SMALL-SCALE ROTOR EXPERIMENTS WITH ON-BLADE ELEVONS TO REDUCE BLADE VIBRATORY LOADS IN FORWARD FLIGHT

A low-tip-speed 7.5-ft diameter hingeless rotor with one on-blade elevon control surface on each of the two blades was wind tunnel tested for advance ratios from 0.1 to 0.3 at two rotor speeds (450 and 760 RPM) and at low to moderate thrust coefficients. The purpose of this study was to investigate dynamic response characteristics and to determine the effectiveness of on-blade elevon control to reduce blade vibratory loads. Dynamic response characteristics were investigated at high advance ratios up to 0.6 for non-thrusting conditions. All elevon excitations were open loop. Primary measurements included elevon deflection and blade root flap bending and torsion moments. The tests successfully demonstrated the effectiveness of on-blade elevon controls for significantly reducing or canceling individual 3, 4, and 5/rev harmonic blade vibratory flap bending moments at representative forward flight advance ratios. Elevon effectiveness determined from complementary discrete frequency and continuous frequency response function measurements affords a very useful means of evaluating the potential influence of tailoring structural dynamic and aeroelastic effects to reduce vibratory loads.