. This accomplishes all the “balances” we are wanting – the reason for balancing all the moments is to hold the CG in a fixed position relative to the RTV – preferably forward of the RTV. The advantage of a HS large enough to do this is that the CG can be not only “balanced” with the other moments, but it can be physically positioned and held FORWARD of the RTV – a truly stable condition, especially if the HS is actually loading downward to accomplish this (countering a slightly high prop thrustline IMHO, and balancing the forward CG). When we talk about a HS adequate to just “balance” or counteract the other airframe moments, we are not readily assuring the CG to be forward of the RTV – we are only trying to balance it exactly on the RTV – NEUTRAL static stability! When the very large HS just simply overpowers all other moments on the airframe to hold the airframe level, the CG can actually be positioned at a specific location forward of the RTV – in other words, the pitch attitude of the airframe can be essentially maintained constant relative to the free airstream. Essentially I am suggesting that “over-balanced” is even better than” balanced” static moments!

My experience with the Magni, and I bet Ron Herron could verify this with the LW, is that there are really few penalties with a very large volume HS. Remember, even though the airframe attitude and CG might be maintained very tightly, the pilot’s cyclic control still can move the rotor (RTV) independently of the airframe and thus provide exceptional maneuverability and control. As soon as the free airstream direction changes as a result of the rotor AOA and vector change, the HS immediately adjusts the pitch attitude and the CG back to it’s “fixed” position relative to the RTV. And, the forward CG and large HS dynamic effects immediately start the pitch changing in that direction to get it back aligned with the free airstream immediately!

The only real penalties I see with a very large HS are the physical strength and work it might take to resist the inherent stability forces during severe maneuvers such as Birdy’s 90 degree turn. - and, the inertia and MOI penalties (to maneuverability) that may be associated with the necessarily heavier and longer structures for such a large HS.

- Greg Gremminger

[raghu]

The only real penalties I see with a very large HS are the physical strength and work it might take to resist the inherent stability forces during severe maneuvers such as Birdy’s 90 degree turn. - and, the inertia and MOI penalties (to maneuverability) that may be associated with the necessarily heavier and longer structures for such a large HS.

- Greg Gremminger



To add to the penalties, I guess there is the issue of slightly decreased effciency- increased drag due to the stab (small really in the context of draggy gyros) and down force by stab which the rotor has to compensate for.

[Greg Mitchell]

Hello GyroGreg,

I'm off to town to pick up HT 4130 parts for Butterfly/Monarch kits. I had a quick read and will do so again this arv. Thanks again Greg.

Best regards to you and Steph,

Mitch

[gyrogreg]

I agree the drag and extra rotor load could be penalties - but again I don't think they have to be significant. For instance, the Magni can carry 600 Lbs useful load at 90-100 mph with less than 100 % of it's 100 HP engine. The secret is probably paying good attention to rotor efficiency and airframe drag. The HS can be very efficient if it is a clean airfoil on a long arm. Well contoured wing tips probably help this efficiency also bu effectively increasing the aspect ratio of the HS. Just an example that these don't have to be significant penalties.

[Udi]

For most gyros, the best rotor drag (best L/D) happens at around 90 mph (mu~0.35). What makes the gyro so draggy at airspeeds lower than 90 mph are the airframe, wheels, control surfaces, etc. The Magni is a good example of an aerodynamically clean open frame gyro.

Udi-

[birdy]

I like this Gyrogreg bloke,he just keeps posting well explained,easy to understand and non biased articles,keep it up mate.

Greg,you say that the HS reacts immediatly to air flow changes.I agree.Only it is not imediate enough when you are close to the ground.
I said a couple of pages back,"It isn't a problem to lose 10' when you are at 100',but when you are already at 10' there is no room to spare,"
In other words,If I'm cruising at 10',in windy conditions I can see air speed changes befor I hit them,wether by the dust,movements in the grass,trees or cloud shadows.[After flying a trike for a couple o hundered hours in these conditions you can nearly "see" the air,you feel every single little bump there is.]
Because of this foresight,instinct or whatever it is, you can react,prepare for what is coming befor you hit it,and not loose any alt.

This is probably not only in tune with the craft but also the air.Being in tune ,and staying in tune by always having to fly it,is what saves my neck in the small % of the time I'm in these situations.
No stab can PRE-REACT.And when you spend alot of your fling time close to the ground,A HS is of little benefit,given it's slight reaction delay,[half a second is about 10 feet in a strong down draught.]

I'll never argue against H stabs,they are just not for me and my situation.
Thank you for your clear head and open mind.

[RHerron]

Greg, Birdy and all,

I don't know if anyone remembers or not, but in 1997 or '98 I flew the 70 hp., elevator-equipped Little Wing at Mentone during the manufacturer's showcase with Ernie Boyette in a 618 Dominator.
We did an aerial chase which got pretty radical at times.
Enough so that I got "chastized" by the safety officer (Doug O'Connor) and grounded for the day, primarily for "directing energy toward the crowd" in a steep turn at the edge of the alotted flight area.
My point is that the machine was plenty agile. even with 20 sq. ft. of horizontal surface on a 10 ft. from CG moment.
Ernie managed to stay in the "zone" so averted any trouble from the powers that be, due to being a better pilot most likely!
While there is no doubt some drag penalty
when one adds more surface of any kind like a HS, it is minimal and certainly a penalty you can live with.
The Rotax 914-powered Little Wing will carry over 500 lb. useful load (and stay under 1100 lb) and still cover the ground pretty well too as evidenced by Andy Keech's recent non-stop flight.
The unfaired wheels and engine probably contribute the highest to overall drag on this machine.

Nobody will have issues with the HS and flying close to the ground. Maintaining exact, precise control is exactly what you get.

Birdy's machine is a very close-coupled unit with little mass sticking out past two arms' length. This is what makes it so nimble, not because it doesn't have a HS.

I would love to see some videos of these mustering fellows at work. I am certain it is amazing stuff.

[Greg Mitchell]

Greg G,

As always Greg, informative and detailed, thanks.

Udi, Ron, Rahgu, Birman and all I thank you for helping me see it.
The term adequate had always intrigued me, ie; just adequate or more than adequate ect.

Best regards,

Mitch

[birdy]

Spaceman,back on page 3 ,you asked me to try the "power up/down" thing.
Well I'v flowen both machines since and tryed it out.[unfortunatly I forgot about it yesterday when I was mustering,not that I had the chance to anyway.]
I'm not sure if this is what you wanted,but this is what I did.

RAF,914,no stab.Holding the stick still by bracing it between my knees.20k gusty warm day.[I'd have to wait for months for a calm one.]
S&L,add power.
The most noticable change was the torque roll.The pitch didn't change straight away,but did slowly nose up,to a point and settle in to a steady cilmb.

S&L,power off,
The nose initialy rises,the air speed drops,then the machine settles in to a vertical decent with the nose coming back to the origional cruise attitude.Power on and the nose drops a little,air speed is regained and cruise attitude returnes.

Open frame,912,mustering machine,no stab.
S&L,stick braced as before in RAF,power added.
The nose rises after a short moment as the RAF,settled to a steady climb.
Power cut, no initial attitude change,air speed drops to about half cruise, nose steadily drops,then settels in to a steep decent.[same as a power off landing attitude.]Noticed the stick wanted to go forward when power was cut,and wanted to come back when power was added.
Same mustering machine,cruising with free stick.[trimmed]
Flew for 10 minuits at 100',streight line,cross wind gusting to 20k.
Was personaly, very supprised that I had to put no pressure on the stick,for the hole 10 minuts.[Dose this mean I can't fly afterall]Some power adjustments was all that was needed.[to avoid the trees ]Evan the track didn't change much,only slight rudder to correct the gusts.

All this means bugger all to an ignorant cow grower,but I would be interested in an unbiast assesment.


Yes Paul,I can hear you already,"that is not a true FIXED test."
I know that,but if I was fibbing about any of it I would only be fool'n myself.So I made sure I didn't cheat myself by letting the stick move.[It was at least as steady as the one in your video.]And because my hand was jammed between my knees,I could feel the slightest movement,if I let it move,who am I kidding???

[StanFoster]

Birdy: Your input is interesting. Do you have any cattle mustering photos?

[Aussie_Paul]

Hey Birdy, I have no reason to doubt what you say about your testing what so ever.

Actually I don't really care if it is stick free or stick fixed.

I don't think that a gyro has to meet the true stick fixed testing to be very safe. It is just that I would be foolish not to at least attempt to design to the best.

The ultimate pitch stability test is the true stick fixed test, as per Geg G's explanation.

The second best is the stick free. Once again as per Geg G's explanation.

If it won't pass the stick free tests then it won't pass the stick fixed ones.

Your results are intersting, and informative.

Will you have both machines at BS?

For me to compare what I have been finding I would appreciate some comments on the 2 machines.

Is there a pod on the Rosco machine?

Rotors used on each machine?

When you addapted the Raf to the 914 how did you arrange the engine thrust line, and what did you do for a pre rotator?

Any other mods that you may have done in the process. eg. stepping keels, mast changes, etc.

It is my job as a designer and tester of our gyroplane project to question everything. That is the way I am.

It took me a while to be able to conduct unbiased testing.

Counting the days.

I have got all the maps out. Can you give the lat and long of your place or the name of the station?

I take it that you are approx 150 kilometers n/east of Alice.

Aussie Paul.

[GyroRon]

Don't ya just love ignorance? It is a proven fact - not opinion - that a horizontal stab makes the gyro much safer and does not affect the gyros ability to manuver in any appreciable way. the same thing with people out there still preaching that HTL gyros are better for themselves for reasons such as more stable on the ground, or they don't want to climb to get in their machines etc....

What I think it comes down to is the fact that until these people get a chance to fly and experience what flying a gyro that is designed properly and is very stable and safe - such as a Dominator or a little wing or magni etc... - These people will not know or be able to truely understand how good these machines fly compaired to their current lesser designs.

If a person gets comfortable in a HTL or non stabed gyro, they get comfortable and see no way that these changes can make such a difference that these changes are worthwhile.

Or they perhaps flew in a machine that had a stab or had CLT but the machine was still set up wrong and that gyro flew poorly and this reinforced the old timers position on his own machine.

the difference between a Stable Stab equipped near CLT machine and a gyro without the stab and or with a HTL, is the latter will KILL you in a blink of a eye if you let it get away from you. The stable gyro is trying to SAVE you if you screw up. What a choice right??? A machine that you have to fight to stay alive in or a machine that wants to try to help save your Ass???

I have flown several different gyros in the few years I have been involved with gyros and I can tell you I would be able to turn as tight and manuver with the best gyro pilot in the world in a bone stock Dominator. I can't speak for the rest of the stable gyros out there but I can tell you a Dominator will go exactly where you want it to and at the same time not be trying to kill you either.

I would just love to be around or to see it caught on video, when some of these old timers got a chance to take up a single place dominator. The look would be worth a million bucks!

But the fact remains that these old timers only know what they are experienced with. They might agree with the science behind what were saying here, but they are Comfortable with what they fly now and so think the changes will be worthwhile. I see all these stupid excuses, a stab will make me less manuverable.... a tall CLT machine is too easy to tip over...... I think long landing gear machines are ugly...... HTL makes the gyro more stable..... All HOGWASH.

It is very true the old Uni cycle example that is used many times in these discussions. Imagine the poor old guy who has always ridden a unicycle... We all know a bicycle is much more stable and less dangerous. It is true in this case that the unicycle is more manuverable, but only at very slow speeds, but I believe it makes no difference. Anyhow can you just imagine the look on the face of that old guy after his first BIcycle ride??? It is the same thing here with gyros.

