Simplified sonic-boom prediction

SUMMARYA simplified method for the calculation of sonic-boom characteristics fora wide variety of supersonic airplane configurations and spacecraft operatingat altitudes up to 76 km has been developed. Sonlc-boom overpressures and sig-nature duration may be predicted for the entire affected ground area for vehi-cles in level flight or in moderate climbing or descending flight paths. Theoutlined procedure relies to a great extent on the use of charts to providegeneration and propagation factors for use in relatively simple expressionsfor signature calculation. The computational requirements can be met by hand-held scientific calculators, or even by slide rules. With little sacrifice inaccuracy, complete calculations can often be obtained in less time than isrequired for the preparation of computer input data for the more rigorous cal-culation methods. A variety of correlations of predicted and measured sonic-boom data for airplanes and spacecraft serve to demonstrate the applicabilityof the simplified method.INTRODUCTIONAs the understanding of sonic-boom phenomena has advanced, and the abil-ity to provide accurate predictions of sonic-boom phenomena has improved, theactual prediction process has become quite complex. For conventional air-plane configurations, the usual procedures as described in references I and 2call for employment of several sophisticated computer programs covering air-plane geometry and aerodynamic considerations as well as the wave propagationaspects of the problem. For spacecraft operating in the sensible atmosphere,it has become the practice (ref. 3) to rely on wind-tunnel tests of small butdetailed scale models and specialized computer programs for extrapolation ofthe data to full-scale conditions. In either case, the process is complex,lengthy, and expensive and requires the services of one or more skilled prac-titioners of the art.The results of a recent study indicate that for many purposes (includingthe conduct of preliminary engineering studies and the preparation of environ-mental impact statements), sonic-boom predictions of sufficient accuracy canbe obtained by using a simplified method which does not require a wind tunnelor elaborate computing equipment. Computational requirements can in fact bemet by hand-held scientific calculators, or even slide rules. In addition,successful use of the method is not highly dependent on the skill and knowl-edge of the person performing the calculations.This prediction technique results from a simplification of the purelytheoretical methods described in references I and 2, which have been shown toprovide quite acceptable estimates of sonic-boom phenomena for a wide range offlight conditions for conventional airplane configurations. A recent wind-tunnel study (ref. 4) has shown that purely theoretical methods may be appliedto prediction of sonic-boom phenomena for extremely blunt bodies at highsupersonic speeds, provided that propagation distances are large relative to