Longitudinal Incremental Reference Model for Fly-By-Wire Control Law using Incremental Non-Linear Dynamic Inversion

In this paper a control architecture including an incremental physical reference model is presented for the longitudinal channel of an incremental non-linear dynamic inversion flight control law to provide fly-by-wire capabilities for a piloted fixed wing turboprop demonstrator aircraft. The reference model is formulated in terms of dynamics with respect to the maximum angle of attack in the angle of attack domain, and with respect to trim values for pitch rate and load factor. Together with the incremental dynamic inversion this relieves the use of uncertain trim tables for the control law. A blended control variable is proposed to provide intuitive control over the whole flight envelope. A compensation algorithm adjusts the reference model trajectories in case of actuator limits or rate limits predicted by the control allocation. An error controller formulated in terms of equivalent load factor dynamics is proposed, together with a conversion to pitch rate acceleration for the incremental non-linear dynamic inversion.