A system to vary the stability and control of a deflected-jet, fixed-wing vtol aircraft

Abstract

SUMMARY A system to provide variable control power and augmented stability for a hovering VTOL aircraft is described. of the two jet engines is deflected to provide lift for hovering flight. Bleed air is taken from the engines and used for reaction control at the wing tips and tail for attitude control while hovering. Two sets of reaction nozzles are used on the modified X-14A. actuated by the pilot; the other set, which uses electric servo-driven noz- les, was added to generate variable-stability control moments about all axes, Variable-stability modes provided are rate damping, cross-coupling cancella- tion, augmented pilot control, and stiffness with maneuverability cutout. The control system for one axis is outlined, and criteria for dividing bleed air between the two sets of nozzles are presented. The development of the nozzles for constant flow and pilot safety controls are discussed. On the Bell X-14A aircraft the exhaust The original set is mechanically INTRODUCTION In aircraft handling qualities research,variable-stability aircraft make possible the exploration of a wide range of the fundamental aircraft param- eters, such as damping and control power about each axis. Such a research aircraft enables the pilot to evaluate combinations of variables under real- istic flight conditions involving specific tasks. Investigations of new handling qualities concepts, exploration of characteristics of aircraft in the design stage, or improvements of existing aircraft may all be accomplished. The technique for varying control power and dynamic response depends on supplying commands to the control surfaces, or auxiliary control devices, in addition to the pilot's normal commands. These additional commands are deter- mined on the basis of both pilot command and aircraft motions. Servo- mechanisms are convenient for introducing these commands into the control system. Variable -stability systems are quite flexible since commands can easily be varied in amplitude, mixed in various 'proportions, reversed, or even adjusted to put the aircraft into an unstable condition. The concept of variable -stability aircraft is particularly valuable in the solution of