  In this paper, we propose an effective unified control law for accurately
tracking agile trajectories for lifting-wing quadcopters with different
installation angles, which have the capability of vertical takeoff and landing
(VTOL) as well as high-speed cruise flight. First, we derive a differential
flatness transform for the lifting-wing dynamics with a nonlinear model under
coordinated turn condition. To increase the tracking performance on agile
trajectories, the proposed controller incorporates the state and input
variables calculated from differential flatness as feedforward. In particular,
the jerk, the 3-order derivative of the trajectory, is converted into angular
velocity as a feedforward item, which significantly improves the system
bandwidth. At the same time, feedback and feedforward outputs are combined to
deal with external disturbances and model mismatch. The control algorithm has
been thoroughly evaluated in the outdoor flight tests, which show that it can
achieve accurate trajectory tracking.
