T-tail transonic flutter wind tunnel test part 1: Sealing system design and model testing

This paper presents the test setup improvements and the experimental results of the recent T-tail transonic flutter test performed at ONERA S2MA pressurized wind tunnel in November 2022. The test campaign is the culmination of flutter investigations initiated in Clean Sky 1’s “Smart Fixed Wing Aircraft Integrated Technology Demonstrator” program where U-tail configurations were studied [1]. The current presented work was performed in the frame of Clean Sky 2’s Airframe ITD program in partnership with Dassault Aviation. First, the paper presents the sealing system developed to improve the test setup and tackle issues encountered in the previous 2016 test campaign. Air leakage from the fuselage at the root of the tail wing model led to unwanted aerodynamic effects, and asked for more post-processing efforts to be taken into account. Efforts were made to develop a sealing system solution involving labyrinth sealing and fine gap tuning during dynamic displacements of the test setup while keeping a healthy model dynamic behavior. The heavily instrumented model allowed the validation of the sealing solution during the wind tunnel tests without any negative impact on the aeroelastic characteristics of the T-tail model. Then, the wind tunnel test and its associated experimental results and observations over four geometrical configurations of T-tail model are presented, with variations of yaw and dihedral angle of the horizontal stabilizer. Both steady and unsteady aerodynamics were investigated, including Mach number variations (from M=0.7 to M=0.925), forced pitch motion excitation frequency, angle of attack, and stagnation pressure variations. The remotely configurable test setup and safety system allowed a controlled investigation of aeroelastic instabilities apparition beyond flutter onset. The extensive database measured helped understanding aeroelastic instabilities occurring on a T-tail model, and permitted to confront numerical capabilities to predict flutter instabilities in transonic regimes. The numerical restitutions using high-fidelity CFD tools are presented in a companion paper [2].