When air is flowing at subsonic speed, it acts like an incompressible fluid. As discussed earlier in this chapter, when air at subsonic speed flows through a diverging shaped passage, the velocity decreases and the static pressure rises, but the density of the air does not change. In a converging shaped passage, subsonic air speeds up and its static pressure decreases. When supersonic air flows through a converging passage, its velocity decreases and its pressure and density both increase. [Figure 3-74] At supersonic flow, air acts like a compressible fluid. Because air behaves differently when flowing at supersonic velocity, airplanes that fly supersonic must have wings with a different shape.
High-Speed Aerodynamics – Compressibility Effects
ASA – AMT General, Airframe and Powerplant Prepware for 2017. Get ready for your FAA AMT Knowledge Exams with the most trusted source in aviation training. Includes the contents of the Computer Testing Supplement, with the same FAA legends, figures, and charts you’ll be issued at the testing center before you take your official test.