Yaw Instability

[JonVos]

Has anyone run into yaw instability problems while using Air Command non tall-tail style rudders with a horizontal stab? In flight I have to keep constant pressure on the pedals or the rudder will go full deflection either left or right, resulting in an extreme yaw. It's more pronounced at higher power settings, but apparent throughout the speed and power range. Is this a common problem or is it just me?

[fiveboy]

Im sure better technical minds than mine will chime in but clearly that cannot be right.

I have the tall tail and no such issues.

My sense is that perhaps your controls are too tight? Seems like the rudder should go back to straight back in flight. I was taught that with rare exception (and on take off and landing) you dont need to use your feet almost ever.

What you posted creeps me out - I hope one of the more experienced builder/designer/engineering types can help cuz Its not right.

Then too I wonder if you took off the front pod whether you would still have the issue? Could it be on off center?

[groundhog]

sounds like the pivot point is behind the aeirodynamic center.Let these minds see some pictures,include profile pics looking down on the pivot point

[gyromike]

Has anyone run into yaw instability problems while using Air Command non tall-tail style rudders with a horizontal stab? In flight I have to keep constant pressure on the pedals or the rudder will go full deflection either left or right, resulting in an extreme yaw. It's more pronounced at higher power settings, but apparent throughout the speed and power range. Is this a common problem or is it just me?

I experienced something similar to this myself. 582 AC, no pod, keel extension with the standard tail and stabilizer. I noticed that with my feet off the pedals a gust of wind would start it yawing without settling down, so I decided to see if it was the same in either direction.

Cruising around at 50-55 mph, I tapped the rudder and it started oscillating in yaw, getting progressively worse. I stopped it and tried the other rudder and got the same result. I never let get past two cycles as it was a bit unnerving. If I put my feet on the pedals it would stop instantly though.

Never took my feet off the pedals after that.

I can do the same thing on my Bensen and it just returns to normal with little overshoot.

[CLS447]

I think I would tighten up the nut that holds the tail on! Do you have the plastic or aluminum tail block?

I bought one because it was available...when I switched them, sure enough the plastic one was broke in two. It could not escape though because of the bolts.

I got tired of holding right pedal so I finally bent the trim tab on the back of the tail....problem solved!

[DennisFetters]

I think I would tighten up the nut that holds the tail on! Do you have the plastic or aluminum tail block?

I bought one because it was available...when I switched them, sure enough the plastic one was broke in two. It could not escape though because of the bolts.

I got tired of holding right pedal so I finally bent the trim tab on the back of the tail....problem solved!

Right! First check the tail block and make sure it is not cracked. They are made of plastic to help absorb some the vibration and loads, but as plastic, they do age over time.

Tighten the attachment bolt some until there is a little resistance, bend the trim tab... believe it or not, it's there for a reason and not just good looks, and you should be OK.

It is a flying tail, and will never be as stable as a two piece tail, but in the day, that is what we had to do to make it light enough to meet the ultralight category. It works well enough if set up correctly.

[CLS447]

Dennis.....you made my day !

BTW...I love those SS snubbing washers ! The little things make me happy !

[DennisFetters]

Dennis.....you made my day !

BTW...I love those SS snubbing washers ! The little things make me happy !

Good God.... Thats all it takes?? I'm gonna sent everyone some.

[C. Beaty]

All-flying vertical tails are inherently unstable without either an antiservo tab or a spring detent centering mechanism.

The pivot axis of an all-flying tail must be slightly ahead of the aerodynamic center in order for it to trail downstream. If the pivot is behind the aerodynamic center, it will flop to one side or the other and try to swap ends if feet are removed from rudder pedals.

With a tail designed to trail downstream, centering springs, one loaded against the other, don’t provide a strong centering force.

When hit from the side by a gust, such a rudder trails downstream and provides little “weathervane” effect. In effect, the gust doesn’t really see the vertical tail but does see the area forward of the mast.

The cure is either an antiservo tab or a fin-rudder combination.

If there’s enough mechanical friction in the pivot to make the rudder “sticky,” then perhaps some stability is possible if one is satisfied with such an arrangement.

[Greg Mitchell]

Jon Vos,

When we had the AC tails on the early Butterflys we had a similar problem., at speed.
The Larry had the new T tails built with mass balance tubes and sometimes weight in the leading edge of the vertical section. "Problem solvered".

