Minimum Sonic Boom Shock Strengths and Overpressures

Abstract

THE question of the minimum realizable sonic boom shock pressure rise is, in a sense, a closed one. For any given aircraft weight, flight Mach number and altitude, if the aircraft is sufficiently long, then shock waves may be avoided altogether. This is a consequence of two phenomena: the slow evolution of the signature toward its asymptotic shape in a homogeneous atmosphere¹; the “freezing” of the signature shape that occurs because of the nearly exponential increase in atmospheric density with distance below the aircraft². Typical length requirements for total elimination of the shock waves in the aircraft signature are beyond our present structural capability³. Ferri⁴ has pointed out, however, that within the lengths at present under consideration for the Boeing 2707 (318 feet), it is possible to design realistic aircraft with overpressures below those given by the far-field lower bounds⁴.