Calling Nick Lappos - Blade Stall
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Finally a breakthrough AnFI.
I used a concept from lecture 2 rotorcraft.
Then again you quoted an equation from lecture 1 aerodynamics, so it seemed appropriate.
But we make progress because you now acknowledge that BET is a fundamental concept in rotor blade design. BET gives an equation that has both RRPM squared and RRPM terms. So when you say "how wrong are you?" the answer is "completely." When you chose to "cancel rotor speed squared" you appear to have left a variable based on rotor speed. So your theory is not "independent of rotor speed" as you so clearly stated.
When it is that simple why go further? We could of course introduce forward flight and resolve the different demands on advancing and retreating side. We could introduce tip effects, perhaps play with some vortex wake models. I could task some BEM work ... but then why bother? Something academically accepted as fundamental, admitted by yourself, contradicts your assertion.
Remember that you brought in your ability to extract the Apache's speed from the video in sufficient accuracy to support a calculation of g to one decimal place in order to support your theory.
Your explanation as to how you can use the background as a reference when it is moving at an unknown speed through the frame and is at an unknown distance will not pass the red face with anyone who has tried to optically track targets.
I used a concept from lecture 2 rotorcraft.
Then again you quoted an equation from lecture 1 aerodynamics, so it seemed appropriate.
But we make progress because you now acknowledge that BET is a fundamental concept in rotor blade design. BET gives an equation that has both RRPM squared and RRPM terms. So when you say "how wrong are you?" the answer is "completely." When you chose to "cancel rotor speed squared" you appear to have left a variable based on rotor speed. So your theory is not "independent of rotor speed" as you so clearly stated.
When it is that simple why go further? We could of course introduce forward flight and resolve the different demands on advancing and retreating side. We could introduce tip effects, perhaps play with some vortex wake models. I could task some BEM work ... but then why bother? Something academically accepted as fundamental, admitted by yourself, contradicts your assertion.
Remember that you brought in your ability to extract the Apache's speed from the video in sufficient accuracy to support a calculation of g to one decimal place in order to support your theory.
Your explanation as to how you can use the background as a reference when it is moving at an unknown speed through the frame and is at an unknown distance will not pass the red face with anyone who has tried to optically track targets.
I was reading that all AH-64D/E's have a Maintenance Data Recorder, so, assuming someone was smart enough to take advantage of that, plus the fact that the machine has digital data for those parameters typically needed for recreating a flight profile, the hard data that answers the conjecture in this thread are probably well known by the investigators.
So AnFi - you are 3 nil down now - ball vs accelerometer - failed, speed calculation not including parallax error - failed, maths in rotor calculations - failed.
Anything else to add? Bearing in mind you have said your 'final' piece several times now.........
Oh, I forgot - the ball and parallax were just diverting sidelines that you were forced to argue - except that you introduced them to try and show how clever you were.......
Anything else to add? Bearing in mind you have said your 'final' piece several times now.........
Oh, I forgot - the ball and parallax were just diverting sidelines that you were forced to argue - except that you introduced them to try and show how clever you were.......
As for MDR - that might not include cockpit information, it depends on whether it is part of CVFDR set up or a stand alone maintenance data recorder.
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This whole thread is starting to resemble something from a Monty Python sketch
Monty Python: The Argument Sketch
I'm astounded that AnFI hasn't used the 'S' word yet
Still, his red-faced and screaming Herr Hilter impression
is jolly amusing to a mere know-nothing Ukrainian tractor driver - but at least I can spell - even if I don't understand all this advanced mathematics about conning angles 
Monty Python: The Argument Sketch
I'm astounded that AnFI hasn't used the 'S' word yet
Still, his red-faced and screaming Herr Hilter impression
is jolly amusing to a mere know-nothing Ukrainian tractor driver - but at least I can spell - even if I don't understand all this advanced mathematics about conning angles
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Crab "So AnFi - you are 3 nil down now - ball vs accelerometer - failed, speed calculation not including parallax error - failed, maths in rotor calculations - failed."
NO !
ball vs accelerometer ... all i said was that the ball is a crude accelerometer in as far as it shows the direction component of the the g experienced in that plane - TRUE
Speed calculation parallax NO the paralax error is negligable being 50% ish of the length of the arm if at full extension through an assumed 30deg ie about 1ft in 250ft NOT RELEVANT (even if taken to the extreme)
I have allways been saying that there is indeeed a very small (baby out with the bathwater) difference , I have repeatedly asked dc/da to quantify that term which HE HAS REFUSED TO DO. Most experts agree with me that the Nr^2 model is universally accepted to a reasonable degree of accuracy.