People are just too proud to admit to themselves that there is a better - Anything - than what they already got. If these old timers had a more open mind and just tried a well sorted CLT and Stab equipped machine you can bet the farm that that old timer would see the light and sing a different tune -

I don't mean to offend anyone here but facts are facts. Some of you are flying gyros that are trying to kill you. And we know that there is a better way to fly now. why roll the dice????? Gyro accidents are very rare where there is a survivor.

[scottessex]

D*mn! I ride a unicycle, Now I feel hurt. :(



Just kidding, It has been an interesting discussion.
But I do ride a unicycle, even rode one of those high thrust line 6ft tall ones once. ;D

And I am going to put a larger stab on my gyro!

[PTKay]

Gentlemen,

it seems that still some of you cannot understand the point.

The unicycle example is excelent....

But I have a better one:

a motorcycle - this is obviously, whith its 2 weels way less stable than a car (or even a quad).

If you try to drive it hands off, it will kill you. Like the HTL gyro with no HS.

And these 2 wheel machines DO kill people, as the statistics says 5 times more effective than a car.

So why all these idiots still DO drive motorcycles (I think there is enough of them also among you, I have seen some nice hogs pics here on the forum).

Would you really try to persuade a hog rider to give up his machine and switch it for a perfectly stable Oldsmobile ???

Gentelmen, just try to think about what I tried to tell you, and PLEASE, stop calling each other names, "old fasioned" etc...

This really brings nothing.

There are on this Globe milions of people drivig motorcycles and starting a crusade to stop them, because cars are more stable and safe is obviously ridiculous...

Live and let live....

PTKay

[StanFoster]

Ron: I know some of those comments are directed at me... :(

I have used a few of those criteria you have posted....I dont feel however I am stupid.

All I can say is that there are a lot of us ol timers that have had no problems with flying our improper setups.

There is a heck a lot more to it than just having a perfect setup. Heck,,that dominator that is posted under my Paxton buddies thread..is totaled. We all know that the Dominator is one of the best flying machines out there. What happened? Like I said ...there is more to it than having the perfect setup. A person has to be comfortable flying. I trained myseld in my Bensen,,.Air Command and now my RAF. I trained at each level till I was comfortable. I was going to seek training in my RAF and even was setting up with Ron Menzie. Mainly because of the stuff I have read like its going to fall out of the sky. Then ,...just like my Air Command...I first hand experience it...and the biggest surprise to me so far is that there ISNT any surprises with the way they handle.

I have seen guys fly the pattern for two years never leaving the airport. These white knuckle fliers are contributing heavily to the accident rate. They arent relaxed.

Dont take me wrong here....I just cant keep quiet when referred to as stupid.

[Gordon Gibson]

GyroRon

Your reply # 91 has several fundamental and utterly basic tenements that if applied would eventually (hopefully) 'turn the tide' in the experimental gyro movement towards basic areodynamic common sense with regard to gyroplane design.

You are to be commended. If I didn't live so bloody far away I would Fed Ex you some stone tablets so you could inscribe some of the more pertinent comments therein.

Thanks, Gordon Gibson.

Safe flying is not necessarily cheap. Cheap flying is not necessarily safe. Gyros need to be CLT (or close) with HS's.

[Udi]

Will you guys cool off???

The questions in this thread WERE NOT whether high thrust line, no-stab, gyros are as stable and safe as CLT/stabbed gyro. This argument was settled a long time ago thanks to Ernie Boyette and his Dominator. Statistics don't lie. The crash rate of these, as well as other, stabbed/CLT gyroplanes is significantly lower than that of old generation gyros. Today we also understand the theory why this is so, and many people are doing a fantastic job delivering this knowledge to the masses.

There were two questions: Does a horizontal stab affects the agility of the gyroplane. The opinion of most experts was that, to the most part, a stabbed gyro can do most everything that a none stabbed gyro can - and usually it can do it better. The only exception to this rule may be for extreme pilots, like Superman Birdy, who is performing maneuvers that most of us can only dream of doing.

The second question was whether an oversized stab could be detrimental during extreme weather conditions. In particular, could an extreme updraft drive the tail into the rotor? Again, all the experts said no.

If anyone is still not convinced we can talk about it more, but lets do it in a respectful fasion.

Thanks

Udi-

[Chuck Irby]

I agree with Udi. In addition, I ain't reedin this thread no more. I've enjoyed all of it I can stand.

[Spaced]

Throwing a bit more petrol on the fire.
It appears that birdy's machine has the TL lower than the CG.
Power applied nose up, power off nose down.
Perhaps a bit of food for thought.

[mceagle]

Definately food for thought because Birdy's gyro is exactly the opposite. The thrust line is considerably higher than the C of G

[GyroRon]

Stan, I wasn't aiming at you so please don't take it that way. If I wanted to call you stupid I would have done that already in our private emails. 8) I know that once you get around to experiencing a machine like a Dominator for yourself you will be sold. It is just the way this thread has gone on and on about this nonsence and I guess I posted with a bit too much emotion. I guess the Ken J and Craig Wall in me jumped out on that one ;)

[GyroRon]

PT Kay, do you ride motorcycles much? I will agree they are far more dangerous than a Car or truck but unstable is not the case my friend. Once rolling the only reason for needing to hold the handlebars is to pull in the clutch or brake levers and to give it throttle. I have a throttle lock on my bike - a poor mans cruise control - and once on the highway I take both hands and put them in my pockets quite often. The bike isn't trying to kill me, just all the Soccermoms on Cell phones and the old people who can't see over the steering wheel ;D

[GyroRon]

Stan did bring up a point about his friends totalled Dominator - I was told he landed in a crab and the machine rolled over - Anyway, Correct me if I am wrong but I believe there hasn't been not one Accident involving Dominators other than a flip over on landing. No fatal accidents at all.

And just a note, I am sure roll overs are as common if not more so to the low to the ground HTL machines. Look at all the Raf 2000's that have flipped over, and I am sure Aircommands and Bensens and so on and so forth have all had plenty of roll overs.

But back to my point.... as far as I know Zero dominator accidents and zero fatal crashes. How many RAF crashes? Aircommand? Sportcopter? Soma? Bandit? Etc...

I am not out here to Down someone elses pride and joy. I am just stating my opinion, and that is that given a choice the Dominator - Sparrowhawk type gyroplane - and even better the Little wing - is Much better machine for ANY gyro pilot for any mission. Newbies, old timers, Cattle mustering folks, All of us are much better off in one of these types of machines than what a lot of us are currently flying.

I am not a safety Nazi, but I believe there is a significant added risk to flying these - Bad - design gyroplanes over the newer - Better - design options. If I was to try to be a safety nazi I would say not to fly a gyro at all and stick to fixed wings where the wings will still be there and the plane will still fly with negative G's etc... OR I would say not to fly at all, it is just too risky.

[StanFoster]

Ron: I guess I am getting thin skinned on hearing how bad an Air Command and RAF handle. I just dont see it.....thats my opinion. I could not help but to respond. I will just respond with pictures of Illinois territory happily and safely zooming underneath. :)

Nothing but positive posts, no matter whats said. :)

[birdy]

Gyroron
Maybe you are directing your fire at me,that's cool ,I'v got broad shoulders to go with my thick head. :)
If you are shoot'n at me ,you should not talk about ignorance. >:(

You know zip about what I do,the conditions I do it in and least of all,the machine I fly.You also don't know that I had stabs on both of my machines,and I KNOW the mustering one is more ajile without it.
You also assume I'd argue against CLT.Try to find anywhere in this or the oz forum where I have.CLT is logical to me,why would I argue against it??Just because I don't have CLT machines don't mean I don't agree,I just think it is not the deamon some make it out to be,for some people.[to an extent.]

Paul,both machines will be at BS,we can have a good long yarn there over a couple o rums.I'v only one mob of ferel bulls to yard and sell and then I'll run the STEED in,I'll run the RAF in on friday. ;)

Chuck mate,don't sulk,I like your SHORT and humerous posts. ;D

[Chuck Irby]

When I stated, above, that I wasn't going to read this thread again, I meant it.... at that time. However, then I saw that my favorite poster (the Birdman) had made a new post to it, I couldn't help myself, I had to read it. Then, just like it was a damn soap opera, I had to go back and read every post that I had missed. I had no idea, until now, but I now know that I am addicted to this thread. HELP!

[mceagle]

Ron said,
"as far as I know Zero dominator accidents and zero fatal crashes"
Check out the NSTB report of an accident dated 8 Sept. 02
This is only one however in an otherwise excellent safety record.

[gyrogreg]

This Adler accident is an example of one concern when the "Power INStability" is too extreme. It can't be known for sure, but this could be a "precession stall" accident where, upon sudden power reduction, the severe nose / pitch attitude change could pitch the airframe more than enough to immediately stall one or both rotor blades. - about 10 degree sudden spindle angle change. This is one reason why it would be much preferable to have some limits on "Power instability" - how much the trimmed airspeed / airframe pitch attitude changes as a result of a power (thrust) change.

The proposed LSA standard is pretty liberal in its limits for "Power Stability". The LSA standard calls for no more than a 10% trimmed airspeed change upon a power change from Minimum Power Required airspeed (MPRS) to either full power or idle power. Additionally, the standard calls for no more than 20% trimmed airspeed upon a power change from MPRS to power off. These trimmed airspeed deviations are a bit moderate, but those airspeed changes should not result in an immediate spindle angle change of more than 10 degrees.

It must be pointed out that this Adler gyro was not a stock Dominator. The machine had been purposefully modified by the builder to be an even lower prop thrustline than normal - adhering to some theories (improper in IMHO) that the lower the prop thrustline, the better. Such a severe UNBALANCED prop thrustline offset would have certainly aggravated the "Power Stability" tolerances of that machine. Also, I have seen reports that the builder was experimenting with over-size rotors on this gyro - to improve performance in the high density altitude conditions in which he was flying. A larger rotor would be turning much slower and could be more susceptible to precession stall or loss of rotor RPM upon reduced g-loads (such as in a sudden nose-down pitch change. So, the conditions of this accident may have been at the extremes of these conditions and may not transfer to the standard design of this model - but this demonstrates the possible necessity for designers and pilots of these machines to recognize the issues with a highly unbalanced large prop thrustline offset. (Notice I am inferring any highly unbalanced prop thrustline - high or low! Severe sudden pitch changes upon sudden power changes could, theoretically, produce a precession stall - it doesn't matter which direction the pitch movement is - if a sudden high spindle angle change is made, it is possible to stall one or more blades IMMEDIATELY – you don’t have to wait for the rotor to slow down! However, a nose-down direction of the sudden spindle angle change - as possible in the Adler accident case - would be a worse direction because it could also immediately induce more nose down movement once the gyro airframe attitude rotates nose-down to the point where the CG is aft of the RTV. At that point, the negative g load could progressively compound the nose-down pitching toward a buntover. (not a PPO!) The nose-down pitching upon a sudden power reduction in the case of this Adler machine, would be compounded because both the loss of nose-high prop thrust and the existing UP-LOADED HS would quickly pitch the nose toward neutral attitude and lower - negative G-Load stability and buntover (RTV moving forward and past the CG quickly because of the sudden unbalance of static moments on the airframe.) Another mechanism in this configuration – very low prop thrustline – can contribute to a sudden severe nose-down pitch change. The fully immersed HS, when power is applied, is enhancing the HS lift – when power is applied. Upon a reduction of power, the HS lift enhancement is considerably less – perhaps ½ the lift force. Initially, upon power loss, that is good, because it immediately reduces the nose-down moment from the HS. BUT, upon the nose pitching below level HS AOA, the HS contributes less nose-up moment to counter the nose-down inertia of the airframe at this point – the CG continues to move aft of the RTV and aggravates the g-load divergent pitch reaction toward buntover.

