Thursday, March 22, 2007

Aircraft carrier

An aircraft carrier is a warship whose main role is to deploy and recover aircraft—in effect acting as a sea-going airbase. Aircraft carriers thuo depend on local bases for land-based aircraft. Modern navies, who work such ships, treat aircraft carriers as the centerpiece of the fleet, a role before played by the battleship. The change, part of the growth of air power as a significant part of warfare, took place during World War II. Unescorted carriers are careful vulnerable to attack by other ships, aircraft, submarines or missiles and so travel as part of a carrier battle group.
Flight deck configuration
Aircraft carriers have a flat-top deck, the flight deck that serves as a take-off and landing area for aircraft. Aircraft take off to the front, into the wind, and land from the rear. The carrier steams at up to 35 knots (65 km/h) straight into the wind throughout take-off in order to increase the apparent wind speed, thereby reducing the necessary speed of the aircraft relative to the ship. A steam-powered catapult is used to propel the aircraft forward assisting the power of its engines and allowing it to take off in a shorter distance than would otherwise be necessary, even with the headwind effect of the ship's course. on the other hand, when landing on a carrier, aircraft rely upon a tailhook that catches on arrestor wires stretched across the deck to bring them to a stop in a shorter distance than normal. Since the end of WWII it has been ordinary to direct the landing recovery area off to port at an angle to the line of the ship. This allows launching of aircraft at the same time as others land.
The above deck areas of the warship are intense to the starboard side of the deck in a comparatively small area called an "island". Only a very few carriers have ever been intended or built without an island and such a configuration has not been seen in a fleet sized carrier.
A more recent configuration, used by the Royal Navy, has a 'ski-jump' ramp at the front end of the flat deck. This was developed to help launch VTOL (or STOVL) aircraft (aircraft that are able to take off and land with little or no forward movement) such as the Sea Harrier. Though the aircraft are capable of flying vertically off the deck, using the ramp is more fuel efficient. As catapults and arrestor cables are unnecessary, carriers with this arrangement reduce weight, complexity, and space wanted for equipment.


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