How WRONG IS IT ? Answer NOT SIGNIFICANTLY. it is further LESS significant if dealt with at greater speeds and induced flow representing a pullout scenario....
although it is true that that does bring in the additional considerations (that I have already alluded to) of different speeds across the cycle.... and I have suggested that that is well mapped by the Ct/Sigma curve introduced by NL
SO NO !!! it's nil 3 crab
Fohn spelling not my strong point ask Crab (even though I also ironically had to teach him some basic grammer wrt An FI, he was TOTALLY WRONG about that too)
the 'S' word !!! ??? I HAVE used it repeatedly SSSSSSSquared !!!!
HOW WRONG IS IT ? Not significantly! if you want to refute that then QUANTIFY IT !!!!! you have not, probably cannot. You are throwing the baby out with the bathwater and you know it, or PROVE OTHERWISE (you can't) what is the coefficient of the Nr^-1 term normalised to TRT = 1 ?????
You can't or won't because it shows that your clever little nit picking point is essentially irrelevant, and you know it.
NL and most texts in a crude model accept that Nr^2 is valid, it is only in as far as those assumptions are used that I claim that my statement is valid too.nyou can't dispute that and if you do you have no honour
this is not a place where you can have a serious debate with sincere people attempting to explore the validity of a hypothesis, NL has not uderstood the point and has checked out i think I should follow his lead
NO !
ball vs accelerometer ... all i said was that the ball is a crude accelerometer in as far as it shows the direction component of the the g experienced in that plane - TRUE
Speed calculation parallax NO the paralax error is negligable being 50% ish of the length of the arm if at full extension through an assumed 30deg ie about 1ft in 250ft NOT RELEVANT (even if taken to the extreme)
I have allways been saying that there is indeeed a very small (baby out with the bathwater) difference , I have repeatedly asked dc/da to quantify that term which HE HAS REFUSED TO DO. Most experts agree with me that the Nr^2 model is universally accepted to a reasonable degree of accuracy.
How WRONG IS IT ? Answer NOT SIGNIFICANTLY. it is further LESS significant if dealt with at greater speeds and induced flow representing a pullout scenario....
although it is true that that does bring in the additional considerations (that I have already alluded to) of different speeds across the cycle.... and I have suggested that that is well mapped by the Ct/Sigma curve introduced by NL
SO NO !!! it's nil 3 crab
Fohn spelling not my strong point ask Crab (even though I also ironically had to teach him some basic grammer wrt An FI, he was TOTALLY WRONG about that too)
the 'S' word !!! ??? I HAVE used it repeatedly SSSSSSSquared !!!!
HOW WRONG IS IT ? Not significantly! if you want to refute that then QUANTIFY IT !!!!! you have not, probably cannot. You are throwing the baby out with the bathwater and you know it, or PROVE OTHERWISE (you can't) what is the coefficient of the Nr^-1 term normalised to TRT = 1 ?????
You can't or won't because it shows that your clever little nit picking point is essentially irrelevant, and you know it.
NL and most texts in a crude model accept that Nr^2 is valid, it is only in as far as those assumptions are used that I claim that my statement is valid too.nyou can't dispute that and if you do you have no honour
this is not a place where you can have a serious debate with sincere people attempting to explore the validity of a hypothesis, NL has not uderstood the point and has checked out i think I should follow his lead
...and the judge's decision is......reserved.
It is just pure coincidence that the coning angle goes up as the rotor RPM go down. There is no relationship, nothing to see here...everybody please move on and take your angry little arguments with you.
Thank you.
It is just pure coincidence that the coning angle goes up as the rotor RPM go down. There is no relationship, nothing to see here...everybody please move on and take your angry little arguments with you.
Thank you.
You can't or won't because it shows that your clever little nit picking point is essentially irrelevant, and you know it.
The complete irrelevance is this ultimate coning angle - do the blades cone up as Nr decreases? Yes we all know that.
Is there an ultimate angle beyond which they won't go because of some special mathematical relationship that only you understand? I don't think so.
You are forgetting the practical when dealing with the theoretical - different rotor designs will have different physical limits to their coning - the blades themselves in a teetering head, the physical limits of the hinges in an articulated head, and the limits of deformation in the elastomeric hinges in a semi-rigid head (titanium star bending on a Lynx).