Chuck,

What about mass balancing of the T Tail? My tail is very well behaved.

Mitch

[Heron]

It flutters if not properly balanced.
I saw one of the early Golden Turbo tests and amazed be the "flapping" around.
Heron

[Chuck Roberg]

I was going to say something. But then I saw a couple of good replies.

[C. Beaty]

Heron is quite correct; a tail not balanced about the aerodynamic center (~1/4 chord) can flutter.

Normally, we think of flutter as something pretty fast but stuff not perfectly rigid can have a type of slow aerodynamic instability that can be fairly called flutter.

The sketch shows why all all-flying tails ought to have antiservo tabs. Without such, the natural tendency is to weathervane the wrong way.

[Greg Mitchell]

My question is when mass balanced correctly....I do not get any tail flutter.

Depending on proximity to prop these T and Tall Tails can have weight in the leadiung vertical fin reducing the amount of forward mass in the balance tube, ie tube is shorter.
With no weight in the leading vertical edge, the tube is longer with more weight in it.

I know Larry says if the all flying tail is balanced (fine tuned there is no need for the anti servo tab.

Thoughts on this please.

Mitch

[CLS447]

I have always liked my Air Command rudder...simple & effective !

[C. Beaty]

Flutter and weathervane stability are two different phenomena, Mitch.

Lets look at a weathervane; a tail at one end and an arrowhead or something at the other with the pivot at the balance point. With a rigidly attached tail, the thing always points into the wind, same as we’d like for our flying machine.

Suppose the tail was hinged slightly ahead of its aerodynamic center. The tail would trail downwind and could not swing the arrow into the wind; in fact the aerodynamic pressure on the arrow would cause it to swing downwind even though the tail might have be balanced about its ¼ chord point. If the hinge on the tail was sticky, the arrow might swing into the wind. It centering springs were stiff enough, it might also swing the arrow into the wind. If the springs were weak, it might still point onto the wind in a wobbly sort of way, oscillating back and forth.

The Cessna Cardinal has an all flying horizontal stabilizer and has noseweights for ¼ chord balance but it also has a powerful antiservo tab. There are other aircraft with all flying tail surfaces but the Cardinal in the one that immediately comes to mind. I expect that all use antiservo tabs.

[gyromike]

The Cessna Cardinal has an all flying horizontal stabilizer and has noseweights for ¼ chord balance but it also has a powerful antiservo tab. There are other aircraft with all flying tail surfaces but the Cardinal in the one that immediately comes to mind. I expect that all use antiservo tabs.

One of the first planes I flew was a Piper Cherokee. It had a stabilator on it with an anti-servo tab too.

[Riff Raf]

Has anyone run into yaw instability problems while using Air Command non tall-tail style rudders with a horizontal stab? In flight I have to keep constant pressure on the pedals or the rudder will go full deflection either left or right, resulting in an extreme yaw. It's more pronounced at higher power settings, but apparent throughout the speed and power range. Is this a common problem or is it just me?

What kind of air command?

[fiveboy]

What is an anti servo tab exactly?

[karlbamforth]

It is like a trim tab but is connected in such a way that it automatically opposes movement of the main control.

http://en.wikipedia.org/wiki/Servo_tab

[mceagle]

Most people that flew AirCommand's socially were never even aware of this problem - unless they took their feet off the rudder pedals or broke a rudder control. The oscillations would progressively get worse and I believe that the gyro would have swapped ends if allowed to continue. One pilot reported having to bring the power back to idle before he could centre the rudder and power on again. He also reported loosing a considerable amount of height before effecting recovery.
Like Chuck said, this is a common problem associated with most fully flying tails without an anti-servo tab. If the tail has enough "trail" it should be able to be straightened with a blast of power, but in any case it will tend to align itself with the local airflow, and if that happens to be coming from the side, then so be it.

[Greg Mitchell]

Flutter and weathervane stability are two different phenomena, Mitch.

Chuck, thanks. This simple statement and visualizing the graphic you posted, (whilst laying up a tall tail today) woke me up.

So, You can balance a tail and get rid of the flutter but if you have your feet off the pedals when you get hit by a side gust, then your weathervan stability is not what it should be.

I apprerciate your descriptive explanation.

