0 G flight condition

fara

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All good points and perhaps one of the pieces missing is not necessarily at the instructor level knowledge wise it is sometimes having the chance to pass on that information. Your recent accident gets emotive at some point because being blunt about potential issues in the circumstances causes obvious offence but it doesn't make it less valid. We waited some months and made a similar conclusion about the Lord Cavalon crash. The route to a safer future in the US is to have some regulatory protection/authority to stop a wilful owner/pilot from piloting a new machine too soon [and / or with little knowledge or experience] just because they can and with no real authority for those who might know better to stop them. Nice to debate with everyone over the years, take care and for those running the forum thank you for the efforts making something for others to engage with.

Hi Phil:
Well take a look at Sport Pilot Gyroplane (PTS - Practical Test Standards) from FAA.
Link: https://www.faa.gov/training_testing/testing/test_standards/media/faa-s-8081-29.pdf

There is exactly one mention of testing the knowledge portion of PIO or unloading the rotors and pushover.
H. Performance and Limitations:
...
2. Understands the cause, effect, and avoidance procedure of “power pushover” and “pilot induced oscillation.”

This references FAA 8083-21

Which starts to talk about gyroplanes starting in Chapter 15.
In Chapter 21, it covers PIO and Power Pushover. There is no talk about torque effect or even why a roll input won't work if rotor is unloaded.
The sum total of explanation on how one can unload the rotor is as follows:
"Removing the rotor force is often referred to as unloading the rotor, and can occur if pilot-induced oscillations become excessive, if extremely turbulent conditions are encountered, or the nose of the gyroplane is pushed forward rapidly after a steep climb."

That's it. Its not wrong. Its correct but that is all there is about unloading the rotor in FAA gyroplane manual that instructors are supposed to use with their students. The treatment of this subject is so minor and in passing that it just does not garner the attention and time that it deserves between a student and an instructor. It needs a bit more emphasis and more time and discussion between student and CFI in ground briefings and ground school. The recommendation on how to load rotors back is also unclear and points to manufacturers manuals. This is because at the time of writing there were pissing matches going on in the gyroplane community about center line thrust and horizontal stabilizers and their effects. Those did not serve anyone but that's hindsight.

This is a definite area of improvement that FAA needs to undertake in their new Gyroplane manual when they write it. Also, special emphasis areas in testing knowledge needs to focus on this subject as well in testing the knowledge of the student in a check-ride.

As best as I know in the UK for a make/model, CAA requires 2 hours of flight with an instructor for transition. Depending on type of change that's hardly enough but could be. I would think going from tandem to side by side or vice-versa would require and warrant more hours. So regulation cannot adequately solve the issue. In the end its really up to us to use our best judgment. Each make/model has a slight different feel and it would behoove us as pilots to make sure we get competent in something before acting as PIC, whatever it takes.

Chris Lord's accident was unfortunate. For many of us in the industry in Florida, we already kind of knew what the issue was in control circuit assembly from the start in that machine even though it took many months for FAA/NTSB to release their final report. Chris or even AutoGyro USA did not have the information about assembly and subsequent initial testing of the aircraft and the grounding of the aircraft by the first test pilot. No one checked the control circuit assembly adequately after the grounding. Not even Chris. Of course this all came to light to me after the accident. If I knew this before the accident, I would have called Chris and told him about where to focus his effort or not to fly it.
I certainly knew about it a couple of months after the accident but out of respect I would not publicly say that till after the report was released. In terms of Chris flying it faster than published Vne, I do not know if that had any direct relationship specifically to this exact accident. At face value it does not seem that way. I think that is the point Vance is making though it seems like you two guys have gotten on the wrong side of each other. His point in this regard does seem somewhat valid to me and some of your points are valid as well. For sure transition to another make and model should be done, whether it is mandated by law/regulation or just best judgment. In the US FAA does not usually mandate transition from one make/model to another in any category. Only requirements are things like high performance/complex endorsement from a CFI in airplanes etc. These are not make/model based however but complexity and performance (HP) based. FAA expects us to act as adults and be responsible.
 
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Philbennett

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Does anyone beside Phil Bennett think that transition training would have helped Chris Lord deal with the control failure?

In my opinion there is nothing scientific about repeating gossip and building a hypothesis based on the gossip.

Phil Bennett appears to be using Occam's razor to distract from his reliance on gossip to form his theory about what happened in Utah.

He appears unconcerned that some of the gossip has been refuted on the Rotary Wing Forum or that Occam's Razor is about scientific investigation rather than unfounded speculation.

Definition of Occam's Razor by Merriam-Webster:
A scientific and philosophical rule that entities should not be multiplied unnecessarily which is interpreted as requiring that the simplest of competing theories be preferred to the more complex or that explanations of unknown phenomena be sough first in terms of known quantities.