So why postulate that there is an ultimate coning angle? Do designers use it? No. Could or would pilots use it? No. Do engineers consider it? No.
So therefore, on the subject of irrelevance - where does your rather muddled argument and proposed theory stand????
And, just as a reminder - these were the statements from the beginning of the thread
Accurate?????Relevant????
Interesting youtube is littered with these 'high speed stall' accidents
The point about coning angle is really interesting. There is effectively a conning angle at which a disk is in effect stalled, regardless of RRPM.
RRPM 'cancels out of the maths' when you look for stall.
and
Quote:
cone is proportional to the ratio of Lift (L) to Centripetal Force (Cf)
both L and Cf are proportional to RRPM^2
take a helicopter in the hover at low load and low RRPM (such that it is very close to stall AoA)
measure the cone
if load is increased the RRPM has to be increased to increase Lift
the AoA remains just short of stall and the coning angle is unchanged.
that coning angle is the coning angle just short of stall
The point about coning angle is really interesting. There is effectively a conning angle at which a disk is in effect stalled, regardless of RRPM.
RRPM 'cancels out of the maths' when you look for stall.
and
Quote:
cone is proportional to the ratio of Lift (L) to Centripetal Force (Cf)
both L and Cf are proportional to RRPM^2
take a helicopter in the hover at low load and low RRPM (such that it is very close to stall AoA)
measure the cone
if load is increased the RRPM has to be increased to increase Lift
the AoA remains just short of stall and the coning angle is unchanged.
that coning angle is the coning angle just short of stall
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AnFI - I don't need to "measure how much". I've posted something that readers of this thread can go check for themselves, think about and come to their own conclusions if they want to.
Ascend Charlie - I agree it is evident to anyone with experience. However to the casual observer, or someone who is ab initio, the simplicity of AnFI's original assertion, accompanied by shiny maths and glittery technical words, may seem quite compelling. This is my concern.
The concept is, from my interpretation of the original posts, as follows
Lift is proportional to rho and v squared
Inertial forcings is proprtional to mass, radius and v squared
given a constant density, mass and radius, and substituting in rotor speed for v then through the mathematics of the equation for coning angle, it is possible to "approximately" cancel out rotor speed leaving a constant relationship between lift and coning angle.
The concept is explored within the context of limiting thrust from the disc, i.e. As rotor speed slows, it is necessary to apply more pitch to the blade to derive the same lift, so you hit CLmax "earlier", beyond that the blade stalls and can no longer sustain the lift required, but the inertial forces are lower due to the reduction in rotor speed. Both the aerodynamic and the inertial forces are proportional to rotor speed squared, and so, according to AnFI's proposition there is approximately an "ultimate coning angle" fixed irrespective of rotor speed.
This concept is used in the original original post to try and explain why by looking at the coning angle it can be determined when a pilot ran out of lift capability during a manouevre and it isn't necessary to concern yourself with rotor speed. But if we turn it on its head things are more worrying
If the CLmax is reached approximately at an "ultimate coning angle" irrespective of rotor speed then the disc is essentially self-limiting. The inertia will balance out the aerodynamics, any attempt to put more pitch on when at that "ultimate coning angle" will result in loss of lift as CLmax is exceeded. What is true for the disc must be true also for the blade, therefore an "ultimate coning angle" must also represent an ultimate self-limiting flap angle ... all independent of rotor speed.
The proposition ultimately leads to a concept that any rotor is self-limiting in flap allowing any amount of blade pitch to be applied at whatever Nr% and the physics just takes care of it as CLmax is always reached at approximately the same angle, close enough that it doesn't matter.
I'm not going to recommend any pilots give it a go on rotor run down that's for sure.
Ascend Charlie - I agree it is evident to anyone with experience. However to the casual observer, or someone who is ab initio, the simplicity of AnFI's original assertion, accompanied by shiny maths and glittery technical words, may seem quite compelling. This is my concern.
The concept is, from my interpretation of the original posts, as follows
Lift is proportional to rho and v squared
Inertial forcings is proprtional to mass, radius and v squared
given a constant density, mass and radius, and substituting in rotor speed for v then through the mathematics of the equation for coning angle, it is possible to "approximately" cancel out rotor speed leaving a constant relationship between lift and coning angle.
