The drag rise Mach number of the Convair 990 airplane was significantly delayed by utilizing the area-rule principle in a manner not previously reported in the literature. The principle was applied locally to the nacelle-pylon-wing region in a full-scale flight test to improve the maximum speed capability. The results of the full-scale investigations which led to the final airplane configuration are presented. The final modifications to the aircraft for delaying the drag rise included a forward pylon fairing, an aft pylon fairing, and four terminal fairings added to the inboard sides of the nacelles. This configuration was incorporated into the final airplane design without major aircraft redesign or modification. The methods employed to identify and isolate the interference drag phenomena on the airplane and the analytical approach to the problem solution are explained. The results and data analysis include the incremental effects of the various modifications, surface pressure distributions, stabilized speed point data, and pilot observations on Mach buffet characteristics. A criterion was established which will add to the fundamental understanding of the causes of interference drag and the methods for alleviating the resultant drag rise. Examples of configurations suggesting potential application of the technique are pylon-mounted engine nacelles on wings or fuselages and externally mounted stores.
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Kutney et al. (1964) studied this question.