PIO.....once and for all!!!!!

[Ron R]

In the 3 or so years I've been around gyros, there always seems to be a bit of a disagreement about what to do with a PIO. The ONLY thing that everyone seems to agree with is..........REDUCE POWER! After that, it seems to be dependant on who you're talking to. In the Gyroplane Flight Manual, it states that it can be induced by the unexperienced pilot being too slow to respond. TO WHAT??? It seems that the best approach is to do NOTHING after reduction of power. Hold steady stick (or a little back) and let it dampen itself out. It would seem that any correction would only ADD to the oscillation. Just like when I was training and flying through wind gusts, I would just hold steady, and let the machine adjust itself, being careful not to add to a potentially bad situation. Is ANY of this correct? I'd just like to see it down on paper, (or on screen) for sure. Rotorcraft Magazine made mention of this in the last issue and seems to be along my line of thought. Thanks for any input. Ron R.

[Victor Duarte]

i cant speak for gyros, but when i was trying to hover in a bell 47 with an instructor, that was the father of an ex GF.. he just told me to do nothing, excepted to add a little collective.. he explained it very well , and every one can understand : it s a matter of self control vs natural reflexes.. just push someone standing, his natural reflex will be to step forward.. no way to control that (excepted if you re prepared to that).

[MikeBoyette]

Ron R,
Just about all problems in a gyro , short of hitting the ground can be corrected by reducing the power. The type of problem and severity determine how much and how fast of a throttle reduction you need. Most of the time if you are in the early stages of pio you can chop the throttle and let the machine right itself. Obviously the more stable the machine the less likely you are to get into such a situation. A properly designed machine and loads of training is the best advice anyone can give you.

[Harry_S.]

From personal experience...

Yank the throttle back and neutralize the stick; simultaneously. You will approach a vertical descent...then recover with cyclic and throttle.

I have read that with power reduction, put your machine into a hard bank. That may/may not do it but I know what I said above...made my recovery from certain death. I've been there!!!

[Udi]

...I have read that with power reduction, put your machine into a hard bank...

One question that I have never gotten a satisfactory answer to is, how do I recover from a "nose-high event"? In a fixed wing, you recover from a nose high event by adding full power and lowering the nose, even if that means going to negative G.

In a gyro, this kind of event is much more difficult to deal with. For one, with the nose very high and full power, the engine rather than the blades supports some of the weight of the gyro, and the blades are partly or mostly unloaded. You are at a risk of losing too much RRPM. Second, if you "push down" the nose you would only make the problem worse by unloading the blades even more. Third, if your gyro has a HTL, you are risking a PPO.

One option to deal with a nose high situation is to cut power and let the nose drop naturally. This is the advice I got from one instructor. I am not happy with this advice.

Another option is to enter the gyro into a hard bank at full power and pull back on the stick. This would keep the rotors loaded. This would be my preferred recovery.

Udi

[Chopper Reid]

[QUOTE=Ron R]In the 3 or so years I've been around gyros, there always seems to be a bit of a disagreement about what to do with a PIO. The ONLY thing that everyone seems to agree with is..........REDUCE POWER! After that, it seems to be dependant on who you're talking to. In the Gyroplane Flight Manual, it states that it can be induced by the unexperienced pilot being too slow to respond. TO WHAT??? ]


If you have been taught to fly a gyro by a "good " instructor, then I'm at a loss how you are going to PIO, no matter what type of gyro you fly or how inexperienced you are.

Udi, what manourve has got your gyro "nose very high " ?

[pwendell]

Udi,

I practised entry into and recovery from rapid rates of decent -- flight below minimum level flight speed -- with both power on and power off. In the AAI modified RAF, it works both ways. To enter this state with power, I simpley pulled back on the stick slowly while adding power, until the pitch was so high the gyro couldn't maintain enough airspeed for level flight with full power. With power off, simple incrase pitch until you're decending vertically. To recover with power on, you add power, if it isn't already full, and simply relax back pressure and let the nose come down to re-establish the proper pitch, just as you do with power off. It recovers much more quickly, of course, with power.

