Flying qualities of aircraft with actively augmented pitch and yaw stability

Abstract

Ignoring the dynamics of the automatic control loop hardware, the effects have been studied on rigid body mode stability, gust response and pilotVs control of aircraft in which relaxed longitudinal or directional stability is augmented by various alternative feedbacks to the elevator and rudder respectively. It is shown that \\'indirect\\' augmentation by such methods as feedback of pitch rate, integral pitch rate or normal acceleration in the longitudinal case or lateral acceleration in the directional case can give rise to significant adverse characteristics, which could limit the amount of instability which can be so corrected or which may demand additional corrective feedback loops. \\'Direct\\' feedback of incidence or sideslip on the other hand will restore in most respects behaviour virtually indistinguishable from that of naturally stable configurations, provided these quantities can be sensed accurately and reliably. Particular attention is drawn to difficulties with indirect feedbacks in maintaining stability near and beyond the stall and to gust response characteristics.