FLIGHT-DETERMINED AERODYNAMIC-NOISE ENVIRONMENT OF AN AIRPLANE NOSE CONE UP TO A MACH NUMBER OF 2

The aerodynamic-noise environment of a Fiberglas nose cone for a fighter-type airplane was measured over a Mach number range from 0.8 to 2. The measurements were obtained at altitudes of about 26,000 feet and 40,000 feet for a dynamic pressure range of approximately 200 lbsq ft to 1,000 lbsq ft. The data showed that the aerodynamic-noise level on the surface of the cone increased with free-stream dynamic pressure. The average noise pressure varied from approximately 0.001 of the lower dynamic pressures to approximately 0.0005 of the higher dynamic pressures. The noise level in the octave bands below 2,400 cycles per second showed large deviations from the mean, which would cause serious error in structural-fatigue tests when such tests are based on the average level. Variations in angle of attack of from 1 to 5 had negligible effect on the noise levels however, at an altitude of 40,000 feet and an angle of attack of approximately 0 degrees, intermittent increases in noise levels were measured.