DESIGN OF A FLIGHT CONTROLLER FOR HYPERSONIC FLIGHT EXPERIMENT VEHICLE

Abstract

ABSTRACTNational Aerospace Laboratory (NAL) and National Space Development Agency (NASDA) of Japan launched a hypersonic flight experiment vehicle (HYFLEX) for flight experiment of reentry phase to the top of the atmosphere in 1996. Flight condition in the experiment varied from an altitude of 107km and a speed of Mach 15 to an altitude of 30km and a speed of Mach 2. This paper describes design of a flight control system of the HYFLEX and evaluation of robustness against variations of command inputs and aerodynamic coefficients. A nonlinear simulation model that describes the vehicle motion has been made using the data obtained from wind tunnel experiments by NAL and NASDA. Linear models are computed from the nonlinear model for every second of the flight, assuming that the flight is a quasi‐trimmed one. Because the vehicle has a cylinder‐like configuration and takes a large angle of attack and a bank angle, coupling between longitudinal and lateral‐directional motions cannot be neglected; hence, the linear models include coupling terms. Averaging the linear models yields a nominal model for controller design, where the type‐1 linear quadratic (LQ) servo controller is employed for attitude control. Since the flight condition varies so much, it is difficult to control the vehicle using a single set of control gains. Therefore the flight period is segmented into eight intervals, for each of which a nominal linear model is computed, and then eight sets of feedback gain matrices are computed and scheduled as a function of flight time. The effectiveness and robustness of the flight control system are examined through computer simulation. Simulation results indicate that the control system works well even when attitude commands and aerodynamic parameters considerably deviate from nominal ones.