Stabilizing pylon whirl flutter on a tilt-rotor aircraft

The pylon whirl flutter speed of a tilt-rotor aircraft is increased by incorporating a multipleinput multiple-output controller. Pylon whirl flutter is modeled with a semispan wing and a three-bladed proprotor. The semispan wing has beamwise bending, chordwise bending, and torsion motion. The blades are rigid and undergo flap and lag motions. Aerodynamic loads of the wing and the proprotor are obtained from quasi-steady strip theory. Flap and lag motions are shown to be significant. The controller is a linear quadratic regulator of the uncoupled, unstable, modal variables. To reduce the influence of external disturbances and measurement noise, the modal variables are estimated with a Kalman-Bucy filter. An example shows feedback of vertical wing motion can increase the stability speed of the Bell XV-15 wind tunnel model by twenty percent.