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Aviation History
1954
1954 - 0896.PDF
408 FLIGHT LOW-LEVEL BOOMING The Sonic Shock-wave as an Offensive Weapon? VARIOUS theories have been put forward as to the effects of sonic shock-waves aimed at the ground, parti cularly in relation to their effect on human beings, animals and buildings. When the first sonic booms were made in this country by the Hunter, Swift and D.H. 110 there was a series of reports of minor damage caused on the ground. Yet, though the noise was certainly distinctive, and even alarming to people not expecting it, the destructive power of the shock-wave was soon proved almost negligible. The booms originated at high level and aimed at the crowds at Farnborough last year found their target but produced nothing more than enthusiastic interest, as was the intention. The subject, however, appears in a very different light in an article published in our American contemporary Aviation Week, where William J. Coughlin quotes some of the results and theories arising from flight tests of the North American F-100, the first operational aircraft capable of exceeding Mach 1 in level flight near the ground. The first public demonstration of the destructive power of sonic shock-waves was given when the F-100 was shown to Pressmen at Palmdale, California, last October. On that occasion the air craft made a very fast, low pass at 200ft near, but not directly over, a U.S.A.F. administration building. Window- and door frames made of 4in by 2in and 4in by 4in timber were shattered, and slivers of glass several inches long embedded in the walls of rooms inside the building. The journalists were impressed. Coughlin states that "anyone who observed the Press demonstration of the F-100 . . . would agree to the potential value of a shock-wave as a possible panic weapon." The damaged building at Palmdale was evidently a wooden-frame structure of the type common in America. The major effects of sonic shock-waves are probably con fined to damage to relatively weak structures, including humans, and to the causing of panic. But effect there is. Due to the difficulty of radar-tracking aircraft flying low down at supersonic speed, the first warning of the presence of such an aircraft would probably consist in the sudden impact of its shock-wave. Coughlin quotes Raymond H. Rice (vice-president and chief engineer of North American) as saying that such waves may, in the not-too-distant future, be expected to attain an intensity of 50 Ib/sq ft—equivalent to the instantaneous arrival of a 140 m.p.h. hurricane. The blast would be short-lived, but its shock and oscillatory qualities, not to say the element of surprise, would be considerably greater than that of a hurricane. North American spokesmen have gone as far as to lay down some desirable qualities of a future "fighter-boomer." Ideal speed for best effects is stated to be Mach 1.2 to 1.5; the aircraft should have as large a cross-sectional area as possible, consistent with its ability to achieve the desired Mach num ber. Since its shock-wave would be its only weapon, it would need to carry no offensive stores, and its radius of action would therefore be considerably greater than that for a com parably armed fighter-bomber. George Welch, the company's senior engineering test pilot, reports that he has flown the F-100 past an F-86 at well over Mach 1 without any adverse effect on the latter—the F-86 pilot "didn't feel anything." North American consider that a fabric-covered airframe, on the other hand, would be split open by the shock-waves if the F-100 passed close by. For safety's sake the F-100 is not allowed to fly supersonically within 5,000ft of private aircraft or airliners, nor are level supersonic flights permitted below 10,000ft; and sonic dives are forbidden within 15 miles of any inhabited area. There is, however, thought to be little danger of irrespon sible low flying in sonic aircraft when they come into service. Raymond H. Rice is quoted as saying "Lest I cause some to worry unnecessarily about low-flying friendly aircraft, it should be understood that low flying at supersonic speed takes a great deal of pilot skill and advance planning. It is almost inconceivable that this could ever be done inadver tently, and it is certain that irresponsible people would never Apres moi le deluge: from such a height as this the "fighter boomer" might trail its wake of destructive shock-waves over a suitable target. be permitted to control such machines of destruction." The various opinions quoted above suggest some fairly simple conclusions. Though the destructive power of the sonic shock-wave is considerable, it would probably be in effective against robust targets. Its surprise-value, also, must be offset by the fact that it would be extremely difficult to maintain any form of continuous bombardment. A stream of aircraft "bombarding" a target would run into one another's slip-streams, and a single machine would require some time to turn full circle and return to the same spot. Supersonic low flying in hill country would probably prove exceedingly difficult, if not more dangerous to the pilot than to his target. Yet a sonic shock-wave, well directed, might serve to remove flimsy camouflage from small, well-concealed targets. In arctic areas, moreover, a "bang" might remove windows and doors from living quarters, rendering them uninhabitable by exposing their inmates to the bitter climate. Windowless or doorless hangars might also become too cold to allow maintenance work with bare hands on delicate equipment. In the type of attack carried out on airfields during low-level sweeps of World War II, the fighter could make one only very fast pass over an airfield, relying for success on the element of surprise. It was highly dangerous to return for a second attack, because the defences would by then be alerted and prepared. During that one fast pass the pilot had to pick his target and manoeuvre his aircraft to fire, all in the space of a few seconds. An aircraft travelling at sonic speed, on the other hand, would now merely have to fly straight over the airfield under attack, with some certainty of achieving sur prise, and trail its wake of shock-waves over the area, prob ably with considerably greater effect than a hasty spread of cannon shells. Whatever the future applications of aimed shock-waves may be, the introduction of safety regulations covering sonic flying indicates that a new problem is emerging. Recent references in Parliament to future British aircraft capable of level supersonic flight may herald the occurrence here of phenomena similar to those experienced in the case of the F-100, and of the introduction of comparable regulations to minimize the effects.
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