Development and Whirl Flutter Test of the Maryland Tiltrotor Rig

The first whirl flutter test of the Maryland Tiltrotor Rig (MTR) was recently completed in the Naval Surface Warfare Center Carderock Division 2.44 m by 3.05 m (8- by 10-ft) large subsonic wind tunnel. The MTR is a 1.45 m (4.75-ft) diameter, three-bladed, semispan, floor-mounted, optionally powered, flutter rig. This paper describes the major features of the MTR and the results obtained from the first successful flutter tests. Parametric variations of rig features include wing profile on and off, gimbal free and gimbal locked hub, powered and freewheeling rotor, and straight and swept-tip blades. For the freewheeling rotor condition, the rotor speed is trimmed to 1050 RPM by setting blade collective. The gimbal is trimmed to zero first harmonic flapping by setting blade cyclics. Model configurations were tested up to 100 kt windspeed. The model was excited by oscillating the swashplate at the wing-pylon natural frequencies. Eight speed sweeps were carried out to acquire frequency and damping data on different model configurations. Frequency and damping of the wing beam and chord modes were extracted using the moving-block method.