This accident also points out a bit of presumption many people make. The presumption is that the rotor RPM must have dropped - due to reduced g-loads. There is an alternate mechanism in this type accident - "precession stall". A sudden severe spindle angle change - cyclic input exceeding the stall AOA of one or more blades, could immediately cause severe flap – exceeding the flapping and cyclic ranges - with the same results as reported in the full NTSB narrative report on this accident. The rotor does not have to slow down from the reduced g load – it can simply stall one or more rotor blades outright, without ever slowing the rotor before its destruction!

This points out that such “pitch related” accidents are not necessarily full “buntovers” or PPO. Once the airframe pitches severely for any reason – sudden power change, incipient buntover, pilot over-reaction – precession stall is likely: Sudden rotor blade stall and sudden dissymmetry of lift that exceeds the teeter and cyclic freedom of movement – blade severe flapping and bending and contact with the airframe. This mechanism would be virtually indistinguishable from the slow rotor or negative g mechanisms that are popularly assumed.

Not pointing fingers, just using this example to illustrate one of the reasons for considering the “Power Stability” of a gyro – the “balance” of the prop thrustline by the HS. The idea is that the HS must be reacting to the prop thrust to “balance” the airframe attitude so that changes in prop thrust will be “balanced” or countered by the HS reaction to propwash. Or, another way to do this is to just have a very large HS that will overpower the other static pitch moments and prevent sudden severe airframe pitch changes – even upon severe power changes!

[Chuck Irby]

GyroGreg,

An excellent, and very informative post.

Thank you!

[StanFoster]

Greg: Your posts are so imformative. I am always sifting back through them gaining more information.

Hey...I am looking forward to talking with you more at Shelbyville. I will definately be flying my RAF down and staying for another day this time.

Stan

[GyroRon]

Yes that gyro was NOT a dominator.

[mceagle]

Greg, another good post as usual.

I wonder how many gyroplane accidents could have been caused by just such scenarios and have been passed off as negative “G” or PPO. To the casual onlooker it could quite easily look that way.
I am going to get myself in hot water here but I firmly believe that there is a push towards “technical” safety in preference to pilot safety, where in fact they should be one and the same thing.
Let me further explain. Statistics show that pilot most at risk is the low gyroplane hour pilot, so he is the one safety design issues should be addressed towards.
The low hour pilot has less experience, less than positive reactions and reaction times and generally, less knowledge of the mechanics and aerodynamics of gyroplanes. He is normally OK, but when confronted with a situation somewhat less than ordinary, he may not have the automatic reactive skills required to make the right corrective movements, indeed he may even make the opposite movement after his first attempt at a “nudge” in the right direction didn’t appear to produce the required correction (most Instructors will know what I mean). In the wrong situation, the result could be “Good night John-Boy”.
The main consideration in safety should be to lessen the possibility of the low hour pilot being able to get himself into an unrecoverable situation. (My considerable attention to the low hour pilot is because he is most at risk, and anything done to improve his safety should automatically flow on to the rest of the Gyroplane community). A typical example of improving safety is the fitting of ABS braking systems to most modern cars, where now even an inexperienced driver cannot lock the wheels and loose control when braking and turning to avoid an object.
To stop the inexperienced pilot getting into an unrecoverable situation, we must minimise the possibility of his getting into that situation on the first place.
We cannot do much about the weather, except cautioning the pilot about flying in bad conditions. Of course good thorough training is a must, but even so, it is only the first stage in pilot education. Lastly the Gyroplane itself must be made as safe and as forgiving as possible. This is the subject that is being given most consideration at the moment and for a good reason – it is a very complicated issue.
Focus is mainly on the stability of the gyroplane itself but to a lesser extent, we should also consider the pilot, or rather the gyroplane/pilot combination. It matters little if the gyroplane passes a stability test, and then it is flown by the new owner, sitting on the edge of the seat with a lap belt only, using the joystick and the throttle to balance the upper half of his body. Having daylight between the pilots back and the seat is more common in the low hour pilot, not only because they have not yet learnt to relax but also because most gyroplanes are designed without any consideration for pilot comfort or ergonomics. Just check out the poor seating comfort in a RAF 2000 and you will know what I mean. If a pilot was to be comfortable and relaxed in his cockpit then he stands a far better chance of maintaining complete control over his aircraft. Total control over a joystick depends on the pilot’s stability in his seating position. This is a point that is mostly overlooked, and is why I am also a believer in the fitting of shoulder harness, which seems to be a sore point in the United States. If a pilot is secure and comfortable in his seating position, he stands a far better chance of maintaining control in an awkward or abnormal attitude, than he would if pilot induced or atmospheric “G” forces influenced his body.

The gyroplane itself should have basic stability considerations that make it easier and less fatiguing to control for the low hour pilot. Such considerations should start right from ground handling (taxiing) through to any manoeuvre expected to be able to be used in normal flight, at any power setting, including sudden engine failure.
There would appear to be little consideration given to ground handling, which is a shame. Good ground handling makes the transition from ground to air so much more comfortable that there is less workload for the pilot and consequently less stress. There are still many pilots around that “fear” the take off, and cannot wait to get the aircraft into the air to sort it out. In all fairness to the gyro, in many cases this is the fault of poor instruction.

The in air handling of the gyro has three parameters – pitch, roll and yaw. Stability in roll does not seem to be a big problem with gyros. I did have a student at one stage that managed to pendulum the gyro about the roll axis consistently and it was quite unnerving. The funny thing was that this student did not have any problems about the pitch axis. This is not the fault of the gyro but that of the pilot and is corrected with normal training.
Stability in yaw appears to be coming more of a concern with the fitment of nose cones and pods. There is no rocket science required here and is easy to make a gyroplane stable in yaw. It is just a pity that some manufactures have allowed gyroplanes onto the market with less than adequate yaw stability. It must be remembered also that good yaw stability must be available under all conditions, including engine failure and with doors fitted. After reading recent posts, I wonder how some gyros would fare with both the doors fitted and an engine failure at the same time.
Stability in pitch is the main one that causes us grief. Once again, if we look after the low hour pilot, then the stability improvements should flow on to the rest. The gyroplane must be designed so that the possibility of it doing something that can catch the pilot unawares is minimised. There are no arguments about the need for positive dynamic stability in pitch, and this can be achieved for almost any gyroplane configuration in normal flight. It is when other possible conditions of flight are encountered that the pursuit of stability becomes more complicated. We should really be listing these other possible “conditions” and treating them with the importance that they deserve. That is, the stronger the possibility of an untoward event happening, the higher the priority it should be given. Most pitch stability issues have been given ample air time so I do not intend to go over most of that which has already been adequately covered. However there is one instance where I disagree with popular belief and that is the behaviour of the gyro with sudden power changes.
I believe that the gyro should track straight and level with a sudden change in power, with no sudden pitch change that might encourage a low time pilot to take corrective action. The gyro would still behave in the correct sense and climb as airspeed increased or lower the nose and descend as airspeed decreased, but it should not be subject to sudden (possibly violent) pitch changes.
At first thought this seems easy (barring other considerations) – just put the thrust line through the C of G. This will not do the job, not only for the reasons that Greg has mentioned above but also because of the fact that the C of G of the rotor disc is up to a foot above the pitch pivot in the rotor head, causing a movement back or forward under acceleration (or deceleration). This tilt back or forward of the “Rotor Head” causes the rotor disc to tilt back or forward, initiating a tendency for the gyroplane to climb or descend. This secondary reaction can only be stopped with a firm enough grip on the joystick to stop it moving forward or back. If the pilot is using the correct “float the stick” method, it may be too late if the acceleration or deceleration is caused by something other than a prepared pilot.

The tendency to pitch under accelerative forces can be countered by a thrustline that is higher than the C of G by an amount that depends on the height of the centre of mass of the rotor disc above the pitch pivot and the available accelerative force. This thrust line offset should be balanced against the PPO tendency under reduced “G” conditions. My experience has proven to me that the offset can be considerably more than is being popularly suggested (2”) and full power can be applied under reduced “G” conditions without the tendency to PPO. Put simply, the induced increase in angle of attack of the rotor disc moves the rotor thrust vector forward, which counteracts the PPO tendency, and keeps the gyro in a more level attitude.
The result is the same under severe deceleration (eg sudden engine cut or seizure). The induced decrease in disc angle of attack moves the rotor thrust vector rearward, which counteracts the tendency for the gyro to nose up and again keeps it in a more level attitude.

The opposite scenario becomes interesting – when the thrustline is below the C of G. In both instances, acceleration and deceleration, the pitching tendencies are greater rather than reduced, because the tendency for the low thrust line to raise or lower the nose is now amplified by the shift in the rotor thrust vector. I would suggest that it would be impossible to maintain control in such a machine in the event of sudden full power fluctuations such as may be encountered in a fuel starvation situation.

Balancing all these forces becomes a very delicate operation and I do not believe that any one design can achieve all. Ideally gyroplanes set up different ways would be required to do different jobs and each would have to be treated with respect and flown within different set parameters.

And of course there is no substitute for good and thorough flight training from a competent Instructor.

[birdy]

Ahmen,I got sore eyes reading it all but I reckon you'r pretty well spoton.
BTW,dose anyone know how to make the RAF seats more comfortable???My legs go dead after a couple of hours of sitting still,and I don't have any natural padding on my cheeks. ;D

[StanFoster]

Tim: Good post and right on as well. I have always said CLT is the best setup.......especially for new pilots. Your student with problems with the roll axis is a good example. Obviously the pitch axis is the hardest to learn.

If one is not relaxed while flying...then he needs all the stability he can find.....either in a Dominator....SparrowHawk...Magni...

Just being relaxed is a form of stability. Birdy has to be very relaxed to do his awesome cattle mustering. :)

[GyroRon]

Relaxed means confident in ones piloting and confident in the machine and confident in the weather and so on. I agree with Stan you need to be relaxed when flying and comfortable and confident of yourself and your machine. But let me add my two cents.

One is that no matter what you fly, if you are not relaxed comfortable and confident then you need to stay on the ground till you are. No matter what you fly - CLt or HTl or whatever - you shouldn't be up there scared of this or that or just being a nervous wreck.


Two all the relaxing and comfort and confidence in the world does not make ANY flying machine totally safe.

[Doug Riley]

There was a fatal crash of something that really WAS a Dominator in New Hampshire 2-3 years ago. Based on the eyewitness account of an experienced gyronaut who watched, it appears that the pilot simply didn't know how to fly gyros beyond the crow-hop stage. He blasted off to pattern height and fell out of a turn.

Even a Dominator won't fly itself. You can still get so far behind the power curve that you mush out of the sky. Having the thrustline below the CG can be a hindrance in this case; the gyro does tend to nose up and slow down at higher power settings, and you have to know not to let it do that. Simply powering back will drop the nose and maintain airspeed.

Tim McEagle, your comment about the rotor mass lagging and pulling back on the spindle would be convincing if we were dealing with NASCAR racers that will snap your neck when you put the pedal down. The acceleration in an aircraft when the throttle is opened, however, is so gradual that you can barely feel it. It isn't an important factor in stick pressures.

The rotor does tend to tip back away from the direction of travel as airspeed increases, as a result of increasing dissymetry of lift and increased flapping angle. This is sometimes called "rotor blowback." The "offset" in the offset gimbal head is designed to counteract it.