Hang on for once answer the questions posed to you.

Do you or do you not cover the check A and limitations in your transition training?

Do you prefer to ignore the obvious and simple FACT that this was first solo OR prefer to construct a complex scenario of failure? [and square that with your view of the Chris Lord accident!]

What is gossip? Be explicit.

Thank you for the definition of the term I gave to you.... you might think I understand what it is!!! hahaha unbelievable.

Fara exactly and now wait for paragraph after paragraph as to why Vance believes nothing should change.

In the UK the 2 hours is minimum BUT the hours are not the real point what it does is ensure the new owner MUST seek out an FI and MUST do some work. If the FI thinks the candidate is hopeless then he can simply prevent the wilful from going flying in their new aircraft and report the issue to the CAA.

No one checked the control circuit assembly adequately after the grounding.

Yet having aired concerns about the vibrations, the question over the fly off of hours you might think someone in the chain might have paused for thought?
At face value it does not seem that way. I think that is the point Vance is making though it seems like you two guys have gotten on the wrong side of each other.

No doubt and actually do I think transition training is the cause of course it isn't the whole story but it is part of it and then look at the gaul of AutoGyro USA Bob Snyder to say to the NTSB that the aircraft is controllable with the controls disconnected by referring to the POH.... yeah OK bob do a circuit that way and see how it works out.

Maybe Lord is a weaker example but low time / new pilots with no transition training if you were going to make an impact in a short time frame it might be a good starting point.

Can I ask while we are on - what bit about Utah do you consider "gossip".
 

Vance

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Hang on for once answer the questions posed to you.

Do you or do you not cover the check A and limitations in your transition training?

Do you prefer to ignore the obvious and simple FACT that this was first solo OR prefer to construct a complex scenario of failure? [and square that with your view of the Chris Lord accident!]

What is gossip? Be explicit.

Thank you for the definition of the term I gave to you.... you might think I understand what it is!!! hahaha unbelievable.

Fara exactly and now wait for paragraph after paragraph as to why Vance believes nothing should change.

In the UK the 2 hours is minimum BUT the hours are not the real point what it does is ensure the new owner MUST seek out an FI and MUST do some work. If the FI thinks the candidate is hopeless then he can simply prevent the wilful from going flying in their new aircraft and report the issue to the CAA.



Yet having aired concerns about the vibrations, the question over the fly off of hours you might think someone in the chain might have paused for thought?


No doubt and actually do I think transition training is the cause of course it isn't the whole story but it is part of it and then look at the gaul of AutoGyro USA Bob Snyder to say to the NTSB that the aircraft is controllable with the controls disconnected by referring to the POH.... yeah OK bob do a circuit that way and see how it works out.

Maybe Lord is a weaker example but low time / new pilots with no transition training if you were going to make an impact in a short time frame it might be a good starting point.

Can I ask while we are on - what bit about Utah do you consider "gossip".
I am unfamiliar with the term “check A”. I go over the POH and limitations at great length in transition training.

I don’t share your affection for arguing Phil Bennett so I am sharing what I see and what has been written.

Gossip: Spread rumors or tell people the personal details of others’ lives, especially maliciously.

I have seen the video where Phil pretends to know what happened to Chris Lord based on gossip about Chris Lord, the builder, the pilot who refused to fly the aircraft, the aircraft, the customer who didn’t want the aircraft and what Phil imagined everyone believed. Phil wasn’t there and it is just gossip.

About the Utah accident; Phil wrote that the representative who provided the transition training did not approve solo flight when Richard’s mother told Richard that he did. Someone is wrong and that is a good example of the hazard of basing conclusions on gossip. Not everyone hears and interprets the gossip the same way.

Just like with Chris Lord’s accident; in time more will be revealed in the Utah accident. Until then I will not pretend to know what happened.

In the interest of the Rotary Wing Forum I am making an effort to not feed a troll. Hopefully Phil Bennett will see there is nothing here to argue about and nothing can come out of his reply that will benefit anyone.
 
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Mike G

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I see that there have been no comments to Jean Claude’s post about low g levels and bunting I presume this means that either everybody understood and agreed with it, that nobody understood it or that everybody was distracted by the thread drift due to our resident CFI gladiators fighting to be the one to the write last post

I suspect few of you realised what JC was actually telling you. That’s not really surprising because his post was, as usual, fairly succinct and put a lot of information into a very small post.

He actually explains 3 theoretical results that, if demonstrated to be correct, could be very important.

