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

摘要

This investigation focuses on the efficiency ofrnan active auxiliary rudder system in diminishingrnvertical tail buffeting. Low–speed wind tunnelrntests are conducted on a 1/15–scale EF–rn2000 model representing a single–fin high–rnagility fighter aircraft. A specific fin modelrnhas been manufactured fitted with a computer–rncontrolled auxiliary rudder providing harmonicrnoscillations. The fin is instrumented to measurernthe unsteady surface pressures, the fin tiprnaccelerations and the auxiliary rudder moment.rnFor defined rudder oscillations the surface pressurernfluctuations increase with increasing frequencyrnand deflection angle. Consequently, thernroot–mean–square surface pressures are shiftedrnto higher levels even at high incidences andrnsideslip. It indicates that for closed–loop conditionsrnthe buffet pressures may be reduced by asrnmuch as 18 percent. Also, the rudder momentrndoes not decrease over the incidence range regardedrn(0u000431 deg), thus substantiating the effectivenessrnof the auxiliary rudder concept. Single–rninput single–output control laws are employed tornreduce buffeting in the first fin bending and torsionrnmode. The tests demonstrate that with activerncontrol fin tip acceleration spectral densityrnpeaks at the frequencies of the first eigenmodes can be reduced by as much as 60 percent up tornincidences of 31 degree and even at sideslip ofrn5 degree.