At moderate angles of attack, the vortex flow over swept-wing
aircraft develops quasi-periodic velocity fluctuations in the vicinity
of the vertical tails. This paper presents hot-film measurements
of velocity spectra in front of the vertical tail tip chord of a 1/32-scale
YF-22 and F-117 model and over corresponding flat plate delta wings with
sweep angles of 47.7° and 67.0°, respectively. Spectral results
for all four configurations exhibited narrow-band, sharp peaks, whose frequency
scaled linearly with freestream velocity at a constant angle of attack.
The variation of the Strouhal number based on mean aerodynamic chord is
presented for a range of angles of attack and compared with previous data
on other swept-winged configurations. While the narrow-band spectral
phenomenon exists on all configurations tested, the Strouhal relationships
for the isolated wing configurations do not match with full configuration
results at all angles of attack. The presence of the body, inlets,
and other geometries affect the development of the fluctuations and the
corresponding spectral results.