CORRELATION OF FIN BUFFET PRESSURES ON AN F/A-18 WITH SCALED WIND-TUNNEL MEASUREMENTS

Buffeting is an aeroelastic phenomenon occurring at high angles of attack that plagues high performance aircraft, especially those with twin vertical tails. Previous wind-tunnel and flight tests were conducted to characterize the buffet loads on the vertical tails by measuring surface pressures, bending moments, and accelerations. Following these tests, buffeting responses were computed using the measured buffet pressures and compared to the measured buffeting responses. The calculated results did not match the measured data because the assumed spatial correlation of the buffet pressures was not correct. A better understanding of the partial (spatial) correlation of the differential buffet pressures on the tail was necessary to improve the buffeting predictions. Several wind-tunnel investigations were conducted for this purpose. When compared, the results of these tests show that the partial correlation scales with flight conditions. One of the remaining questions is whether the windtunnel data is consistent with flight data. Presented herein, cross-spectra and coherence functions calculated from pressures that were measured on the High Alpha Research Vehicle (HARV) indicate that the partial correlation of the buffet pressures in flight agrees with the partial correlation observed in the wind tunnel. Background For high performance aircraft at high angles of attack, vortices emanating from wing/fuselage leading edge extensions (LEX) burst at some flight conditions, immersing the vertical tails in their wake, as shown in Figure 1 for the F/A-18. The resulting buffeting of the vertical tails are a concern from airframe fatigue and maintenance points of view. A summary of previous wind-tunnel 1-