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-12- III. CONCLUSIONS AND RECOMMENDATIONS Conclusions 1. Current understanding of sonic boom loadings and of the responses of building materials and assemblies to such loadings is insufficient to assess accurately what kinds and amounts of physical damage will occur. The probability of material damage being caused by sonic booms generated by aircraft operating supersonically in a safe, normal manner is very small. a. The variability of individual boom signature parameters under different climatic and geographic conditions and for different types of aircraft and aircraft operations can not now be described with any great degree of statistical significance. Carefully conceived, properly instrumented test programs can improve this description capability: see Report on Generation and Propagation of Sonic Booms, dated October 1967. b. Currently, it is only possible to describe generally the nature of poten- tial-material-and-building assembly responses, expressed as functions of sonic boom signatures. Present description capabilities can only "explain" why wide-spread damage does not occur—itcan not explain "damage" that either is alleged or does occur. Continued over-flight test programs can not materially improve this description capability. c. Currently, it is not possible to describe the effects of "normal" environ- ment (such as thunder,wind gusts, and street traffic) which contribute to the repetitive, vibratory loading of buildings and structures and to which the sonic boom is additive. 2. A wide variety of materials and assemblies is potentially susceptible to damage even as a result of wind gusts or sudden pressure waves or earth tremors. Many of these potentially susceptible items are more apt to be damaged by repetitive loadings (say, on the order of several thousand) in combination with the chang- ing of physical properties of the materials as a result of aging and environmental exposure rather than by a single exposure. The most critical materials and assemblies which need to be explored are listed on pages 5 and 6.
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-13- 3. Currently, the majority of sonic boom damage claims and the largest dollar cost result from window glass breakage. 4. Thus far, few sonic boom damage claims have involved earth structures (or other materials stored at their normal angle of repose), foundations, or natural formations, but if such damage does occur, the effect and the cost can be troublesome. 5. With the advent of commercial supersonic flights over populated areas, some form of nation-wide boom-monitoring system may be required. 6. Two legal-structural problems warrant early attention to avoid establish- ment of inequitable legal precedents. Recommendations 1. At least two types of sonic boom simulators for testing on the order of eight-foot square panels of typical construction materials and twenty- foot on a side cubic assemblies should be immediately designed and constructed. 2. A physical response research program, comprising the following elements in descending order of importance, should be immediately undertaken and vigorously pursued: a. Repetitive tests in simulators of a wide range of damage susceptible materials and assemblies listed on pages 5 and 6. b. Static and dynamic laboratory tests of commonly used glass and glass systems. c. Acceleration and expansion of ESSA's sonic boom studies. d. Census, by sample survey, of window panes in the selected cities listed on pages 8 and 9. e. Evaluation of environmental parameters of material and building responses to natural phenomena. f. Theoretical study of critical earth structures. 3. An interdisciplinary group, including engineers and lawyers, should be appointed to study legal-structural considerations of commercial SST operations. 4. Contracts should be let to several competent companies specializing in instru- ment-data-recording-and-retrieval systems to propose the characteristics for an economical monitoring system, and to accomplish preliminary cost effectiveness analyses of the proposed system.
OCR for page 12
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TL 574 .355 N31 1968 c.l National Research Council (U.S.). Committee on SST Report on physical effect TL 574 .855 N31 1968 c.l National Research Council (U.S.). Committee on SST- Report on physical effect? of the sonic boom