He calculates that:

  • 1) If in a zoom climb you push to between 1.0 & 0.7 g then at the top of the climb (apex of the curve) the Rrpm will reduce but not have reduced enough to be potentially unrecoverable. This is based on the assumption that the power/thrust and the g remain constant throughout the climb part of the bunt.
    If at the top of the climb you just level out the airspeed and Rrpm will increase to the S&L values applicable to the power setting (& mass and DA) you have.
    If, after the apex, you continue to push at the same g level the airspeed and Rrpm will increase and you will find yourself in a powered dive.
    Conclusion: a push from S&L to 0.7g should not create a potential bunting accident, neither will a zoom climb followed by a push to 0.7g provided power and g remain constant.
  • 2) For g values less than 0.7, the Rrpm will decrease but should not descend to the critical non-recoverable Rrpm before you reach the apex and if the push is stopped at the apex the gyro continues to fly S&L as the airspeed and Rrpm increase.
    Conclusion: any zoom climb followed by a low g (down to 0 g) push should be recoverable from the apex of the flight curve. This is shown in the curves presented by JC earlier.
  • 1612806569504.png
  • You can see that at 0.4 g (right hand curve) the gyro arrives at the apex (“Level”) earlier (@ 2.6 secs) than at 0.6 g (@ 3.7 secs) and that the Rrpm is higher (about 320 rpm) at that moment than for 0.6 g (about 310 rpm) and therefore there is a bigger safety margin for recovery. You can also see that if the push is stopped at the apex the gyro continues to fly S&L as the airspeed and Rrpm increase.
  • 3) This part is counter intuitive and will, I hope, stimulate a more interesting technical debate than the current personal dispute that has dominated this thread of late.
    For g values below 0.7 g the loss of Rrpm is higher at the higher g levels (or lower at lower g levels). This means that a 0.6 g bunt will cause the Rrpm at the apex to be nearer to the non-recoverable 300 Rrpm than the same bunt at lower g levels. You can see in the following curves
  • 1612807141305.png
  • that show that the Rrpm at the apex of the 0.4 g bunt is higher (about 320 rpm) than that of the 0.6 g bunt (about 310 rpm). It also shows that if you continue to push after the apex the Rrpm continues to fall until it arrives at the non-recoverable Rrpm of 300.
I stress that these are theoretical results for debate so we don’t want anybody going out to test the validity of these calculations.

Mike G & thanks to Jean Claude for some clarifications
 

Vance

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I don’t know enough about rotor aerodynamics to debate Jean Claude.

I approached practicing for an air show slowly and methodically and without preconceptions at considerable altitude before flying the same routine at a lower altitude. I do not recommend flying a gyroplane like this. I am sharing this experience because there seems to be some confusion about how it works and what to expect.

Based on advice from Sport Copter who makes my blades I don’t let the rotor rpm on The Predator (30 foot eight and a half inch chord Sport Rotors) get below 275 rotor rpm.

A steep climb at full power in The Predator will reduce rotor rpm before I enter the curve with my G meter still reading 1.

As I entered the curve my G meter moves toward .6Gs and my rotor further slows.

I terminate the climb and the curve when I see the rotor rpm approach 275, typically near the apex of the curve.

The Predator has a slightly low thrust line in relation to the center of gravity.

I practiced the same routine in a Cavalon with a high thrust line in relation to the center of gravity and discovered as I approached the apex of my climb that without any cyclic input she would start to nose over unless I reduced power.

I felt that if I began a descent at the top of the climb my rotor rpm would continue to decay. I did not have a minimum safe (recoverable) rotor rpm in the Cavalon. I never saw below .6Gs.

On the Gmeter the red and green marks are the telltale.
 

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fara

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I see that there have been no comments to Jean Claude’s post about low g levels and bunting I presume this means that either everybody understood and agreed with it, that nobody understood it or that everybody was distracted by the thread drift due to our resident CFI gladiators fighting to be the one to the write last post

I suspect few of you realised what JC was actually telling you. That’s not really surprising because his post was, as usual, fairly succinct and put a lot of information into a very small post.

He actually explains 3 theoretical results that, if demonstrated to be correct, could be very important.

He calculates that:

