Dependence of Integrated Vertical-Tail Buffet Loads For F/A-18 on Sensor Density 941140

The unsteady pressures acting on the vertical tails of a full-scale F/A-18 fighter aircraft were studied to gain a better understanding of tail-buffet loads that frequently occur on fighter aircraft when operating at high angles-of--attack. Data for the study were acquired during two test entries in the 80-by 120-Foot Wind Tunnel wherein the aircraft was tested at wind speeds up to 100 knots and at angles of attack from +20° to +40°. For the purposes of this paper, the tests differed only in that, during the first wind-tunnel entry, the pressure transducers were more sparsely spaced and covered less of the fin than during the second entry. After the analysis methods for the unsteady aerodynamic pressures and loads are described, the results for the time-averaged, power-spectral analysis are presented for the tail-fin bending moments. Comparison of the results obtained in the two wind tunnel tests clearly show that an accurate determination of the spectral resolution and the tail fin bending moments requires spacings between pressure sensors that are at least as small as those used in the second test. Since the aircraft was equipped with a removable leading-edge extension (LEX) fence to reduce tail-buffet loads, the effect of sensor spacing on spectral resolution and tail-fin bending moments is also demonstrated for that configuration.