FUSELAGE STATE-FEEDBACK FOR AEROMECHANICAL STABILITY AUGMENTATION OF A BEARINGLESS MAIN ROTOR

An experimental program has been conducted to demonstrate the benefits of applying active rotor control techniques to improve aeromechanical stability characteristics of a Bearingless Main Rotor (BMR) model, Th e model is based on a four-bladed concept with a flexure, between the hub and each blade, which accommodates flatwise, edgewise and torsiona l (pitch) motions, The flexure is enclosed by a torsionally stiff cuff that is cantilevered to the blade/flexure joint at its outboard end a nd shear-restrained to the flexure at its inboard end, The shear-restr aint includes an elastomeric damper to stabilize edgewise motion. The model was tested in hover over a range of rotor thrust and rotational speed conditions. Numerous data were acquired for uncontrolled or open -loop and closed-loop feedback control, with the latter using fuselage state parameter feedback. The state parameters included fuselage pylo n position and velocity, applied individually in both pitch and roll d irections. The control approach used a fixed-gain controller which tra nsformed the fuselage state measurements into swashplate cyclic comman ds. The results in this paper show that aeromechanical stability margi ns can be greatly improved, and instabilities occurring within the ope rating envelope eliminated, by the application of active control.