  • 1) If in a zoom climb you push to between 1.0 & 0.7 g then at the top of the climb (apex of the curve) the Rrpm will reduce but not have reduced enough to be potentially unrecoverable. This is based on the assumption that the power/thrust and the g remain constant throughout the climb part of the bunt.
    If at the top of the climb you just level out the airspeed and Rrpm will increase to the S&L values applicable to the power setting (& mass and DA) you have.
    If, after the apex, you continue to push at the same g level the airspeed and Rrpm will increase and you will find yourself in a powered dive.
    Conclusion: a push from S&L to 0.7g should not create a potential bunting accident, neither will a zoom climb followed by a push to 0.7g provided power and g remain constant.
  • 2) For g values less than 0.7, the Rrpm will decrease but should not descend to the critical non-recoverable Rrpm before you reach the apex and if the push is stopped at the apex the gyro continues to fly S&L as the airspeed and Rrpm increase.
    Conclusion: any zoom climb followed by a low g (down to 0 g) push should be recoverable from the apex of the flight curve. This is shown in the curves presented by JC earlier.
  • View attachment 1151559
  • You can see that at 0.4 g (right hand curve) the gyro arrives at the apex (“Level”) earlier (@ 2.6 secs) than at 0.6 g (@ 3.7 secs) and that the Rrpm is higher (about 320 rpm) at that moment than for 0.6 g (about 310 rpm) and therefore there is a bigger safety margin for recovery. You can also see that if the push is stopped at the apex the gyro continues to fly S&L as the airspeed and Rrpm increase.
  • 3) This part is counter intuitive and will, I hope, stimulate a more interesting technical debate than the current personal dispute that has dominated this thread of late.
    For g values below 0.7 g the loss of Rrpm is higher at the higher g levels (or lower at lower g levels). This means that a 0.6 g bunt will cause the Rrpm at the apex to be nearer to the non-recoverable 300 Rrpm than the same bunt at lower g levels. You can see in the following curves
  • View attachment 1151560
  • that show that the Rrpm at the apex of the 0.4 g bunt is higher (about 320 rpm) than that of the 0.6 g bunt (about 310 rpm). It also shows that if you continue to push after the apex the Rrpm continues to fall until it arrives at the non-recoverable Rrpm of 300.
I stress that these are theoretical results for debate so we don’t want anybody going out to test the validity of these calculations.

Mike G & thanks to Jean Claude for some clarifications

I completely missed JCs post where he put the surprising result that rotor RPM will decrease less with lower G than with higher. I just read your and his post. I have to do some more thinking.
 

HeliSwede

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I know an instructor who did not solo his client till they had over 100 hours of dual instruction.
I soloed one client at 90 hours of dual instruction.
I soloed at 54 hours of dual instruction.
I had a client Wednesday with 21 hours of dual and I was not able to solo them because they did not meet the standards despite that being our primary goal.
We had a non-pilot come to us who purchased a new $500,000 R44 and then... wanted to get his heli license. Our most seasoned CFI 11,000hrs gave this guy 100hrs of dual and ended up have to tell him to sell his new helicopter and never fly. The student would get very close to getting a solo sign off, but then a day or two later, he flew like it was his first time at the controls. Obviously a very sad experience, but the CFI did the right thing for sure. So, you are so right, it takes as long as it takes, even if it it takes 2x or 3x more hours than required, or never! I'm so encouraged when I hear stories of CFI's turning a student away when it become obvious that they can not safely operate an aircraft or possibly even a car! Many times this means the company is also turning away an aircraft sale (and profits), but again the right thing to do!
 

fara

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I see that there have been no comments to Jean Claude’s post about low g levels and bunting I presume this means that either everybody understood and agreed with it, that nobody understood it or that everybody was distracted by the thread drift due to our resident CFI gladiators fighting to be the one to the write last post

I suspect few of you realised what JC was actually telling you. That’s not really surprising because his post was, as usual, fairly succinct and put a lot of information into a very small post.

He actually explains 3 theoretical results that, if demonstrated to be correct, could be very important.

He calculates that:

  • 1) If in a zoom climb you push to between 1.0 & 0.7 g then at the top of the climb (apex of the curve) the Rrpm will reduce but not have reduced enough to be potentially unrecoverable. This is based on the assumption that the power/thrust and the g remain constant throughout the climb part of the bunt.
    If at the top of the climb you just level out the airspeed and Rrpm will increase to the S&L values applicable to the power setting (& mass and DA) you have.
    If, after the apex, you continue to push at the same g level the airspeed and Rrpm will increase and you will find yourself in a powered dive.
    Conclusion: a push from S&L to 0.7g should not create a potential bunting accident, neither will a zoom climb followed by a push to 0.7g provided power and g remain constant.
  • 2) For g values less than 0.7, the Rrpm will decrease but should not descend to the critical non-recoverable Rrpm before you reach the apex and if the push is stopped at the apex the gyro continues to fly S&L as the airspeed and Rrpm increase.
    Conclusion: any zoom climb followed by a low g (down to 0 g) push should be recoverable from the apex of the flight curve. This is shown in the curves presented by JC earlier.
  • View attachment 1151559
  • You can see that at 0.4 g (right hand curve) the gyro arrives at the apex (“Level”) earlier (@ 2.6 secs) than at 0.6 g (@ 3.7 secs) and that the Rrpm is higher (about 320 rpm) at that moment than for 0.6 g (about 310 rpm) and therefore there is a bigger safety margin for recovery. You can also see that if the push is stopped at the apex the gyro continues to fly S&L as the airspeed and Rrpm increase.
  • 3) This part is counter intuitive and will, I hope, stimulate a more interesting technical debate than the current personal dispute that has dominated this thread of late.
    For g values below 0.7 g the loss of Rrpm is higher at the higher g levels (or lower at lower g levels). This means that a 0.6 g bunt will cause the Rrpm at the apex to be nearer to the non-recoverable 300 Rrpm than the same bunt at lower g levels. You can see in the following curves
  • View attachment 1151560
  • that show that the Rrpm at the apex of the 0.4 g bunt is higher (about 320 rpm) than that of the 0.6 g bunt (about 310 rpm). It also shows that if you continue to push after the apex the Rrpm continues to fall until it arrives at the non-recoverable Rrpm of 300.
I stress that these are theoretical results for debate so we don’t want anybody going out to test the validity of these calculations.

