Ski-jump ramp

In aviation, a ski-jump is an upward-curved ramp that allows aircraft to take off from a runway that is shorter than the aircraft's required takeoff roll. By forcing the aircraft upwards, lift-off can be achieved at a lower airspeed than that required for sustained flight, while allowing the aircraft to accelerate to such speed in the air rather than on the runway. Ski-jumps are commonly used to launch airplanes from aircraft carriers that lack catapults.

Early aircraft carriers could launch aircraft simply by turning into the wind and adding the ship's own speed to the airspeed experienced by the aircraft. After World War II, naval aircraft became so heavy that aircraft catapults were needed to accelerate aircraft to takeoff speed, and it was feared that even a catapult might one day not be enough. A NACA study from 1952 proposed the use of a ski-jump after the aircraft catapult to assist aircraft in taking off.

In 1973, Lt Cdr D.R. Taylor of Britain's Royal Navy proposed the ski-jump for use with the Harrier Jump Jet, and initial testing with various ramp angles was carried out at RAE Bedford, using the two-seat Harrier demonstrator G-VTOL.

A fixed-wing aircraft must build up forward speed during a lengthy takeoff roll. As the forward velocity increases, the wings produce greater amounts of lift. At a high enough speed, the lift force will exceed the weight of the aircraft, and the aircraft will become capable of sustained flight. Since the aircraft must reach flight speed using only its own engines for power, a long runway is required so that the aircraft can build up speed. On an aircraft carrier, the flight deck is so short that most aircraft cannot reach flight speed before reaching the end of the deck. Since lift is less than gravity, the aircraft will lose altitude after the wheels leave the flight deck and possibly fall into the sea.

A ski-jump ramp at the end of the flight deck redirects the aircraft to a slight upward angle, converting part of the aircraft's forward motion into a positive rate of climb. Since the aircraft is still traveling at an inadequate speed to generate enough lift, its climb rate will start to drop as soon as it leaves the flight deck. However, the ski-jump launch has given the aircraft additional time to continue accelerating. By the time its upward velocity has decayed to zero, the aircraft will be going fast enough for its wings to produce enough lift. At this point, the aircraft will be in stable flight, having launched from the carrier without ever dipping below the height of the flight deck.

...
Wikipedia