RAMP UP Deck-mounted ski-jump assembly marks key step toward U.K. carrier-based JSF operations
Guy Norris, Aviation Week & Space Technology / 19 Aug 2013 pp.33-34
"...The 200-ft.-long ramp is the longest ever fitted to a carrier and, like the Queen Elizabeth-class carriers (QEC) themselves, is the first of its type to be purpose-designed from the outset for F-35 operations. Angled at 12.5 deg., the ramp wiii be 20-ft. high and is designed to reduce the required deck roll on takeoff by up to 50%, or allow an increased payload of up to 20%. The ramp achieves this by boosting vertical velocity, giving the aircraft a ballistic launch profile that provides it with additional time to accelerate to flying speed.
However; the ski ramp imparts added loads on the landing gear during launch and, because these can be increased by even small variations in the surface of the ramp or by the interface with the deck, developers are paying special attention to the build tolerances. David Atkinson, who leads JSF/QEC integration activities for BAE Systems, says the requirement for build accuracy is even greater than for previous ski jump designs because the F-35 has a wide tricycle gear. This makes it more exposed to variability than the narrower footprint of the tandem main gear of the Harrier, for which the concept was originally conceived in the 1970s. In addition, the center section of the carrier deck is cambered to prevent pooling of water, further complicating the interface with the ramp.
"You have to allow for the effect of deck-plate bumps and sags, and when the ship is floated up we will go over it with laser mapping to measure the actual tolerances achieved in build," says Atkinson, who was speaking at the American Institute of Aeronautics and Astronautics Aviation 2013 conference in Los Angeles.
The ramp has been designed by BAE and Lockheed Martin, rather than the shipbuilders, and is configured with two curves. The initial entry or "cubic" curve leads to a let-down or "ellipse" section that provides the launch point for the aircraft. The ramp's makeup provides a positive climb rate and no more than a zero sink rate if wind-over-deck conditions are less than expected...."