Analysis of Rotorcraft Pilot-Induced Oscillations Triggered by Active Inceptor Failures

Abstract

The use of active inceptor systems allows for control of the aircraft even during mechanical failures within the control inceptor. For the specific case of isometric failure, whereby the inceptor ‘freezes’ in position, a virtual force-displacement model is used to continue to provide control input. Experimental flight tests using the German Aerospace Center’s (DLR) research helicopter (ACT/FHS) has shown the potential to encounter pilot-induced oscillation (PIO) tendencies when flying using this mode. This paper presents results from a simulation campaign undertaken to confirm whether PIOs may be exposed through this use of control and/or the resultant severity. The results show that the isometric failure mode caused severe PIOs. Unacceptable failure characteristics were reported by all four pilots. The use of offline prediction tools showed the incipience of PIO. It is recommended that specific PIO investigations are undertaken during > the evaluation of active inceptor failure modes.