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Aviation History
1985
1985 - 2360.PDF
Getting hooked It looks like something out of a science-fiction movie—a giant crane that snatches aircraft out of the sky and tucks them into undercover hangars. Sceptics say that the idea of SkyHook is about as far-fetched, but British Aero space argues differently. Two men in particular, BAe test pilot Heinz Frick and SkyHook project manager Diggy Mottram, are convinced of SkyHook's potential. They are the men behind its design and they are pushing its advantages, not least the added flexibility it could give to an already versatile aircraft such as the Sea Harrier. The idea came about in autumn 1981, when BAe conducted an analysis of where it was going with the Sea Harrier and how to keep the production line healthy. One notion contemplated was the removal of all things not necessary for combat, making the aircraft lighter and cheaper. By removing the undercarriage and other equipment, the Sea Harrier could be made 1,5001b lighter. "Then we looked at how the Royal Navy was operating its aircraft. It has always needed large ships for landing and launch ing its aircraft—the US Navy needs even bigger ships," says Frick. "We had, from time to time, landed aircraft on smaller ships and there had been some overseas interest in this idea, but on the whole these countries did not have ships big enough. Perhaps, if we could land on smaller ships, we could interest more people. But you need a lot of skill to land an aircraft on a small ship. In rough weather it can be practically impossible." Frick, an experienced Harrier pilot, points out the dangers of landing and At a demonstration at Dunsfold this year British Aerospace demonstrated a mockup of the SkyHook concept for the first time. Karen Walker reveals what the designers of SkyHook have in mind. launching from a ship deck. Turnaround is complicated; when the ship lurches and rolls, the aircraft and crew move with it; and perhaps the most dangerous time is on take off, when the aircraft is not quite flying but no longer attached to the deck. "We needed something that could grab the aircraft on the deck and secure it," says Frick. And so SkyHook (now a regis tered trade name) was born. Basically, it is a crane that captures the Harrier in the hover and places it where required. The crane is equipped with an active control system and sensors so that the pickup mechanism is space-stabilised while allowing movement of the crane base caused by the ship's motion. SkyHook—and the whole concept is still in the very early stages—is intended to stabilise up to Sea State 6. So, a 4,000- tonne destroyer travelling at 15kt would be able to roll up to + or -15°, pitch up to + or -7°, and heave up to plus or minus about 5m. The crane itself would be a structure about 9 tonnes in weight, excluding ship attachment reinforcement. The base moves with the ship within an elliptical envelope while inertial sensing techniques space-stabilise the crane head. Close-up of SkyHook pick-up device Lock-on jack - Maximum freedom of movement 24 The head incorporates the lock-on jack and associated gimbals, the lock-on jack positioning system, and a docking cradle. The gimbal mounting allows the jack to engage automatically the aircraft's pick up probe anywhere within a 10ft cube about 14ft below the crane head. Engineers' calculations show that, on average, the crane would require approxi mately 500 continuous h.p. (installed). At a ship speed of 15kt, for vertical motion (pitch and heave) it would demand a peak power of some 750 h.p., while lateral motion (roll and yaw) would need some 1,300 h.p. Frick points out that maximums of both pitch and heave and roll and yaw would not occur simulta neously. At Sea State 6, with the ship trav- * elling at 15kt, ship motion would exceed FLIGHT International, 3 August 1985A
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