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Unformatted text preview: 1 There is a famous little story, untrue of course, of the pilot who flew his plane beyond the sound barrier and then got trapped there because of insufficient reverse thrust to get back below the speed of sound. Another case of perpetual motion. 1. It is a large loss in propulsive energy due to the formation of shocks that causes wave drag; this is a shock formation about an airfoil. Up to a free-stream Mach number of about 0.7 to 0.8, compressibility effects have only minor effects on the flow pattern and drag. The flow is subsonic everywhere. As the flow must speed up as it proceeds about the airfoil, the local Mach number at the airfoil surface will be higher than the free- stream Mach number. There eventually occurs a free stream Mach number called the critical Mach number at which a sonic point appears somewhere on the airfoil surface,...
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- Spring '08