EXPERIMENTAL INVESTIGATION OF NONLINEAR AERODYNAMIC DAMPING OF PARTIAL AIRPLANE ASSEMBLY

Low speed wind tunnel testing of partial assemblies of aircraft fuselage and its horizontal tail surfaces are performed using a special dynamic stability balance. Experiments were aimed for investigating the effects of airplane aerodynamic components on the nonlinear behaviour of pitch damping in a range of moderate angles of attack. The function of balance is based on the method of forced pitch oscillations of geometrically similar model in straight parallel air flow. Damping coefficients are determined from analysis of motion records. Measurements are performed in range of flow velocities at different oscillation frequencies. Obtai-ned results proved linear dependence of damping derivative on flow velo-city, and independence of the nondimensional damping in pitch derivate on the oscillations nondimensional frequency. Strong nonlinearity in the dependence with angle of attack is observed, which is related to the creation and seperation of vortices on fuselage sides. The research pro-ved strong favourable contribution of quasi-slender fuselages to the nonlinear character of aerodynamic forces of their aircraft assemblies.