Rotor Dynamics and Helicopter Stability

High and Low Drag Helicopters. A parameter which has not hitherto received any attention is the value of the fuselage drag. For any particular helicopter the drag will depend on the extent to which it is carrying bulky external loads, and the top speed under the high drag condition will clearly be substantially reduced. It might therefore be thought that any investigation of the high drag helicopter at a value of? of, say, 0·3, would be unrealistic since, for one thing, the engine power requirements would be inordinately high, and for another, the rotor blades would be very severely stalled. However, such an investigation is not, in fact, valueless, and we shall find a posteriori, that although the high speed case is effectively an idealised one, it will nevertheless serve the purpose of throwing up in a much emphasised form certain (apparent) discrepancies, which, in the low drag case, would hardly have merited attention. In the high drag case, however, the discrepancies cannot be dismissed so lightly, and we shall be obliged to investigate their cause. In so doing we shall obtain a much greater understanding of the underlying physical phenomena.