Tim, Mate thanks for that. I'm thinking My Monarch with centering springs and nicely balanced to rid it of flutter, might need a device like Allan put on his for the very reason you and Chuck have described with weathervane stability. Allan is still flying his Monarch with the AC tail on it.

I dont think/believe that the AC tails are mass balanced. Allan said he gets into a particular part of his flight envelope and it flutters and he thought, I seem to recollect, he said it might have been divergent had he not got onto it. My memory is shot, so I hope I got that right.

Mitch.

[docrob]

[U]Aerodynamics for Naval Aviators[U] and other aerodynamics texts differentiate between "stick fixed" and "stick free" stability. If a control surface is secured in some way so that it cannot be moved by the local wind, the stability is always higher. That's what Mike observed when he put his feet on the pedals and the yawing stopped. That's why V-tail Bonanza pilots keep their feet on the pedals in turbulence -- really so their passengers don't barf on them from the constant yawing -- not really countering the yaw, but just "fixing" the rudder. In boosted controls on bigger aircraft, the boost system adds stability by providing a sort of irreversible that prevents the local wind from moving the control surface. When we tighten the mounting hardware, put centering springs on, or keep our feet on the pedals, we are, in effect, providing a "stick fixed" condition, which makes the machine more stable. Anti-servo tabs do this aerodynamically by opposing any attempt to moved the control away from a centered position. And as Chuck pointed out, you almost have to have all the planets in alignment to get this with all flying controls, though they have a lot of good qualities if you can overcome this characteristic.

Dr. Rob

[DennisFetters]

During the thousands of hours I have flying all types of Air Commands with flying rudders, I have never experienced a side-gust that caused my rudder to deflect. Yes, the theory is there and looks plausible, but the reality of it happening has never shown itself to me, and I can safely say that I have flown the Commander in more deferent weather conditions and pushed its envelope further than anyone. It's just a little hard for a fart-size side gust to penetrate through a comparative hurricane force wind shielding around the rudder by the prop-wash. If there were a side gust that big, you got other problems more serious that will be getting your attention.

I have had the Commander up to 120mph many times with the four cylinder Arrow engine, and I have never had the rudder flutter. I have had an open frame Commander, without horizontal stabilizer attached to it, up to 85mph, almost ever flight, and have never had the rudder flutter....

That is, on a Commander that was set up correctly. If your rudder post is loose, then the rudder will flutter side to side. Just make sure it is tight. I have also experienced excessive rudder looseness when someones tail wheel plate bolts that support the rudder block were loose. Also I have seen excessive rudder movement on machines that extended their rear keels.

Again, the flying rudder is not the most stable type, but in the day, it was the best solution to achieve the weight requirements, and it has proved to work well since the 1980's since I introduced it, even until present day, and is still being widely used and imitated around the world.

I will say, that I would not use it again on a new design because the weight restrictions are better than days of old.

[dinoa]

My experience when extending the keel and going CLT on the Air Command was immediate full rudder deflection when removing pressure on the pedals. Before the conversion it would fly straight if trimmed correctly. The tail also periodically enters a buffet area around 70mph in its new location probably being shed by the pod.

I'm making a tall tail with anti servo tab as a permanent fix and in the meantime will follow Dennis' suggestion by looking for looseness.


Dino

[JonVos]

Wow. Firstly I'd like to thank everybody that's responded so quickly to this post! I'm always amazed at how many really intelligent folks are here on the forum, and I appreciate you all sharing information like this... it really means alot. I'm typing this from a hotel computer in central wisconsin, but as soon as I get back home I'll take and post some pics of the tail. A few of you have mentioned mass balancing. Is there some way to test the mass balance of a tail or is it just something that's designed into the surface?
I've talked to some folks in my local gyro club who've also had similar problems with these type of tails, and most seem to say that the instability problem goes away when the horizontal stab is relocated from the rudder surface to the airframe structure below the tail. I'm sure this isn't a design flaw, but perhaps the dihedral of the horizontal has something to do with it? The attachment points aren't the strongest and the support struts seem like they can be easily bent.
I've removed and inspected my tail, bearings, and bearing blocks. The bearings move freely, the block is made of aluminium and is not cracked. The control cables are snug, but not tight enough to cause any control binding.
As far as an anti-servo tab is concerned, I'm not sure how I'd go about incorporating a tab onto the rudder. Has anyone done this with an A/C type rudder? I know the Dominator tall tail uses one, but that's the only application I've seen.
Again, thanks to all who responded so quickly.