Mike G & thanks to Jean Claude for some clarifications

Ok so this is pretty messed up at face value and yes I did miss JC's post earlier completely, meaning I never even saw it for reasons you listed.

Talking out loud. This is scenario concerning below 0.7 G flight condition. So the Rotor RPM decrease is proportional to the time spend in less than 0.7 G condition not just dependent of value of G force. So as we go below 0.7 G the behavior is predicted to be related to time spent in that condition and exact value of G force, with larger effect seemingly coming from the sustained time in the lower G condition not from lower exact value of low G force.
In fact lower G force value suggests that the time spent to get to the apex is also "lower or less" and hence the apex will be reached sooner and rotor RPM have not gone so low that they cannot be recovered with proper recovery technique/actions.
There is however, the caveat that lower G force value case, if gyro is continued to be pushed over the apex (top) will get the rotor RPM lower in short order to the point of no recovery which is assumed (?) to be 300 RRPM.


Mike I took the rotors down to 310 rotor RPM last week and just today I took the rotors down to 320 RRPM. I can increase it again by doing a coordinated bank turn. Is 300 RRPM unrecoverable? How is that value selected and under what criteria and assumptions?

I know JC uses a lot of discrete math constructs to do his modeling of behavior. I am not sure yet that this is completely what happens and would have to ask some questions. I will send you some comments separately first.
 

Brent Drake

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And this is where you are confused on the issues, overlook the obvious and refuse to acknowledge what is happening on a year to year basis.

I don't know if that is just stubbornness because you don't like the messenger, are just oblivious to what should be obvious or some other reason.

No doubt your attitude to training is as diligent as you say and good for you. Yet if you have a pilot who already holds a gyroplane pilot licence then he doesn't need to listen to you. He can tell you to poke your opinion and there is nothing you can do to put a halt to any madness that you as an FI might have a better idea of than the pilot shortly to have an accident.

Chris Lord killed himself and pax in a Cavalon with less than half a dozen hours on make/model. Fara had his customer crash on his first solo and not only did the that individual not want to do a fuller transitional phase to the model he didn't even elect to do what he did with a current FI. Aside from the conflict of commercial work it seems a lot of responsibility to shoulder with literally zero control.
For reference, Chis Lord was a mechanical failure. A bolt came out of the control tube.
 

Philbennett

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I am unfamiliar with the term “check A”. I go over the POH and limitations at great length in transition training.

I don’t share your affection for arguing Phil Bennett so I am sharing what I see and what has been written.

Gossip: Spread rumors or tell people the personal details of others’ lives, especially maliciously.

I have seen the video where Phil pretends to know what happened to Chris Lord based on gossip about Chris Lord, the builder, the pilot who refused to fly the aircraft, the aircraft, the customer who didn’t want the aircraft and what Phil imagined everyone believed. Phil wasn’t there and it is just gossip.

About the Utah accident; Phil wrote that the representative who provided the transition training did not approve solo flight when Richard’s mother told Richard that he did. Someone is wrong and that is a good example of the hazard of basing conclusions on gossip. Not everyone hears and interprets the gossip the same way.

Just like with Chris Lord’s accident; in time more will be revealed in the Utah accident. Until then I will not pretend to know what happened.

In the interest of the Rotary Wing Forum I am making an effort to not feed a troll. Hopefully Phil Bennett will see there is nothing here to argue about and nothing can come out of his reply that will benefit anyone.

No Vance sorry this is important not to troll - but for general flight safety and communication to others. I'm not spreading malicious "gossip" as you call it. In the case of Chris Lord I'm just reading the actual comments and actual events of people interviewed by the NTSB and the facts of the matter as presented by the NTSB. Are you now now suggesting that the builder, the pilot who refused to fly the aircraft, the text messages to AutoGyro USA about a variety of doubts are untrue or if opinion based on these factors is now malicious?

