Thrust line vs center of mass

I feel that safety is an important measure of a gyroplane and no doubt power push overs are dangerous.

Theory is great and people much more informed than I may be able to accurately predict what is going to happen under specific conditions with a gyroplane.

Reality is much better because there is no guess work.

The reality is that a line of gyroplanes made by Magni with the one of the highest thrust line in relation to the center of gravity has one of the best safety records in this country.

I have flown an M24 in winds that should have kept us on the ground and found it surprisingly docile.

Most of my clients passed their proficiency check ride in a Magni M16 after having been trained in a gyroplane with near centerline thrust (The Predator) and so far I have a hundred percent pass rate.

The Flight instructor I use most often for proficiency check rides flew The Predator and felt it handled very similar to the Magni. He flew to commercial standards with no demonstration and very little instruction from me.

Another gyroplane with the thrust line well above the center of gravity (RAF2000) has one of the worst safety records.

This is the problem with imagining that a single feature governs the flight characteristics of a gyroplane.

In my opinion flight characteristics of a gyroplane are the result of a complex system.Predator and Paul' Magni.jpg
 
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Dear Vance,
when a gyroplane enters in a ppo situation , it can't recover this means : death of the pilot
when a gyro get's out of it's flying envelope it can't go back in the envelope like it can be the case for a fixed wing aircraft ( for example : stall limits)
a test pilot can't go to the limit without risking it's life because there are no parachutes on the gyros
hence it is impossible to define the flying envelope of a gyro otherwise then by making a stability study and taking big margins
the fact that most of stock htl gyros have prooved to be stable because there have been zero or very few people that suffered this kind of accident simply means that if the maker does not make a stability study the clients have been the long terms test pilots ... i accept to beta test a soft but not a gyro
but I am sure that the serious makers have conducted serious stability studies they should issue for each of their machines to put an end to the discussion

You are going to be the long term test pilot for the aircraft you designed jm-urbani and the maker did not do a stability study.

When it comes to Magni there are other test pilots I can confer with.

In my opinion there are enough Magni flying that if there was a design defect we would have seen more crashes.

I prefer a near centerline thrust gyroplane because I like how it flies, not because I think it is safer than a Magni with its high thrust line.

So far I have been able to recover from piloting errors in a gyroplane.
 
When the forward speed is almost zero at the top of the trajectory, how large a not too little plate?

jean if you mean what will prevent low to zero G if someone flies a parabola to generate low G. Nothing. But that maneuver is a known maneuver to create low G. It should never be done in a Gyroplane of any thrust line. Gyroplanes are not aerobatic Aircraft just as trikes are not. In both if you do a deliberate parabola, and a tumble or torque roll or more likely a combo of both starts it’s not going to be good thing. That case will likely also be fatal for a LTL Gyroplane. In fact in Florida a few years ago a Dominator had a fatal because the pilot was new and got into PIO on takeoff and flew up, down, up, and then down and done. Do I blame Dominator? No. The pilot was not ready. He unloaded the rotor. This idea that somehow the tail configuration and thrust line will save you when your rotor is gone is a figment of imagination that has never been proven. I believe the effort is to make it easier to avoid getting to that situation.

The volume of tail needed is dependent on the high thrust line offset. For instance we are 4 inch high thrust line and I can dump the stick forward somewhat quickly at idle in testing without any problem with the HS volume we have. Where adequate is enough more is going to be a bit better. So it’s a compromise in what you are willing to accept. The way rigging is setup putting abrupt power input tends to raise the nose slightly and slow you down slightly in an AR-1. However there is no guarantee of any kind when the pilot flies a parabola deliberately unloading the rotor. Without an aerodynamic surface like an elevator, good luck. It’s essentially the same question as asking an airplane designer what will happen if the airplane elevator came off at the top of the parabola. Most likely you are dead.
 
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Based on my own observation, or on detailed reports from experienced pilots whose word I trust, it is possible to throw the stick forward fairly aggressively in either a Dominator or an M-16 without causing a PPO. I did the same (not on purpose!) in my Gyrobee with downloaded, immersed stab at full throttle at 70 mph. I floated up against my seatbelt but nothing else scary happened.

So we have some data points indicating (at the very least) more PPO resistance in these models than in the Bensen in the old Japanese video. That pilot did the same thing and died. But...

Do we know where the edge is? My throttle was WOT on the 'Bee; how about those other two? Would a parabolic flight path unload the rotor longer and precipitate a PPO? Or a loss of RRPM sufficient to cause retreating-blade stall (=catastrophic flapping)? As JM says, no one wants to try this just to see what happens.