Certainly, radical pitching movements of the airframe are indesirable. The frame movements necessary to maintain airspeed with throttle changes are rather gentle, however, and shouldn't scare anyone nor lead to PIO -- especially since the HS that helps to produce these motions also damps out oscillations.

It's very possible that Steve Adler's machine DID have radical pitching reactions to throttle changes. It would take a controlled experiment to discover whether these movements were big and sudden enough to cause a precession stall. Such a stall requires several degrees of pitch motion in a SINGLE rev of the rotor, or about 1/6 of a second. That is some fast pitching and is difficult even to picture, short of an engine-powered PPO.

[gyrogreg]

Tim (mceagle),

Very good points in your post. I do believe that the pilot may be the most important ingredient in gyro safety – stability or otherwise. But not necessarily for stability and control reasons! I believe that a good stable gyro, one with inherent control reactions that respond logically and properly to control inputs, and that do not over-excite the pilot into over control, will nearly prevent the common gyro pitch related accidents. We do know that a gyro can be design so that there is very little effort or expertise required to fly it – landing it is another matter!

I believe the judgment of the gyro pilot is the most important ingredient – not necessarily their flying skill. The pilot must be able to make good decisions, recognize and assess and compensate for risk factors, etc. Decision making include decisions on what gyros to fly, when and how to fly them. Those decisions must consider the capabilities and limits of the machine and the proficiency and limits of the pilot.

This is why I make so much emphasis on the technical knowledge elements of gyro stability. I do not do this to push one design over another. I do this so that gyro pilots might better recognize the limits and capabilities involved. Knowledge is the basis of making good decisions. When a pilot buys or flies a gyro without the basic knowledge to assess those issues, they might very well walk into unknown problems. Such pilots may “not know what they don’t know”.

This is the reason behind my work on the ASTM Gyro standard, and why I am wanting so badly to get it approved and released – so we can reference it as our “gospel” to educate the gyro community better – so that they might make better decisions.

Have you seen my article on Gyro Decision Making – linked below. A pilot can probably fly even the most dangerous aircraft if they have a good knowledge base to recognize and accommodate the limits of the machine and its pilot.

---------------------------------------------------------------------

Another point you make is very very good: I also suspect that many accidents may not really be a “PPO” or “buntover”. It is very possible that many of these accidents are simply precession stall from too quick and strong of cyclic input from either pilot over-reaction or airframe severe movements. This can be from both pitch and roll cyclic inputs. I often hear it explained to me that this or that accident was not PPO! Some people defending a particular design explain that the tail “rose up into the rotor” or the pilot “pulled the rotor down into the tail”!!!!! These really may not be PPO or buntover by the definition of PPO or buntover! But both an airframe’s severe reaction to an external uncommanded input, or the gyros reaction to an over-reaction of the pilot are stability related issues. If the airframe inherently took care of all outside uncommanded disturbances, and if the airframe reaction did not excite pilot over-reaction, those same accidents would not occur. A stable airframe, one that does not require excessive pilot input to stabilize it, will not cause or provoke such accidents. A stable airframe pays off in many, many ways!!!!!!!

Your point about the pivot axis of the rotor spindle is another good point about why a slightly high CG can be benefitial. I do not intend to dis the CLT people, apparently some of these can be made very stable too - Sparrow Hawk example. I can just explain the moments and reactions easier with a properly "balanced " slightly high prop thrustline.

- Greg Gremminger

[quadrirotor]

Greg; where can we consult the proposed "Gospel"?

[gyrogreg]

Consult the ASTM Gyroplane standard:

Not able to at this time - it is still in development. But, it is close to beeing approved - hopefully final ballot in April. The ASTM members working on the standard, all have access to the full standard during development. As members of ASTM, they can also choose to get a copy of approved ASTM standards.

But, there is a bit of a difficulty, the final document will be copyrighted as the property of ASTM. They are in the business of selling standards documents. The EAA and FAA and others made the decision to use the expertise and resources and tools and credibility of the ASTM, in order to best develop the standard - a standard with the worldwide credibility of the ASTM process behind it. But, this does mean that the ASTM owns the final document. After it is approved, you would be able to purchase it for a fee - $150 - $200? This is really intended for the manufacturers and regulating authories, and insurance companies, etc. to purchase and use in their business of selling and regulating and insuring aircraft.

BUT, this will not hinder us. The ASTM understands that a major intent of the FAA and us is to use this document to spread the "gospel" of safe gyros - to the gyro community worldwide. The ASTM has told me we can publish sections of the standard. Once released, I intend to publish articles on specific sections of the standard - break it into more understandable segments - with a layamen's explanation of what it means and how to design for it and check it on your gyro. I may never get to cover all the issues in the ASTM Gyroplane Design and Performance standard - many sections on structure, cockpit design, etc. But, I intend to cover the important elements quickly and concisely and continuously in the gyroplane magazines.

The ASTM Design and Performance standard does not really cover everything you might think the "gospel" would cover. It does not tell you how (prescribe) to design to meet the standard. It does tell you what the design must do to meet the requirement - static stability requirements, dynamic stability requirements, controllability and maneuverabiulity requirements, landing gear drop test requirements, etc. The standard also does not tell you how to test to verify how to meet these requirements (There may be a follow on "Test Methods" document developed if the industry needs one later!)

So, we hope to spread the "gospel" according to ASTM in the gyroplane media. This means we will not only provide the specific wording in the standard, we will explain it in plain language, we will suggest ways to design for that requirement, and we will suggest ways to test if you meet the reqiurement. I have already done some of this in articles and posts on static stability - Power, G-Load and Airspeed static stability. But, when I do it next time, I hope I can reference the specific requirement in the ASTM D&P standard!

Please note, this standard will not be a REQUIREMENT for most gyro people or manufacturers. It will be a guideline. Only manufacturers who intend to sell gyroplanes under the new U.S. Light Sport aircraft rules would have to meet the requirements in the standard. We will present the requirements of the standard as reinforced guidelines. You can choose which ones to meet or which ones not to meet - but you will make those choices, hopefully, with a thorough understanding of the issues and risks and limitations of your particular gyro.

One thing we do expect from this though, is that ALL gyro manufacturers will have strong market and consumer pressures to meet the standard - or the important parts of it. Once we have an "educated consumer" market, we expect those customers to be making more requirements, ask more questions, expect better answers of manufacturers - if they are going to sell their products. Through consumer knowledge, we hope to influence safer gyros. But if you want to build or sell a gyro that does not meet this standard, you would be free to do so. Other organizations, such as Aviation Authorities in other countries, insurance companies, etc., might also use the standard or require adjherence to this standard or specific parts of it. This ASTM standard will be recognized worldwide, and such authorities can use parts of or add to the requirements in the standard for their own purposes. Such as a civil aivation authority in TimBukToo might require meeting all to the standard and additionally restrict the approved gyro to one seat!

In the U.S., you could still build and fly gyros that do not meet even any of the standard - and still fly it in the Ultralight or Experimental category. But, hopefully, you would be encouraged to adhere to some of the standard as guidelines for your own safety.

-Greg Gremminger :( :D

[Udi]

Greg - thanks for the update and for all the great work you are doing to promote gyro safety. I really hope the FAA will adopt the proposed standards; this may help gyroplanes become part of mainstream aviation. This process is long over due, and it could not have started without people like you stepping up to the plate and doing the necessary work. Thanks again!

With regard to the Adler accident, I agree with everything that Greg and Doug said, and I would like to add my own little twist. As Greg and Doug have said, one likely scenario was an engine out event. There may have been other factors involved, but lets assume that that was the root cause.

In a low-thrust-line gyro, the rotor RTV is located far behind the CG, to counter the engine nose-up pitching moment (cause by a very low engine thrust line). This is a very stable condition, as long as everything is ok. When the engine quits, however, the engine nose up moment disappears; and the nose drops quickly (pulled down by the back RTV), possibly causing precession stall, or even reversal of the rotor AOA.

The key here is that this all happened too quickly for the pilot to be able to react. An effective damping force would have slowed down the rate of nose down pitching, possibly allowing proper pilot recovery response. In gyros, this usually means a large stab, located far behind the CG. In this particular case, the gyro had a Dominator stab, located in the prop wash, not too far behind the CG.

The Dom stab is very effective when immersed in the prop wash. When the engine stops (if this is really what has happened), the power of the stab becomes smaller because there is no longer prop wash to boost power, and the location of the stab (behind the bulky airframe/engine) prevents clean airflow. I am wondering whether a larger stab, mounted in the free air, far back, may have saved the day by making the pitching rate significantly slower.

We talk a lot about dynamic stability. Although pitch damping is part of the normal pitch stability requirements, it plays an especially important role in extreme diversions. Pitch damping is a linear function of the size of the stab, and a **square** function of the distance of the stab from the CG. For these reasons, I would personally opt for a keel-mounted stab, located as far back as practical, over a close-coupled stab located inside the prop wash.

Udi-

[quadrirotor]

Why Gyro does not deserve the same treatment as any aircraft ?:
-design by aeronautical engeneers (let's say someone as Martin Hollman)

-testing in a wind tunnel (or some kind of... a frame on a trailor...) to confirm figures and behavior in static and dynamic states, loss of power and so on...
http://www.wingco.com/

-test flight by a test pilot...

[Doug Riley]

Udi: I know that you know that the problem is how far back "practical" can be. The space in which we can locate a tail on a pusher gyro is a triangle. Its top line is the line of the rotor blades in their flapped-back and drooping position. It has a vertical leg in the plane of the prop, but that area is the area of least leverage, and hence not very interesting. The bottommost leg is the ground in nose-up rotation... and that's the one that really limits our ability to put a non-immersed HS very far back.

We need to be able to rotate a bit on takeoff and landing to avoid excessive speeds for each. (I speak with some experience about this. The Gyrobee has a lower-than-usual rock-back angle because of frame geometry. You have to alter your "balancing" takeoff technique as a result, and a full flare landing is going to put the the tailwheel down significantly before he mains. It would be nice to have more tailwheel clearance on the 'Bee.)

As you extend the tail boom back into the "unimmersed zone," however, you make the rock-back angle shallower and shallower. Eventually, you have no rock-back at all. That's OK with a taildragger, since it's rocked back all the time. With tri-gear, however, the limit on ability to rotate is undesirable.

Energizing the HS with prop blast helps overcome the twin problems of limits on tail boom length and the very low-speed abilities of the gyro. I like an HS configuration that's partly in and partly outside the blast, such as is probably the case with the Magni and is definitely the case with the Gyrobee.

A gyro with (a) centered thrustline, (b) a body that doesn't produce large pitching moments and (c) a Dominator-style HS is probably fine as long as the HS is not run at a lot of negative incidence. If it IS set up that way, there'll be a large nose-down swing when the engine quits. Too much of that is bad, as most of us seem to agree.

[Greg Mitchell]

Gentlemen,

Thanks for perservering with this thread, McEagle, Greg, Doug, Udi, the last couple of pages has furnished even more info and shed more light on this topic for us all.

Regards,

Mitch.

[mceagle]

Doug,
The acceleration ability of the type of gyro commonly used here for mustering (912S) is I think significant. I know one can out accelerate my V6 sedan from 40mph to 80 mph (as you say, not NASCAR acceleration) but still enough to feel the pressure in the seat back rest. When you do accelerate or decelerate you can feel the joystick trying to move forward or back in response. Try it solo in your 912S Dominator trainer and let me know what you come up with - your opinion is certainly very valuable. If I am barking up the wrong tree I would like to know.