The concept is explored within the context of limiting thrust from the disc, i.e. As rotor speed slows, it is necessary to apply more pitch to the blade to derive the same lift, so you hit CLmax "earlier", beyond that the blade stalls and can no longer sustain the lift required, but the inertial forces are lower due to the reduction in rotor speed. Both the aerodynamic and the inertial forces are proportional to rotor speed squared, and so, according to AnFI's proposition there is approximately an "ultimate coning angle" fixed irrespective of rotor speed.
This concept is used in the original original post to try and explain why by looking at the coning angle it can be determined when a pilot ran out of lift capability during a manouevre and it isn't necessary to concern yourself with rotor speed. But if we turn it on its head things are more worrying
If the CLmax is reached approximately at an "ultimate coning angle" irrespective of rotor speed then the disc is essentially self-limiting. The inertia will balance out the aerodynamics, any attempt to put more pitch on when at that "ultimate coning angle" will result in loss of lift as CLmax is exceeded. What is true for the disc must be true also for the blade, therefore an "ultimate coning angle" must also represent an ultimate self-limiting flap angle ... all independent of rotor speed.
The proposition ultimately leads to a concept that any rotor is self-limiting in flap allowing any amount of blade pitch to be applied at whatever Nr% and the physics just takes care of it as CLmax is always reached at approximately the same angle, close enough that it doesn't matter.
I'm not going to recommend any pilots give it a go on rotor run down that's for sure.
However - the pig is getting tired
but you don't know any of the distances involved - the helicopter is at least many hundreds of feet from the camera and your super accurate reference points (somewhere in the woods) are thousands of feet away.
Given how 'exact' you claimed your speed measurements were and the fact that you ignored (because you hadn't even realised it existed) the parallax - how on earth is anyone expected to trust any of your other 'approximate' assertions and convenient assumptions.
Speed calculation parallax NO the paralax error is negligable being 50% ish of the length of the arm if at full extension through an assumed 30deg ie about 1ft in 250ft NOT RELEVANT (even if taken to the extreme)
Given how 'exact' you claimed your speed measurements were and the fact that you ignored (because you hadn't even realised it existed) the parallax - how on earth is anyone expected to trust any of your other 'approximate' assertions and convenient assumptions.
I admire the many reasonable attempts to arrive at a sensible conclusion through logic, science and debate. However if logic and common sense always prevailed we wouldn't need nearly as many warning labels as seem to exist, one of which springs to mind - don't feed the animals..
Here is a link to the MDR. Answers some posted questions:
http://ktferrera.com/images/STSI/FTP/MDR.pdf
Looks like it should have survived the crash.
http://ktferrera.com/images/STSI/FTP/MDR.pdf
Looks like it should have survived the crash.
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Yes dc/da !!!
that is very close to exactly what I am saying, the points of difference are not worth getting into at this stage, you are the first person (other than perhaps AC) who seems to be getting it. If we can keep this constructive then I think we could make a difference.
I still think to have the difference would be interesting
If you have a think about it it would be a curve (i suspect fairly subtle, practically irrelevant) of how UCA changes with Nr, to go with the function that is dUCA/rho (straight line?)
I think it would be fair for YOU to elucidate the difference to UCA that the departure from Nr^2 would give. can you quantify it ?
After all I accepted your challenge to derive some maths and did so within the assumptions that I made, (including addressing points you LATER made wrt twist etc) Anyway don't bother if you don't feel like it, I might do it if I get the chance.
[Crab ONLY - do we really have to waste our time arguing about an irrelevant point that you are disingeuously abusing to try and demean me?
Especially when you are not even right. [i]I was assuming that the camera was stationary as far as is relevant whilst panning. If we allow for your (ridiculous) supposition that it moves laterally as it pans, and we take the MOST EXTREME example of moving the camera whilst panning, we say the holder of the camera has 3 ft arms, we assume the ratio of distance to the helicopter to distance from helicopter to background is about 1:25 seems reasonable we find that it makes no difference within the tolerance of the measurments 1 part per 250 is not relevant {{{EDIT INSERT, that is 1 in 250 of the measured path length, NOT the distance of the helicopter or background which is completely unimportant}}} and I most definately don't claim such an irrelevant degree of accuracy.
and in any case the measurments I never claimed were particularly accurate. The only accurancy I was going for at that stage were to see if the EXPERT OPINION was anywhere near correct , which it WAS NOT (20-30kts, ridiculous !!! ). please don't come back to me on this parallex w.o.t. please try and understand what dc/da has said, he's really close, and I think you would enjoy the point if you 'got it'. try it you'll like it ]
that is very close to exactly what I am saying, the points of difference are not worth getting into at this stage, you are the first person (other than perhaps AC) who seems to be getting it. If we can keep this constructive then I think we could make a difference.