Utah - the representative of Silverlight had no authority to send the accident pilot solo because permission wasn't required. That was the point I made [long ago lost] about regulation. As I've said before the source of the comment you suggest is gossip posts here and was part of the chain of events, his conversation was with the pilot who was conducting this transitional training, is that gossip or could it be reasonably expected to be true? Whilst Richard's mother may have heard what she heard it was unlikely to be anything else because no doubt at the point the accident pilot went solo the "safety pilot" had some level of confidence in the flights success - although given the limited time in the same aircraft it is also not such a leap of imagination to think that someone getting things right 2 out 3 times means there is still a +30% chance of failure.

Those comments and the facts of the matter [i.e. the pilot was in Utah with a "safety pilot" not in Florida engaging in a wider course of training with an FI], the video itself and that it was literally 30 seconds into the first solo that lead me to the comments I made and my use of the term Occams razor.

There is a world of difference in pretending to know what happened and simply commenting upon what one can plainly see on a piece of film and reflecting upon that in conjunction with comments made by people who actually were there and part of the chain of events.
 

Mike G

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Vance wrote “I don’t know enough about rotor aerodynamics to debate Jean Claude.”

Neither do I and in my opinion I could count on one hand the number of people who could seriously debate autogyro “rotor aerodynamics” with Jean Claude, and I’d still have some fingers left over.

Vance and Fara

I should perhaps give a little background.

These calculations/curves came about as Jean Claude was analyzing some bunting data recorded during my testing of the Gyro Warning System (GWS) and to help me he created some curves for my gyro like the ones posted earlier. He and I were (still are) trying to find if there was/is a better set of parameters to predict a bunting scenario than the one I'm currently using in my GWS. He then used them as a basis to illustrate his ideas here in Fara’s thread.

I have been sharing my recorded data with Jean Claude for a long time now and he often compares it with his calculations and we try to understand what causes any differences. Usually it’s simply instrumentation or my flying that isn’t precise enough and occasionally Jean Claude realizes that he can tweak or improve his performance calculation based on real data.

So the minimum safe Rrpm of 300 rpm I talked about earlier is based on my gyro with its 8.2 m rotor. This is not a fixed number for all gyros. This number is calculated for a given combination of gyro model and rotor diameter, chord and pitch.

Vance if your predator in display trim has a cruise Rrpm of less than 320 rpm then, according to JC’s calculations 275 is about right for you.

Fara

So the Rotor RPM decrease is proportional to the time spend in less than 0.7 G condition not just dependent of value of G force. “

I think the “time spent” is due primarily to the value of the G. At lower G values you arrive at the apex earlier simply because you’ve pushed the stick harder. Added to which is the fact that at lower G values the rotor is doing less work (carrying less weight) and hence induced drag is lower.

So as we go below 0.7 G the behavior is predicted to be related to time spent in that condition and exact value of G force, with larger effect seemingly coming from the sustained time in the lower G condition not from lower exact value of low G force.”

I think we’re saying the same thing, if so then yes.


In fact lower G force value suggests that the time spent to get to the apex is also "lower or less" and hence the apex will be reached sooner and rotor RPM have not gone so low that they cannot be recovered with proper recovery technique/actions.”

My understanding is that even if you go to 0 G if you recover at the apex your Rrpm should not have fallen below the minimum safe Rrpm for your particular gyro rotor combination. What JC is saying is that you will be nearer to the minimum safe Rrpm at 0.65 G than at lower G values.

However Vance raises a very valid point in that these calculations assume a centre line thrust. As you approach 0 G in a typical Euro design gyro with a debatable high thrust line and that relies on an offset rotor lift vector to counter engine torque you then run into the probability of a power push over/torque roll combination.

This suggests to me that while the basic initiator of most bunt type accidents is low G, it is the consequential PPO/torque roll that actually does the damage at the apex rather than the rotor simply slowing down.

If this theory is correct it would further emphasize Chuck Beaty’s and Doug Riley’s call for manufacturers to work at eliminating this coffin corner. My GWS will warn the pilot he’s getting close to the edge and needs to make the appropriate corrective action, Chuck and Doug’s solution would give him a much better chance of survival if he didn’t have or ignored the warning.

Mike G and thanks to JC for clarifications
 

fara

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Vance wrote “I don’t know enough about rotor aerodynamics to debate Jean Claude.”

Neither do I and in my opinion I could count on one hand the number of people who could seriously debate autogyro “rotor aerodynamics” with Jean Claude, and I’d still have some fingers left over.

Vance and Fara

I should perhaps give a little background.

These calculations/curves came about as Jean Claude was analyzing some bunting data recorded during my testing of the Gyro Warning System (GWS) and to help me he created some curves for my gyro like the ones posted earlier. He and I were (still are) trying to find if there was/is a better set of parameters to predict a bunting scenario than the one I'm currently using in my GWS. He then used them as a basis to illustrate his ideas here in Fara’s thread.

