Calling Nick Lappos - Blade Stall
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dCl
I'm sorry, it must seem to you that this thread got hijacked, and in a sense it was because I thought the best way to bring it to a satisfactory conclusion was to restate the debate from the original thread.
You did a fine job of pointing out the missing bits in the original analysis, and AnFI has actually credited you with that, although you need a beady little eye to spot that in his posts. He now talks about a band of UCAs rather than a single UCA, so I think the original argument is dying if not dead.
Therefore, the absolutely fair criticism of AnFI is that his concept of UCA independent of Rrpm was absolutely technically flawed, maybe significantly (see challenge below). But a far more serious criticism is that it was actually completely irrelevant in a situation where Rrpm is largely constant. This is a frequent observation with AnFI posts as Crab points out, the pursuit of some hobbyhorse (eg. UCA, twin reliability) outside any useful context, even though there may be a nugget of truth riding on the hobbyhorse.
Challenge: If AnFi wants to go into battle about UCAs again, then there are two possibilities:
1. either his technical skills are sufficient to model the additional inflow term and throw up some numbers for max coning angles at different Rrpms, or;
2. they are not, in which case he needs to be a bit more gracious to the experts on this forum who might have those skills and ask them a favour without effectively extracting an entire lecture course in aerodynamics for free.
PS to Jellycopter's point, I don't actually think AnFI should be criticised for hypothesising about an UCA and having the courage to present his ideas to this forum, but rather for his rather grudging (it's there, but you've missed out another Rrpm term which still cancels) and dismissive (it's there, but its effect on the UCA is negligible) acknowledgement of the inflow point. If I were an expert I would say stuff you, go stew in your own juice then if that's the reward I get for trying to help. AnFi I think reads that differently, as some kind of paranoid conspiracy of experts to trying to protect their ivory tower from a plucky amateur.
I'm sorry, it must seem to you that this thread got hijacked, and in a sense it was because I thought the best way to bring it to a satisfactory conclusion was to restate the debate from the original thread.
You did a fine job of pointing out the missing bits in the original analysis, and AnFI has actually credited you with that, although you need a beady little eye to spot that in his posts. He now talks about a band of UCAs rather than a single UCA, so I think the original argument is dying if not dead.
Therefore, the absolutely fair criticism of AnFI is that his concept of UCA independent of Rrpm was absolutely technically flawed, maybe significantly (see challenge below). But a far more serious criticism is that it was actually completely irrelevant in a situation where Rrpm is largely constant. This is a frequent observation with AnFI posts as Crab points out, the pursuit of some hobbyhorse (eg. UCA, twin reliability) outside any useful context, even though there may be a nugget of truth riding on the hobbyhorse.
Challenge: If AnFi wants to go into battle about UCAs again, then there are two possibilities:
1. either his technical skills are sufficient to model the additional inflow term and throw up some numbers for max coning angles at different Rrpms, or;
2. they are not, in which case he needs to be a bit more gracious to the experts on this forum who might have those skills and ask them a favour without effectively extracting an entire lecture course in aerodynamics for free.
PS to Jellycopter's point, I don't actually think AnFI should be criticised for hypothesising about an UCA and having the courage to present his ideas to this forum, but rather for his rather grudging (it's there, but you've missed out another Rrpm term which still cancels) and dismissive (it's there, but its effect on the UCA is negligible) acknowledgement of the inflow point. If I were an expert I would say stuff you, go stew in your own juice then if that's the reward I get for trying to help. AnFi I think reads that differently, as some kind of paranoid conspiracy of experts to trying to protect their ivory tower from a plucky amateur.
Last edited by puntosaurus; 27th Oct 2016 at 16:25.
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Sorry ShyTorque, no offence intended with abbreviation of your or anyone’s name.
True, I didn’t come back to you on the difference between Shear Forces (spelt correctly now) and Bending Moments, because one is a product of the other, they are closely related the bending moments create Shear Forces, and the Shear Forces break things. I just really don’t want to get into that, I’m sure you’ll understand.
Maybe a different thread? Or study the relationship yourself?
Lone
That’s a long post and it’s 98% correct, but somethings are a little nuanced in a way I’d like to come back on.
Para 1
Stall, I think we are talking about stall in the sense that for the whole disk the Coefficient of thrust has reach a maximum value, i.e. CtMax, I think most people are happy with that.