I still think to have the difference would be interesting
If you have a think about it it would be a curve (i suspect fairly subtle, practically irrelevant) of how UCA changes with Nr, to go with the function that is dUCA/rho (straight line?)
I think it would be fair for YOU to elucidate the difference to UCA that the departure from Nr^2 would give. can you quantify it ?
After all I accepted your challenge to derive some maths and did so within the assumptions that I made, (including addressing points you LATER made wrt twist etc) Anyway don't bother if you don't feel like it, I might do it if I get the chance.
[Crab ONLY - do we really have to waste our time arguing about an irrelevant point that you are disingeuously abusing to try and demean me?
Especially when you are not even right. [i]I was assuming that the camera was stationary as far as is relevant whilst panning. If we allow for your (ridiculous) supposition that it moves laterally as it pans, and we take the MOST EXTREME example of moving the camera whilst panning, we say the holder of the camera has 3 ft arms, we assume the ratio of distance to the helicopter to distance from helicopter to background is about 1:25 seems reasonable we find that it makes no difference within the tolerance of the measurments 1 part per 250 is not relevant {{{EDIT INSERT, that is 1 in 250 of the measured path length, NOT the distance of the helicopter or background which is completely unimportant}}} and I most definately don't claim such an irrelevant degree of accuracy.
and in any case the measurments I never claimed were particularly accurate. The only accurancy I was going for at that stage were to see if the EXPERT OPINION was anywhere near correct , which it WAS NOT (20-30kts, ridiculous !!! ). please don't come back to me on this parallex w.o.t. please try and understand what dc/da has said, he's really close, and I think you would enjoy the point if you 'got it'. try it you'll like it ]
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Crab "So why postulate that there is an ultimate coning angle? Do designers use it? No. Could or would pilots use it? No. Do engineers consider it? No."
If they don't they should, and i think most do, if there are any that don't don't even go there of course there aren't ANY designers that don't get that idea and its importance
the danger is that helicopters will be designed according to criteria that regulators understand/mandate and they definately don't understand THAT.
Nick can you speak with SKSY designers, what Coning angle to they aim to accommodate?
If they don't they should, and i think most do, if there are any that don't don't even go there of course there aren't ANY designers that don't get that idea and its importance
the danger is that helicopters will be designed according to criteria that regulators understand/mandate and they definately don't understand THAT.
Nick can you speak with SKSY designers, what Coning angle to they aim to accommodate?
AnFi - even I, who greatly enjoys pricking your pomposity whenever it rears its ugly head, have tired of your pointless, circular arguments.
You are not a test pilot, nor an aerodynamicist, nor an aircraft designer nor a recognised academic in aviation-related fields yet you seek to lecture, browbeat and harangue on what is a professional pilot's forum.
I do not understand why, nor do I really care, what motivates you to believe you have such an intellectual grasp of factors that even those who design, make, test and produce the things we professional pilots fly do not (according to you) but perhaps you would be better off writing your scientific treatises to Airbus, Boeing, Sikorsky et al and see how far you get.
Perhaps you should look at the impeccable conduct of someone who clearly is a professional in his field, dCL, and compare the quality and humility of his posts to your insulting and fractious ones.
If you want to be taken seriously - and it would appear your ego demands it - then try logical, concise, scientific and relevant arguments. You never know, someone might actually think you have a point.
You are not a test pilot, nor an aerodynamicist, nor an aircraft designer nor a recognised academic in aviation-related fields yet you seek to lecture, browbeat and harangue on what is a professional pilot's forum.
I do not understand why, nor do I really care, what motivates you to believe you have such an intellectual grasp of factors that even those who design, make, test and produce the things we professional pilots fly do not (according to you) but perhaps you would be better off writing your scientific treatises to Airbus, Boeing, Sikorsky et al and see how far you get.
Perhaps you should look at the impeccable conduct of someone who clearly is a professional in his field, dCL, and compare the quality and humility of his posts to your insulting and fractious ones.
If you want to be taken seriously - and it would appear your ego demands it - then try logical, concise, scientific and relevant arguments. You never know, someone might actually think you have a point.
Lonewolf, the document for the MDR says that it meets ED 55 and ED 56A. Those are the specs governing airline FDR/CVR equipment crash conditions, so the answer looks like yes,indeed.