The CHAIRMAN, in opening the meeting, said that the Author required no introduction As Technical Director of the Westland Aircraft Company since 1952, MR HOLLIS WILLIAMS had been responsible for a very successful family of helicopters, all based on well-established Sikorsky experience Previously, as Chief Engineer of the Fairey Aviation Company, he had been responsible for the development of naval aircraft, and prior to that, as Chief Engineer of General Aircraft at Hanworth, his developments had included the well-known troop-carrying gliders, the Hotspur and the Hamilcar He was a member of Council of this Association and a Fellow and Silver Medallist of the Royal Aeronautical Society He was also a helicopter pilot, having undertaken a conversion course under BASIL ARKELL in 1946, as a result of which he now held Royal Aero Club helicopter certificate No 13

The stability of the ‘flying platform’ type of helicopter is investigated in order to determine the margin of stability and ease of control to be expected and to show the effects of the system, weights, inertias, dimensions and aerodynamic forces

This paper deals with the theory of stability in hovering and the theory is illustrated by a numerical example of a ‘typical’ pilot and platform

The stabilizing actions of the pilot are assumed to take the form of controlling moments at his ankles in linear response to errors in his attitude, rate of change of attitude, horizontal velocity and horizontal acceleration, the constants of proportionality being termed control constants

Within this framework it is shown that in the absence of delay in the pilots’ response it always is possible to stabilize the platform Further, the size of the control constants required is determined solely by the weight and centre of gravity height of the pilot, the forces involved being of the same order as those used in standing