Transition Flight Control of Two Vertical/Short Takeoff and Landing Aircraft

Abstract

We propose two nonlinear approaches for the autonomous transition control of two vertical/short takeoff and landing aircraft. The first aircraft, referred to as the V-1 aircraft, is a fixed-wing fighter equipped with a vectored thrust and lift fan. The second aircraft is a tilt rotor. We provide nonlinear models for the transition from hover to forward flight. Both control problems are nonlinear, nonaffine, and have redundant inputs. Furthermore, some control inputs must reach specified end values when the transition has been completed. However, there is a key difference between the two aircraft. The V-1 aircraft can be controlled to rapidly increase velocity and pitch angle simultaneously, whereas the tilt rotor aircraft cannot, because linear and angular acceleration require conflicting control inputs from hover. For the V-1 aircraft, a method is applied whose key point is that a new controlled variable is appended to decrease the redundancy of the control inputs. For the tilt rotor aircraft, a second method is applied that transfers the problem into a two-time-scale problem. Nonlinear optimization is adopted to make the specified input approach the specified end value. We also consider problems associated with cases in which insufficient control power limits the ability of the aircraft to achieve commanded controlled variable rates. Simulations show that both approaches achieve the transition control successfully.