I have been sharing my recorded data with Jean Claude for a long time now and he often compares it with his calculations and we try to understand what causes any differences. Usually it’s simply instrumentation or my flying that isn’t precise enough and occasionally Jean Claude realizes that he can tweak or improve his performance calculation based on real data.

So the minimum safe Rrpm of 300 rpm I talked about earlier is based on my gyro with its 8.2 m rotor. This is not a fixed number for all gyros. This number is calculated for a given combination of gyro model and rotor diameter, chord and pitch.

Vance if your predator in display trim has a cruise Rrpm of less than 320 rpm then, according to JC’s calculations 275 is about right for you.

Fara

So the Rotor RPM decrease is proportional to the time spend in less than 0.7 G condition not just dependent of value of G force. “

I think the “time spent” is due primarily to the value of the G. At lower G values you arrive at the apex earlier simply because you’ve pushed the stick harder. Added to which is the fact that at lower G values the rotor is doing less work (carrying less weight) and hence induced drag is lower.

So as we go below 0.7 G the behavior is predicted to be related to time spent in that condition and exact value of G force, with larger effect seemingly coming from the sustained time in the lower G condition not from lower exact value of low G force.”

I think we’re saying the same thing, if so then yes.


In fact lower G force value suggests that the time spent to get to the apex is also "lower or less" and hence the apex will be reached sooner and rotor RPM have not gone so low that they cannot be recovered with proper recovery technique/actions.”

My understanding is that even if you go to 0 G if you recover at the apex your Rrpm should not have fallen below the minimum safe Rrpm for your particular gyro rotor combination. What JC is saying is that you will be nearer to the minimum safe Rrpm at 0.65 G than at lower G values.

However Vance raises a very valid point in that these calculations assume a centre line thrust. As you approach 0 G in a typical Euro design gyro with a debatable high thrust line and that relies on an offset rotor lift vector to counter engine torque you then run into the probability of a power push over/torque roll combination.

This suggests to me that while the basic initiator of most bunt type accidents is low G, it is the consequential PPO/torque roll that actually does the damage at the apex rather than the rotor simply slowing down.

If this theory is correct it would further emphasize Chuck Beaty’s and Doug Riley’s call for manufacturers to work at eliminating this coffin corner. My GWS will warn the pilot he’s getting close to the edge and needs to make the appropriate corrective action, Chuck and Doug’s solution would give him a much better chance of survival if he didn’t have or ignored the warning.

Mike G and thanks to JC for clarifications

Hi Mike and JC
Thanks for the reply. Yes we are saying the same thing and at least it shows that I understood your communication correctly. So it seems to me that in an AR-1 with 8.6 m with 8.5" chord rotors where the general cruise is at 350 RRPM, an unrecoverable RRPM would be considered to be approximately around 295 RRPM. A 45 degree pitch up already gets us to 0.7 G

In an AR-1 although it’s high thrust line, per a double hang test and some SW calcs it’s high thrust line by 4.75 inches and it’s engine is angle 1 degree to make the thrust line pass through closer to the CG. The result is that when power is applied in an AR-1 it actually pitches up slightly and slows down about 5 knots and stabilizes there in trim and when power is removed it pitches down and speeds up about 5 knots and stabilizes there in trim. That’s completely opposite of say ELA G7 or Magni M16 from my personal flying. However the torque roll is another issue. Simple application of Gurney flaps on either side of the stab to create differential lift may be warranted but on a lower location of stab the effect when power is not there like on an idle glide at fast speed the control issues that may create need to be looked at and balanced in the this idea as well.

Of course a properly trained pilot can cut the power in half a second upon first signs of trouble and that eliminates all these power induced issues completely. And that is the proper trained reaction that instructors need to drill in. The only place where cutting power is not the first step in an attitude related emergency in a gyroplane that I can think of is getting caught flying behind the power curve close to the ground. Everything else, pretty much cut the power and ...

What I would like to know is when rotor RPM gets lower close to but not at an unrecoverable number and since this modeling by JC assumes a constant speed which usually is unlikely in such an incident which are generally following a PIO and related speed as well as RRPM changes, are we likely to see flap starting to set in because if so you are still toast.
 
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Jean Claude

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What I would like to know is when rotor RPM gets lower close to but not at an unrecoverable number and since this modeling by JC assumes a constant speed which usually is unlikely in such an incident which are generally following a PIO and related speed as well as RRPM changes, are we likely to see flap starting to set in because if so you are still toast.
I agree the "non-recoverable" Rrpm depends on the forward speed. But it depends little enough to allow me to simplify my explanatory drawing with a "minimum recoverable Rrpm" line.
 