As a first step to a rigorous answer, it would be nice if a mathematically-minded person (hey, don't look at me) worked out equations to "model" these types of event. The equations would not be short. To be useful, they'd have to account for such factors as the lift curve of the H-stab, its immersion or not, its lever arm, the mass moment of inertia of the airframe (besides its plain old mass), aircraft airspeed, the thrust and slipstream speed of the prop in flight at the given airspeed, the lift curve of the rotor and the rotor's rate of compliance with cyclic inputs. In the downdraft scenario, the speed and direction (maybe even the velocity gradient) of the downdraft would also be relevant.

Obtaining the raw data to feed into such a model would be a project in itself. Rotor makers, quick now, what's your rotor's compliance rate? [sound of crickets]. Airframe makers, what's the thrust that your powerplant applies to your airframe at airspeed X at WOT (you know of course that it it can be either higher or lower than static thrust)? ...Didn't think so.

My point? Without data and analysis, we don't know what we don't know. We don't know how close to the edge Aircraft X is. Given this level of knowledge (or rather un-knowledge), keeping the thrustline near, at or slightly below the CoM represents a commonsense, abundance-of-caution approach.
 
A few months back, someone suggested flying some gyroplanes using remote control.
That would allow the finding of 'the edge' w/o undue risk.
Accuracy would seem to be high as it was all empirical data, not 'calculated'.
But...…. you'd have to crash at least one of each type of aircraft unless you were confident in applying the results to others.
Great discussion.
Brian
 
A few months back, someone suggested flying some gyroplanes using remote control.
That would allow the finding of 'the edge' w/o undue risk.
Accuracy would seem to be high as it was all empirical data, not 'calculated'.
But...…. you'd have to crash at least one of each type of aircraft unless you were confident in applying the results to others.
Great discussion.
Brian
I was remembering the exact same thing... the RC tests. I was also wondering if this could somehow be a cooperative effort with the University Student projects the PRA has organized. I wonder if GyroPedia / Phil Harwood would be interested in being involved in such a study.
 
Instrumentation and recording would be key. Otherwise, you'd wreck a lot of very expensive hardware just to obtain some sensational videos.

I'd suggest, as a first step, testing rotors on a ground-vehicle rig. Still not that cheap, but more so than remotely crashing $100K gyros. And, with luck, you won't destroy your test equipment.

Interesting parameters would include disk lift curve, RPM decay rate at low and zero disk AOA, behavior at negative disk AOA and cyclic-pitch compliance rate. A few rotors would be destroyed in the process, so safety from flying debris and thrashing, curled-up blades would be an issue.

Jim McCutchen did some of this type of testing when he was developing Skywheels; obviously a long time ago. The electronics are better, smaller, and cheaper now.
 
someone who takes off on a steep ascent and suffer an engine failure and make the error to push the stick too early to regain airspeed as the ground is not far below, will not aim at getting in the danger zone , destiny will have put him in this situation

someone who suddenly panic during ascent and tries to secure his seat belt will unwillingly be in a zero G situation

someone seeing at the last moment a power line and who will pull the stick hard to pass above will unwillingly in a zero G situation

in many small airfield I had to accelerate a lot and then pull hard the stick at the last moment to pass above a row off trees , of curse I was trained to zero G situations and I did reduce engine thrust and carefully pushed the stick ahead, but with no doubt my ass was not pressing the seat anymore

in those situations we are in danger, ok training must focus on taking off with reasonable ascent rates, avoiding flying low so that there is no reason to jump over any obstable and on avoiding taking off from inadequate airfields but sheet happens and we have to be trained to pull back the throttle first and then push the stick gently even if the ground is not far below

this was the heart of my training coz in France in the 90's when gyros were not what they are now we suffered a lot of casualties , and it is not because not htl have now huge HS ( and certain like yours small high thrust offsets) that this hazard must not be adressed

This is interesting. So if one goes up on a steep ascent (say 30 to 40 degree deck angle) and the ground is close, I sure hope he builds speed before going up or he can't go to those deck angles with slow speed and he doesn't know about HV curve. So if he has speed why does he need to shove the stick forward so abruptly? And secondly he has had an engine out right so where is the power in the PPO. Your reasoning seems lost to me. Without power at least in AR-1, you can shove it forward quite a lot. Its stupid to do it like that but it does not get into danger. I suspect its the same for other models with effective HS

Sudden panic with seat belt loose in steep ascent ... why is that. Just sit tight till you level out and trimmed and then tighten it and take some ground school and lessons on checklists

Yeah I would say this pilot needs more training and attitude adjustment because these are hazardous actions.
 
