Whirl Flutter Test of Swept-Tip Tiltrotor Blades

Abstract

The first whirl flutter test of the Maryland Tiltrotor Rig (MTR) was recently completed in the Naval Surface Warfare Center Carderock Division (NSWCCD) 8- by 10-ft large subsonic wind tunnel. The MTR is a Froude-scaled, 4.75 ftdiameter, threebladed, semispan, floor-mounted, optionally powered, flutter rig. This paper focuses on the swept-tip blades developed for this test. The swept-tip begins at 80%R and sweeps aft 20° to alleviate whirl flutter. Whirl flutter testing was performed in four con gurations for both blade geometries. The frequency and damping of the wing beam and chord bending were collected at wind speeds up to 100 kt. This paper directly compares whirl utter results between the straight and swept-tip blades and demonstrates higher wing chord damping using swept-tip blades in freewheel conditions, even at lower flight speeds.