[C. Beaty]

With the tail laid on its side on a piece of angle iron, it should balance about the hinge line. This can be done with the least additional weight by mounting the balance weight as far forward as possible; the photos of the Butterfly tail being a good example.

The antiservo tab can be operated with a push-pull cable if friction is properly addressed. Use plastic lined bicycle shifter cable housing with a solid push-pull wire; say .032” hard drawn music wire. Avoid kinks or sharp bends in the housing.

[Chuck Roberg]

As far as an anti-servo tab is concerned, I'm not sure how I'd go about incorporating a tab onto the rudder. Has anyone done this with an A/C type rudder? I know the Dominator tall tail uses one, but that's the only application I've seen.

The Sparrow Hawk Gyro has an anti-servo tab. Maybe you can get a hold of Jim Genotte and take a look at his.

[Heron]

I wonder if loose cables can increase this problem? Mr. Fetters?
It remings me of an old Jeep, one quart of turn before it catches made for an interesting drive on hard conditions.
Heron

[OuterMarker]

So, to understand...I'm from the South and sometimes a bit slow to understand...
1. Remove rudder and inspect rudder block for damage and replace if necessary.
2. Tighten the rudder shaft nut until there is a slight pressure on the rudder bearings.
3. Inspect rudder cables to determine condition and replace if necessary.
4. Adjust rudder cables to a "snug or firm" condition without trying to stretch the cables.
5. Keep your feet on the rudder pedals at all times.
Is that about it?

[Chuck Roberg]

5. Keep your feet on the rudder pedals at all times.

Again I bring up the Sparrow Hawk.

With the anti-servo tab and just flying around. I can keep my feet off the rudders and on the floor. I just let the anti-servo tab do it's thing. Or you can use the rudder pedals as foot rests.

[fiveboy]

It is like a trim tab but is connected in such a way that it automatically opposes movement of the main control.

http://en.wikipedia.org/wiki/Servo_tab

EXCELLENT. thanks

[JRB549]

No matter what, play it safe with both feet on pedals @ all times. MURPHY'S LAW never sleeps!

[DennisFetters]

I wonder if loose cables can increase this problem? Mr. Fetters?
It remings me of an old Jeep, one quart of turn before it catches made for an interesting drive on hard conditions.
Heron

Cable length is adjusted to achieve two purposes.

1. To adjust the right amount of deflection into the tail, which should be 1.5" offset to the right (2-stroke Rotax engines) from the center of the keel to the far leading edge of the tail when pedals are straight.

2. To adjust cable length so that the steering dampeners have the proper spring tension and travel.

Adjustments are made by twisting the cables, but only going tight on the windings, never loose. It should never take but a few turns to make the necessary adjustments. If it takes excessive winding, then somethings wrong. You can damage the cables if you need to apply too may turns, and if it slips out of your hand it will kink, and is no longer usable.

Do not apply this method of cable adjustments to other applications unless the manufacturer says too. It is application dependent in many cases.

[DennisFetters]

My experience when extending the keel and going CLT on the Air Command was immediate full rudder deflection when removing pressure on the pedals. Before the conversion it would fly straight if trimmed correctly. The tail also periodically enters a buffet area around 70mph in its new location probably being shed by the pod.
Dino

You are correct. I forgot about that characteristic when I flew with the extended keel that someone modified.

That is due to the way the prop-wash is contacting the rudder when it is further back. When it is in the location where designed, the swirl contacts both sides of the rudder more evenly and at the correct angle, causing it to be more natural, but when you move the rudder farther away, the swirl tends to cone in and contact one side of the rudder more than the other and in a different place, causing it to turn. After it turns, the sharp leading edge stalls the airflow causing a higher pressure area on the back side working against the front side with the airflow, which has lower pressure.

Was not a good combination.

[gyro]

The extended keel is the main problem....Dennis is right the wash smacks the tail and causes it to deflect much more than the short keel. I have flown both (original stock) and estended. Mine would always deflect to the left when I released pressure from the peddles.

[JonVos]

Thanks Dennis. That answered my question. When I performed my CLT conversion, the kit came with a keel extention that I installed. Having never flown the machine prior to the conversion, I really had no basis for comparing it's before/after flight characteristics. Is there a simple fix or do I need to buy/install a tall tail kit?

