Full-Scale Prop-Rotor Stability Tests on the XV3 at High Advance Ratios

Tests in the 40-by-80 foot wind tunnel were made at airspeeds from 40 to 195 knots. The aircraft was mounted with and without roll freedom. Rotor pylon configuration variables included the following: swashplate stabilization by mechanically coupling the swashplate to the wing or fuselage; pylon restraint stiffness and damping; hub restraint; and delta-three combined with swashplate retardation. Time histories were recorded of pylon motions and rotor loads following pulse-type excitations of the pylon. It was found that damping of the low frequency whirl mode increased with swashplate stabilization, pylon stiffness, and hub restraint.