It was found using wind-tunnel tests of airplanes with T empennage that the critical speed of antisymmetric flutter (based on composition of bending and torsional oscillations of the vertical tail) has an abnormally strong dependence on stabilizer deflections and angle of attack. This specific kind of antisymmetric flutter is characterized by relatively large amplitudes of oscillations of the stabilizer in its plane. Additional work of the induced drag forces on the in-plane component of oscillations might explain the nature of this kind of flutter. The numerical method for flutter analysis is described, which takes into account the effect of angles of attack and sideslip and aerodynamic control angles on flutter critical parameters. The method is based on a modification of the vortex lattice method and allows for induced drag when computing generalized aerodynamic forces. Numerical results for the flutter critical speed compare well with test data for a dynamically similar model of the civil airplane T-shaped empennage.
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