Based on my own observation, or on detailed reports from experienced pilots whose word I trust, it is possible to throw the stick forward fairly aggressively in either a Dominator or an M-16 without causing a PPO. I did the same (not on purpose!) in my Gyrobee with downloaded, immersed stab at full throttle at 70 mph. I floated up against my seatbelt but nothing else scary happened.

So we have some data points indicating (at the very least) more PPO resistance in these models than in the Bensen in the old Japanese video. That pilot did the same thing and died. But...

Do we know where the edge is? My throttle was WOT on the 'Bee; how about those other two? Would a parabolic flight path unload the rotor longer and precipitate a PPO? Or a loss of RRPM sufficient to cause retreating-blade stall (=catastrophic flapping)? As JM says, no one wants to try this just to see what happens.

As a first step to a rigorous answer, it would be nice if a mathematically-minded person (hey, don't look at me) worked out equations to "model" these types of event. The equations would not be short. To be useful, they'd have to account for such factors as the lift curve of the H-stab, its immersion or not, its lever arm, the mass moment of inertia of the airframe (besides its plain old mass), aircraft airspeed, the thrust and slipstream speed of the prop in flight at the given airspeed, the lift curve of the rotor and the rotor's rate of compliance with cyclic inputs. In the downdraft scenario, the speed and direction (maybe even the velocity gradient) of the downdraft would also be relevant.

Obtaining the raw data to feed into such a model would be a project in itself. Rotor makers, quick now, what's your rotor's compliance rate? [sound of crickets]. Airframe makers, what's the thrust that your powerplant applies to your airframe at airspeed X at WOT (you know of course that it it can be either higher or lower than static thrust)? ...Didn't think so.

My point? Without data and analysis, we don't know what we don't know. We don't know how close to the edge Aircraft X is. Given this level of knowledge (or rather un-knowledge), keeping the thrustline near, at or slightly below the CoM represents a commonsense, abundance-of-caution approach.

It can be modeled and nothing will say any different on any configuration that we don't already know. You fly parabolas and you are at high risk. Can you get away with flying them. Yes to a point but as pilots we need to not get into where is the edge. They are a known maneuver that creates low G situation. Do not go there. None of the teetering gyroplanes or helicopters are equipped to handle low or zero G. End of story. I don't care if its cruciform tail close up or triple tail farther back. Tools and designs are created to give pilot control and some time to not get to these places but if the pilot wants to go there, the same control will allow him to and nothing is going to save him/her from themselves
 
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my reasoning seems lost to you ? Fara don't take me for more stupid then I am, when I spoke about engine failure during take off I did not tell you that the risk was a Power Push Over risk... I am not stupid enough to forget that when the engine stops there is no more engine thrust to push you over

you automatically reply because you always feel attacked every time we speak of stability ...

if you think that it is useless to train pilots to manage this situation you can discuss it with pascal that you know and who has trained and certified more then 400 pilots and instructors, who won the French gyro Championship the first and only time he participated, who took a large part in the DTA gyro development and design and who makes hundreds or rotors every years as you know.

I saw him many times briefing pilots before this particular part of the training and he has always insisted loudly saying that at all cost the pilot must never push the stick violently and wait that the gyro is on a flat attitude to push the stick frankly .. explain him that there is no danger ...

as for the seat belt not secured , it happened to one of our hangar mate, and pascal was the first at the foot the wreck and found our friend with the head cut in two parts .. the bea find out that he had not secured his belt because even if he had been ejected from the gyro at the moment of the impact the seat belt was intact..

believe me this man had been properly trained, in montelimar we learn to make the check list including the seat like then anywhere else in the world , this day he was nervous, he was late and wanted to fly for the first time alone with the doors of the gyro, and as he knew that it was more touchy (smaller yaw stability), unless he was told to delay this flight he did it and died.

What I meant is that Sheet happens Fara and that caution and training people to ascend reasonably and avoid getting in bad situations was important

I did not say that in those situation the AR-1 would be lethal

I did not say that pilots should take off from small landfield with raws of trees at the end of the runway, I did not say that pilots could fly low having to jumps obstacles ... I meant that in life doing wrong is happens, even the best pilots are sometimes stupid or imperfect ...

