Control law synthesis for an airplane with relaxed static stability

Abstract

The synthesis of a command and stability augmentation control law for a transport airplane is presented. To improve fuel efficiency, the airplane has a relatively small horizontal tail surface and therfore has unsatisfactory inherent longitudinal stability. Over a wide range of center-of-gra vity locations and the full flight envelope, the control law furnishes 1) task tailored column force gradients; 2) excellent dynamic responses for normal acceleration, pitch rate, and speed; and 3) better than f =0.5 damping for the phugoid and short period modes. The control law is based on linear quadratic Gaussian synthesis at a single operating point. The gains are scheduled as functions of dynamic pressure and airplane flap position. The control is the elevator command and the sensors are column force, normal acceleration, pitch rate, airspeed, longitudinal acceleration, and vertical speed.