My article was in no way intended to belittle the CLT believers but rather to throw another spoke into the stability wheel for discussion. I believe that good design consideration (or modifications) should be able to make practically any configuration safe as long as it falls within certain parameters. The problem is that we cannot set accurate parameters because they vary so much with every aircraft - eg. the thrustline of the Little Wing could probably be 10" from the C of G and it would still pass stability tests whereas the RAF with a 10" offset has proven to be unstable.

I guess (as Greg has said many times) the final proof will have to be in the flight stability tests, regardless of the configuration.

[Udi]

Doug,

Some rough measurements from my Air Command: A tall tail would be installed at about 42 inches from the CG. My current low stab is located about 66 inches from the CG. Assuming the same stab is installed in both places, the keel mounted stab will have 66/42=1.6 times the power of the prop stab, and 1.6^2=2.7 times the damping!

Granted, when the prop is blasting on the tall stab it probably has about the same power as the keel mounted stab, and maybe even more at very low airspeeds. But consider again the case of an engine out event - the keel-mounted stab will have almost three times more damping than the tall tail stab.

This is by no means a stab (ha ha) at the tall tail - Dominators and their clones are excellent machines with a great safety record. But designers must take into account events in which the prop blast is not there. And we shouldn't look down upon gyros with no tall tail - their design may have merit.

Udi-

[gyromike]

Udi,

If the engine is out, what is the stabilizer damping? There is no pitching force being applied to the frame by a dead engine.

No power.
No Power Pushover.

Or am I missing something?

[Aussie_Paul]

I agree a little bit Mike. How do you have a PPO with the engine stopped?

Aussie Paul.

[gyrogreg]

Mike and Paul,

Good questions in the pursuit of knowledge. Knowledge is Safety! Only with a good knowledge base can good decisions be made!

There is a persistent misunderstanding at the root of your questions. First, let me say, that it is perfectly true, that you can’t have a PPO (Power Pushover) without an “unbalanced” high propeller thrustline. You also can’t have a PPO, by definition, if there is no “power” to “push it over”. BUT, a PPO is only one form of a buntover. It is entirely possible to buntover any gyro – no matter what the propeller thrustline, or whether there is power (prop thrust) applied or not. (Sometimes Doug Riley likes to call another form of a buntover as a “Drag Pullover”!)

Perhaps too often, a buntover has been described as a PPO because it is relatively easy to envision that a high prop thrustline can initiate a buntover. A PPO by definition requires power (prop thrust) applied to be called a PPO. But, a high prop thrustline is just one possible mechanism that can initiate a buntover. Anything that causes or initiates the nose rapidly lowering in pitch – especially if or when the CG is aft of the RTV – can initiate a buntover.

It might help if you would review some explanation of terms in the Glossary of Gyro Terms (http://www.magnigyro.com/USA/feature_articles/GyroTerms.pdf):

Bunt-Over:
A sudden uncontrolled forward tumble about the pitch axis in a gyro; unrecoverable fatal. A buntover is a self-sustaining divergent nose-down pitching motion, accelerated and propagated by rapidly changing or diminishing balancing moments on the airframe. Typically, when the nose-down pitch of the airframe and/or rotor disk reaches a certain point, the nose-down pitching self-perpetuates and accelerates (positive feedback) to result in a full forward tumble. “Power Push-Over” is one form of a “Bunt-Over”, but not necessarily the only form of a bunt-over. A “Bunt-Over” is not necessarily a Power Push-Over. Without adequate gyroplane configuration design, a bunt-over can be initiated by wind gust, pilot over-reaction, or sudden power changes. See also “Power Push-
Over” and “Power Torque-Over.”

Power Push-Over – PPO:
By definition, PPO is a specific variety of bunt-over that is the result of a high propeller thrustline that is suddenly no longer balanced by other moments on the airframe – thereby, the “power” pushes the nose over downward. Therefore, by definition, a Power Push-Over can only occur in a high propeller thrustline configured gyroplane. But, a PPO is not necessarily the only form of a “Bunt-Over”. A PPO is self-sustaining when the balancing rotor thrust is rapidly decreased at zero or near zero angle of attack of the rotor disk. See also “Bunt-Over.”

With no power applied, and all other configuration and HS issues being the same, a high prop thrustline and a low prop thrustline (and a CLT) will all have exactly the same static and dynamic stability factors! With no power applied, either one can just as readily buntover if there is some action or reaction that causes the nose to rapidly lower so that the RTV becomes forward of the CG. At that point, the progressive action of reducing G-load with the CG aft of the RTV causes more nose-down pitch action and a very fast and progressive buntover. (As I’ve suggested before, at some point the rapid and extreme angle change of the spindle will likely stall one or more rotor blades – precession stall – before an actual “buntover” can occur!)

Take the case of an “unbalanced” high prop thrustline: This is the configuration with which the preponderance of “buntover” accidents can occur, and it may be exactly correct to call these PPO! In smooth and unchanging flight, with power applied, the nose is forced lower to possibly even the point where the CG is already aft of the RTV. This situation is prone to a buntover – the PPO variety - if anything causes the nose to rapidly pitch lower where the g-load on the rotor is caused to reduce. This is the too frequent mechanism of buntovers. This is the popularly visualized PPO version of a buntover – at lower g-load, the drag of the rotor is reduced and the thrust of the propeller pushes it over. Many people can visualize this, but this is not technically correct in its reasoning. What really is happening is that the reduced g-load on the rotor causes further nose-down pitch action – incipient “buntover” – because the “BALANCE of ALL static moments on the airframe is upset. It is not technically correct to consider only the balance of just two of the static moments on the airframe (the prop thrust balancing the rotor drag! The complete and more accurate way to consider the mechanisms of buntover is to consider all of the moments on the airframe, of which prop thrust and rotor drag are only two of those moments. The confusion many people have with this is that you can’t mix rotor lift, rotor drag and rotor thrust in the same analysis. Rotor thrust is the resultant of both rotor drag and rotor lift. Visualizing only rotor drag leads to this popular misunderstanding. However, it is very true that the majority of “buntover” accidents have occurred in “unbalanced” high prop thrustline machines, and this is probably the most risky configuration. At high power settings, this configuration is set up for a buntover – that can more likely happen when power is applied.

Now, take the case of a low prop thrustline: With power applied, this machine cannot, by definition PPO! And, with power applied, it is highly unlikely that it can buntover – in any form. But, with no power applied, this configuration is not so impervious to a buntover! In high speed flight especially, with no power applied (high speed descent), the CG is not so securely forward of the RTV. A buntover is still possible if there is a sudden nose-down pitching of the gyro – suddenly reducing g-load on the rotor. This action can move the RTV forward of the CG and the decreasing g-load on the rotor causes the nose to progressively pitch lower – incipient “buntover”. This nose-lowering, CG aft of the RTV situation is possible upon a sudden power reduction from normal, high power flight. As described by others above, the sudden reduction of power starts the nose pitching downward, and without immediate and proficient pilot reaction on the cyclic, the gyro can enter the G-load unstable condition (CG aft of the RTV) and the buntover can progress. This mechanism for a buntover certainly cannot be called a PPO – but the results are the same! And this mechnaism for a buntover probably does not occur so often because it might be more rare that a sudden power reduction happens during high speed flight. But, also, simply high speed flight without the “stability augmentation” of power applied on this low prop thrustline configuration, makes that gyro fly with less stability margin of safety when power is low or off. Many gyro configurations might be very safe and stable in certain corners of their “flight safety envelope”, but pilots should at least be aware of corners of the flight envelope that might not present such margins of safety. In many cases, over-confidence has led to poor or mistaken decisions with fatal results!

I think this is an important issue that gyro pilots should understand, because, to not appreciate this issue leads to over-confidences and misunderstanding of the limits of your particular gyro. To fly any gyro with the presumption that it can’t do anything bad (because it has CLT or a low prop thrustline or a HS) can lead to poor decision in gyro operation. The stability parameters that we are defining in the ASTM gyroplane standard are intended to minimize such possible issues in any corners of the flight envelope. The “Static Power Stability” requirement directly addresses this issue (and others). Flight testing is tho only real way the margins of safety can be determined for any gyro configuration. The requirements of the ASTM standard will describe such flight performance criteria (already addressed in several PR and other articles and numbers of posts by myself and others)

[Chuck Irby]

WOW! I left for just over two days and was overwhelmed with the email and new posts. It looks as though it might take quite a while to catch up.

[gyrogreg]

Mike,

Your question about what is the HS damping if the engine is dead perhaps this needs more explanation. Many people have difficulty understanding and differentiating the concepts of STATIC stability and DYNAMIC stability. “Damping” is an issue with DYNAMIC stability – that the “dynamic” oscillations lessen, and how quickly. The HS actually performs a dual role on an aircraft, and especially on a gyroplane. “Damping” is the benefit that a HS provides for DYNAMIC stability. The term “balancing” better defines the benefit of the HS for static stability issues. Your term “pitching force” as you are using it referring to a dead engine, actually refers to the static effect of a change in the “balance” of all the “pitching forces” (moments about the CG of the aircraft). With or without the engine running, the HS provides dynamic stabilization effects from it’s lift forces produced by its movement through the air. Without the engine running, it is still producing a “balancing” moment for all the other static moments on the airframe. And without the engine running, it is still acting as a “dynamic dampener”, damping the natural pitch oscillations of the gyroplane. There are still static and dynamic stability issues whether the engine is running or not. There are still static and dynamic effects and benefits of the HS, even without the engine running. Your question is actually mixing terminology between “pitching force” – a static stability issue – and “damping” a dynamic stability issue. This suggests there is need for a bit more basic explanation about static and dynamic stability, and what a HS does for each of these.

First, I recommend that you review some additional related terminology in the Glossary of Gyro Terms:
DAMPING,
DYNAMIC,
DYNAMIC STABILITY,
STATIC,
STATIC STABILITY,
HORIZONTAL STABILIZER
MOMENT

Static stability means that the aircraft (or any other free moving object) would tend to return to a steady state condition – if disturbed or changed from that condition. For instance, a steady state for a gyroplane in level smooth flight would be that the rotor is supporting 1 g load. Another steady state condition at the same time would be that the aircraft is flying at 60 mph. If anything disturbs this condition (wind, pilot action), the system will, if it is STATICALLY stable, try to return to that 1 g and 60 mph steady state. This system is statically stable.

A statically unstable system would be one that, once disturbed from either 1 g load or 60 mph would not tend to return to that steady state. Instead, it would tend to “diverge” to a worse deviation – 0.9g would go to 0.8g, then to 0.5g, then to 0.0 g, then to – 0.5g! 62 mph would diverge to 65 mph, then to 75 mph, etc. etc. Here you can see the makings of a buntover! The static pitch stability of a gyro is an issue to consider, with or without the engine running.

Dynamic stability is the way in which the aircraft, upon a disturbance, returns to its steady state. Does it do so slowly, quickly, with no over-shoot, or does it oscillate around the “steady state” condition, how fast are the oscillations, how quickly do the oscillations “dampen” out?. There is no such thing as DYNAMIC stability if the aircraft is not first STATICALLY stable – it just simply diverges from the steady state condition and does not try to get back to that condition. These “dynamic” oscillations can occur on only a statically stable gyro, but with or without the engine running. The dynamic pitch stability of a gyro is an issue to consider, with or without the engine running.

Dynamic stability is most often characterized by two parameters: What is the natural oscillation frequency of the gyroplane as it attempts to restore to the steady state condition. How quickly do those oscillations “damp” out. The HS has little aerodynamically to do with the natural frequency of pitch oscillations. The HS has everything to do with the “damping” rate of the oscillations. The HS may be the only passive “dampener” available for gyros! A highly “damped” gyro will tend to return to its steady state without overshooting or oscillating around the steady state condition. This “damping” effect occurs whether the engine is running or not running. The “damping” effect of the HS may be affected by the engine propwash – amplified or more effective if immersed in the propwash, and the point that Udi was making is that it may be less effective without the engine running if it’s effectiveness is enhanced when heavily immersed in the propwash.