Acamacho

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Hace mucho tiempo que se habla de los peligros del casi 0 G, pero no he encontrado por ningún lado las diferentes formas de remediar este evento, si las hay, una vez iniciado, he leído que haciendo un giro (180º) coordinado, Podría detener algunos, pero no he escuchado, para qué eventos serían válidos.
Saludos
 

fara

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Hace mucho tiempo que se habla de los peligros del casi 0 G, pero no he encontrado por ningún lado las diferentes formas de remediar este evento, si las hay, una vez iniciado, he leído que haciendo un giro (180º) coordinado, Podría detener algunos, pero no he escuchado, para qué eventos serían válidos.
Saludos

Acamacho:
Google translation of your post is

"The dangers of almost 0 G have been talked about for a long time, but I have not found anywhere the different ways to remedy this event, if there are any, once started, I have read that by making a coordinated turn (180º), I could stop some, but I have not heard, for what events they would be valid.
regards"

Well that is exactly what we are talking about. Is there anyway after to get to very low G that you can recover? What JC is saying is that first its not very low G that gets our rotor RPM too low to recover. Its actually slightly higher than very low G because the time sustained in that to get there is longer. As we understand that and verify it, we have to think what else is needed to give pilot a chance to get out from this terrible mistake as things are happening very fast. To allow the best possible chance for the pilot to recover, a warning of getting close to the edge like Mike G. GWS along with training to cut power immediately and loading the rotor by smoothly pulling slightly behind the neutral stick or (center line thrust + a mechanism to counter torque roll in machine design) is needed to elongate the time for pilot to react and get out. This will still take trained muscle memory response. you cannot remain in the situation you are in and guess what to do. Pilot action cannot be completely removed from the equation. At best we can give him/her a shot. May be an extra second or two to correct and react. But a warning system setup correctly like the GWS is prevention and that is always better than a cure.

Usually a pilot who has gotten to this point is so far off the boat, I don't think he is ready to react the way needed in time to be bluntly honest but the only other option is Ballistic Parachute. In the trike world in trainers we use BRS quite commonly because the same problem in trikes with low G control loss

Your idea to do a coordinated turn would work if you still have some control and rotor force in hand. That would definitely increase g force. You may read Mike G's message above with the graphs that even stopping the parabolic pushover, may be reducing a little power and flying out at a tangent at top of parabolic path may be adequate per JC's modeling before you get to rotor RPM that is completely at a point of no return.
 
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Acamacho

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Thanks, I don't know what happened with the translator who didn't do his job and put it in Spanish, this is the reason for not writing more in the Forum, although some colleagues have offered to translate it, I think it's a nuisance, I hope they have a little consideration with me.
 

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Anyway, I would like, if possible, by whoever has that experience, to know, if they exist, because until the device comes out, we will have no other way, how to avoid that problem if we realize that it can happen and react in time to avoid it if possible.
Thank you
 

Vance

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Anyway, I would like, if possible, by whoever has that experience, to know, if they exist, because until the device comes out, we will have no other way, how to avoid that problem if we realize that it can happen and react in time to avoid it if possible.
Thank you
In my opinion with a high thrust line gyroplane the best thing to do in a low G situation is to reduce power.
 

fara

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Anyway, I would like, if possible, by whoever has that experience, to know, if they exist, because until the device comes out, we will have no other way, how to avoid that problem if we realize that it can happen and react in time to avoid it if possible.
Thank you

Well it doesn't just happen. It happens for reasons whether they be control circuit failure, PIO and pilot action related or severe weather flights. You can tell in your seat that things are not at 1 G. You should see if any of your airplane flying friends have done weightless maneuver and if someone has done it safely, perhaps you can go with them to experience it. It requires certain actions to make you go light in the seat or even come off for a mere second. It good to experience what that feels like. Its important to really fly the aircraft. All the rest is second to that primary target. Sometimes I run into a few airplane pilots here and there who have kind of lost their primary stick and rudder feel and are too much into only numbers and avionics and so on.I-don't-always-fly-but.jpg
 
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Guys, Too many CFI's and students have died demonstrating low G recognition in Robinson Helicopters before Robinson came out with a safety notice prohibiting such maneuvers. If you want to see what negative Gs feels like do it in a car over a hill or in a fixed wing (within safe legal limits of course). In addition, flying into a dust devil or even flying to close to (but not in) a severe storm will take a two bladed rotorcraft apart very quickly with or without the very best avionics installed in the aircraft. One should be well trained and then fly as safely as humanly possible, but even so, there will always be some risks associated with flight that will never be 100% eliminated. So let's do our best and not increase your flight risk by by exploring the flight envelope. Leave that to the professional test pilots, who even though are well trained and equipped, also suffer losses on occasion. Be careful and fly safe!
 
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