Unsteady pressure and load measurements on an F/A-18 vertical fin

Tail buffet on a rigid 6% scale model of the F/A-18 was investigated in the Institute for Aerospace Research 1.5 m trisonic blowdown wind tunnel. Strain gauges were installed on the port fin to measure normal force, root bending and torsion moments. The starboard fin was instrumented with 24 fast-response transducers on each surface for unsteady pressure measurements. Static tests at constant angle of attack were performed to compare the loads and moments from the strain-gauged fin with those determined from pressure measurements. Pitch oscillations of the model were carried out at low frequencies. The mean angle of attack, amplitude of oscillation, and Mach number were varied to note the effects of delay in LEX vortex burst on the vertical fin buffet loads. The envelopes of the unsteady force and pressure signals, rms variations with angle of attack, and probability densities were evaluated to study the characteristics of the normal force and pressures fluctuations on the vertical fin.