Flutter Modeling and Suppression for a Strut-Braced Wing

Abstract

High aspect-ratio aircraft require different design modeling from those with traditional moderate aspect ratios. High aspect-ratio aircraft are generally more flexible structures than the traditional wing; therefore, they require modeling methods capable of handling a flexible structure even at the preliminary design stage. An investigation of flutter properties for a two-dimensional airfoil was conducted to approximate flutter characteristics for thin, high aspect ratio wings in application to the Truss-Braced Wing project at Virginia Tech. Assumptions are made to maintain linearity of the model for the purposes of this study. A three degree-of-freedom model was developed from the standard two-degree-of-freedom model to investigate airfoil parameters that affect flutter in thin, high aspect ratio wings. The study shows that these model parameters will have a negative effect on the flutter velocity, frequency, and mode shapes under certain conditions. A simple beam model is developed to study a three dimensional wing system; this study focuses on a strut-braced wing configuration optimized for minimum take-off gross weight. Flutter suppression methods based on ballast mass placement are investigated for the three-dimension strut-braced wing configuration. Sensitivity studies for ballast mass and acceleration based active control methods are shown. * Nomenclature I xx,zz = Moment of inertia K = Stiffness K h,g,α = Spring stiffness L = Aerodynamic lift M = Aerodynamic moment M = Ballast mass P, Q, R = External loads Q i = Generalized force S x,z = Static moment T = Kinetic energy U = Flight velocity U F = Flutter velocity V = Potential energy α = Pitching torsion displacement, also angle of attack (positive nose-up) ω = Frequency ω F = Flutter frequency ρ = Density τ = Non-dimensional time a h = Non-dimensional distance from the half-chord to the elastic axis b = Semi-chord g = Horizontal bending displacement (positive aft of the elastic axis) h = Vertical bending displacement (positive downward from the elastic axis) k = Reduced frequency m = Airfoil mass m = Mass q i = Generalized coordinate r = Displacement u = Horizontal displacement component w = Vertical displacement component x = Distance in horizontal direction, positive aft z = Distance in vertical direction, positive down 2 of 23 Downloaded by CARLETON UNIVERSITY LIBRARY on November 28, 2014 | http://arc.aiaa.org |

Challenges, Ideas, and Innovations of Joined-Wing Configurations: A Concept from the Past, an Opportunity for the Future

“…Reference [46] analyzed a two-dimensional airfoil modeling of a high aspect-ratio wing. The model was based on Theodorsen function aerodynamics.…”