High-Speed Aerodynamics – The Speed of Sound

Sound, in reference to airplanes and their movement through the air, is nothing more than pressure disturbances in the air. As discussed earlier in this section, it is like dropping a rock in the water and watching the waves flow out from the center. As an airplane flies through the air, every point on the airplane that causes a disturbance creates sound energy in the form of pressure waves. These pressure waves flow away from the airplane at the speed of sound, which at standard day temperature of 59°F, is 761 mph. The speed of sound in air changes with temperature, increasing as temperature increases. Figure 3-75 shows how the speed of sound changes with altitude.

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