An investigation of the feasibility of reshaping stick commands to improve hovering control of unstabilized jet-lift aircraft

Abstract

Summary. The Report examines the feasibility of improving hovering control of unstabilized jet-lift aircraft by reshaping stick commands. From basic theoretical considerations it is shown that the open-loop properties of any linear dynamic system operating in an environment without external disturbance can be altered to those of a lower order system by means of a suitable shaping function. Thus there may be numerous shaping laws which, in principle, could simplify control of hovering aircraft. However, it is felt that practical applications of the concept would depend upon the performance of the mechanical system, which must operate under the limitations of control power available and which must satisfy certain safety requirements. A hydraulic integrating mechanism designed to meet such conditions was chosen for detailed study. Simulated hovering flight studies were conducted to observe the effect of variations of mechanism parameters on pilot performance and a discussion on optimum controls is included. A practical hovering control circuit for jet-borne vehicles was thence proposed on the basis of a compromise between mechanism characteristics desirable for normal operation and those that would be necessary to provide adequate control in the event of hydraulic failure.