“we don’t know what the G load was” true, but my calculation puts it at 2.7g (21deg/s at 90kts is 2.7g), which is probably achieved at about CtMax, and if he had more capacity to pull g then he maybe would have used it. I accept that he (also) probably ran out of energy from the engine (engine power limit) and consumed some RRPM energy as well as Height Energy. According to NL’s excellent graph (from a different type) he had quite a lot of energy available, if (assuming) my speed calculation is close, accounting for the height he had, and the amount of time in which he spent it. 5sec of Max power is equivalent to at least 200ft (Energy), so he spent that height in 2 seconds equivalent to a lot of engine power (maybe 2.5 times), PLUS more than full engine power. One can infer that he was most probably at CtMax.
Para 2
Stall, call it what you like, but I mean running at CtMax. YES the CA is "an effect not a cause”, but it is related by relationship of TRT to Cf (is anyone disputing THAT?) CA=TRT/Cf. So far from being irrelevant, it tells us that for a given RRPM that the TRT is some multiple of Cf (which is a product of Nr^2). The key is even if the blades are going slowly the TRT that can be made is also less, as is the Cf (by the same proportion), so the CA is the same, drooped or not.*
Para 3
Yes also agree, but in this case the helicopter WAS doing about Vy (which as everybody here knows is the place where best use of energy is made to make TRT), so the amount of surplus Thrust that could be made was near it greatest.
Para 4
“AnFI's estimated are based on ground speed” good point, since it is airspeed that is important, and I did not assess the wind speed, so there is room for error there.
“If the Apache was below that airspeed as the final pitch and pull was attempted, it was already in energy debt.“ YES true “IF", but I say it was not below that airspeed (which could of course be wrong, but it is my working figure from my measurement, and if we work with THAT figure then it was not, according to you too). It doesn’t seem like the Airspeed reduced much, and was probably funded by height, but even if it was MY 90kts is an AVERAGE, so regardless of whether it burned KE or not there was quite a lot of energy around (AND he would have been pretty close to the flat bottomed curve of the "sweet spot”) (most surplus from the engine, and height (unmeasured) equivalent to substantial power over a 2 second period). I agree however that he was probably maxed on those too and did in fact also consume energy from the Nr as well (which you point out is not a low inertia rotor (so substantial energy derivable from Nr). He burned a lot of energy, and I think he was at CtMax, all (my) working numbers point at that (particularly 2.7g)
Para 5
Yes in gets hungrier for energy, (and if the Ct is already maxed, then the harder you pull the hungrier it gets, with no increase in TRT, so no additional G) ('Pull more get more party' is over) (at UCA)
Para 6
“Whatever angle the blades cone to is a reaction to that bundle of forces and effects on the disc/blades” Namely those detailed in Para 2 above, which make CA not irrelevant but a direct indicator of how much of the capacity of the Rotor is being used. Please don’t just glaze over at that relationship, it is fundamental. Ca=TRT/Cf
Para 7
Agree completely.
Punto
“AnFI has actually credited you [dc/da] with that, although you need a beady little eye to spot that in his posts. He now talks about a band of UCAs rather than a single UCA”
and challenge.
Yes I did, but I qualified it (as you rightly said) as being insignificant.
The reason I say it is insignificant is that it might be more significant in the illustrative thought experiment I presented of loading a hovering helicopter with progressively more weight as Nr is increased, such that CtMax is maintained, since indeed the IndFlow would change (and worsen the situation wrt CtMax), however this is much less relevant at speed where the increased Induced Flow with weight is much less significant. I said it was baby out with the bath water, not a First Order effect.
AND in any case and regardless, when CtMax is reached that also would be CAmax (UCA) (at a constant RRPM). Agree?
AND furthermore, I think the onus is on dc/da to quantify HIS point. I was asked to quantify mine and give assumptions, which I did, I am entitled to make my assumptions. I make the assumption that Increased Induced flow is not relevant, and under that assumption I presume dc/da agrees with me? QUESTION
The ‘family of UCAs' is in part developed through the discussion here, but also falls out of the maths too. e.g. it is dependant on density (linear), and it also is a function of the Ct fall off that NL gives with speed (in one of his excellent graphs).
“even though there may be a nugget of truth riding on the hobbyhorse.” quite a substantial nugget !
