Performance and Loads of a Lift Offset Rotor: Hover and Wind Tunnel Testing

Abstract

The results of hover and wind tunnel tests of a reduced-scale, model rotor operating with lift offset are presented. The two-bladed rotor had a diameter of 2.03 m and constant cross section untwisted blades. Measurements include steady and vibratory hub loads, as well as control angles and pushrod loads. The rotor system was tested in hover and at advance ratios between 0.21 and 0.53, at collective pitches ranging from 3° to 10°, achieving blade loadings in excess of 0.10. At each forward flight operating condition, sweeps of lift offset up to 15% were performed. In forward flight, the rotor effective lift-to-drag ratio was found to increase with increasing advance ratio and lift offset, with a maximum increase of 40% compared to the zero lift offset case. Vibratory loads increased with advance ratio, with the largest loads in the two- and four-per-revolution harmonics. Lift offset is shown to modify vibratory hub forces and moments transmitted to the fixed frame, increasing vibratory rolling and pitching moments while decreasing vibratory thrust and torque.