Automatic Control of Harrier Maneuver of an Agile Fixed-Wing UAV

In this paper, a gain scheduled linear state feedback based longitudinal control is applied to an agile fixed-wing unmanned aerial vehicle (UAV) to achieve transition between level flight at low angle of attack (cruise at angle of attack (AOA) = 4° and level flight at high angle of attack (harrier level at AOA = 50°. For both the level flight regimes, the elevator deflection and propeller rotations per minute (RPM) are computed using a linear quadratic regulator (LQR) control designed about the respective trim states. For cruise to harrier and harrier to cruise transitions, a minimum time optimal trajectory is generated off-line and the same is tracked using a linear state feedback control. Simulations of the control implemented on a longitudinal model of an agile fixed-wing UAV which includes propwash, wing downwash, flat plate post-stall aerodynamics and actuator constraints (first order dynamics, saturation and rate limit) are carried out. The results show that the control scheme is successful in achieving transition between cruise and harrier level flights.