#592 Sound Speed

The speed of sound (otherwise known as Mach 1) varies with temperature. At sea level on a 'standard day', the temperature is 59°F, and Mach 1 is approximately 761 mph. As the altitude increases, the temperature and speed of sound ___ decrease until about 36,000 feet, after which the temperature ___ steady until about 60,000 feet. Within that 36,000 – 60,000 foot range, Mach 1 is about 661 mph. Because of the ___ , it is possible for an airplane flying supersonic at high altitude to be slower than a subsonic flight at sea level. The transonic band (the 'sound barrier‘) extends ___ around Mach 0.8 — when the first supersonic shock waves form on the wing — to Mach 1.2, when the entire wing has gone supersonic.