Active Tiltrotor Whirl-Flutter Stability Augmentation Using Wing-Flaperon and Swash-plate Actuation

The effectiveness of active control employed via actuation of a wing trailing edge flap (wing-flaperon) and the rotor swashplate is examined for improving the whirl-flutter stability characteristics of the semi-span model of the XV-15 tiltrotor, over a wide range of conditions including variations in forward airspeed and operating RPM. Limits are enforced on the magnitude of control gains utilized based on assumptions on the maximum allowable flaperon/swashplate deflection and the expected magnitudes of disturbances experienced by the model. Full-state feedback, linear quadratic regulator (LQR) optimal controllers that are scheduled with respect to airspeed and RPM show significant improvement in the stability characteristics. However, constant-gain controllers and output-feedback controllers are appealing due to their simplicity; and the performance of such controllers (designed using a moving-point optimization scheme) are examined in terms of their robustness to variations in RPM and airspeed. Results show that for wing-flaperon actuation, constant gain (non-scheduled) full-state feedback controllers are robust over a fairly wide RPM range and increase critical whirl flutter speeds by as much as 90 knots at the cruise RPM, over baseline. Using output feedback of wing-states is as effective as fullstate feedback. For swashplate actuation constant-gain, full-state feedback controllers are robust over an even wider RPM range and increase the whirl flutter speed by as much as 75 knots at the cruise RPM. However, with swashplate actuation, feedback based on wingstates alone shows a reduced robustness to variation in RPM, suggesting that measurement or estimation of certain rotor states might be necessary. However, if the swashplate actuation limits are increased from a nominal value of ± 1 deg to ± 2 deg, control based on wing-state feedback is robust to large variations in RPM (over a range including both the cruise and the hover RPM of the XV-15).

[1]  W Nixon Mark,et al.  An Experimental Evaluation of Generalized Predictive Control for Tiltrotor Aeroelastic Stability Augmentation in Airplane Mode of Flight , 2001 .

[2]  David J. Piatak,et al.  Technical Note: Hover Test of a Soft-Inplane Gimballed Tiltrotor Model , 2003 .

[3]  Farhan Gandhi,et al.  Design optimization for improved tiltrotor whirl flutter stability , 2007 .

[4]  Farhan Gandhi,et al.  Tiltrotor Whirl Flutter Alleviation Using Actively Controlled Wing Flaperons , 2004 .

[5]  W Nixon Mark,et al.  Aeroelastic Stability of a Soft-Inplane Gimballed Tiltrotor Model in Hover , 2001 .

[6]  Anna Kathleen Tyler Howard.  The Aeromechanical Stability of Soft-Inplane Tiltrotors , 2001 .

[7]  Eric L. Hathaway,et al.  ACTIVE AND PASSIVE TECHNIQUES FOR TILTROTOR AEROELASTIC STABILITY AUGMENTATION , 2005 .

[8]  Ken-Ichi Nasu.  Tilt-rotor flutter control in cruise flight , 1986 .

[9]  David J. Piatak,et al.  Aeroelastic stability of a soft-inplane gimballed tiltrotor model in hover , 2001 .

[10]  W Nixon Mark,et al.  Tiltrotor Vibration Reduction Through Higher Harmonic Control , 1997 .

[11]  Farhan Gandhi,et al.  Optimized Aeroelastic Couplings for Alleviation of Helicopter Ground Resonance , 1997 .

[12]  Johannes M. Vanaken.  Alleviation of whirl-flutter on a joined-wing tilt-rotor aircraft configuration using active controls , 1991 .

[13]  Farhan Gandhi,et al.  Concurrent Optimization Of Aeroelastic Couplings And Rotor Stiffness For The Alleviation Of Helicopter Aeromechanical Instability , 1999 .

[14]  J. M. Van Aken,et al.  Alleviation of Whirl-Flutter on Tilt-Rotor Aircraft Using Active Controls , 1991 .

[15]  G Kvaternik Raymond,et al.  Exploratory Studies in Generalized Predictive Control for Active Aeroelastic Control of Tiltrotor Aircraft , 2000 .

[16]  Farhan Gandhi,et al.  Modeling Refinements in Simple Tiltrotor Whirl Flutter Analyses , 2003 .

[17]  W. Johnson.  Optimal control alleviation of tilting proprotor gust response , 1977 .

[18]  David J. Piatak,et al.  Aeroelastic Stability of a Four-Bladed Semi-Articulated Soft-Inplane Tiltrotor Model , 2003 .

[19]  Inderjit Chopra,et al.  Stabilizing pylon whirl flutter on a tilt-rotor aircraft , 1991 .