22nd Congress of International Council of the Aeronautical Sciences, Harrogate, UK, 28 August - 1st September, 2000
Paper ICAS 2000-3.10.2

FIN BUFFET LOAD ALLEVIATION USING AN ACTIVELY CONTROLLED AUXILIARY RUDDER AT SIDESLIP

C. Breitsamter, B. Laschka
Lehrstuhl für Fluidmechanik, Technische Universität München, Germany

Keywords: active control, fin buffeting, vortical/unsteady flows, high angle of attack

This investigation focuses on the efficiency of an active auxiliary rudder system in diminishing vertical tail buffeting. Low–speed wind tunnel tests are conducted on a 1/15–scale EF– 2000 model representing a single–fin high– agility fighter aircraft. A specific fin model has been manufactured fitted with a computer– controlled auxiliary rudder providing harmonic oscillations. The fin is instrumented to measure the unsteady surface pressures, the fin tip accelerations and the auxiliary rudder moment. For defined rudder oscillations the surface pressure fluctuations increase with increasing frequency and deflection angle. Consequently, the root–mean–square surface pressures are shifted to higher levels even at high incidences and sideslip. It indicates that for closed–loop conditions the buffet pressures may be reduced by as much as 18 percent. Also, the rudder moment does not decrease over the incidence range regarded (031 deg), thus substantiating the effectiveness of the auxiliary rudder concept. Single– input single–output control laws are employed to reduce buffeting in the first fin bending and torsion mode. The tests demonstrate that with active control fin tip acceleration spectral density peaks at the frequencies of the first eigenmodes can be reduced by as much as 60 percent up to incidences of 31 degree and even at sideslip of 5 degree.

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