[DennisFetters]

Thanks Dennis. That answered my question. When I performed my CLT conversion, the kit came with a keel extention that I installed. Having never flown the machine prior to the conversion, I really had no basis for comparing it's before/after flight characteristics. Is there a simple fix or do I need to buy/install a tall tail kit?

I'm sorry, but I really don't have an answer since you have the CLT conversion, I don't deal with that nor have I put any time into trying to improve the flying characteristics of a Commander with a CLT conversion to make it fly as nice as one without.

Good luck.

[Heron]

I thought of leting this one go, but can´t . . .
so here it goes
Mr. Fetters, come again Sir?
Heron

[Passin' Thru]

I thought of leting this one go, but can´t . . .
so here it goes
Mr. Fetters, come again Sir?
Heron

Heron, replace the "or" with "nor" and it makes more sense.:p

[Friendly]

Chuck, or Pete
Should the yaw be trimmed with the tail offset or with the servo tab? I adjusted mine by the rudder cables making the tail offset with the rudder pedals centered

[DennisFetters]

Heron, replace the "or" with "nor" and it makes more sense.:p

Sorry, I fixed it, thank you for pointing it out.

[OuterMarker]

Ok...a newbie here....A/C 503, CLT upgrade and extended keel. I haven't flown a pattern yet and I'm currently adjusting rudder cables with turnbuckles. In this configuration what should the rudder offset be, if any? I assume the rudder cables should be taught, but not so tight as to deform the aluminum parts. Also, while doing a hang test, let's assume the results show a 2 degree nose down attitude with a half tank of fuel in the seat tank. What should the stab be set to with respect to positive or negative degrees.

thanks....
Just trying to work out the bugs before getting air under the tires...

[DennisFetters]

Ok...a newbie here....A/C 503, CLT upgrade and extended keel. I haven't flown a pattern yet and I'm currently adjusting rudder cables with turnbuckles. In this configuration what should the rudder offset be, if any? I assume the rudder cables should be taught, but not so tight as to deform the aluminum parts. Also, while doing a hang test, let's assume the results show a 2 degree nose down attitude with a half tank of fuel in the seat tank. What should the stab be set to with respect to positive or negative degrees.

thanks....
Just trying to work out the bugs before getting air under the tires...

I'll let a CLT Commander guy answer all of that. I never set one up, just flew'em.

[dinoa]

Ok...a newbie here....A/C 503, CLT upgrade and extended keel. I haven't flown a pattern yet and I'm currently adjusting rudder cables with turnbuckles. In this configuration what should the rudder offset be, if any? I assume the rudder cables should be taught, but not so tight as to deform the aluminum parts. Also, while doing a hang test, let's assume the results show a 2 degree nose down attitude with a half tank of fuel in the seat tank. What should the stab be set to with respect to positive or negative degrees.

thanks....
Just trying to work out the bugs before getting air under the tires...

I set my rudder cables as they were when HLT that is 1.5" offset to the right as Dennis mentioned. Tightening the cables excessively will only compress the spring cartridges in the rudder pedals until they bottom out and then you will have a direct connection between nosewheel and rudder which isn,t the way its designed to be. I would tighten until the the spring cartridges are compressed enough so they can't disassemble during extreme rudder application.

According to the manual the horizontal stabs should be set parallel to the keel and the gyro should hang 0 to 5 degrees nose down. I've found that after going CLT my gyro is overly stable. When I reduce power it requires increasing back pressure on the stick. This is flying it with the heavy 25ft Sky Wheels rotor and a 2" mast extension for rotor to prop clearance. I'll see what the trim forces are like with the lighter Dragon Wings and do a double hang test before messing with the HS incidence.

Another unwanted consequence of extending the keel 22" was that the crosswind landing capability was reduced by about a half. The gyro doesn't slip as well when cross controlled.

Hopefully violent rudder deflection with feet off, buffeting and lack of slip capability will all be resolved with the new tall tail.


Dino


Dino

[Lspav8r]

Only having flown fixed wing aircraft I dont understand why anyone would take there feet off of a flying surface control ,even if it is a vertical one. Even if there is no tendancy for the rudder to move off center. Kinda like climbing a shear rock wall. You want at least three points of contact at all times.

This is just my opinion though.

