Active Load Control of an Articulated Composite Rotor Blade via Dual Trailing Edge Flaps

Abstract

A new active load control method for blade bending moment reduction is introduced and evaluated via simulation. The concept involves straightening the blade by introducing dual trailing edge flaps in a conventional articulated rotor blade. An aeroelastic model is developed for a helicopter composite rotor with trailing edge flaps, and the rotor blade airloads are calculated using quasisteady blade element aerodynamics. Classical incompressible theory is employed to predict the incremental trailing edge flap airloads. The objective function, which includes vibratory hub loads, bending moment harmonics and active flap control inputs, is minimized by an integrated optimal control/optimization process. A numerical simulation has been performed for the steady-state forward flight of advance ratio 0.35. It is demonstrated that through straightening the rotor blade, which mimics the behavior of a rigid blade, both the bending moments and vibratory hub loads can be significantly reduced. The proposed active load control method with 1/rev control input can reduce the flapwise bending moment by 32% and the vibratory hub loads by 57%, simultaneously, without a significant change of trim condition. Hybrid design yields a 25% reduction of the required flap deflection when compared to the pure active control.