Calling Nick Lappos - Blade Stall

[puntosaurus]

Wow ! You really could start a fight in an empty bar ! I give up on the peacemaking front. Have at it boys. I'll do the tea on my own.

[[email protected]]

That is just reiteration of the same stuff AnFi - no new arguments and definitely no NEW DATA.

You haven't linked to any actual accidents, just listed some you think might be relevant.

Do you know how they measure the movement of stars??? They use accurate reference points not guesswork.

You only acknowledged the 'average speed' when it was pointed out, your original assertion was that 90 kts was the impact speed. Very magnanimous of you to say Nick made an 'easy' mistake but you haven't proved your accuracy at all.

an average pitchup rate of 21deg/s is quite meaty and produces 3g at 90kts, clearly beyond the capability of the rotor even if energy funded adequately.

how have you 'measured' this? More guesswork presented as facts

As I pointed out - your 'coning exam' is simply an algebraic expression that you have inserted convenient numbers into - it is not proof in any way shape or form.

Ref My experience in these manoeuvers, not going there, as previously flogged to death.

what you mean to write is NONE.

NO evidence, NO proof (mathematical or otherwise) and NO credibility AnFi.

[[email protected]]

Punto - as you have seen, trying to get clear, unambiguous answers from AnFI, especially without having your intelligence and understanding questioned, is like trying to nail jelly to the wall.

[puntosaurus]

The heart of the issue, despite many diversions, is whether reaching the non-linear part of the lift curve and pilots lack of understanding of that phenomenon is a contributory factor to these incidents.

Nick, the eponymous hero of the thread, has I suspect made up his mind, but is wisely keeping his own counsel. He knows that the protagonists enjoy mud wrestling more than he does. Besides which, if he wants a technical discussion on this issue, he can probably reach in to his rolodex and find about a hundred people better qualified than us to engage with.

Given that Nick has actually participated in engineering design and actual manoeuvrability flight tests that underpin the certification of this actual aircraft, I'm inclined to defer to him. Nevertheless, the data he posts do indicate that it is theoretically possible that the non-linear part of the curve could be reached transiently.

So we must acknowledge that possibility until such time as the Gods choose to descend again and provide us with further runes to read.

[AnFI]

Punto
Sorry about that
I thought I had done what you asked in respect of Lone and BA
then agreed with what you said, agreed that you had got the point, and just suggested that it is interesting
Then answered your question (not to me it's true) about what happens.
Then agreed it's tea time !

as well as patiently answering all kinds of diverse points about how to measure the speed etc etc etc etc
what NL had to say was fantastic and i've only complemented him on that. that he's so wrong about the speed is no adverse reflection on him, it's hard to guess a speed from a video clip

and no one has answered any of my questions once.

did ANYONE actually see the 2 second loop video I posted a link to?


Crab you are just antagonising again. answer any of my questions to you, like I have the decency to do for you.
"how have you 'measured' this? More guesswork presented as facts" NO! and I included my measurement and working from that about 100 posts ago. 21deg/s
I don't mean to say that you are stupid but anyone else can make up their mind by following your question about speed measurement and then your response about measuring the speed of stars. I challenge anyone to do that and not reach the conclusion I have. (Nailing a jelly fish to the wall ! ANSWER MY QUESTIONS TO YOU !)
Challenge !

[[email protected]]

did ANYONE actually see the 2 second loop video I posted a link to?

yes, and it took me a while to realise why you were so insistent - you have adjusted the video to make the sample ie just 2 secs as small as possible so it is more difficult to see how you have fudged it.

In order to make the distance travelled over time match your assessment of speed, you have increased the speed of your clip relative to the original - not by a lot, but by just enough to make anything but a detailed analysis look OK.

It is much like the crude way that filmmakers used to speed up actions shots in movies by running the film through faster.

It is only evident when you watch the original alongside your doctored clip.

[Brian Abraham]

BA you might have missed it but I did list some well know incidents by shorthand "there are accidents where the rotor has hit it's max thrust (regardless of energy). 2Apaches, 1 H269(possible energy issues too), 1 NH90"

Well known accidents? I have absolutely no idea to which accidents you may be referring. I'm afraid you've not attempted to answer the question at all. Listing a number of aircraft types doesn't constitute an official accident report, nor do you explain why the particular report is incorrect in its summation as to cause. Flip me off if you wish, I couldn't care less, but should you do so it only confirms you're on a hiding to nothing.

[Evil Twin]

AnFI mate, when you're in a hole, stop digging. This entire thread, though entertaining, is increasingly farcical.

[jellycopter]

I don't know conclusively whether Anfi is right or wrong. I guess by the number of nay sayers that are vastly more qualified than I, that the collective knowledge would suggest the latter.

