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1957 Ins. L.J. 15 (1957)
Is Sonic Boom an Explosion

handle is hein.journals/inslj19 and id is 15 raw text is: Is Sonic Boom an Explosion? By JOHN I. HOPKINS and JOHN J. McINTOSH As there are no court decisions deciding the above question, the authors have sought to answer it by carefully explaining the phenomenon of sonic boom O N October 14, 1947, Charles Yeager became the first man to fly an airplane faster than the speed of sound. Ground crews and nearby residents heard a terrific noise and felt vibrations. When other planes subsequently exceeded the velocity of sound the same vibrations and noise were noticed. For the lack of anything else to call it, airmen labeled it sonic boom. A velocity equal to the velocity of sound, or approximately 760 miles per hour, is said to have a Mach number equal to unity. The abbreviation would be M equals 1. We say approximately 760 miles per hour, since the speed of sound depends upon the absolute temperature. In other words, a missile or aircraft might not have to go quite 760 miles per hour to reach the speed of sound at a particular spot in the sky, whereas it might have to go faster else- where to do so. Aeronautical engineers classify, according to the Mach number involved, four speed ranges: subsonic, transsonic, supersonic and hypersonic. Subsonic corresponds to any Mach number less than unity, such as M equals .75; transsonic would be approxi- mately M equals 1; supersonic would be between M equals 1 and M equals 4.5; and hypersonic would be greater than M equals 4.5. If M equals 1 represents a speed of 762 miles per hour, a plane or missile travel- ing at M equals .75 would be going almost 572 miles per hour; and at M equals 4.5, it would be going 3,429 miles per hour. What takes place at supersonic speeds was not clearly understood by many of the experts until actual experiments were con- ducted by pilots in airplanes capable of exceeding the speed of sound. Some physi- cists thought it was impossible to exceed Sonic Boom the speed of sound, referring to it as a barrier or brick wall in the sky. Little thought was given to the fact that high powered guns were already shooting shells that were traveling faster than sound and with no difficulty. Until the first aircraft actually exceeded the speed of sound, there was no unanimity of thinking as to the possibility of doing so. In fact, there was a good deal of superstition about it. For- tunately, there were a few scientists who believed it could be done. However, until it was actually (lone the skeptics were most pronounced. In their writings about supersonic speeds the scientists give no thought to the insur- ance claim men who might be troubled with sonic boom claims. The scientists stay with the airplane, which is miles away and has reached the area of no signal (100 per cent supersonic) by the time the sonic boom is felt and heard on the ground. The claim men are also in the area of no signal, but of an entirely different kind. With no signal from the experts as to what sonic boom is, they are placed in the position of not know- ing how to treat claims resulting from it. In order to have a better foundation for understanding sonic boom, let us digress somewhat and review a few of the laws of physics and the laws of man. Since sonic boom has at least two undisputed characteristics of explosion-a noise and energy-Nwe will use a simple example of explosion for this review. If an air com- pressor tank ruptures as a result of too much air pressure, or if a stick of dynamite ruptures because of the tremendous pres- sure developed by the gases and the heat from :ombustion, an explosion occurs. Both the legal and scientific minds are in com- plete concurrence on the fact that -there

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