An Investigation of Lifting Effects on the Intensity of Sonic Booms

Abstract

SummaryThis paper is a brief summary of an investigation made to check the effect of lift on the shock noise of aircraft flying at supersonic speeds. The method of Hayes has been combined with the theory of Whitham to predict the asymptotic shock strength of wings carrying lift and of combinations of bodies and lifting wings. (A similar, but not quite as general, method was derived by Walkden in Ref. 6.) Whitham's formula, including only the volume term, has been used extensively to predict the boom intensity of aeroplane type bodies and the agreement with experiment has, so far, been quite reasonable. The test data obtained to date extends only up to about 40,000 ft. altitude and the calculations of this paper show that under those conditions the shock noise of the aircraft tested so far will, in most cases, be dominated by the volume term. It is shown that at higher altitudes lifting effects will dominate for even the small fighter and they will dominate over most of the altitude range for large bomber and supersonic transport aircraft. The boom intensity due to lift decreases with altitude as h–¾ which compares to pa½ h–¾ in the volume case (pa = pressure at altitude h). It is insensitive to Mach number (for M > 1·4), wing loading, wing plan shape and lift distribution. A simple rule for calculating the shock noise due to combined volume and lifting effects is proposed which is applicable to configurations with wings located towards the rear of the fuselage. The rule states that the shock noise of an aircraft carrying lift is equal to the shock noise due to volume (neglecting lift) or the shock noise due to lift (neglecting volume), whichever is the greater. A chart is presented from which rapid estimates can be made of the shock noise of lifting wing-body combinations.