Testing gyros for buntovers potential

[gyrogreg]

Originally Posted by WaspAir

Yikes!
Good luck guys -- I hope you get some useful data without incident.
Personally, I won't be caught above 0 kts IAS and/or 0 ft AGL without the "full, free, and correct" motion of all controls that's been on every checklist I've ever used. I just can't get past the cringing that comes from even hearing the term "jam stick".

If a gyro requires such constant attention on the stick, you already have your answer! That gyro is statically unstable, like constantly having to work at balancing a yard stick upright in the palm of your hand. Stable gyroplanes and aircraft do not require constant attention on the stick! A stable gyro will fly indefinitely at a near constant airpseed with a fixed stick - even in turbulence! The stick fixed position should determine a constant mean airspeed - determined by power and stick position. Any deviation from that attitude or airspeed should tend to immediately correct for that deviation! That is because a stable aircraft has a restoring pitch moment when there is any deviation from steady state pitch and airspeed - the definition of static stability.

A stable gyro requires much less attention to the stick than a helicopter - a helicopter, without stability augmentation is basically statically unstable* - but this does not need to apply to gyroplanes. The examples Chuck quotes above, where the locked stick must be immediately released, are perfect examples of dynamically iunstable unstable gyros, and they can very likely buntover if pushed a little harder with the right disturbance and an inattentive pilot! - fixed stick or not! If they actually still oscillate before the pilot has to take over, with just a little more power or airspeed, that gyro will be statically unstable and primed to buntover!

A well stabilized gyro requires much less attention to the stick than similarly sized airplanes in the same turbulence. This is partly because the rotor is less sensitive to wind deviations. But it is also because the stable gyro forces immediate restoring cyclic into the rotor - and the rotor very powerfully starts restoring the steady state. This is one of the most remarkable features of a stable gyroplane, one that astonishes every doubting Thomas airplane pilot until they actually experience it themselves. That is one of the most fun things to demonstrate to FW pilots in a gyro - find the most turbulence you can find and have THEM fly in it! I have sold a few gyros (Magnis) to FW pilots for just that reason!

It might be difficult to design a gyro that would not have phugoid oscillations, and therefore be AOA statically stable, at MPRS or less. That's why I say to start at that airspeed - then increase airspeed in small increments. At the point where oscillations start growing instead of settling out, you do still have static AOA stability - you are still safe from buntover, but stop there and don't go any higher airspeed because you are losing your static stability safety margin.

Thanks, Greg

* Ironically, a helicopter with an effective HS on the long tail moment arm - lots of dynamic and static stability - becomes more and more AOA and airspeed statically stable at higher airspeeds. That alone should be enough hint about what to do with gyros. Where do you think the thrustline is on a helicopter? It is at the rotor level - very HTL! And yet, they can fly stable at higher airspeeds if they employ a good HS. And, a helicopter in those conditions, also does not require a lot of constant attention to the stick. (Cobra and Apache pilots have lots more things to do than to just fly the helicopter.) In all aircraft types, the only attention the joystick should require is for the pilot to command a deviation from the steady state condition.

- Now is about the time someone complains that the stable gyro won't be any fun then! It will be a "lead sled"! Come on, where are you? Speak up! Let's see if you know the difference between a fixed wing and a non-fixed wing! Anyone want to explain the difference as it relates to maneuverability and controllability?

[PW_Plack]

... -use lateral stick movement to keep the gyro level, but keep pressure on the chain or "jam stick" to maintain that stick pitch position...

Either a stick or a chain will cause any movement of the stick in the roll axis to create a change in stick pitch position, since the locks will hold the stick in an arc, not in a straight lateral line. Is this significant?

[gyrogreg]

Originally Posted by PW_Plack

... -use lateral stick movement to keep the gyro level, but keep pressure on the chain or "jam stick" to maintain that stick pitch position...

Either a stick or a chain will cause any movement of the stick in the roll axis to create a change in stick pitch position, since the locks will hold the stick in an arc, not in a straight lateral line. Is this significant?

