Stability Analysis of Whirl Flutter in a Nonlinear Gimballed Rotor-Nacelle System

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Whirl flutter is an aeroelastic instability that affects propellers/rotors and the aircraft on which they are mounted. The complexity of its behaviour and analysis increases significantly with the addition of nonlinear effects. With their long and flexible rotor blades, tiltrotor aircraft are particularly susceptible. This paper investigates the impact of structural nonlinearity on the whirl flutter stability of a basic gimballed rotor-nacelle model, compared to a baseline linear stiffness version. A 9-DoF model with quasi-steady aerodynamics and blades that can move both cyclically and collectively in both flapping and lead-lag motions was adopted from existing literature. The nonlinearities investigated in this paper are cubic and quintic softening and hardening introduced to the gimbal flapping stiffness. The investigation is conducted through a combination of bifurcation and eigenvalue analyses, supplemented by time simulations. In some cases, the nonlinearities are shown to cause whirl flutter behaviour to exist in parameter value regions that are predicted to be stable by linear analysis. This impact is fully captured in the redrawn system stability boundary.
Original languageEnglish
Title of host publicationProceedings of the 75th Forum of the Vertical Flight Society
Place of PublicationPhiladelphia, Pennsylvania
PublisherVertical Flight Society
Number of pages16
Publication statusPublished - 7 Jun 2019
EventVertical Flight Society's 75th Annual Forum and Technology Display - Philadelphia, United States
Duration: 13 May 201916 May 2019

Publication series

NameAnnual Forum Proceedings
ISSN (Print)1552-2938


ConferenceVertical Flight Society's 75th Annual Forum and Technology Display
Country/TerritoryUnited States


  • Whirl flutter
  • gimballed rotor
  • Stability
  • Bifurcation analysis
  • continuation method


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