To: Nick Lappos. .. .The individual in question likened the asymmetrical airfoil to that of a wing on an airplane. He indicated that when the control stick is pulled back the aircraft will if the necessary speed is present go into a loop. He indicated that the wing was moving in relation to a theoretical point in space assuming the loop was a perfect circle. He further indicated that an asymmetrical airfoil on a helicopter rotor would want to do the same thing as the aircraft wing. But, it can’t because the blade is restrained by the pitch bearings and the pitch horn / pitch link and because of that the blade will try to climb (outside loop) when pitch is increased. He stated that since it can’t react like a wing then the blade will flex (twist). He also said that this would be the root cause of vibration that did not exist on helicopters using NASA 0012 airfoils. He also said for that reason helicopter blades would always be symmetrical.. .. .Hopefully I got it right because it was a part of a lecture at Sikorsky back in 1956. The man teaching that class was the chief aerodynamicist for Sikorsky.. .. .Evidently he was wrong because just about every helicopter has asymmetrical airfoils but then again modern helicopters have a hell of a lot more vibration than their older cousins do and most have various systems to dampen that vibration.. . . . <small>[ 05 March 2002, 04:36: Message edited by: Lu Zuckerman ]</small>