UNSTEADY PRESSURE AND LOAD MEASUREMENTS ON AN F A-18 VERTICAL FIN/

Tall buffet on a rigid 6% scale model of the F/A-18 was investigated i n the Institute for Aerospace Research 1.5 m trisonic blowdown wind tu nnel. Strain gauges were installed on the port fin to measure normal f orce, root bending and torsion moments. The starboard fin was instrume nted with 24 fast-response transducers on each surface for unsteady pr essure measurements. Static tests at constant angle of attack were per formed to compare the loads and moments from the strain-gauged fin wit h those determined from pressure measurements. Pitch oscillations of t he model were carried out at low frequencies. The mean angle of attack , amplitude of oscillation, and Mach number were varied to note the ef fects of delay in LEX vortex burst on the vertical fin buffet loads. T he envelopes of the unsteady force and pressure signals, rms variation s with angle of attack, and probability densities were evaluated to st udy the characteristics of the normal force and pressures fluctuations on the vertical fin.