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]

[quote author=PTKay link=board=6;threadid=589;start=0#msg5825 date=1079289920]
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 !

[/quote]

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.