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

Michael Jones, Miles Barnett
2019 AIAA Scitech 2019 Forum   unpublished
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
more » ... 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. Nomenclature A G = Aggression, deg/s 2 F θ1s = Pilot control force input, longitudinal axis, Ṅ F θ1s = Force rate of change, longitudinal axis, N/s H sF = Ratio of vehicle rotational rate to pilot control input force, deg/s/N K = Control input rate limit, deg/s S = Power spectral density, − t = Time, s t 1 , t 2 = Start and end time of current oscillation cycle, s t 3 = Difference between last vehicle rate output peak and last pilot input peak, s q = Vehicle pitch rate, deg/s x L = Percentage change in control input, % Φ = Phase distortion, deg δ c = Control input displacement from trim, % δ θ1s = Control displacement, longitudinal axis, % θ 1s = Swashplate attitude input, longitudinal axis, deg τ s = Added time delay, control input channel, ms τ pθ = Vehicle phase delay, ms ω BW θ = Longitudinal vehicle bandwidth, deg/s ω G = Power frequency, −
doi:10.2514/6.2019-0104 fatcat:yayikgbigjba7f3edlbo45np34