Paul, Not really! The gyro is still flying without pilot stabilizing pitch inputs. It would be very difficult for the pilot to learn how to put in stabilizing pitch inputs with this lateral stick action only. In moderate turbulence, once it is level at the power and trimmed (stick position) airspeed, there are norrmally not a lot of lateral inputs required anyway.

If you really wanted to be precise with the "jam stick", you could square the base of the "jam stick" - against the flat instrument panel, so lateral movements on the corner of the stick would compensate the pitch input! Do the geometry. But, this is not necessary. Just do it the simple way - it will be very revealing! The difference between a well stabilized gyro and a gyro that starts losing its dynamic stability is very convincing! Remember, at the power/airspeed point where it starts losing its dynamic stability, it is still oscillating and therefore still AOA statically stable - and incapable of a buntover at that apoint. But, don't press beyond that loss of dynamic stability point! You found your Vne!

- Greg

[C. Beaty]

* Ironically, a helicopter with an effective HS on the long tail moment arm - lots of dynamic and static stability - becomes more and more AOA and airspeed statically stable at higher airspeeds. That alone should be enough hint about what to do with gyros. Where do you think the thrustline is on a helicopter? It is at the rotor level - very HTL! And yet, they can fly stable at higher airspeeds if they employ a good HS. And, a helicopter in those conditions, also does not require a lot of constant attention to the stick. (Cobra and Apache pilots have lots more things to do than to just fly the helicopter.) In all aircraft types, the only attention the joystick should require is for the pilot to command a deviation from the steady state condition.

A helicopter rotor, like a propeller produces a line of thrust, not thrust applied to a point.

The thrust produced by a helicopter rotor acts in a straight line that is very nearly coincident with the tip plane axis. The horizontal component of the forward tilted thrust line supplies the propulsive force.

A helicopter can be either nose heavy or tail heavy, depending upon how the projected thrust line passes relative the aircraft’s CG. The only difference is that it doesn’t have propeller thrust to contend with.

Generally, helicopters without horizontal stabilizers are always tail heavy at forward airspeed. The aerodynamic drag of the fuselage swings the CG aft of the rotor thrust line, the rotor thrust line being fixed in space by operating conditions.

An exception is the synchopter, with the outboard blade tips moving aft. A synchopter has an unbalanced component of rotor torque acting about the pitch axis that provides a nose up moment on the airframe. Think of a dragster with cambered wheels doing wheelies.

[jvitable]

How you guys have knoted and twisted this great sport with all this bull amazes me.I had no idea we had so many distinguished aeronautical enginners in the group.Since (it seems to me) that 90+% of all gyro accidents are caused by lack of training or bad judgment we could spend our time more wisely in this area.Why don't all you geniuses sell me your death machines cheap(that is if you own one).Problem solved!!! LC PS-then you will have the money to buy a nice Sofa with airbags---be safe-Joe PSS-all joking aside I believe most crashes are caused by the angle of the dangle being out of synchronization with those two small nuts located just behind the control stick-this problem can be corrected by replacement of said small nuts with a larger size--!!!!

[WaspAir]

Originally Posted by Not Yet

Either one of these devices can be instantly disabled to allow full movement of the stick. What is the problem?

I, for one, won't fly when there is any foreign object loose in the cockpit that could possibly jam any control (cyclic, pedals, or whatever, accidentally or on purpose), ESPECIALLY when one is intentionally flying into turbulence, as explicitly suggested here. If/when your stick falls out in rough air, it sounds like just the beginning of a potential new problem to me. Perhaps my CFI attitude is too conservative for some of you, but I'll leave the macho to others, and plan to live a long time.

Originally Posted by Dean_Dolph

I can't think of, but may be wrong, any scenario where an emergency would cause the test pilot to want or have to push the stick forward. In fact, in a gyro, this reaction is kinda a no, no anyhow!
. . .
Haven't thought this thru this long enough to suggest a restraint that doesn't present problems of its own.

There's a reason that there is forward travel on the cyclic -- if it was not needed for any flight regime, we could just put in a permanent stop. I want it available when I fly. I agree on the restraint problems, for the reasons I mentioned above.

