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Aviation History
1931
1931 - 0185.PDF
FLIGHT, FEBRUARY 27, 1931 CATAPULT LAUNCHING OF AIRCRAFT : This photograph of a Fairey III F seaplane being catapulted off is reproduced by courtesy of the Admiralty. AIRCRAFT CATAPULTS Scottish Firm Markets Two Successful Types D1UE chiefly to a policy of reticence on the part of Britishmanufacturers, the impression appears to have gotabout that foreign countries have stolen a march onGreat Britain in the matter of catapults for launching aircraft. The United States have been experimenting withand making use of catapults for a number of years. France also has produced catapults, and Germany, notably theHeinkel firm, has had on the market for a considerable period a catapult which was used experimentally for the launchingof civil aircraft from liners. What Great Britain has been doing has not hitherto been permitted to become known.A short time ago, however, photographs were published (see FLIGHT of October 24, 1930) of a catapult with whichexperiments in launching had been carried out at the Royal Aircraft Establishment at Farnborough. Now it has becomepossible, by the courtesy of the Admiralty and of the makers, to publish more detailed particulars of a very powerful cata-pult manufactured by Mactaggart, Scott and Co., Ltd., of Loanhead, Edinburgh. Actually two distinct types areavailable—one known as the extending structure type, and the other known as the fixed type, in which the actual trolleyused for supporting the aircraft is similar to that used in the extending structure type. The fixed type is intended foroperating from ships in which the track rails are fixed to the deck, the actuating mechanism being housed below deck.The following notes will deal mainly with the extending structure type, in which the rails are so arranged that theline of take-off can be adjusted to any angle desired, and is not confined to the fore-and-aft line of the ship. The Mactaggart, Scott and Co. extending structure typeof catapult consists of four main parts : the trolley, the main extending structure, the actuating mechanism, and theoperating gears. For a total weight of 19 tons, the catapult will launch any type of aircraft, landplane, float seaplane,flying boat, or amphibian. The launching speed varies according to the weight of the aircraft. Thus a machineweighing 8,000 lb. is catapulted off at a speed of 57 m.p.h. A machine weighing 7,000 lb. is launched at 60 m.p.h.,while a 6,000-lb. aircraft is launched at 63 m.p.h. The length of the catapult stowed is 46 ft., and the length fullyextended is 75 ft. 9 in. The total length of run for the air- craft is 64 ft., of which 50 ft. 6 in. is accelerating travel and 13 ft. 6 in. is retarding travel (the aircraft actually is released during the retarding travel). The mean acceleration obtained depends, of course, on the launching speed. In the case of the 57 m.p.h. launching speed the mean acceleration is 2-15 g. For 60 m.p.h. it is 2-38 g., and for 63 m.p.h. it is 2-62 g. The Trolley That part of the catapult on which the aircraft is mountedis known as the trolley, and consists of a rectangular frame- work of four steei channels carrying the four legs by which theaircraft is attached to the trolley. At each corner of the trolley frame are two wheels mounted on special high-dutyroller bearings. The object of fitting two wheels at each corner is that, as the main frame consists of a fixed frame andtwo moving frames running inside the fixed frame, the wheel track varies according to whether the trolley is on thefixed frame rails or on the rails of the extending frames. When on the latter, the inner wheels support the trolley.When the trolley is over the fixed frame portion, however, it runs on its outer wheels. At the forward end of th trolley is a pair of struts whichterminate at the top in jaws or forks. These forks engage with trunnions on the aircraft. The two struts, or legs, atthe rear corners of the trolley frames, similarly end in forks, which support the rear trunnions on the aircraft. Slopingfrom the tops of the forward struts down to the rear cross shaft are two diagonal members, which are actually telescopicstruts with oleo gear incorporated. When the aircraft is being launched, the thrust is deliveredto the aircraft through the front forks. The rear forks serve to hold the aircraft at the correct angle of incidence, and tothis end the rear struts of the trolley are adjustable in length. The adjustment provides for a range of incidence from 0degrees to 12 degrees. To prevent the aircraft from being pulled out of the forks under the thrust of the airscrewwhile the trolley is stationary or travelling at low speed, detents are fitted which lock the trunnions to the forks.Not until the trolley has travelled a certain distance and has attained a speed at which the acceleration is greater than the 177
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