A.K. Padthe, P.P. Friedmann, M. Lopez, J.V.R. Prasad

Linearized time-periodic models are extracted from a high fidelity comprehensive nonlinear helicopter model at a low-speed descending flight as well as a cruise condition. A Fourier expansion based model reduction method is used to generate linearized time-invariant models from the time-periodic system. The linearized models, intended for studies examining the interaction between on-blade control and the primary flight control system, are very large in size with a few thousand states each. Therefore, a truncation method based on Hankel singular values is used to reduce the size of the LTI models. The reduced-order LTI models are then verified against the nonlinear model by comparing the hub load responses to an open-loop flap deflection. However, on-blade control is usually implemented in closed-loop mode, therefore, the reduced-order LTI models are verified for closed-loop performance fidelity. The higher harmonic controller is used with the 2/rev-5/rev harmonic components of the flap deflection as the control input and vibratory hub loads are the output. Closed-loop performance of the full-order LTI model, reduced-order LTI model, and the nonlinear model is compared at both the low-speed descending flight and the cruise flight conditions. The flap deflection histories and the vibratory loads predicted using the full-order and the reduced-order LTI models agree very well at both flight conditions when the flap deflection is limited to be less than 2°. The results show that the reduced-order LTI models capture all the relevant dynamics and are suitable for studying closed-loop on-blade vibration control and its interactions with the primary flight control system, as long as the dynamic stall effects are not significant.

41th European Rotorcraft Forum 2015

Conference Paper

englisch

21,0 x 29,7 cm, 21 Seiten

DGLR-Bericht, 2016, 2016-01, 41st European Rotorcraft Forum 2015; S.-; 2016; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aerodynamic stalling;aircraft control;controllers;deflection;feedback control;flapping;flaps (control surfaces);flight conditions;flight control;helicopters;loads (forces);low speed;nonlinearity;vibration damping;vibratory loads

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2016