Friction, Freeplay and Flutter of Manually Controlled Aircraft

The effect of nonlinear friction and freeplay in the control system on flut- ter is investigated for the case of light aircraft with manually operated control surfaces. A standard linear modal subspace model of the aeroelastic system is extended with nonlinear terms, so that time-domain simulations can be per- formed. Furthermore, the harmonic balance method is employed to obtain a frequency-domain formulation, which allows a convenient, though approxi- mate, computation of the stability boundary. Comparison with time-domain analyses for the case of a full aircraft configuration show that typical magni- tudes of hinge friction can stabilize oscillations with small displacement am- plitudes, while large amplitude motion remains unstable. Harmonic balance methods can be used to determine if such a behavior is present, but time- domain computations are necessary to evaluate the response of the system to a given excitation.QC 2012020