Ref ‘the Challenge’ from Punto I asked dc/da multiple times to quantify the term. It’s HIS objection, the onus was on HIM to substantiate it. It MIGHT be significant, quantify it, show us how significant it is. Is it the baby or the bathwater, is it a 'hair on the egg’? Or is it indeed a substantive point? PARTICULARLY at speed.
Does he agree that under the assumption of that effect not being significant the main point holds ‘true’?
The piece where he points to an Ω term on the bottom is (I say) wrong and highly distorts the significance of Ω.
I quote the piece here and explain why (I say) it is wrong below that.
dc/da
"Unlike a fixed wing, a rotary wing is rotary. Therefore the "v" that any aerofoil element experiences relies on rrpm and the element's distance from the hub let's say Ωr . However the downwash the element is seeing is independent let's call it u.
Therefore
α = arctan(u/ Ωr)
Assuming a small angle
α = (u/ Ωr)
And substitute
κ = ρ.A. (u/ Ωr).a /2m.
As you can now see, there is a term for rotor speed in your equation. Q.E.D. "
why that's wrong
Well the α term should say (P-u/ Ωr) where P is pitch
I don’t think you can leave out the Pitch of the blade.
So by substitution we have
κ = ρ.A. (P-u/ Ωr).a /2m
would expand out to
κ = (ρ.A. P.a /2m) - (ρ.A.(u/Ωr)/2m)
so the "κ = ρ.A. (u/ Ωr).a /2m" overstates the dependancy of κ on Ω, which is too naughty to say QED, and relegates it to an examination of the baby by looking at the bathwater.
AND in any case THAT also assumes that P is not varied, which is NOT a fair assumption.
AND furthermore where u is negligible as in the case of a helicopter pulling out of a dive at 90kts, then the term almost disappears.
AND furthermore in the ‘thought experiment’ of increasing the Nr and increasing the weight correspondingly the u value WOULD NOT be independent of Ω, but it would be dependant on it, thus reducing the assumed error further (to zero, by cancelling)
So while I do freely admit the proposed relationship MAY NOT be EXACT, I do say that any difference is just bathwater and not a substantive point. Quantifying the difference might be quite complex and subtle, but at least we can say it is comparatively small.
So I say that my point (whatever it was) still holds ‘in essence’.
AND the onus would be on dc/da to substantiate his objection otherwise.
So with respect to the Challenge Punto
1 I’d say that I have covered why that term is NOT substantial.
So the answer is that UCA it does not (substantively) vary with RRPM, which is the point
2 If someone contends that it does vary with RRPM THEY should qualify it, and we’ll see if it is substantive or irrelevant.
Sorry if I did not answer anyone’s important point. “the pig is getting tired"
True, I didn’t come back to you on the difference between Shear Forces (spelt correctly now) and Bending Moments, because one is a product of the other, they are closely related the bending moments create Shear Forces, and the Shear Forces break things. I just really don’t want to get into that, I’m sure you’ll understand.
Maybe a different thread? Or study the relationship yourself?
Lone
That’s a long post and it’s 98% correct, but somethings are a little nuanced in a way I’d like to come back on.
Para 1
Stall, I think we are talking about stall in the sense that for the whole disk the Coefficient of thrust has reach a maximum value, i.e. CtMax, I think most people are happy with that.
“we don’t know what the G load was” true, but my calculation puts it at 2.7g (21deg/s at 90kts is 2.7g), which is probably achieved at about CtMax, and if he had more capacity to pull g then he maybe would have used it. I accept that he (also) probably ran out of energy from the engine (engine power limit) and consumed some RRPM energy as well as Height Energy. According to NL’s excellent graph (from a different type) he had quite a lot of energy available, if (assuming) my speed calculation is close, accounting for the height he had, and the amount of time in which he spent it. 5sec of Max power is equivalent to at least 200ft (Energy), so he spent that height in 2 seconds equivalent to a lot of engine power (maybe 2.5 times), PLUS more than full engine power. One can infer that he was most probably at CtMax.
Para 2
Stall, call it what you like, but I mean running at CtMax. YES the CA is "an effect not a cause”, but it is related by relationship of TRT to Cf (is anyone disputing THAT?) CA=TRT/Cf. So far from being irrelevant, it tells us that for a given RRPM that the TRT is some multiple of Cf (which is a product of Nr^2). The key is even if the blades are going slowly the TRT that can be made is also less, as is the Cf (by the same proportion), so the CA is the same, drooped or not.*
Para 3
Yes also agree, but in this case the helicopter WAS doing about Vy (which as everybody here knows is the place where best use of energy is made to make TRT), so the amount of surplus Thrust that could be made was near it greatest.
