Rotor Design Options for Improving XV-15 Whirl-Flutter Stability Margins

Abstract : Rotor design changes intended to improve tiltrotor whirl-flutter stability margins were analyzed. A baseline analytical model of the XV-15 was established, and then a thinner, composite wing was designed to be representative of a high-speed tiltrotor. The rotor blade design was modified to increase the stability speed margin for the thin-wing design. Small rearward offsets of the aerodynamic-center locus with respect to the blade elastic axis created large increases in the stability boundary. The effect was strongest for offsets at the outboard part of the blade, where an offset of the aerodynamic center by 10% of tip chord improved the stability margin by over 100 knots. Forward offsets of the blade center of gravity had similar but less pronounced effects. Equivalent results were seen for swept-tip blades. Appropriate combinations of sweep and pitch stiffness completely eliminated whirl flutter within the speed range examined; alternatively, they allowed large increases in pitch-flap coupling (delta-three) for a given stability margin. A limited investigation of the rotor loads in helicopter and airplane configuration showed only minor increases in loads.

[1]  Edwin W. Aiken,et al.  Improving Tiltrotor Whirl-Mode Stability with Rotor Design Variations , 2000 .

[2]  Inderjit Chopra,et al.  Aeroelastic Analysis of Advanced Geometry Tiltrotor Aircraft , 1995 .

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

[4]  D P Chappell,et al.  2107. Methodology for Estimating Wing Weights for Conceptual Tilt-Rotor and Tilt-Wing Aircraft , 1992 .

[5]  D. C. Dugan,et al.  The History of the XV-15 Tilt Rotor Research Aircraft: From Concept to Flight , 2001 .

[6]  Omri Rand,et al.  The Influence of Composite Induced Couplings on Tiltrotor Whirl Flutter Stability , 1998 .

[7]  Popelka David,et al.  Results of an Aeroelastic Tailoring Study for a Composite Tiltrotor Wing , 1995 .

[8]  T. M. Gaffey,et al.  The stopped-rotor variant of the proprotor VTOL aircraft , 1970 .

[9]  David J. Piatak,et al.  Aeroelastic Tailoring for Stability Augmentation and Performance Enhancements of Tiltrotor Aircraft , 1999 .

[10]  Mark W. Nixon.  Parametric studies for tiltrotor aeroelastic stability in high-speed flight , 1992 .

[11]  Julian Wolkovitch,et al.  Application of the joined wing to tiltrotor aircraft , 1989 .

[12]  Troy M. Gaffey,et al.  The Effect of Positive Pitch-flap Coupling (Negative δ 3 ) on Rotor Blade Motion Stability and Flapping , 1969 .

[13]  Wayne Johnson,et al.  Calculated performance, stability and maneuverability of high-speed tilting-prop-rotor aircraft , 1986 .

[14]  W. Johnson,et al.  CAMRAD - A COMPREHENSIVE ANALYTICAL MODEL OF ROTORCRAFT AERODYNAMICS AND DYNAMICS , 1994 .

[15]  Wayne Johnson,et al.  Rotor Design for Whirl Flutter: An Examination of Options for Improving Tiltrotor Aeroelastic Stability Margins , 1999 .

[16]  Mark W. Nixon,et al.  Parametric Studies for Tiltrotor Aeroelastic Stability in Highspeed Flight , 1993 .