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Russian helicopter airshow crash
- Thread starter Randy Daytona
- Start date
That's not how this works. That's not how any of this works.
I understand that the main rotor blades can't stall, they create their own lift, but if a helo pulls up into the vertical and the lift generated goes from the vertical to the horizontal and the airframe slides back down, wouldn't that be considered a stall? I'm not arguing............just curious.
No. A stall is when a lifting body no longer creates more lift than drag*. The direction that lift is being created (the lift vector) is irrelevant.
*Past the critical angle of attack lift is still being generated, however the airflow is separated from the lifting body creating a low pressure area (drag)
*Past the critical angle of attack lift is still being generated, however the airflow is separated from the lifting body creating a low pressure area (drag)
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Okay, I got it (well I knew it). Lift is always created with speed, but the vector may pull you into an immovable object like the ground.
It's not a stall in the traditional sense but I see what you're saying. The end result could be similar. Or far worse. The h-60 prohibited aerobatic flight but I imagine you could depart controlled flight. OCF in a helo is a really bad idea. Many FW aircraft have procedures for OCF or ejection seats; no such things in helos.
What we're talking here, and pointy nose types people will be able to relate, is an energy management issue as it relates to extreme nose high in a helicopter. Since the wing never stalls and is providing a lift vector at all times, you are really talking about a shift in that vector, never really a wing element loss of lift involving critical AOA, etc.
About as dynamic as you can get in an H-60 without breaking NATOPS you can execute something akin to a wing over (rotor over). When doing this the aircraft bleeds off speed rapidly as you convert airspeed to altitude.(~35-45 nose up) What's different in a helicopter, is the ability to push the tail around with far more response than you get in something fixed wing waiting for your roll rate to do the job. Immagine an infinitely effective rudder regardless of wind over the control surface. You just push the tail through the turn. It's way tighter than what you can achieve in an airplane and the end result is the same (180 of heading change).
My point here is that if I immagined taking this maneuver past the 45 nose up limit, I'm pretty confident I could use the tail rotor to push me back around to a nose low attitude and then pull it out.
The real limit to a helicopters manueverability are its flapping and lead/lag limits, the type of head it has (underslung - old school hueys or TH-57, fully articulated - H-60, or rigid rotor head - new hueys and cobras, the redbull helicopter, or most aircraft build more recently), and the displacement of the bladeroot from the blade hub (larger rolling moment generated the further from center you go)
About as dynamic as you can get in an H-60 without breaking NATOPS you can execute something akin to a wing over (rotor over). When doing this the aircraft bleeds off speed rapidly as you convert airspeed to altitude.(~35-45 nose up) What's different in a helicopter, is the ability to push the tail around with far more response than you get in something fixed wing waiting for your roll rate to do the job. Immagine an infinitely effective rudder regardless of wind over the control surface. You just push the tail through the turn. It's way tighter than what you can achieve in an airplane and the end result is the same (180 of heading change).
My point here is that if I immagined taking this maneuver past the 45 nose up limit, I'm pretty confident I could use the tail rotor to push me back around to a nose low attitude and then pull it out.
The real limit to a helicopters manueverability are its flapping and lead/lag limits, the type of head it has (underslung - old school hueys or TH-57, fully articulated - H-60, or rigid rotor head - new hueys and cobras, the redbull helicopter, or most aircraft build more recently), and the displacement of the bladeroot from the blade hub (larger rolling moment generated the further from center you go)
I'd argue doing a true rotor over does break NATOPS because you're exceeding your 30 degrees/s. However I'm a huge fan of doing pitch backs/reversals (which keep the ball centered and thus keep the yaw rate lower).
And I agree, they'd be even more fun if you could go to 60 or more.
And I agree, they'd be even more fun if you could go to 60 or more.
Interesting point. The limit being on "hovering turns", I didn't really apply it to a low energy/slow airspeed turn. In my mind, it's always been governed more by the 3710 aerobatic flight 45/60 constrants (and more restrictively the 45 AOB NATOPS limit), but I might be fairly accused of sea lawyerng this...
But then Again, I'm just now emerging from my young and stupid years... Maybe you're right.
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Good point. I was never really clear why it mattered if you were hovering or not. I kind of chalked it up to the fact that it's easier during most regimes of flight to exceed that turn rate in a hover than during any other part of the flight (other than a rotor over). Maybe Bert can shed some light on that. I'm also curious why we still have the limit now with the fancy EGIs. Hopefully the answer isn't "because that was the limit in the legacy aircraft."
Quite a few things go into calculating the limit, structural loads, the actual aero, FLM, what they are willing to test to (which = $ and time), torque limits (especially for stoping the rotation), what they think you need to be able to do, and what they think a fleet pilot is capable of doing without screwing it up. I don't know what drove the equation, but would bet money on #4 and #6.
As for distinguishing the limit between in and out of a hover, I'm pretty confident it is a hover number and they weren't ever worried about button hooks or rotor overs.
Which is interesting since the 45* thing is FLM, I would think "they" would also want to reduce the the number of rotor overs (as in to zero) for similar reasons you mentioned above (Tq, stress, etc). Assuming you take the 30*/s limit literally and it's a hovering only limit (which I'm not arguing, by the way), I can't think of anything that legally prevents you from doing a rotor over, but maybe I'm forgetting a limit buried somewhere in there. It wouldn't be the first time.
Saw this the other day - interesting aerodynamics improvements on the blades for a claimed 30% increase in top speed. 194 knots is cooking for a traditional helo.
http://www.popularmechanics.com/military/a18904/russian-attack-helicopter-upgraded-increase-speed/
http://www.popularmechanics.com/military/a18904/russian-attack-helicopter-upgraded-increase-speed/
Did they ever solve it's tendency to cut off it's tail? I'd heard that the Hind doesn't have very good hover performance due to the area of the wings but that the wings to provide a substantial portion of lift in forward flight so it's almost a compound helo.Saw this the other day - interesting aerodynamics improvements on the blades for a claimed 30% increase in top speed. 194 knots is cooking for a traditional helo.
http://www.popularmechanics.com/military/a18904/russian-attack-helicopter-upgraded-increase-speed/