Para 4
“AnFI's estimated are based on ground speed” good point, since it is airspeed that is important, and I did not assess the wind speed, so there is room for error there.
“If the Apache was below that airspeed as the final pitch and pull was attempted, it was already in energy debt.“ YES true “IF", but I say it was not below that airspeed (which could of course be wrong, but it is my working figure from my measurement, and if we work with THAT figure then it was not, according to you too). It doesn’t seem like the Airspeed reduced much, and was probably funded by height, but even if it was MY 90kts is an AVERAGE, so regardless of whether it burned KE or not there was quite a lot of energy around (AND he would have been pretty close to the flat bottomed curve of the "sweet spot”) (most surplus from the engine, and height (unmeasured) equivalent to substantial power over a 2 second period). I agree however that he was probably maxed on those too and did in fact also consume energy from the Nr as well (which you point out is not a low inertia rotor (so substantial energy derivable from Nr). He burned a lot of energy, and I think he was at CtMax, all (my) working numbers point at that (particularly 2.7g)
Para 5
Yes in gets hungrier for energy, (and if the Ct is already maxed, then the harder you pull the hungrier it gets, with no increase in TRT, so no additional G) ('Pull more get more party' is over) (at UCA)
Para 6
“Whatever angle the blades cone to is a reaction to that bundle of forces and effects on the disc/blades” Namely those detailed in Para 2 above, which make CA not irrelevant but a direct indicator of how much of the capacity of the Rotor is being used. Please don’t just glaze over at that relationship, it is fundamental. Ca=TRT/Cf
Para 7
Agree completely.
Punto
“AnFI has actually credited you [dc/da] with that, although you need a beady little eye to spot that in his posts. He now talks about a band of UCAs rather than a single UCA”
and challenge.
Yes I did, but I qualified it (as you rightly said) as being insignificant.
The reason I say it is insignificant is that it might be more significant in the illustrative thought experiment I presented of loading a hovering helicopter with progressively more weight as Nr is increased, such that CtMax is maintained, since indeed the IndFlow would change (and worsen the situation wrt CtMax), however this is much less relevant at speed where the increased Induced Flow with weight is much less significant. I said it was baby out with the bath water, not a First Order effect.
AND in any case and regardless, when CtMax is reached that also would be CAmax (UCA) (at a constant RRPM). Agree?
AND furthermore, I think the onus is on dc/da to quantify HIS point. I was asked to quantify mine and give assumptions, which I did, I am entitled to make my assumptions. I make the assumption that Increased Induced flow is not relevant, and under that assumption I presume dc/da agrees with me? QUESTION
The ‘family of UCAs' is in part developed through the discussion here, but also falls out of the maths too. e.g. it is dependant on density (linear), and it also is a function of the Ct fall off that NL gives with speed (in one of his excellent graphs).
“even though there may be a nugget of truth riding on the hobbyhorse.” quite a substantial nugget !
Ref ‘the Challenge’ from Punto I asked dc/da multiple times to quantify the term. It’s HIS objection, the onus was on HIM to substantiate it. It MIGHT be significant, quantify it, show us how significant it is. Is it the baby or the bathwater, is it a 'hair on the egg’? Or is it indeed a substantive point? PARTICULARLY at speed.
Does he agree that under the assumption of that effect not being significant the main point holds ‘true’?
The piece where he points to an Ω term on the bottom is (I say) wrong and highly distorts the significance of Ω.
I quote the piece here and explain why (I say) it is wrong below that.
dc/da
"Unlike a fixed wing, a rotary wing is rotary. Therefore the "v" that any aerofoil element experiences relies on rrpm and the element's distance from the hub let's say Ωr . However the downwash the element is seeing is independent let's call it u.
Therefore
α = arctan(u/ Ωr)
Assuming a small angle
α = (u/ Ωr)
And substitute
κ = ρ.A. (u/ Ωr).a /2m.
As you can now see, there is a term for rotor speed in your equation. Q.E.D. "
why that's wrong
Well the α term should say (P-u/ Ωr) where P is pitch
I don’t think you can leave out the Pitch of the blade.