Originally Posted by C. Beaty

What’s the big deal? Both Dick DeGraw and his wife Carroll have been flying gyros with stick locks for years. . .

Stories of survival are not enough to convince me of safety, and shouldn't be for you, either. People survive lots of stupid actions and bad design choices, as much of the discussion on this forum confirms.

Can you imagine what the NTSB report will say if something goes wrong, after you intentionally introduce a control jamming device in your aircraft? "Probable cause: pilot intentionally fouled his own controls; Contributing factors: overconfidence, poor planning, and stupidity."

What's principally bugging me here is the implicit call to everybody to go out and try this and report the results (i.e., "I would appreciate any comments or flight testing feedback on these concepts.", along with directions/pictures on how to do it). If you've got Society of Experimental Test Pilots credentials, a carefully designed protocol, data capture arrangements that will survive any accident, good insurance, and back-ups for your back-ups (anybody here wear a 'chute?), be my guest. If you're just going to play Test Pilot For A Day, I wish you and your family well, but won't be joining you.

Lack (so far) of a better test regimen doesn't make this a good one for the community at large to be trying out. I'd put this in the "professional on closed course; don't try this at home" category. Let's not have people out there getting themselves hurt in the name of safety.

[Chuck_Ellsworth]

Originally Posted by jvitable

all joking aside I believe most crashes are caused by the angle of the dangle being out of synchronization with those two small nuts located just behind the control stick-this problem can be corrected by replacement of said small nuts with a larger size--!!!!

That opinion sounds like it comes from someone who has a brain 1/10 th. the size of his nuts.

[C. Beaty]

A spring detent mechanism produces a snap back to center action when the controls are released, the same as the centering mechanism on swinging saloon doors, Waspair.

Yet, without the foggiest idea of the device under discussion, you conclude that anyone discussing anything connected with gyros is by definition, feebleminded.

You are an inspiration. But don’t you believe your brilliance is wasted those of us that are less gifted than you?

[jvitable]

Originally Posted by Chuck_Ellsworth

That opinion sounds like it comes from someone who has a brain 1/10 th. the size of his nuts.

Upchuck---very poor comeback---as usual--maybe my brain was affected when preforming unlimited aerobatics in a 727 locked at full RPM and full throttle--If they ever have a Biggest Puke on the Planet contest you are destined for fame .You have already saved more lives than "penicillin"-seems you would be happy!!!There is not another sport out there that is tearing itself apart as we are.No one begs a person to fly a gyro.No one forces a person to fly a gyro.It is personal choice-if I had overwhelming concerns about their safety I would get out of the sport!You ignored the main portion of my text and focused on "nuts"We have gone from CLT to onboard flight recorders to telling flyers to experiment with locking down the control stick--We should be focused on picking the correct gyro for the individual-plenty of flight training which includes using good judgment(like don't take off on your first flight in a snowstorm)(you probably blamed that fatal crash on RAF also.Again your hate for RAF drives you to destroy the sport for everyone-only then will your failure be vindicated.The biggest shame is you are doing a good job of it. I am one of only a very few(obviously) crying out in the wildernest!!!!!

[WaspAir]

Originally Posted by C. Beaty

A spring detent mechanism produces a snap back to center action when the controls are released, the same as the centering mechanism on swinging saloon doors, Waspair.

Yet, without the foggiest idea of the device under discussion, you conclude that anyone discussing anything connected with gyros is by definition, feebleminded.

You are an inspiration. But don’t you believe your brilliance is wasted those of us that are less gifted than you?

You're awfully quick to switch from the subject to personal venom. I'll keep my poison pen in the drawer for now and give you a measured response.

First, the device under discussion is a jam stick as pictured in post #2. That's quite a bit more than a foggy idea. You raised the spring detent by analogy with your "what's the big deal?" comment and a list of people who have tried stick-fixing devices, but that isn't what we've all been talking about.

I quoted a snippet (to save space) from you to challenge the nature of your reasoning; just because some survive doesn't mean a practice should be recommended to others. After all the RAF brouhaha on this site, I would think you, of all people, would agree that survival by some doesn't establish the wisdom of a practice or a design.