[JonVos]

I would agree that keeping one's hands/feet on the controls is definitely a good thing. My main issue with this whole thing has always been something everyone, no matter if you fly fixed wing, rotorcraft, or a cardboard box, should be familiar with, and that's static stability. Any well designed/constructed aircraft should have both positive static and dynamic stability. Since I've experienced negative static stability about the yaw axis of my gyro, I was curious if I'd done the conversion correctly or if anyone else had experienced this. I'd imagine the place to bring up the hands/feet off topic would be under "Pilot Technique"

[Lspav8r]

I would agree that keeping one's hands/feet on the controls is definitely a good thing. My main issue with this whole thing has always been something everyone, no matter if you fly fixed wing, rotorcraft, or a cardboard box, should be familiar with, and that's static stability. Any well designed/constructed aircraft should have both positive static and dynamic stability. Since I've experienced negative static stability about the yaw axis of my gyro, I was curious if I'd done the conversion correctly or if anyone else had experienced this. I'd imagine the place to bring up the hands/feet off topic would be under "Pilot Technique"

I was merely stateing that taking your feet off of a flying surface control sounds like a very foolish thing to do. I had nothing against your post regarding the instability problem you were experiencing. I do believe the statement was made that this only happened when the controlling factor (feet) were removed from the rudder pedals. and that sir, in my humble opinion is something I would never do, even if the surfaces were in balance. I for one am not one to stunt fly ( and I realize this is for another thread as well) any aircraft untill I had PLENTY of time in it. and when I say stunt fly that includes taking your controlling members IE feet and hands off of anything while in flight. But I guess you wouldnt have known of this instability issue had you not done that .:typing:

[gyromike]

'Stunt flying' sounds a little extreme, don't you think?

I hope you aren't expecting a fully flight-tested aircraft if you are going to fly gyros. Especially if you are going to be doing any building yourself.

[karlbamforth]

I fly fixed wing all the time and fly for extended periods hands/feet off its not a problem.

Its well known that rotorcraft need to be controlled all the time but most fixed wing are happy once trimmed correctly.

[Lspav8r]

I fly fixed wing all the time and fly for extended periods hands/feet off its not a problem.

Its well known that rotorcraft need to be controlled all the time but most fixed wing are happy once trimmed correctly.

I too fly hands off on trimmed fixwing aircraft AFTER I have many many hours in them. Now to my point on buntovers and PPO.

If in fact gyros fly hands off when in trim flight, then I would assume they are a stable machine. Some WRONG application of either power settings or control surfaces or a combinatioin of both must mitigate the events encountered IE buntover/PPO and not an inherantly unstable conditioin for I can not believe that anyone would be allowed to market a design that was inherantly unstable, furthermore anyone would buy/build such an unstable aircraft. I mean why would we do something knowingly, that could kill us? More on this later.:noidea:

Jim

[OuterMarker]

I flew a Pitts a few times...it was a lot of work to fly..very unstable.......as it should be!!! Every little air bump upset it and pushed it around...after a half hour you just wanted to land. Getting back into a stable airplane was like riding in a big Lincoln....smooth and stable!!! Aircraft, which includes gyros, are designed for a certain mission and as long as you fly them within the designed performance envelope, they meet safety standards...but they don't have to be stable...why, isn't there 4th and 5th generation fighter jets that have to be flown by computers because they are so unstable?

[Doug Riley]

av8r Jim:

The homebuilt-aircraft world (in the U.S., at least) is very, very different from the world of certified aircraft. In our world, anyone is allowed to market anything. Many homebuilt designs (both FW and gyro) are, in fact, quite unstable, either by design or by accident.

Stable behavior in hands-off mode is not a reliable indicator of the underlying stability of the aircraft. Most gyroplanes are equipped with a servo mechanism known as an offset gimbal rotor head that, up to a point, is able to mask an aircraft's fundamental instability. Lock the stick (thereby locking out the servo mechanism) and the aircraft will show its true colors.

In a gyro design that is susceptible to PPO (not all are), it is usually possible by adept use of the controls to prevent the aircraft from doing what it very badly wants to do (go upside down when rotor angle of attack is suddenly reduced while the power is high). Learning the tricks of handling such mis-designed craft takes awhile. The new pilot is vulnerable until he does learn, though.

In the homebuilt world, it is up to the aircraft buyer to smoke out the unstable designs. No government body or trade organization is doing so for you. Nearly all "designers" are under-capitalized and under-informed amateurs who aren't doing this for you, either.