So by substitution we have
κ = ρ.A. (P-u/ Ωr).a /2m
would expand out to
κ = (ρ.A. P.a /2m) - (ρ.A.(u/Ωr)/2m)
so the "κ = ρ.A. (u/ Ωr).a /2m" overstates the dependancy of κ on Ω, which is too naughty to say QED, and relegates it to an examination of the baby by looking at the bathwater.
AND in any case THAT also assumes that P is not varied, which is NOT a fair assumption.
AND furthermore where u is negligible as in the case of a helicopter pulling out of a dive at 90kts, then the term almost disappears.
AND furthermore in the ‘thought experiment’ of increasing the Nr and increasing the weight correspondingly the u value WOULD NOT be independent of Ω, but it would be dependant on it, thus reducing the assumed error further (to zero, by cancelling)
So while I do freely admit the proposed relationship MAY NOT be EXACT, I do say that any difference is just bathwater and not a substantive point. Quantifying the difference might be quite complex and subtle, but at least we can say it is comparatively small.
So I say that my point (whatever it was) still holds ‘in essence’.
AND the onus would be on dc/da to substantiate his objection otherwise.
So with respect to the Challenge Punto
1 I’d say that I have covered why that term is NOT substantial.
So the answer is that UCA it does not (substantively) vary with RRPM, which is the point
2 If someone contends that it does vary with RRPM THEY should qualify it, and we’ll see if it is substantive or irrelevant.
Sorry if I did not answer anyone’s important point. “the pig is getting tired"
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AnFI - I think you've missed the point of the theta term in the post which I gave you the equation according to BET.
You choose whether or not you think BET can be simplified. Others may choose differently.
We appear to have moved away from just the hover for the analysis. I am not sure how, in the original proposition of an ultimate coning angle, the cyclical forcings are accounted for independent of rotor speed.
You choose whether or not you think BET can be simplified. Others may choose differently.
We appear to have moved away from just the hover for the analysis. I am not sure how, in the original proposition of an ultimate coning angle, the cyclical forcings are accounted for independent of rotor speed.
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Or study the relationship yourself?
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dc/da
you are right I did miss it, but
a I was taking your QED example before that, and I had taken it as an expression of twist, so not pertinent to the point. Am I wrong to do that?
The hover case, it was just a simple thought experiment only intended toillustrate the point. The cases we are discussing are dynamic and have a whole other arguement asociated, I don't propose to go there.
You didn't answer MY question, can I assume the answer is YES?
ShyTorque
Mechanical engineering isn't my thing, but I had thought that Bending Moments in a case like this were resolved by Shear Forces, I could well be wrong, and defer to your assurance if you say that is wrong, in the desire not to get into a debate about that too, but feel free to explain if you think that is important.
you are right I did miss it, but
a I was taking your QED example before that, and I had taken it as an expression of twist, so not pertinent to the point. Am I wrong to do that?
The hover case, it was just a simple thought experiment only intended toillustrate the point. The cases we are discussing are dynamic and have a whole other arguement asociated, I don't propose to go there.
You didn't answer MY question, can I assume the answer is YES?
ShyTorque
Mechanical engineering isn't my thing, but I had thought that Bending Moments in a case like this were resolved by Shear Forces, I could well be wrong, and defer to your assurance if you say that is wrong, in the desire not to get into a debate about that too, but feel free to explain if you think that is important.
So, some excellent posts from Lonewolf and Punto - yet AnFi still isn't listening.
AnFi - still waiting for the answer to the timing calculation for the apache speed. Or is that something else you realise you have got wrong.
And btw shear and bending are not the same.
AnFi - still waiting for the answer to the timing calculation for the apache speed. Or is that something else you realise you have got wrong.
And btw shear and bending are not the same.
AnFi - so we come to yet another inaccuracy that you hadn't appreciated in your arrogance.
There is an accepted way of calculating the speed of an object from a video - you could try googling it but I will help you out and it doesn't involve the use of a stopwatch.
You need to know the frame rate of the video and then use software (VLC for example) to measure the movement of the object between each frame. Then after doing that for 50 frames, you will have an accurate time scale (of 2 secs if the frame rate is 25 fps) and, depending on how you measure the distance, and accurate one from which you can accurately distill the speed.