From my very limited experience, the most likely and most dangerous situation in which you're likely to find yourself nose high during normal operations is an inadvertant takeoff with low airspeed and high angle of attack. (Don't ask:eek: )This is when the gyro is allowed to come off the ground, or forced to come off the ground, with insuffcient airspeed. Because the gyro is so close to the ground, recovery has to made with full power and the nose does have to pushed slowly down to increase airspeed in order to prevent the gyro from falling back onto the runway. Again, this was managable, but not fun, in the modified RAF. I can imagine that this could be scary in an HTL, especially since gusty conditions can contribute to takeoff at low airspeed/high AOA.

Disclaimer: The techniques I learned may not be applicable to, and may even be dangerous in, other types of Gyros. Do not try them without professional instruction.

[birdy]

Ron,to your "TO WHAT??? " question.
I think what causes the most,if not all PIO situations with a new pilot is a combination of nerves and control lag.
Every fresh solo pilot will be nervous,and when the machine hits it's first bit of turbulance and the nose pitches slightly he'll react immediatly,but coz the machines responce is'nt immeadiate he adds more control,just as the machine responds to the first input.Because of the "double" input,the machine overreacts so the pilot overcorrects.The combination of increased heart rate and control lag will ensure an aggrivated pitching machine.The best thing,if you have enough altitude I reckon is to reduce power and hold the stick back a little from center untill the machine settles,which it will do.
If you don't have alt to spare,then the same but with the stick held in the cruise position.[Surely,being a SCG,I don't need to add a disclaimer]


I can't for the life of me think wot would cause an old hand to pio.

[Chopper Reid]

I cant think why anyone correctly trained to fly should POI in the first place . I just reckon that too many accidents are the result of very poor training full stop regardless of the type of gyro you fly !!
If, however, someone should stuff up, then your remedy of power off and holding stick back is the best way to controll the situation.

[Aussie_Paul]

Birdy said, "Ron,to your "TO WHAT??? " question.
I think what causes the most,if not all PIO situations with a new pilot is a combination of nerves and control lag.
Every fresh solo pilot will be nervous,and when the machine hits it's first bit of turbulance and the nose pitches slightly he'll react immediatly,but coz the machines responce is'nt immeadiate he adds more control,just as the machine responds to the first input.Because of the "double" input,the machine overreacts so the pilot overcorrects.The combination of increased heart rate and control lag will ensure an aggrivated pitching machine.The best thing,if you have enough altitude I reckon is to reduce power and hold the stick back a little from center untill the machine settles,which it will do.
If you don't have alt to spare,then the same but with the stick held in the cruise position.[Surely,being a SCG,I don't need to add a disclaimer]


I can't for the life of me think wot would cause an old hand to pio." The trouble with experienced people in whatever they do is they learn to adjust and make it look so easy!!!!! As I always say, "I never look at a gyro unless I look at it through the eyes of a student who is ready for solo. Is this gyro going to help or hinder the students chance of success." I believe that it is an instructors responsibility to know the difference.

That is why the average recreational gyro pilot should build the most stable gyro possible!!!!! I would call that common sense, what would others call it.

Birdy, when I got my first Raf in 1997 I had a very experienced mustering pilot porpoise gently while cimbing out. It only took a few seconds for him to adjust. My pitch unstable Raf had a different lag and feel to the musters pitch unstable gyro. :eek:



Aussie Paul. :)

[Hognose]

The "back off the throttle and wait for it to damp out" approach is a good one in a gyro that is <i>statically and dynamically stable.</i> Some gyros are not even statically stable and many are not dynamically stable. (Static stability is a prerequisite for dynamic stability, and dynamic stability is that "damping out" action).

David Bird makes an excellent point about the role that fright plays in PIO. If you have a machine that is unstable, the oscillations may not damp out, but continue. In some ships they may actually be divergent with no human input. It is next thing to impossible to expect a human not to act in this situation.

We've seen a number of probable PIO accidents in the last few years (absent a flight recorder or credible eyewitnesses, it's hard to break out PIO from PPO mishaps) and some of them have been experienced pilots with a significant amounts of dual from respected instructors.

