Science of travel through the Earth's atmosphere, including aerodynamics, aircraft structures, jet and rocket propulsion, and aerial navigation. It is distinguished from astronautics, which is the science of travel through space.
In subsonic aeronautics (below the speed of sound), aerodynamic forces increase at the rate of the square of the speed.
Trans-sonic aeronautics covers the speed range from just below to just above the speed of sound and is crucial to aircraft design. Ordinary sound waves move at about 1,225 kph/760 mph at sea level, and air in front of an aircraft moving slower than this is ‘warned’ by the waves so that it can move aside. However, as the flying speed approaches that of the sound waves, the warning is too late for the air to escape, and the aircraft pushes the air aside, creating shock waves, which absorb much power and create design problems. On the ground the shock waves give rise to a sonic boom. It was once thought that the speed of sound was a speed limit to aircraft, and the term sound barrier came into use.
Supersonic aeronautics is concerned with speeds above that of sound and in one sense may be considered a much older study than aeronautics itself, since the study of the flight of bullets (ballistics) was undertaken soon after the introduction of firearms. Hypersonics is the study of airflows and forces at speeds above five times that of sound (Mach 5); for example, for guided missiles, space rockets, and advanced concepts such as HOTOL (horizontal takeoff and landing). For all flight speeds, streamlining is necessary to reduce the effects of air resistance.
Astronavigation (navigation by reference to the stars) is used in aircraft as well as in ships and is a part of aeronautics.
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