Aerodynamic active control for EF-2000 fin buffet load alleviation

This paper presents results of an experimental study to assess the use of an active auxiliary rudder in reducing vertical tail buffeting of single-fin high-performance fighter aircraft. Low-speed wind tunnel tests are performed on a 1/15-scale EF^2000 model. A specific fin model has been fabricated equipped with a computer-controlled auxiliary rudder providing harmonic oscillations at varying frequency and maximum deflection angle of 5 degree. The vertical tail is instrumented to measure the unsteady surface pressures, the fin tip accelerations and the auxiliary rudder moment. For open-loop rudder oscillations the surface pressure fluctuations increase with increasing frequency and deflection angle. Consequently, the root-mean-square (rms) values of the buffet pressures are shifted to higher levels even at high incidences. This indicates that for closed-loop conditions the rms fin surface pressures may be reduced by as much as 18 percent. The rudder moment does not drop over the regarded incidence range (0°÷31°), thus proving the effectiveness of the auxiliary rudder concept. Single-input single-output control laws are applied to alleviate vibrations (buffeting) in the first fin bending mode. Controller efficiency and stability parameters are evaluated by numerical simulations with the fin as a single degree-of-freedom system. The tests show that with active control the power spectral density of the fin tip accelerations at the first bending mode can be reduced by as much as 60 percent up to angles of attack of 31 degree.