SAE International Flutter Initiation Under Steady - State and Accelerated Free Stream Velocities 2011-01-2785

The motivation for the present investigation of damped motion through energy dissipation due to material properties and bifurcations is to better understand the fundamentals of flutter, with applications to elastic and viscoelastic composite flight and automotive vehicles. The traditional approach to determining flutter in a linear aeroelastic system, such as a wing, is to define flutter as the lowest velocity at which simple harmonic motion first occurs. This legacy definition is demonstrable using a Duncan-Ellis flutter engine that replicates the motions of a pitch-plunge wing. While simple harmonic motion is a useful rule of thumb definition, such a definition does not adequately and sufficiently describe the behavior of the wing before or after flutter. Further, the traditional definition could provide a misleading flutter velocity point. Damped motion is modeled with some modifications to the governing equations of an aeroelastic wing and the analysis reveals that the true flutter point requires an expanded definition. The modifications also reveal that bifurcation of the motion of a linear elastic small deformation wing is possible before any flutter point is reached. Material failures leading to ultimate velocities and structural lifetimes in addition to and independent of flutter velocities are also explored. The analysis and results have immediate applications to flexible composite aerospace lifting surfaces (UAVs, MAVs) and to automotive spoilers (rear wings). Proper analysis of light weight high strength composite lifting surfaces can significantly improve performances.