It's a common reaction of pilots to dismiss their dead buddy as a screw-up. It's whistling past the churchyard a bit, isn't it?

cheers

-=K=-

[Doug Riley]

The "theme" I try to pass on to students about gyro flying is that "less is more." Large, abrupt movements of either stick or throttle are to be avoided. A cetain laziness -- almost sleepiness -- in control movements will usually prevent overcontrol. Nerves ARE a big part of the problem; the nose comes up in turbulence or the airspeed is 10 mph higher than the student's target, and he/she panics and either chops the throttle or makes a large stick movement. The gyro overshoots in the other direction, and another over-control occurs.

Interestingly, in the Dominator this is more likely to happen on a low-power approach than at any other time. So cutting power isn't a foolproof fix.

I do think that smoothly REDUCING power will help, as will holding the stick lightly, but still. If you're feeling panicky, hold it still with a LIGHT grip for just a few seconds; you can always add an input in a moment. Any inputs should be pressures, not visible movements of the stick.

PIO should not be a problem with (1) proper training and (2) a stable machine. if you're flying with no training (or without finishing your training), you are asking for trouble. In that case, you should feel lucky that we're willing to talk you down out of a case of your own bad judgment! Ditto if you're flying an unstable machine that readily goes into PIO.

[mceagle]

Might as well throw in an opinion here for what its worth.

Dougs statment "Interestingly, in the Dominator this is more likely to happen on a low-power approach than at any other time. So cutting power isn't a foolproof fix"

Doug this concurs with Gyro Greg's findings, that such a gyro has power augmented stability and under reduced power or no power, the pitch stability can be less than desireable. This is also quite noticable when running competitions on power-off spot landings - even with experienced on-type pilots.

Try as he may, it is almost impossible for an experienced pilot to demonstrate PIO to a beginner. Beginners on the other hand are very talented and can demonstrate PIO (and flight behind the power curve) at a seconds notice. I have found that instantly putting the Gyro into a turn, even a gentle one, will stop the PIO instantly. This can be safer than cutting the power in instances of marginal power and low altitude. A Gyro has a pendulm frequency and PIO is perpetuated by a student applying a corrective movement at the same time as the natural frequency of the Gyro, thus giving a "double" correction. It is interesting to note that even though recovery can be demonstrated by simply holding the stick steady, some students cannot help themselves and continue to "pump" the stick.

I have test flown a machine that was a direct drive with a short prop and a thrust line that would have been close to CLT. This Gyro was close coupled and had a low moment of inertia, and was prone to porpoise continually in flight. It was quite strange and required constant control attention at all times to maintain smooth flight. I still do not know what caused this and when the machine was rebuilt after an accident the problem disappeared.

Perhaps one of the plus's of a low C of G machines is their high moment of inertia, making their natural frequecy slower and easier to control for a student.

[Brian Jackson]

Interesting points, Tim. It never ceases to amaze me, after all the time I spend on this forum, there's new layers of interrelating physics to gyro flight dynamics. Quick question though... You mentioned the gyro on your post (the PIO prone one) as being "close coupled." What does this mean? Does it have to do with the rotor height/distance from the CG? Thanks.

Regards,
Brian Jackson

[Doug Riley]

Tim: I'm not sure of the source of student overcontrolling on approach in the Dominator. It's pretty benign. It does make it impossible to pick out your landing spot because you keep altering your glide angle. I won't sign them for solo, or even put them in the front seat, until they cut it out!

Two possible sources of this kind of overcontrol are

(1) The pitch trim changes as power is changed in a below-CLT machine. This alters the stick pressures and may be confusing until you get used to it (or find the trim button). It's more difficult to have much finesse with the stick when you have to hold a significant steady bias pressure.

(2) The reduced damping effect of the HS once the prop slipstream is diminished (I require that all final approaches be done at idle). This latter is not quite the same as Greg's point; I think he's talking about the AOA stability afforded by a thrustline below the CG, which pushes the rotor thrustline behind the CG -- a good thing, but only true while there's significant prop thrust.

A turn may stop porpoising, but the other time I catch students overcontrolling is when they're coming out of a turn. The adding and subtracting of back pressure at the proper point and in the proper amount in a turn takes awhile to master. Nobody gets it quite right at first. Also, if the turn has been banked much more than 30 degrees, there's enough of a boost in RRPM that the gyro balloons a bit once it's levelled off. That adds to the confusion. I would not be surprised to find that a number of PPO's in unstable craft occur on rollout from a stiff bank, when the inexperienced pilot feels that RRPM balloon, panics and shoves the stick forward.