However, I do have to hold a degree of respect for anyone that thinks a little bit outside the box and is prepared to voice it openly. One of the things I have discovered in my 30+ years as a helicopter pilot is that many of the 'facts' I was taught as a junior pilot were utterly wrong. (See Nick Lappos' Urban Myths thread). I also happen to have a great deal of empathy with Anfi's 'single engine' logic that he thrusts upon this forum on a regular basis.

I applaud you Anfi for being prepared to challenge the accepted norms. Whether you are right or wrong is irrelevant to me really, as I don't plan on exploring Ultimate Coning Angle any time soon. However, I personally find the 'meat' of this discussion (not the purile mud slinging) very interesting.

JJ

[Lala Steady]

Jelly - I don't think anyone here has a problem with 'blue-sky' thinking - simply with the combative, supercilious and generally unpleasant way that thinking is presented.

[AnFI]

BA
The very last thing I intend is to 'flip you off' (or anything else that sounds like that !
It is difficult to respond suffiviently in detail to such a barrage of counter arguement.
I had hoped that the shorthand reference was enough to identify them since they are quite well known ones, and I don't really want to be led down the path of identifying and debating any more specific accidents. Discussing the Greek case has been awkward enough, and is off topic. (one in a lake, dramatic, one in Afgan, one close to home and the Greek one. That is as far as I want to go with that for allsorts of reasons, AND it is off topic). So I am not meaning to be disrespectful, but I am tending to rush these long and boring answers. (BA please read Crabs noise and tell me whether you think he is helping

Especially true when one oaf continuously delights on deliberately wrecking the debate
(read Crabs last nonsense, someone get this idiot off my back please, are YOU happy to align YOURSELF with his points?)

Jelly
Thanks
It is amazingly hard to counter all these points. I suspect that many who agree have stayed silent enjoying the spectacle of a man on the ropes.
Do you find Crabs input helpful?
Now he says I speeded up the clip ! I guess he is suggesting it looks as fast as I have spent 10000 word defending.

NL
has indeed wisely stayed out of it, and I suspect that his popularity with Crab is more valueable to him than wading throuh this treacle here and saying, "I see the point, nobody ever looked at it like that before, I do/don't find it very interesting". Besides I can't think of anything more unpleasant to engage with that the general level of vitriolic ludite drivel, especially if you don't feel great. Its also awkward to come back and say "now I've measured the speed I see I was wrong about that"
It takes a BIG MAN which surely you are?
If you're going to be wrong I don't mind saying so, I am not defferential, nothing personal great respect for you etc etc etc Maybe flick through the rolladex and throw some more crumbs to the mortals.

[[email protected]]

AnFi - surely you must applaud my method:

I have put forward a hypothesis that is technically feasible, contextually plausible and relevant to the thread. And, I have presented it as fact with no data, proof or evidence of any kind.

I can now sit back and refute any criticism of my hypothesis because I have laid the burden of proof on the critic (you).

I could have included some basic algebra to do with speed. distance and time equations but I could save that to support my hypothesis in a 'mathematical' fashion later.

I am surely your most successful student - I have learned much from you oh master - just none of it about helicopters.

[megan]

Had an email from a reader who provided the following, they assure me the info comes from a reputable source.

Load factor is caused by pitch attitude rate and airspeed, so the penalty of waiting a few seconds before pulling out of a dive is that the pitch rate to get the nose level causes a lot more g. The load factor of the rotor reaches a max at about 80% of Vne, if your speed builds too fast you will stall the rotor trying to raise the nose.

When you ask too much from the rotor, it mushes through, and you get an attitude change but your flight path is still unchanged. This means you'll still hit the ground. Stall will limit the load factor, and may cause high vibes and sloppy roll control.

It would seem that rotor stall as proposed by AnFI is a fact of life, just not something taught to we stick jockeys. Must admit my ignorance. Bit like the meaning of Va in the FW world until the NY A300 crash I assume.

[AnFI]

Megan
Yes that's right. and you are the thread starter !
Deep respect for you. It takes a straight bat to command respect. You obviously have some moral fibre.
I would have hoped that the logic was sufficient to convey it, without having to resort to 'credentials', the concept of which has been unfasionable since the First World War.
Perhaps you can see why I was so persistent.

Jelly / AC / Punt thanks for the support, it hasn't been easy

Please read Crabs post above, let me know if you want to be part of that.
Total insincere sabotage and harrassment of this thread from the outset.
Anyone siding with him please identify yourself.

Thank you and (Punt) 'Time for Tea'

[chopjock]

AnFI,
Keep it coming old boy, I agree with almost everything you say on here!
Especially the single v twin rants!

