Improving Tiltrotor Whirl-Mode Stability with Rotor Design Variations
Abstract
Rotor design changes intended to improve tiltrotor whirl-flutter stability margins were analyzed. A baseline analytical model similar to the XV-15 was established, and then a thinner, composite wing was designed to be representative of a high-speed tiltrotor. While the thinner wing has lower drag, it also has lower stiffness, reducing whirl-flutter stability. The rotor blade design was modified to increase the stability speed margin for the thin-wing design. Modest amounts of blade sweep starting at 80% radius created large increases in the stability boundary. Increased control-system pitch stiffness also improved stability. 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 rotor loads in helicopter and airplane configuration showed only minor increases in loads.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2000
- Accession Number
- ADA519432
Entities
People
- C. W. Acree Jr.
- R. J. Peyran
- Wayne R. Johnson
Organizations
- National Aeronautics and Space Administration