Rotorcraft simulation fidelity for low speed manoeuvring using ‘additive’ system identification

Abstract

High fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complex nonlinearities arising from aerodynamic couplings and interferences. This paper explores rotorcraft flight dynamics in the low-speed regime where such nonlinearities abound and presents a new Additive System IDentification (ASID) approach in the time-domain to aid investigations of these complexities. The ASID approach identifies flight model parameters sequentially based on their contribution to the local dynamic response of the system, in contrast with the averaged values of conventional System IDentification (SID) approaches over a whole manoeuvre. The identified 4 degree-of-freedom model shows good predictability using flight test data from the National Research Council’s Bell 412 at hover and how the identified parameters can be used to improve the fidelity of Liverpool’s baseline FLIGHTLAB model of the Bell 412. The approach is also used to study nonlinearities attributed to Manoeuvre Wake Distortion (MWD). A cubic rate term is proposed to model the MWD nonlinearities and first results show good correlation for this nonlinear model structure, demonstrated by its capability to capture the nonlinear response and variations of the stability and control derivatives with response magnitude.