In my opinion, but it is interesting to show pilots what happens at the top of a steep ascent ... maybe not to make them hold the controls at this time but showing people that precisely if you pull pack the throttle and be gentle on the stick there is no reason the think that it is the end entering in panic, it is just like leaving your scuba tank at 30 m and going back to surface in apnea

but anyway I think that I am speaking for nothing you will never even agree to disagree ... anyway

JM

What will happen at the top of a steep climb if you have an engine out in a gyroplane with an HS of proper volume. This will happen:
1) If you do not let the speed bleed off to almost zero and push over smoothly but firmly and then level, you will simply recover back
2) If you are so far behind and so untrained that you let it get to zero airspeed or close then you will take longer to recover and you may hit the ground before you recover fully. For how long look at your gyroplane's HV curve. That's the whole point of those.

Its very simple
 
JM

What will happen at the top of a steep climb if you have an engine out in a gyroplane with an HS of proper volume. This will happen:
1) If you do not let the speed bleed off to almost zero and push over smoothly but firmly and then level, you will simply recover back
2) If you are so far behind and so untrained that you let it get to zero airspeed or close then you will take longer to recover and you may hit the ground before you recover fully. For how long look at your gyroplane's HV curve. That's the whole point of those.

Its very simple

In my opinion it is not simple for someone with limited aviation experience.

I teach engine out on takeoff and despite the briefing and anticipation there is always a moment of inaction when the noise stops.

A Cavalon will nose up and yaw right when power is removed.

The student has had it drilled into him to not push the cyclic forward so he feels overloaded.

There is no trim in so there is little resistance to moving the cyclic forward and this further disorients the student.

The ground is starting to rush up and if the student believes in his heart that the cyclic is the up lever (most students harbor this fantasy well into their training) moving the cyclic forward feels even more unnatural.

This is what training is for and after an unknown number of simulated engine out on takeoffs the process of recovery becomes natural.

In a gyroplane closer to centerline thrust there is not a noticeable nose up tendency and recovery seems more natural to me.

In a low thrust line gyroplane the nose lowers when power is removed and it is less counterintuitive.
 

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The day you come in Montelimar ( which I hope ) we will discuss it with Pascal

I can discuss it with Pascal tomorrow via the net but what should I discuss?
What I described is what happens testing over and over again dozens of times.
 
the fact that engine failures on ascents are not a problem and hence that it is useless to train people to handle this .

That's the message you got from my discussion? Ok. Sorry I guess I will need to learn French to discuss this with you
 
the fact that engine failures on ascents are not a problem and hence that it is useless to train people to handle this .

In my opinion engine failure on takeoff and climb out may be a problem and that is why I teach them even though they are not a part of the FAA practical test standards.
 
here is what you said : "Without power at least in AR-1, you can shove it forward quite a lot. Its stupid to do it like that but it does not get into danger. I suspect its the same for other models with effective HS"

so you mean there is no danger ... and I Am simply telling you that my instructor exactly thinks the contrary is true and that trainees must be trained on this because it is a dangerous situation .

As for my English I am sorry not to master this Language, an other evidence of my stupidity, in our Globalized World many non English speaking people dare to try to speak English and many things are getting lost in comprehension and translation ...

You know what, When an English Man tries to speak to me in French.. Even if he goes to a tough time finding his words or understanding what I say I would never ever tell him that it would be better to Switch to English, but this only the way I Am ...

it reminds me a sketch of a French humorist (Coluche) who was saying : " the problem with Foreign people is both they don't speak French, and that they don't all speak the same Foreign language ..."

I wish I spoke German, Spanish etc .. I Am just able to try to communicate in English, badly as you know ... but anyway I will go on trying

There is danger because as I said if you let it slow down and are not in the right range of HV curve side you will not recover. And of course this is an engine out on takeoff. It’s an emergency procedure. These are required training in US Practical Test Stabdards (Though I read that Vance does not believe it’s in there I do and is part of the broad engine out training item) and probably in most other standards around the world. You cannot sit there and hesitate in making your decision. That’s mainly what the training is for. Generally the problem with steep deck angle climbs is the same angle you go up at is generally the same angle you’ll come down at with an engine out. Better be ready mentally to do that.
The context of what does that have to do with CG and thrust line or having a HS that is part of a cruciform tail close to the prop or back farther That is what the subject here is. Obviously in this particular situation the tail further back and not the cruciform tail close to prop will be better by a bit. That part is simple. Once you have reached above HV curve there and your engine quits on takeoff there is no danger in pushing the stick forward to gain proper attitude and keeping the speed. Hesitating to do that in fact can put you in a dangerous condition and that is why training for this is advisable.

and please your English is a lot better than my French but it seems something was lost due to the medium and language here. I meant no harm. I apologize.
 
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