T-tail Flutter: Potential-Flow Modelling and Experimental Validation

This paper focuses on the benchmarking of three dfferent methodologies based on potential-flow aerodynamics for T-tail flutter prediction, validating them against wind-tunnel measurements and investigating scenarios where lesser T-tail ffects drive the stability behaviour. In order to overcome the inability of the standard doublet lattice method to predict T-tail flutter, three alternatives are considered: (i) incorporation of supplementary T-tail effects as additional terms in the flutter equations; (ii) a generalisation of the boundary conditions and air loads calculation on the double lattice; and (iii) a linearisation of the unsteady vortex lattice method with arbitrary kinematics. Comparison with experimental results evidences that all three models are consistent and accurate for the subsonic aeroelasticity of realistic T-tail cofigurations. The models are then exercised for an empennage with unconventional characteristics, in which the fin natural frequency in torsion is smaller than in bending. It will be shown that in this case ffects that are generally second-order play a major role, and lead to drastically distinct quantitative and even qualitative flutter curves. The paper concludes with flight test results of the Airbus A400M, which complements the scarce literature on T-tail aircraft in flight.