I say accurately measure because the accepted way to do this is to either overlay a scale - you could do this using the known length of the Apache, or use accurate and precise reference points in the video (as dCl did).
None of the accepted methods of ACCURATELY assessing speed from a video have the camera moving (like it is in the apache video) because it adds another level of error.
Can you finally admit that your assessment of the speed of the apache is flawed and cannot be relied upon in any way, shape or form to support any of your hypotheses?
There is an accepted way of calculating the speed of an object from a video - you could try googling it but I will help you out and it doesn't involve the use of a stopwatch.
You need to know the frame rate of the video and then use software (VLC for example) to measure the movement of the object between each frame. Then after doing that for 50 frames, you will have an accurate time scale (of 2 secs if the frame rate is 25 fps) and, depending on how you measure the distance, and accurate one from which you can accurately distill the speed.
I say accurately measure because the accepted way to do this is to either overlay a scale - you could do this using the known length of the Apache, or use accurate and precise reference points in the video (as dCl did).
None of the accepted methods of ACCURATELY assessing speed from a video have the camera moving (like it is in the apache video) because it adds another level of error.
Can you finally admit that your assessment of the speed of the apache is flawed and cannot be relied upon in any way, shape or form to support any of your hypotheses?
As for the rest of your post - sticks and stones etc.....
Smells of desperation.
You have been put back in your box on your technical, mathematical and aerodynamic theories by people far more knowledgable than me (and you) but you still keep whining and calling names - it has gone past the pathetic.
Smells of desperation.
You have been put back in your box on your technical, mathematical and aerodynamic theories by people far more knowledgable than me (and you) but you still keep whining and calling names - it has gone past the pathetic.
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Let us put ourselves in the situation of the pilot in this case.
It's a lovely day at the seaside and he decides to do a wingover. On the way down he decides to do a dive at close to Vne and make a dramatic pullout close to the water. He holds onto the dive a little too long and the physics now demands that he crash.
For a fraction of a second before he begins his belated recovery the G meter, the rotor rpm, and the newly installed experimental coning indicator are showing no signs of distress.
Then he starts the recovery, and the dials begin to move, the G meter starts to climb, the engines back off as the rotors are powered by the flare, and the experimental coning indicator recently fitted scuttles up towards whatever maximum it finds. But none of this is any use to our pilot because the crash is still inevitable.
As he sits in the recovery boat, is he running through a bit of over simplified theory, badly remembered from an early lecture on aerodynamics ? No, the only thing ringing in the pilot's head are the words of his crusty old QHI called Κάβουρας giving him a minimum height to commence pullout from a Vne dive.
Good luck with your aerodynamic discussions AnFI, but I think Κάβουρας does understand the important point.
It's a lovely day at the seaside and he decides to do a wingover. On the way down he decides to do a dive at close to Vne and make a dramatic pullout close to the water. He holds onto the dive a little too long and the physics now demands that he crash.
For a fraction of a second before he begins his belated recovery the G meter, the rotor rpm, and the newly installed experimental coning indicator are showing no signs of distress.
Then he starts the recovery, and the dials begin to move, the G meter starts to climb, the engines back off as the rotors are powered by the flare, and the experimental coning indicator recently fitted scuttles up towards whatever maximum it finds. But none of this is any use to our pilot because the crash is still inevitable.
As he sits in the recovery boat, is he running through a bit of over simplified theory, badly remembered from an early lecture on aerodynamics ? No, the only thing ringing in the pilot's head are the words of his crusty old QHI called Κάβουρας giving him a minimum height to commence pullout from a Vne dive.
Good luck with your aerodynamic discussions AnFI, but I think Κάβουρας does understand the important point.
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AnFI - trying to come back to the original proposition and why I feel uncomfortable with the simplification, or in your terms whether the baby is being thrown as well as the bathwater. I'll try and sum it up in words, there will be inexactitudes in wording.
To calculate the moment of inertia you integrate the masses at each position. A hoola hoop has a different "inertia" to a disc of the same size and weight. It is reasonable to assume that in most cases the mass distribution along the blade doesn't change with rotor speed. For lift you have to do the same. So the real question is do you think that lift distribution along the blade is constant with rotor speed?
To calculate the moment of inertia you integrate the masses at each position. A hoola hoop has a different "inertia" to a disc of the same size and weight. It is reasonable to assume that in most cases the mass distribution along the blade doesn't change with rotor speed. For lift you have to do the same. So the real question is do you think that lift distribution along the blade is constant with rotor speed?
