Effect of Blade Tip Configurations on the Performance and Vibration of a Lift-Offset Coaxial Rotor

Abstract

This present study investigates the effect of blade tip configurations, such as the sweepback angle and anhedral angle, on the performance and hub vibratory loads for the lift-offset coaxial rotor of a 30,000-pound-class high-speed long-range utility helicopter. The rotorcraft comprehensive analysis code, CAMRAD II, is utilized to conduct the performance and hub vibratory load analyses for the present lift-offset coaxial rotor. The total rotor thrust, torque, and individual rotor’s hub pitch moment and hub roll moment are considered the trim targets. The general properties for the lift-offset coaxial rotor are designed from the X2TD, S-97 Raider, and SB > 1 Defiant, which are lift-offset compound helicopters. The rotor performance and hub vibratory loads are studied with the various blade tip configurations including the sweepback angle and anhedral angle. The rotor power when the rotor blade tip considers only the sweepback angle (20°) is lower than the baseline rotor model by 41.25% at 170 knots. The maximum rotor effective lift-to-drag ratio (L/De) for the lift-offset coaxial rotor using only the sweepback angle and the rotor with both sweepback (20°) and anhedral angles (10°) at 170 knots increase by 10.82% and 5.02%, respectively, compared with the baseline rotor model without both sweepback and anhedral angles. The vibration index (VI) for the rotor with only the sweepback angle is higher than that for the baseline rotor model without both sweepback and anhedral angles by 37.14%. Furthermore, when the rotor blade tip has the anhedral angle, the magnitude of the Blade Vortex Interaction (BVI) decreases compared with the rotor without the sweepback and anhedral angles.