Estimation of handling quality parameters of a rotorcraft using open-loop linearized and nonlinear flight dynamic models

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Sakthivel, T.
Venkatesan, C.
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Flight dynamic analysis and estimation of handling quality parameters have become important aspects in the design and development of helicopters. This paper presents a detailed analysis of the procedure for estimating the handling quality parameters such as quickness parameter, bandwidth and phase delay. The flight dynamic model used in this study considers rigid flap model for blade structural dynamics, three states dynamic inflow for inflow calculation and modified ONERA dynamic stall model for sectional aerodynamic loads calculation. The applicability of open loop linearized (uncoupled, and coupled) and nonlinear flight dynamic models in estimating the handling quality parameters is studied. For linearized models, only pulse input is used, whereas in the nonlinear model, two different types of input, namely pulse and step inputs, are used to estimate the attitude quickness parameters. The bandwidth and phase delay are calculated from the frequency responses of helicopter attitude in pitch and roll axes, which are obtained from the time response of nonlinear flight dynamic model for the harmonic excitation of cyclic pitch input. The results show that the attitude quickness parameter depends on the duration of input pulse and the nonlinear open system provides attitude quickness parameter which is different from that of the linearised system. In addition, it is noted that linearized flight dynamic models (8x8) cannot be used for bandwidthphase delay calculations, due to their lower order nature.