AnFi - I have clearly shown that your speed assessment is so full of inaccuracies that it cannot possibly be valid.
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......his crusty old QHI called Κάβουρας
Very good!
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All Greek to me. A very interesting discussion
As a fixed wing pilot I feel that all the discussion of coning angles and centrifugal forces is rather missing the point that ultimately each rotor blade is just a wing moving through the air, albeit in a circular path, and the same physics applies with respect to the aerofoil stalling as it does in linear flight. If the airflow through the rotor disk exceeds the maximum angle of attack for that airfoil, it will stall irrespective of any other factors.
Fascinating stuff none the less.
As a fixed wing pilot I feel that all the discussion of coning angles and centrifugal forces is rather missing the point that ultimately each rotor blade is just a wing moving through the air, albeit in a circular path, and the same physics applies with respect to the aerofoil stalling as it does in linear flight. If the airflow through the rotor disk exceeds the maximum angle of attack for that airfoil, it will stall irrespective of any other factors.
Fascinating stuff none the less.
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So while I do freely admit the proposed relationship MAY NOT be EXACT, I do say that any difference is just bathwater and not a substantive point. Quantifying the difference might be quite complex and subtle, but at least we can say it is comparatively small.
So I say that my point (whatever it was) still holds ‘in essence’.
AND the onus would be on dc/da to substantiate his objection otherwise.
So I say that my point (whatever it was) still holds ‘in essence’.
AND the onus would be on dc/da to substantiate his objection otherwise.
Let's say that for the sake of argument, after some really tricky maths, some heroic assumptions (which because of the spirit of open intellectual curiosity in which you'd embarked on this venture, you would both agree) you jointly conclude that the inflow term drives a 10% sensitivity of CA to Rrpm in the hover and 3% at Vy and 1% at Vne. Now those who care are all a step forward.
At this point you could publish the results, and the aerodynamicists who can follow this can stand back and say, wow that's a good bit of work. Everyone can form their own views as to whether this correction counts as a hair on the egg (what on earth is that ?) or something more significant. And the pilots on this forum can go blissfully about their business knowing that it is totally irrelevant to their work, because the bit that affects them was dealt with a few pages ago.
Or you could conclude, as you hint in the quoted paragraph above, that the point you're making isn't sufficiently important to warrant that level of investment.
Last edited by puntosaurus; 28th Oct 2016 at 15:14.
I did predict the shape AnFi's, 'debating' would take back on page 5 post #88 because I have seen it here many times before.
Now he has been moderated - that has happened before as well.
I do not stalk him or troll him but he has made many threads unreadable and confusing, especially when a simple answer was all that the thread starter had asked for.
Punto - I applaud your position of being prepared to give him chance after chance to turn this thread into something valuable - we will just have to wait and see if there is any humility there.
And it looks like I need to get a new name badge made up
Now he has been moderated - that has happened before as well.
I do not stalk him or troll him but he has made many threads unreadable and confusing, especially when a simple answer was all that the thread starter had asked for.
Punto - I applaud your position of being prepared to give him chance after chance to turn this thread into something valuable - we will just have to wait and see if there is any humility there.
And it looks like I need to get a new name badge made up
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Thank you Crab. You have been a bit of an S.O.B. on this thread, but you're our S.O.B so there you go. The odd thing is I think AnFI is actually the bully. He loves to take someone and twist them onto his own ground so he can torture them. I think if he had the intellectual confidence and humility to take this exercise on he would be a better man for it. Whether he could find anyone to take that journey with him is not clear to me.
Toodles,
Punto
Toodles,
Punto
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Punto
You are a diplomat.
i gave the quantification formulaically but it got modded out along with various other answers and of course my opinion of what Crab has added to the debate.
someone else can take the thought forward if they feel like it
It is not possible to continue to illuminate this subject fairly with the deliberate harassment and the support for that from the 'house', sorry to anyone who was interested.
You are a diplomat.
i gave the quantification formulaically but it got modded out along with various other answers and of course my opinion of what Crab has added to the debate.
someone else can take the thought forward if they feel like it
It is not possible to continue to illuminate this subject fairly with the deliberate harassment and the support for that from the 'house', sorry to anyone who was interested.