Brian,
Your responses indicate to me you might not have fully grasped aerodynamics.
I was pointing out that experienced fixed wing pilots, like the accident pilot, know not to use large control inputs when recovering a stall in a fixed wing aircraft and they wont do it when flying helicopters either. I suspect many helicopter pilots think all fixed wing pilots have an overwhelming desire to push the stick full forward if they experience an engine failure.
My answer applies to helicopters as it does to fixed wing aircraft but, for simplicity, lets stay with fixed-wing aircraft for the moment.
It is proven that the stall of a wing happens at a certain angle of attack [usually around 14degrees] and has little to do with the speed of the wing. Lift [and drag] increases as angle of attack increases but as the wing reaches the stall angle the lift drops off rapidly [but drag keeps on increasing].
Flight manuals state stall airspeeds but neglect to say these are valid for 1g 'level flight' conditions only. Unfortunately, this leads some pilots to believe that they are safe as long as they are above the stall speed. If they are in a turn or any accelerating manouevre the angle of attack of the wing is different compared to that angle required for normal flight at 1g. The harder they manouevre the nearer the angle of attack gets to the stall angle.
The more you 'pull G' the more acceleration you are experiencing and all of this is caused by the increased lift due to increased angle of attack.
Aircraft such as the Pitts and the Extra are built extremely strong [20G design limit for the Pitts I believe] and have very large tail surfaces that allow the pilot to induce large angles of attack on a whim. I have many hours in Pitts and know it as an superb aircraft capable of doing exactly what you tell it to do and thus able to make fools of people with a less than complete understanding of aerodynamics.
In a Pitts you can fly at 130knots and pull the stick quickly and firmly all the way back to bring the wings to near the stalling angle. Application of rudder at this instance causes a slight side slip which causes one wing to go past the stall angle reducing that wings lift considerably whilst the other wing is still generating very large lift. This is how a flick roll is performed - one wing is stalled and the other is not - hence a very high roll rate with very high Gs as well. Its really more like a spin performed horizontally. within less than a second you are down to 70knots. You can push forward for a negative flick but -5G is not for the feint hearted.
To demonstrate non-stalled flight at below 1g stall speed imagine being at the top of a poorly performed loop and find you have 20knots airspeed over the top. As long as you dont pull too hard you wont stall - you continue to fly around the top of the loop - this is because you have not gone past the stall angle of the wing. The wing is still producing lift but not enough to take the weight of the aircraft under 1g.
Ofcourse nobody should try and do a stall manouevre at Vne as it could apply lift forces greater than design limits and capable of bending the aircraft or worse. But it is perfectly possible to do it! Hence it is possible to stall at any speed you want!
Most normal aircraft dont have the tail surface area [read authority] of a Pitts or Extra and this keeps them safe from over control. The aircraft in your video loses its wings most likely because it was flying fast and they pulled too hard taking the angle of attack to a large value [but not to stall angle] where they created so much lift they broke the spar.
So, stall occurs at a certain angle of attack and can happen at any airspeed given the right conditions.
With regard to my comment about an inexperienced fixed wing pilot recovering from a stall with full forward stick - its a very bad technique to teach. The Pitts can demonstrate why very nicely. If you were in a Pitts and recovered from an upright stall by putting full forward stick you would simply stall the wings with a negative angle of attack and without perfect control of the rudder you will almost definately end up in an inverted spin needing a recovery altitude of approx 700 feet.
Ofcourse the simplest way to recover from a stall in any aircraft is to reduce the force on the stick - this will reduce the angle of attack of the wing and allow un-stalled flight to continue. Ofcourse if you are still pointing up gravity is going to cause further effects.
The aerodynamics of a spinning rotor after engine failure are far more complex but still subject to the same angle of attack and relative airflow issues. Hopefully I have demonstrated how a rotating airfoil can stall even at normal rpm. Stalls can happen to helicopter blades and even jet turbine blades.
OOW
Last edited by outofwhack; 19th Nov 2012 at 11:04.