Thrust line vs center of mass

jm-urbani

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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 good opportunity to test a chute too
 

Doug Riley

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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.
 

fara

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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.
 

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fara

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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.
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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jm-urbani

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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.
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) he was really nervous, 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 happens, even the best pilots are sometimes stupid or imperfect ...

In my opinion, 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
 
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fara

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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
 

Vance

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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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jm-urbani

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

fara

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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.
 

jm-urbani

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Vance,
what is sure is that muscle memory is really important, and that without training it is not easy get the right reflex
this happened to me and I did not panic even if it was scaring
I bless pascal to have trained me , and you are right to train people

 

jm-urbani

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I can discuss it with Pascal tomorrow via the net but what should I discuss?
the fact that engine failures on ascents are not a problem and hence that it is useless to train people to handle this .
 

fara

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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
 

Vance

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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.
 

jm-urbani

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That's the message you got from my discussion? Ok. Sorry I guess I will need to learn French to discuss this with you
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
 
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jm-urbani

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Instrumentation and recording would be key. Otherwise, you'd wreck a lot of very expensive hardware just to obtain some sensational videos.
Hi Doug

have a look there :



a part of the site is in English when it comes to speak about rotor dynamics and all the stuff

look at this soft http://volucres.fr/Autogire/page2/index.html

Jean is a super busy engineer but finishing his last gyro he is developing a flight instrument dedicated at recording all the data in order to go on studying rotors ...

it is super exciting ...

I wish I was an intelligent man able to understand all of this ... maybe in an other life
 
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fara

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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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jm-urbani

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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
I was perfectly explained by JC and Rob that the best way to finish in the trees was to do this.... so don't do it
 
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