[Chopper Reid]

[QUOTE=Doug Riley].

I do think that smoothly REDUCING power will help, as will holding the stick lightly, but still. If you're feeling panicky, hold it still with a LIGHT grip for just a few seconds; you can always add an input in a moment. Any inputs should be pressures, not visible movements of the stick.

Agree with you there Doug, SMOOTHLY, doing anything in a gyro I reckon needs to be smooth. This might be the key as well as a lighter touch on the stick. A gyro needs only minimal corrections so any abrupt or large changes of power could make the problem worse for the less experienced pilot. I think that low hour gyro pilots that have a FW licence may be more prone to overcontrolling.

[birdy]

Speak'n of smooth,I reckon I am. ;)
I happened to be do'n a "favor" for a neibour this morning and took the time to think more bout how much input there is in fly'n these things.
The conditions were perfect for the job and for wot I wanted to find out.
@ 25c,40 to 50 kmh breese and plenty of turbulance off the ranges :) .[not to mention some %#*&@# cattle that didn't want to play by the ruels :mad: .]
5 hours later I found that ,unless I was actualy "working" the cattle,just fly'n sort of S/L,100 up and in ground turbulance ,all that I woz do'n was sitting in it and letting the stick "float" with my feet off the peddles. :)
Even when one of his dear old &#$^%$# cows was do'n its best to piss me off,the inputs,while more forceful,were still smooth.
Conciquently,coz I woz think'n of fly'n and not the job,I stuffed it up a couple of times. :o

[Doug Riley]

Birdy, it's that light,floaty grip that does the trick. I learned the same tactic in my old (nowhere near CLT, no HS) Air Command.

The gimbal head-spring combination provides some pitch-stabilizing forces. These forces are designed to overcome the natural angle of attack instability of the rotor (which is caused by flapping). This AOA instability is what some people call "rotor blowback."

"Floating" the stick lets these forces actually manipulate the head a bit in response to changes in AOA and airspeed. With a CLT machine, the gimbal head does a fair job of providing stability as long as head remains free to float. Once the head reaches its stops (either teeter stops or control stops), however, the system hits the limit of what it can do for you. That reaching-the-limit happens in a heartbeat in a very high thrustline, no HS machine. As the prop thrust pushes this kind of machine forward, the rotor and the head quickly reach their stops.

Even in a CLT machine with no tendency to PPO, a frame-mounted HS is helpful. It eliminates the need for a floaty grip, provides damping to smooth out pilot-induced oscillations, and supplements the action of the gimbal head by forcing the nose UP when the G's go DOWN. Once you mount an effective HS, you're actually better off using a slightly firmer stick grip, to link the rotor head to the frame.

(Why am I feeling like a golf teacher here?)

[mceagle]

Agreed Doug. That "ballooning" that you mentioned can be the friend of an experienced pilot and handy in some manouvers.

Brian J. by close-coupled I mean that the major items of mass are concentrated into a small area, generally making the gyro more manouverable and responsive. It is possible that the gyro that I mentioned had the C of M dead on the rotor thrust line causing the instability.

[Aussie_Paul]

When you get into true stick fixed testing the whole ball game changes. I was very surprised when I started that part of my testing. I was quite happy with the stick free results.

A Raf with a reasonable effective stab would fly hands off and handle reasonable gusts, coming back to trim speed. Lock the stick and the first small gust and PPO would begin immediately!!!!!!! Quite frightening actually. :eek:

On Hybrid, by doubling the stab size allowed much bigger gusts to be handled stick fixed.

Training with Hybrid I find that students "can have quite a death grip and not lose control". The aim of course is to have them relaxed BUT to a new aviation person that can be a little difficult during the first couple of hours. The Raf with a stab needed that light grip, whereas Hybrid will not allow the student to lose control as easily, and the student relaxes with less hours dual.

Productivity I think it is called. :D

Aussie Paul.:)



Aussie Paul.:)