So, the question about what is being damped when the engine is dead, simply misses the point. “Damping” is needed whether the engine is running or not. The HS is still providing the damping required to dynamically stabilize the gyro. The HS is still an element of the static “balance” of the gyro – it’s just that without the engine running, there is one less moment or “pitching force” among this static balance of the static moments. When the engine is not running, the remaining static moments on the airframe include: Rotor Thrust (RTV), Airframe Drag (relative to its offset from the CG), HS lift (down-lift or up-lift), and other aerodynamic moments such as a large sloping windscreen pushing the nose down forward of the CG.

[gyrogreg]

Dynamic and Static Stability – a visualization:

As a helpful visualization of these differences between static and dynamic stability, a popular analogy is a round bowl with a marble: With the bowl normally upright, place the marble in the very bottom of the bowl. This is the steady-state condition – the marble stays steady in the bottom of the bowl. Now, place the marble up the side of the bowl a bit, and let go – notice it rolls toward the bottom of the bowl – not up to the top rim. This is the static stability characteristic – the marble tends to go back to the bottom. Wait a while for the “dynamic” oscillations up and down the bowl sides to settle out, and the marble settles back into its steady-state at the bottom of the bowl.

Do this again, but this time note the rate of oscillation up and down the sides of the bowl, and how quickly it settles out and stops in the bottom. These are the “dynamic” characteristics of this statically stable system.

Now, picture a much shallower bowl, one that is maybe only ½ inch tall, but just as wide – the sides of the bowl are not nearly as steep. Now, when you release the marble, even just a few inches from the bottom center of the bowl, the marble still tends to roll back to the middle, but much slower this time. Also note that the oscillation rate as it overshoots the center – it is much slower and probably slower to “damp” to zero. For this example, the Static Stability of the marble is not as strong, and the dynamic characteristics are not the same.

Now, coat the inside of these bowls with a thin layer of felt. This provides friction as the marble rolls. This marble rolls more slowly toward the center, and does not oscillate as much, and may not even overshoot the center. This is the “damping” effect – analogous to what a HS does for a gyro.

Now, take each of these bowls and hold them up in your hands. Now move the bowl quickly sideways and then try to quickly stop the marble back in the steady-state middle of the bowl. Note how the marble responds in each case, and how easily the “pilot” can make it stop back in the middle. In the smaller bowl, it oscillates very quickly and will be most difficult to cause the marble to stop moving. In fact, the “pilot” might easily over-control this system to the point even of PIO. For the wider bowl, where the side slopes are not as steep, the slower oscillations are easier for the “pilot” to stop.

But, when the felt (stabilizer) coating the rolling surface in either bowl, the marble does not “deviate” from steady-state very far, and it is much easier for the “pilot” to restore the “steady-state” of the marble.

Doing all this using a flat plate instead of a curved bowl represents the condition of neutral stability – the marble tends not to try to return to the center of the plate. Now, hold the plate in your hand and introduce a sideways “disturbance”, and try to return the marble back to the center of the plate by your “pilot” action.

Now, do this with the original round bowls upside down. Note that it is very difficult to “balance” the marble on the top center of the upside down bowl. This is an example of Negative static stability. Note, there is no chance that the marble would oscillate around the top center of the bowl if disturbed from the “balanced” center position – “dynamic stability” is not even an issue in this case, it does not tend to oscillate around the steady-state condition, it just rolls off – diverges!! Now, hold the bowl in your hands, and see how hard it is to even keep the marble centered on the top, rounded center of the bowl – this is an example of the skills that need to be developed to fly a system that is negatively stable. Practice this for enough time to actually be able to keep the marble centered on top of the bowl. You’ll find it is easier to do this on the shallower upside down bowl, less negatively stable system! Now, once you have mastered this “balance”, you are now the “stabilizer” – the system (including you, the pilot) are a STATICALLY stable system. Now, see how much work and attention it takes to do this, and also see how easily you can restore the “stable” condition after a sideways disturbance. If you, the pilot, were actually able to stabilize this statically unstable upside-down bowl/marble system, you the pilot must now also provide the “dynamic” stability by trying to keep oscillations around the steady-state center to a minimum. Chances are, if you practice this balance long enough to easily accomplish it, a large enough disturbance might readily be over-controlled by the “pilot” and, initiate either a rapid “buntover”, or maybe even demonstrate PIO before you actually bunted over! Notice that the engine was never running on this bowl/marble analogy!

- Greg Gremminger

[Udi]

I would like to add another explanation of dynamic stability, or pitch damping. Greg's explanation was excellent, as usual, but it may be helpful for some people to hear it in my own lay words.

Damping is the force that is trying to resist any pitching movement, in any direction. Just like a shock absorber in a car. The amount, or magnitude, of the damping FORCE is NOT a function of the angle of attack of the stab. Rather, it is a function of the PITCHING SPEED, or the speed in which the stab is moving up, or down.

To get an idea of how this works, do this easy experiment. Fill your bathtub with water. Take a dinner plate, and submerge it vertically in the tub. Move the plate sideways, perpendicular to the face of the plate, very slowly in the water. Now try moving the plate quickly in the water.

When you move the plate slowly, there is almost no resistance - you can basically just let it move sideways with minimal effort. When you try and move the plate quickly, there is a significant resistance, and you have to put some muscle into it. This resisting force is equivalent to the damping force produced by the stab. It is not trying to return the gyro to it’s stable condition, it is simply resisting the up and down pitching motions.

The same resistance you felt with the plate in water happens with the stab. Slow stab movements up and down produce very little damping force. But when the gyro is making quick changes in pitch, that's when stab damping really kicks in.

This is also the reason why you would want to install your stab as far behind the gyro as possible. The damping force is a square function of the stab distance from the CG. By doubling the distance of the stab from the CG, you are actually quadrupling the damping force because the stab not only moves twice the distance (for any given pitching movement), it also moves twice faster. It’s like moving the plate four times faster in the tub.

Damping is good, and I don't think you can have too much of it.

Udi-

[gyrogreg]

Udi and Mike and all,

Here is another simple representation of Static and Dynamic stability:

The shock absorbers and springs on your car! The shock absorbers are the dynamic "damper"! You know how the suspension acts without shock absorbers - bounces a lot with every bump, and doesn't settle out very quickly. The rate of bouncing is the "natural frequency" of oscillation of the car and the springs.

The springs on the suspension provide "Static Stability" to the suspension system - determines the suspension height "steady-state" position. If the springs were missing, the suspension would bottom out and the shocks would not work at all. No static stability, therefore dynamic stability does not have any meaning because there is not a statically stable steady-state condition to return to - suspension is just bottomed out!

Springs provide a steady state position to which the suspension always tries to return - static stability.

The shock absorbers provide the dynamic "damping" that prevents the suspension from bouncing. The shock absorber is also "tuned" with the car's inertia and springs to quickly return the suspension to steady state without a lot of lag and without a lot of extra bouncing.

Picture how a car rides without any shock absorbers - only springs! Now picture how it rides with only shock absorbers, no springs. Now picture how the combination of both springs and shock absorbers (static and dynamic stability) ride!

Now picture the "pilot" workload if there were somehow a driver control for you to control the suspension - without springs! - without shock absorbers! The pilot would be working very hard. But, with the proper springs and dampers, the pilot (driver) doesn't have to do anything, and even the most severe bumps in the road do not require "pilot" control of the suspension to drive safely. But, without either springs or shock absorbers (or both), think of how dangerous it might be to go down a bumpy road - especially at high speed!

In the gyro, the HS actually provides both functions - statically stable point to always tend to return to, and the dynamic "damping" to make it return to the steady-state condition smoothly without a lot of over-shoot or bouncing or pilot input! The HS provides both Aispeed and G-Load static stability in a gyro. The HS positions the CG forward of the RTV to provide positive G-Load static stability (always tries to return to 1g if disturbed). This forward CG, if balanced by a down-loaded HS, also provides static Airspeed stability (always tries to return to the trimmed airspeed - 60mph? - if disturbed.) The HS in a gyro does even more "double duty" - it also provides the "damping" function similar to the shock absorbers on a car!

For the best and most harmonious control of an aircraft, the static stabilities (Airspeed and G-Load) must perform in harmony with each other and with the dynamic damping. If one or the other is missing, or not tuned in harmony with the other, the control and response to disturbances may not be as good as it can be. - Just like the springs and shock absorbers in a car! That is what makes some aircraft so pleasant and easy to fly, and what contributes to other aircraft being difficult and tiresome to fly! Good "springs" and "shock absorbers" on a gyro also require little or no pilot input and can provide complete stability and safety even at high speed on a "bumpy road"!

- Greg Gremminger

[greg spicola]

Greg would moving the rotor head higher from the CG proved more or less dynamic damping?
Greg

[GeneWeber]

Hi André,

The picture you posted has forced the browser frame to become wide. It is difficult to read the posts scrolling back and forth across the wide frame. Would you do me a favor and edit your post to reduce the size of the photo?

Thanks & Regards,

Gene

[gyrogreg]

Greg Spicola,

I don't think I can tell you what moving the rotorhead higher would do. Depending on other configuration dimensions, this probably could affect the static balance of moments in either direction. A sum of moments paper analysis might have to be done. But. I think that if you were careful to keep the actual RTV in the same location, you might not change anything.

Also, I don't think this would have much affect on the dynamic stability characteristics. Dynamic damping is mostly a function of the HS, at least it is most predicatable with the HS. The natural oscillation frequency (slow is better) might be affected a bit, but mostly just because the higher rotor weight would increase the Moment of Inertia (MOI) of the whole aircraft - that would lower the natural frequency, which would be a good thing - but not much!

A higher weight or inertia of the rotor, could improve the tendency to oscillate and change the natural frequency of oscillation. But, the inertial dynamic rates of the rotor and airframe can combine to make big changes in the natural frequency and a possibld tendency of the two to "resonate" with each other - making the dynamic stability a possibly worse condition. I only mention this to emphasize that there are a lot of other issues going on, and to try to remedy any particular stability flaw would be very difficult to determine without testing.

The only way to truly know what any such simple changes might do would be to flight test it. This is even true for major mods like adding a HS or changing a thrustline. You must flight test it to see what the affects are. Except for a simple recommendation to keep propeller offsets minimal and to installe a large HS, I am always hesitant tp "prescribe" any "fix" for any particular gyro. Even with a moderate prop thrustline offset and large HS, the HS will still need to be tuned (Angle of incidence, size, immersion factor, and position) to achieve the best results.

You asked specifically about dynamic damping. A HS may be the only "passive" pitch dampener I know of for a gyro. "Active" dampers might be a stabilizing autopilot or a WELL experienced pilot. Changing the inertia or MOI of the airframe or rotor, or any combination of harmonic balance between the two will mostly change the natural frequency of oscillation - the damper has little to do with that! Flight testing for dynamic stability is not so easy or safe - and must be done by a professional test pilot experienced in that machine, and with proper safety and protocol preparations. A really good rule of thumb would simply be to have a very large HS. I would suggest, that a HS large enough to do a real good job with the static stability issues, is probably large enough to provide good dynamic damping properties!

[GeneWeber]

Hi Greg,

RE: Post #127
With no power applied, either one can just as readily buntover if there is some action or reaction that causes the nose to rapidly lower so that the RTV becomes forward of the CG. At that point, the progressive action of reducing G-load with the CG aft of the RTV causes more nose-down pitch action and a very fast and progressive buntover.