Sorry if this sounds a bit harsh, but it's the unvarnished truth. This activity is enormous fun, but you alone assume responsibility for all aspects of safety -- not just as pilot, but also as maintenance guy and design evaluator.

[Lspav8r]

av8r Jim:

The homebuilt-aircraft world (in the U.S., at least) is very, very different from the world of certified aircraft. In our world, anyone is allowed to market anything. Many homebuilt designs (both FW and gyro) are, in fact, quite unstable, either by design or by accident.

Stable behavior in hands-off mode is not a reliable indicator of the underlying stability of the aircraft. Most gyroplanes are equipped with a servo mechanism known as an offset gimbal rotor head that, up to a point, is able to mask an aircraft's fundamental instability. Lock the stick (thereby locking out the servo mechanism) and the aircraft will show its true colors.

In a gyro design that is susceptible to PPO (not all are), it is usually possible by adept use of the controls to prevent the aircraft from doing what it very badly wants to do (go upside down when rotor angle of attack is suddenly reduced while the power is high). Learning the tricks of handling such mis-designed craft takes awhile. The new pilot is vulnerable until he does learn, though.

In the homebuilt world, it is up to the aircraft buyer to smoke out the unstable designs. No government body or trade organization is doing so for you. Nearly all "designers" are under-capitalized and under-informed amateurs who aren't doing this for you, either.

Sorry if this sounds a bit harsh, but it's the unvarnished truth. This activity is enormous fun, but you alone assume responsibility for all aspects of safety -- not just as pilot, but also as maintenance guy and design evaluator.

Got a lot out of your post. Very informative. Is there a list of the machines somewhere that have the traits that make them unstable (Buntove/PPO). It would be very helpful to know which ones are in this catagory so as to guide us newbies toward making an informed decision on which one we want to buy/build, and what to do to the bad ones to make them more flier friendly.

Jim.

[Vance]

Hello Jim,

I spend a lot of time with the NTSB reports.

Some of the reports seem more pilot related than others.

Eventually trends become evident.

You are also beginning to discover why some of the threads get so technical.

There is not agreement here on what makes a gyroplane safe.

It is human nature to believe that something is safe if you do it often and don’t die.

We try to learn enough to make an informed decision.

Opinions don’t count for much when there are unnecessary accidents.

Thank you, Vance

[karlbamforth]

Lspav8r

Try a search of this forum for CLT, bunt and PPO I am sure you will find enough to read from now till December.

As has already been mentioned everyone has different opinions of what the best design is, but if you read the threads you will get a good idea of what most here think are good things to have.

[JonVos]

I was merely stateing that taking your feet off of a flying surface control sounds like a very foolish thing to do. I had nothing against your post regarding the instability problem you were experiencing. I do believe the statement was made that this only happened when the controlling factor (feet) were removed from the rudder pedals. and that sir, in my humble opinion is something I would never do, even if the surfaces were in balance. I for one am not one to stunt fly ( and I realize this is for another thread as well) any aircraft untill I had PLENTY of time in it. and when I say stunt fly that includes taking your controlling members IE feet and hands off of anything while in flight. But I guess you wouldnt have known of this instability issue had you not done that .:typing:

Before this becomes a major poop-slinging event, let's put away the Jump-to-Conclusions-Mat for a minute and get some things straight. Never in this or any post have I ever indicated that I've removed my hands/feet from any control. However, during the several hundred hours I've flown my gyro, I have occasionally relaxed my grip on the controls. I can't imagine anyone in the recent history of aviation who's spent his/her entire flying career with a white-knuckled death-grip on the controls. Sometimes you just need to reposition your hands, man! The same holds true with the rudder pedals. I freely admit that I've relaxed my feet on the rudder pedals. I'm not dangling them out in the breeze, but I'm not trying to test the shear strength of my rudder cables either. Most of the time it was because my butt cheeks were getting numb from sitting on a plastic seat with no padding for so long and I needed to adjust myself in the seat. It was in those conditions that I experienced my yaw problem that led to me starting this post. I hope that does a reasonable job of explaining the circumstances to you, so let's just calm down and stick to the topic at hand. I agreed with you that taking one's hands/feet off the controls is a good idea, so let's not go around insulting other peoples piloting technique, ok?