[puntosaurus]

AnFI i'm delighted you've found further support for your proposition, but I'd like to point out that in the original thread that spawned this one you presented it not as stated above, but as the aerodynamic musings leading to an UCA that megan opened this thread with.

Your aerodynamic musings are still highly contestable but fortunately irrelevant to the core issue.

If you'd said on the original thread, "I think rotor stall is a factor in these accidents", or better still "does anyone think rotor stall is a factor in these accidents" I think you'd have had a higher quality debate.

I suspect being liked isn't high up your priority list, but if you want to avoid the bullying and elicit quality input from highly qualified and experienced contributors on this forum (including crab) then you might want to think some more about that.

[dClbydalpha]

Punto, thanks for that I began to wonder whether I was missing the point.

The discussion is not whether you can stall a rotor. There has been lots of discussion here to do with energy management and what happens as blades begin to be worked too hard. All good stuff.

The original proposition is that this always happens at a singular known "ultimate" coning angle. That knowledge of this value would prevent such accidents. This is what I sense most people are uncomfortable with.

[[email protected]]

Is it really 'bullying' to question the proponent of a hypothesis about accuracy, validity of data, logic, mathematical process and relevance of information to that hypothesis?

In scientific circles I believe it is called peer review

If we can now have a reasoned debate about rotor stall then I am all for it but leave the UCA out there with the scientologists.

AnFi - one more attempt to ellicit facts about your apache speed assessment - if you didn't use accurate reference points, what did you use to ensure accurate timing since that is crucial?

[ShyTorque]

Originally Posted by ShyTorque

I think you meant to write "shear loads" but in any case, shouldn't that be "bending loads"?

AnFI, I'd be grateful if you could please answer my earlier question.

BTW, my user name is ShyTorque, not Shytalk.

[Lonewolf_50]

Originally Posted by megan

Had an email from a reader who provided the following, they assure me the info comes from a reputable source.It would seem that rotor stall as proposed by AnFI is a fact of life, just not something taught to we stick jockeys. Must admit my ignorance. Bit like the meaning of Va in the FW world until the NY A300 crash I assume.

Megan, there is no evidence that the rotors stalled in that crash. Do you know something that we don't? What is obvious is that the rotor head reached a "power required exceeds power available" in terms of thrust vector up not being able to overcome vertical speed down, hence impact with the water. I will suggest to you that the rotor head (Apache does not have a low inertia rotor head, and the engines were still trying to keep it spinning) did not slow down fast enough to stall until after impact (at which point it doesn't matter). Yes, I understand what accelerated stalls are, in both fixed and rotary wing. G loading considered (and we don't know what the G load was) there is still momentum and inertia in play in the brief time between recognition that the maneuver was balled up and the attempt to use all (we presume) power available to stop the rate of descent short of the water.


So while your generic point is that rotors can stall (aerodynamics makes no special allowances for helicopters in that regard) asserting that the rotors did stall is assuming some facts not in evidence. The coning angle is an effect, not a cause, of the rotors changing pitch and responding to loads on the blades/rotating wings. It is a reaction to forces on the blades.


Megan, why is the airspeed around the time of impact of interest? Power margin and airfoil efficiency. Depending on the day, weight, and such from the charts in the back of the flight manual, there's a sweet spot airspeed. Based on similarity to Blackhawk in terms of weight and propulsion, I'll estimate somewhere around 70-75 knots for an Apache on a standard day. That is the knee in the curve analogous to L/D max for a fixed wing. We used to refer to that airspeed as "max conserve" because you had the most additional power available at that airspeed, or more to the point, needed the least amount of power to fly level (and thus burned the least amount of gas).


If the Apache was below that airspeed as the final pitch and pull was attempted, it was already in energy debt. If it was above, (say 90, or 80 knots airspeed (AnFI's estimated are based on ground speed due to measurement method) then there was a little energy "in the bank" for the flare but there's a catch, which is where your concern about rotor loading comes in. Trading that extra energy in the flare/pull gets you some benefit but you are likely passing through that sweet spot airspeed and into the beginning of needing more energy.

At this point in the high demand maneuver, you've got a variety of issues working against you. In overcoming your energy debt with that flare, you've increased drag as you've gotten a bit of lift (the blades bite harder) and your AoA goes up ... but your airspeed is still decreasing which isn't helping, and is indeed hurting.

Whatever angle the blades cone to is a reaction to that bundle of forces and effects on the disc/blades.

Put another way, by the time you are wondering whether or not you have reached a critical coning angle you are already far enough behind the aircraft that you are at the mercy of inertia, and altitude available to trade for more energy ... which thanks to the entry altitude of this maneuver the pilot ran out of in a hurry.