I didn't accuse anybody of being feeble-minded, nor did I claim to be brilliant, nor did I suggest that anybody is less gifted than I.

What I did attack is the wisdom of encouraging the readers of this forum to fly their aircraft with devices that will certainly intentionally, and could also accidentally, restrict control movement while intentionally flying through turbulence. I would hate to see a desire for gathering stability data for safety purposes backfire and lead to accidents while that data is being gathered. I don't consider that a responsible way to pursue safety.

My advice to pilots is: (1) don't try it, and (2) always keep your cockpit free of anything that might snag a control at an inconvenient time.

[helipaddy]

I've avoided reading a threads like "Looping a Gyro" and this one, tryin to avoid a mention in the Darwin Awards. this is the realm of a cautious controlled test regime, not "anyone can do it with a bit of chain and a broom handle ". Frightens the bejaysus out of me.
Ill just keep flying plain vanilla
Paddy

[Doug Riley]

These are "experimental" aircraft. We -- supposedly -- are experimenting. Greg's post suggests how to do a CONTROLLED experiment (the only kind that yields any useful information).

Eyeballing a design and blasting off to see what happens is an UNcontrolled experiment. It does nothing to further anyone's knowledge.

[gyrogreg]

Hey guys, we're trying to advance knowledge and understanding for everyone here. Knowledge is paramount to making good decisions. If you are uncomfortable performing these tests, then please don't do them! As with anything in flying or life, approach it in little steps and keep it safe. But, if you want to help advance gyroplane safety and are comfortable with a little experimenting with your experimental aircraft, then we could use the data.

A point to make: The 40 hour Phase I flight test period that all Experimental Aircraft are supposed to do is intended to evaluate the aircraft's safe flight envelope and its limitations. These are actually evaluations you were supposed to have made during your phase I period. We're just trying to help you identify your aircraft's limitations safely and effectively. Wouldn't you prefer to know if or when your aircraft is a loaded mouse trap waiting to kill you? This Dynamic Stability flight test is safe and normal and standard to conduct on any aircraft. If you don't understand why it is safe and how to keep it safe, then please don't do it! And, by the method I described, you are not getting into flight realms that are more dangerous than the flying you normally do. You were supposed to have done this already - in Phase I! If you are worried about dropping a stick into your contols, I hope a pilot is smart enough to figure out how to not do that! If not, please don't do the test!

BTW, the "chain" method does not fall on the floor if you use a long enough chain. If you don't like the chain, use a (non-strechable) nylon chord - same place you can find the chain in a hardware store. That same hardware store will have different size electrical conduit clamps, so take one over to the chain reel and select a chain that fits and slips well in the hole in the clamp. But, I'm sure a pilot is smart enough to figure that stuff out themselves - but if not, PLEASE don't do this testing!

Military helicopter test pilots, doing similar flight tests, have a specially rigged electrical lock on the stick that is engaged while they hold a button on the cyclic stick, and disengages when they release it. What I am suggesting is the equivalent, "poor man's" version.

But, don't attempt this test if you are really uncomfortable with it!

- Thanks, Greg

[Fiesty]

Having worked as a helicopter test pilot for a number of years I perfer the the old ploting board method of cyclic position. Will not jam and will have a record of cyclic stick position. You may return any position later for varification. I started teaching test flight procedures to Army helicopter pilots in 1950. Worked as test pilot on the Army`s H-34 proram in 1955. I taught over 150 pilots test flight procedures, 1950 thru 1954.

[gyrogreg]

Originally Posted by Fiesty

Having worked as a helicopter test pilot for a number of years I perfer the the old ploting board method of cyclic position. Will not jam and will have a record of cyclic stick position. You may return any position later for varification. I started teaching test flight procedures to Army helicopter pilots in 1950. Worked as test pilot on the Army`s H-34 proram in 1955. I taught over 150 pilots test flight procedures, 1950 thru 1954.

Feisty, could you please elaborate on the "plotting board" method? - Greg