I’m unclear about the reduction of G-load in this scenario. Are you implying that the rotor is against the rear stop and the pitching of the frame is causing AoA of the disk to decrease?

You write a thousand words, but could use a few pictures. ;)

Thanks & Regards,

Gene

[gyrogreg]

Hi Gene,

I may be digging a hole here - too much information may be a bit confusing. You asked about the reduction of G-Load when the nose is rapidly lowering being the same for either a high or low prop thrustline when the power is off.

The reduction of G-load becomes progressive if the CG is aft of the RTV because that reduction of G-load causes the airframe to pitch even more and faster nose-down! This is not implying that the rotor or cyclic is near the rear stop, in fact the rotor or cyclic can be in any position. But, to clarify, if the nose is pitching down AND the pilot is not moving the stick to compensate ("fixed stick" condition), the spindle will be moving exactly with the airframe movement. This is an actual cyclic action on the spinning rotor and causes the rotor to follow the airframe to a lower AOA. The lower rotor AOA provides less lift and the g-load is reduced further, further pitching the nose down – when the CG is aft of the RTV.

My point was simply that this would happen the same on a high, or low, or CLT prop thrustline - when the engine is not running (prop thrustline is not a factor because there is no prop thrust!) The condition for this is not that the rotor or cyclic is at a stop position, this condition is simply that the stick is not moved. The point is that the stability of all three configurations - all other configuration issues being the same - would be exactly the same. (Note that a less proficient pilot may “freeze” or over-react on the stick – not a good corrective action in this situation!)

And, pilot reaction to move the stick would have exactly the same results in all three of the scenarios also - if the power is off! The following is a bit more on this g-load reducing scenario. The following applies the same to all three configurations if the power is off. This actually applies to any gyro that has the CG aft of the rotor - for any reason or instance:

If the nose of the gyro is lowering (quickly is worse), and the pilot is not moving or letting the stick move, the AOA of the rotor is also lowering - following the airframe pitch movements through cyclic action. If the CG is, or becomes aft of the RTV at this point, the resultant lower lift of the rotor, presenting a lower or reducing g-load on the airframe, causes the airframe to pitch further nose-down. This is the progressive action of a possible incipient buntover. (Notice the engine power or thrust line is not an issue if the engine is not running.)

Now, what if the pilot does react with a corrective move of the cyclic. With the nose moving down, it would be natural for the pilot to react by pulling aft on the stick to stop the nose moving down. This is the proper reaction, direction at least; but the timing and speed and amount of this cyclic corrective action must be proper. When the nose suddenly pitches down, the pilot, pulling aft on the cyclic, prevents the spindle from actually changing angle. This is good because that helps avoid severe rotor blade cyclic AOA and possible precession stall.

But, if, at the time the nose is lowering, the CG is actually aft of the RTV, or even close to the RTV, aft movement of the stick causes the RTV to move further forward of the CG – a G-load unstable situation. If the pilot’s cyclic reaction is not enough to actually increase the rotor AOA and stop the reducing g-load on the airframe, the airframe would continue to pitch nose-down. That means that the nose will now respond to still reducing rotor lift and g-load reduction by further moving nose lower. If the pilot’s proficiency and reactions are not “trained” for “stabilizing” this unstable condition, the improper or insufficient reaction can induce PIO or simply not be adequate to stop the bunt-over. Just moving the cyclic to position the RTV further forward of the CG in reaction to a quick nose-down pitch movement presents a completely different handling gyro than that pilot may be familiar with – control reactions must be proper and recise when the CG is aft of the RTV! I don’t mean to scare people with this – this is just presenting the mechanism that might occur, on any prop thrustline gyro, if the nose is suddenly moving nose-lower to the point where the CG becomes close to or aft of the RTV. For quick disturbances or transients, it is very possible for the CG to move aft of the RTV (nose-lower), or for the pilot to move the RTV forward of the CG, presenting serious sudden demands on the pilot’s skill. I believe we supposed this possible condition in the event of a sudden power reduction on a low prop thrustline gyro – nose moves down rapidly to and below nose-level attitude. Such rapid sudden and possibly surprising movements may present control difficulties and reversal of stability characteristics requiring skills that the pilot may not reactively have.

In all case, a large HS, “damping” and slowing the airframe pitch movements, dramatically improves the ability of the pilot to adequately correct the transient. But, if the HS is not very effective at that point – loss of prop-accelerated air over a smallish HS – the HS may not be adequate to prevent or allow the pilot to prevent an actual buntover or precession stall.

Gene, I understand you would like some pictures. I would like to do that, but graphics take me a lot of time and I’ve been spending too much of my time on this and the ASTM standards as it is. We would really need moving graphics to depict some of this. I’ve been thinking about this and hope to do that for the articles I plan to write when we finally get the ASTM standards approved. It may take a few times re-reading some of this, but many people tell me that helps them to finally understand the concepts better. I find these forums are of most value to me in “bouncing” some of these ideas off other technically minded people for some peer review. As such, we might confuse some other people, but we will try harder in the magazine articles.

Some of my original PRA articles (Safety Envelope) do have some diagrams that might help. Also, the Glossary of Gyro Terms is intended to help clarify the concepts. You can find all of these on my Magni USA FEATURES web page: http://www.magnigyro.com/USA/features.htm

[quadrirotor]

If you want more theorie on PIO, bunt over, PPO, accident, crash, stability :

http://www.aircraftdesigns.com/gyro2.html

http://www.aircraftdesigns.com/gyro3.html

http://www.aircraftdesigns.com/gyro4.html

[Udi]

Greg,

Since you’ve invited peer review, I will offer one... ;)

Unless you are thinking of a negative RTV (negative G) event, a positive RTV ahead of the CG will always tend to lift the nose of the aircraft (even when the G-force is less than 1G). This is the basic no-stab airframe stability mechanism. Assuming no other pitching moments, RTV behind the CG lowers the nose and RTV ahead of the CG lifts the nose.

For your scenario to work, there must be another pitching force, like a high engine thrust, or low drag, to keep the nose down pitching going against a forward RTV. Otherwise, moving the RTV forward of the CG should arrest the nose down pitching. There must be some sort of a sustaining force to keep the nose down pitching action.

If this was not the case, gyroplanes would have been much more unstable and dangerous to fly.

Udi-

[KenSandyEggo]

Aaaaaah. That's why some of my photos came in so large in another thread. I guess the 1st photo poster sets the parameters. I shrunk mine down to 2 inches and they still hogged the screen and some.

[Udi]

Ken - good to see you posting here again. How are you doing?

When you shrink your pictures, usually the photo software lets you choose your units - inches or pixels. For best results, choose pixels, and shrink the pic to no more than 500-600 pixels wide. This will work well with most people's monitors.

Udi-

[GeneWeber]

Hi Udi,

RE: #139
Unless you are thinking of a negative RTV (negative G) event, a positive RTV ahead of the CG will always tend to lift the nose of the aircraft (even when the G-force is less than 1G). This is the basic no-stab airframe stability mechanism. Assuming no other pitching moments, RTV behind the CG lowers the nose and RTV ahead of the CG lifts the nose.

Exactly. That’s why I didn’t understand why Greg was saying that the mechanism provided positive feedback into the bunt. The RTV forward of the CG should act to pull the nose back up. So I thought perhaps Greg was implying that the rotor was against the back stop, (or as he pointed out, holding the stick fixed). Then I could see that perhaps the airframe pitching forward would lower the disk AoA decreasing the G-load (magnitude of the RTV) to a point where it could not stop the forward pitch, which would further lower the disk AoA ……… bad things happen.

Regards,

Gene

[Doug Riley]

I believe what Greg is saying is that, if the RTV is forward of the CG, it MAY be there because some other force is creating a nose-DOWN moment. That is, the system may be in some sort of temporary equilibrium.* This arrangement is statically unstable with respect to G-load for the following reason:

In low G, the rotor force is reduced. The nose-down moment then is free to do its work, throwing the nose down. This reduces the AOA of the rotor (either stick-fixed or held against the stop). Less rotor AOA, less thrust, more nose-down and so on. It's the same mechanism as PPO, but not necessarily energized by high thrustline. Other nose-down moments can do the same thing.

The trick to legitimizing this "non-PPO-bunt" scenario (IMHO) is to identify WHAT this lethal nose-down force might be. Aerodynamic moment from a windshield, an amphibian boat hull or some such could be involved. An up-lifting HS could do it, too.

Whether any of these forces is strong enough to produce such a violent nose drop that precession stall occurs is an open question, I think. Greg proposes that it could happen, and we can't categorically eliminate that possibility.

*If the system is OUT of equilibrium at a given point in time, then the nose-up force of RTV-ahead-of-CG isn't necessarily being opposed by anything. Such could be the case if you just randomly yanked the stick all the way back while peacefully cruising in a gyro that doesn't have a lifting HS or a de-stabilizing body shape. In that situation, the gyro would respond to the out-of-balance moments by, of course, nosing up. Even if, at that same instant, a downdraft produced a sharp reduction in G-load (and therefore rotor thrust) nothing catastrophic would happen as long as there was no lurking nose-down moment ready to get you the moment rotor G's were reduced. The nose-up response would just be weak.

(I just read Udi's post saying the same thing. I guess that means it must be true?)

[gyrogreg]

Udi,

I think you are correct in most instances. As you suggest, this all depends on other moments on the airframe - during this transient event. I'm not saying a buntover happens every time, but I'm saying it can happen in certain circumstances with some configurations and initiating events.

I think your post implies that you would have to have a negative (reversed, less than zero G) thrust of the rotor (RTV) in order to propagate a further nose-down pitching event - buntover. I maintain that if the CG is aft of the RTV and nose-down pitching has been initiated, and if the rotor is following the airframe pitching to some degree, it DOES NOT require a NEGATIVE lift on the rotor to initiate more nose-down pitching. It only requires a LESSENING of rotor lift to propagate more nose-down pitch acceleration. This is because of the overpowering positive feedback of the changing rotor AOA/lift. When the RTV is forward of the CG, a rapidly lessening rotor disk thrust (decreasing rotor disk AOA) will cause an increasing nose-down pitching moment - dynamically because the decreasing rotor AOA nose-up thrust of the RTV is lessening faster than the increasing forward moment arm can compensate.

I don't know if I'm saying this right. Trying to put it another way, once the CG is aft of the RTV, and if the rotor disk AOA is following the airframe to some degree so that it’s lift is decreasing rapidly, at some point it may only require a LESSENING of the rotor lift to start a nose-down airframe pitch positive feedback acceleration. This lowering nose can couple into reducing rotor disk AOA, and even more nose-down acceleration. The nose pitch has a downward propagating, positive feedback acceleration that could eventually result in zero or even negative rotor AOA. This is called positive feedback, it does not rely on actual reversal of rotor thrust, it only needs a decreasing rotor thrust to possibly propagate into a real nose-down, negative G event – buntover! It works this way, because counter to the linear nose-up moment increase of the forward moving RTV you have suggested, the lift of the rapidly changing rotor disk AOA is exponentially decreasing as the rotor disk AOA approaches zero. At some point in this event, the rapidly decreasing RTV lift is reducing the RTV moment faster than the corrective effect of the forward moving RTV. The “power” of the rotor disk AOA thrust change over-powers the increasing moment arm of the forward moving RTV. If you plotted actual RTV moment about the CG as a function of the nose-down changing airframe pitch angle, the slope of the line would be negative – a statically unstable condition. (At higher airspeeds this is more of an effect than at lower airspeeds because the rotor disk AOA is so shallow and smaller changes in disk AOA result in much larger changes in RTV thrust.) The threshold of this “positive feedback” event is where the rotor disk AOA/thrust is decreasing faster than the RTV moment arm is increasing as a function of the lowering nose pitch angle.. The amount and timing of degree of the rotor following the rapidly pitching airframe is a factor in whether the “threshold” of the self-propagating event is reached. Obviously, this is a function of pilot skill and reactions on the stick. To prevent the rotor disk AOA from overpowering the RTV moment arm stabilizing effect, the best reaction of the pilot would probably be just enough aft stick movement to prevent the rotor disk AOA from changing, or at least changing to the threshold where it overpowers the RTV moment arm.

