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Aircraft CatapultAn aircraft catapult is a device used to launch aircraft from ships — in particular aircraft carriers — as a form of assisted take off. This type of catapult consists of a track built into the flight deck, below which is a large piston or shuttle that attaches up through the track to the nose gear of the aircraft. At launch, a release bar holds the aircraft in place as steam pressure builds up, then breaks (or "releases"; older models used a pin that sheared), freeing the piston to pull the aircraft along the deck at high speed. Within about 4 seconds, aircraft velocity plus wind speed (ship's speed plus head wind) will exceed lift velocity plus 15 knots. Up to and during World War II most catapults were hydraulic. After the war navies gradually converted to steam catapults, which were the only ones capable of launching the heavier jet fighters. At the beginning of the 21st century, navies started experimenting with catapults powered by linear induction motors and electromagnetics. An important factor driving the conversion to electromagnetic catapults is the steady conversion of warships from steam power to gas turbine power, and the resultant loss of readily-available high-pressure steam. As of this writing, except in the United States Navy, Russian Navy and French Navy, catapults have mostly fallen out of use, as most navies prefer to use the McDonnell Douglas (Boeing) AV-8B Harrier II and its derivatives, which are STOVL aircraft, and can be launched from smaller and cheaper ships than CTOL (Conventional Take Off and Landing) aircraft. Russian naval military aircraft can take off from carriers without a catapult thrust.
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