Aerodynamic damping and stiffness determination for aircraft wing flutter speed analysis

The modeling of aircraft wing flutter using statically determined aerodynamic derivatives may not accurately represent the actual aeroelastic system. This paper presents an experimental method for estimating the transient aerodynamic derivatives relative to the airspeed for four 3D airfoil models. The transient aerodynamic derivatives are used to represent the aerodynamic damping and stiffness in aeroelastic equation of motion to determine the flutter speed of the models. An oscillating dynamic aeroelastic test rig with constraint to pitch motion is developed for the wind tunnel test. A set of wing models with NACA 0010, NACA 0012, NACA 0014 and NACA 0018 airfoils respectively, with a wing span of 0.36m and chord of 0.16m (i.e. AR=2.25) are tested in UTM Low Speed Tunnel with the reduced frequencies range from 0.04 to 0.4. From the experiment, the time responses of the wing models during wind-off and wind-on conditions allow the transient aerodynamic damping and stiffness of the wing aeroelastic system to be determined. By varying the stiffness of the mechanical springs attached to the test rig, the effects of dynamically determined aerodynamic damping and stiffness on aircraft wing flutter speed prediction are observed. It is discovered that the aeroelastic equation of motion gives more realistic flutter speed estimation of the models with the inclusion of aerodynamic damping and stiffness with respect to the airspeed which can not be determined from static test. The differences between the computed wing flutter speeds and the referred wing flutter speeds show that this method gives better estimation of aircraft wing flutter speed for both thin and thick airfoils compared to Theodorsen’s method