When and if a gyro’s RTV is forward of the CG, there is basically some threshold of inertia combinations and HS power where some degree of sudden nose-down pitching would cross over into the self-propagating, positive feedback of a buntover. This is why some inadequately “balanced” high prop thrustline gyros have more incidents of “pitch related” accidents (buntovers or precession stalls) – their RTV is already forward of the CG! Once this cross over or threshold is exceeded, just reducing G-load can feed positively back into more nose-down acceleration (or less nose-up acceleration.) It does not take an actual reversal of rotor lift to trigger a positive feedback event – when G-Load instability is present, it only takes enough of a sudden reduction in G-Load to initiate a self-propagating, positive feedback buntover. Once the rotor disk AOA actually goes through to negative lift, then you are precisely correct that this negative RTV event will seal the deal!

I think this is precisely why we have had such a bad accident record with gyroplanes - In gyros that are already "set up" with negative G-Load stability because of their unbalanced high prop thrustline, it doesn't take a terribly bad wind gust or pilot over-reaction to cross the threshold into an unrecoverable forward pitching, positive feedback event!.

Now, complicate the situation, as in most gyros, with nose-lowering down-lifting windscreens, draggy low landing gear, or low offset centers of drag, unpredictable rotor dynamics, resonant inertial combinations, and likely worsening of these effects with changing airframe attitudes and pilot over or under reactions, it becomes easy to see how difficult it might be to predict whether a gyro, any gyro, has a tendency to have a less safe area of its flight envelope. Again, working through paper and mind-game scenarios might be fun and educational, but the final determination must be by actual performance results of flight testing. I don’t present all of these concepts and constructions as totally proven, I present some of these concepts to incite more thinking and discussion, and to broaden awareness toward better risk analysis and decision making in what and how we fly.

This whole discussion is just to emphasize why some degree of “Power Stability” is desirable. The perfect gyro would have no tendency to upset the “balance of static moments” upon a sudden power change, and thus not initiate any rapid pitching events that might exceed this very complicated dynamic threshold. To avoid the above as any real issue, IMHO, the gyro should be reasonably “Power Stable”!

- Greg Gremminger

[Aussie_Paul]

Hi guys, me again :)
I have been reducing the offset of the torque tube to the point that the two bolts almost touch. This is 1/2" offset. I have been from 3/4" of the Raf to the almost standard 5/8", and in between as well.

I believe that for what I am trying to achieve 9/16" will give me the lightness of trim to make the stick easier to push forward on the ground, and to not run out of trim adjustment.

With the 1/2" I have to have a light spring pulling down from the front of the torque tube.

My question is this. What effect will this reduced offset have on the off set gimbal head stability?

Thanks. Aussie Paul.

[rehler]

The offset greatly affects the stability. You want to have a trim spring pulling, but not too hard. No spring pull at all is bad, as there is then no automatic correction to up and down drafts.

I had a 5/8" offset with 25' McCutchen blades which required no trim spring at all (actually I needed one in the front - opposite to what is desired). I went to a 1" and everything was great. Now I will probably go back to the 5/8" offset with my new 27' Sport Rotor blades. It seem that different blades fly at different pitch and require different trim and/or offset.

[Aussie_Paul]

Well today proved that Ken. With the extra trim spring on the front stick fixed was great BUT oh boy the stick free was terrible.

I will rebuild the rotor head tonight with my 5/8" offset.

When I get home from my Easter jaunt I will have another torque tube made with a 9/16' offset if I feel it is needed. This trip will be good test of these new Oz blades and the rotor head setup.

Learning learning learning!!!!!! Just when I thought I knew it all!!!!!!!!! yeah right!!!! LOL

Well starting Monday, early am, I have to sit in Hybrid for 6 hours each day for 4 days.

If I get there and back, boy will I have some stories to tell about my trip, as well as Birdy and his mates.

Aussie Paul.

[gyrogreg]

I would like to comment on the Aircraft Designs links provided by Andre above:

Re:Wind shear on Gyro with HS

If you want more theorie on PIO, bunt over, PPO, accident, crash, stability :

http://www.aircraftdesigns.com/gyro2.html

http://www.aircraftdesigns.com/gyro3.html

http://www.aircraftdesigns.com/gyro4.html

------------------------------------------------

I am usually not so inclined to endorse Martin Hollman's theories of gyroplanes - he and I agree on some, but not all - Sorry, Martin, we have discussed some of these differences.

BUT, I must endorse the gyro3 and gyro4 links above. Martin's son, Eric, in my initial opinion, has provided a very powerful tool to help promote safety in gyroplanes. He has designed a computer program that models the dynamic time reactions of gyroplanes as a function of their configuration. The results are presented graphically in time response curves that everyone should easily interpret and readily see the effects of configuration changes. The resulting graphs present timline visualizations of positive, neutral and negative stability in terms of airspeed fluctuations and angles of attack. The posted results on the links above suggest what we have all theorized - unstable machines can quickly diverge - PIO is dramatically graphed! At first glance, the examples that Eric provides on the gyro4 link are fairly representative of the real world. Some PIO oscillations are in the range of 6 second periods. I suspect they may be actually quicker than this, but this program verifies that gyro natural freqency of oscillations can be very fast! The program results on the new Sparrow Hawk seem to accurately model the actual flight test dynamic stability results reported by Jim Mayfield - about 20 second period and damped. I am impressed that this model applied even to some of Martin's designs, reflect even less than optimum stability for those designs. I suggest this attests to the validity of this computer model because it does not "automatically" promote the Martin's designs as the best. I salute Martin and Eric for this effort and honesty.

Martin is making the program available with his new book. I am anxious to try the program on other gyro configurations for which we have real world data to verify the accuracy of the program. But, whether completely accurate or not, I suggest this program would readily highlight value and effects of configuration changes, if not the exact effects.

I will be encouraging Martin to make this program readily available in the public domain without a fee, as a contribution toward the safety and growth of the sport we all know Martin is as committed to as anyone. You may feel inclined to also contact Martin to encourage at least a trial release of this program to some of the more technical people for a bit of peer review and then possible promotion to the gyro community. I do know that he feels his son should be appropriately compensated for his work, and I agree. but, perhaps a limited release to some technical gyro people for peer review of the program to validate would then help to promote the product. I for one, would like to start providing examples and effects of changes in articles in the gyroplane publications. But, for believability by the entire community, peer review and results comparison with know model properties would be important.

I still do say however, that the only absolute way to determine the true stability characteristics of your gyro is to flight test it. But, this computer model may provide a valuable tool as a good designer stating point. and, it may provide a valuable educational tool for a safer gyroplane community.

- Greg Gremminger

[Doug Riley]

Paul Bruty: The trim spring provides a very valuable pitch stability enhancement... IF the airframe is stable with respect to angle of attack. The spring creates an appropriate stick force gradient: as the gyro speeds up, the torque bar is brought closer to level to reduce rotor AOA. If (only if) the airframe's stance relative to the flight path stays nearly the same, the spring is then stretched by the levelling of the torque bar. This, in turn, makes the stick try to return to a more aft position: a stable stick force gradient.

IF OTOH, as the gyro speeds up the nose dips lower and lower (as the old tailless Air Commands did), this mechanism is partially or totally defeated. A spring on the front end also produces an unstable force gradient: as the torque bar is levelled, the spring force becomes less, tending to level the bar even more. The old Bensen spindle head was rigged with this kind of unstable spring arrangement when it was used with a joystick.

The spring also links the rotor to the airframe in such a way that the rotor follows pitching movements of the frame even if the stick is "floated" or flown hands-off. That's why it's something of a myth to say that the rotor is independent of the frame. In most cases, they are linked by the spring. Unstable movements of the fuselage are therefore fed into the rotor system, even if the pilot lets go altogether.

[Udi]

Originally posted by gyrogreg
I think your post implies that you would have to have a negative (reversed, less than zero G) thrust of the rotor (RTV) in order to propagate a further nose-down pitching event - buntover. I maintain that if the CG is aft of the RTV and nose-down pitching has been initiated, and if the rotor is following the airframe pitching to some degree, it DOES NOT require a NEGATIVE lift on the rotor to initiate more nose-down pitching. It only requires a LESSENING of rotor lift to propagate more nose-down pitch acceleration. This is because of the overpowering positive feedback of the changing rotor AOA/lift. When the RTV is forward of the CG, a rapidly lessening rotor disk thrust (decreasing rotor disk AOA) will cause an increasing nose-down pitching moment - dynamically because the decreasing rotor AOA nose-up thrust of the RTV is lessening faster than the increasing forward moment arm can compensate.

Greg,

Lessening of rotor RTV propagates nose down pitching only when there are other nose down moments acting about the CG. In other words - when a forward RTV is working against a nose down pitching moment, like a high engine thrust line in the RAF, or a low airframe drag, than lessening of the RTV will affect the balance of moments and the net result will be a nose down moment.

In my other post I considered a gyroplane in which there are no other nose down pitching moments. Assume a low thrust line gyro, where the center of drag is aligned with the CG. When the engine quits, there will be a momentary nose down pitching moment, caused by the RTV. The imbalance of moments happens when the engine quits. But as soon as the RTV is moved from behind the CG to ahead of the CG, there will not be any nose down pitching moments. There will not be a positive feedback. The only static moment acting about the CG (ignoring a stab) is the RTV, attempting to arrest the nose down pitching movement. Inertia is the only force that has to be stopped.

Saying it another way - as soon as the RTV is moved in front of the CG, the RATE of nose down pitching will get smaller with time. The RTV will become smaller too as long as the nose keeps on going down, so the question is whether the available nose up RTV moment will stop and reverse the nose down inertia before the RTV goes negative. Once the RTV goes negative the game is over

Udi-

[Doug Riley]

I believe Udi is correct. Acceleration requires the presence of a force. No force, no acceleration.

[Aussie_Paul]

Thanks guys. I guess that I know most of this; I guess I enjoy proving it to myself. I could save a lot of time if I just took your word for it. BUT that is me.

My real question:

Is the inherent pitch stability of the off set gimbal influenced by the amount of offset?

Lets say "With all the head movements and control ratios to meet the normally accepted figures, and a set of blades that will always be used on that head.

Is there a figure for trim spring pressure that will give us stability without having to be very muscular to push the stick forward when on the ground?

This figure would be adjusted by the "off set" amount.

I guess there are two issues.

1) Stability, and

2) The stick pressure forward when on the ground.

Aussie Paul.

[Al_Hammer]

Looking at Martin Hollmann's webpage gave me the idea to try my own version of a gyro stability simulator. And this one won't cost anything.

My goal is to use Hollmann's equations( with some modifications of my own) in a real time-interactive webpage.


(Thanks to those few who provided feedback.)

[quadrirotor]

super!

[GeneWeber]

Hi Al,

A program like this puts an engineering tool into the hands of many builders who would typically have to rely on “best guess” and speculation. It’s obviously a large undertaking to create it. Thank you for applying your talents to this.

Best regards,

Gene