Application of a new compressible time domain aerodynamic model to vibration reduction in helicopters using an actively controlled flap

This paper describes an aeroelastic simulation of a fully elastic hingeless helicopter rotor incorporating a partial span trailing edge flap. Aerodyna mic loads are provided by a new, two-dimensional, compressible flow unstead y aerodynamic model developed for an airfoil/flap combination and unsteady freestream. Aerodynamic toads are approximated in the frequency domain as r ational functions of the Laplace variable using a least squares fit to osci llatory response data. Transformation to the time domain yields a state spa ce model for the unsteady aerodynamic loads. Frequency domain toads are obt ained using a two dimensional doublet-lattice analysis. Vibration control s tudies using the actively controlled flap are presented, with comparisons t o results obtained using quasisteady aerodynamics.