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Aviation History
1947
1947 - 0755.PDF
MAY 15TH, 1947 FLIGHT 441 NAVAL AIRCRAFT at Farnborough launching intervals of one minute were obtained from a cordite-operated accelerator, but com- pressed air was the energy medium now used with hy- draulic control on the front side of the piston'. The air acted directly on the power piston, the motion of which was controlled by the leakage of water from an annulus in front of it. This control was provided by a launching valve, of sluice type, opened under constant force against a dashpot, the orifice of which was varied by the motion of the valve. The piston, ropes and trolley were brought to rest by a "swollen" part of the piston rod, in front of the piston, passing through a choke ring and forcing water through a decreasing annular^rifice formed by this ring and the retardation profile. ™ In present-day installations retardation was effected in 21ft (compared with 96ft for acceleration), giving a mean retardation of 9.2 g and a probable maximum of 12 g. With the towing method this was not so fundamental, as there was no launching superstructure to collapse rapidly. In the American equipment retardation was effected by external buffers, similar to railway hydraulic safety buffers, acting directly on the power piston. On British carriers the maximum build-up of accelera- tion took place in approximately 0.6 sec, but with Ameri- can equipment this was of the order of 0.3 sec. It had been found that after the aircraft broke away from the hold-back there was a drop in load transmitted to the tow- ing hooks, and that this depended on the weight and elasticity characteristics of the aircraft and moving parts. There was a tendency for the oscillating effort to increase with the size of the hold-back breaking load, and this was affected by the characteristics of the undercarriage and airframe. Discussing the stability of aircraft during launching, Mr. Boddington said that little could be said at this stage of the nose-wheel layout. If the nose wheel rested on a plat- form which was part of the deck towing hook, then no stability problems arose, but strength requirements might still be important. This was a serious complication, and at Farnborough it was considered that two hooks should be used on the aircraft. A few launches which had been made with the Airacobra indicated a definite drift of the nose wheel, up to about I2in, but it was probably unfair to quote this case as the nose wheel was stiff and had little or no castering effect. Acceleration Effects From the pilot's point of view the accelerations now used, which were of the order of 3.25 g, caused no discomfort. Pilots agreed that the launch was much more comfortable when the build-up from breakaway to maximum was of the order of 0.6 sec, compared with 0.3 sec. or less. Crew positions, facing forward or aft, caused no embarrassment, provided that there were proper supports. Having summarized the history of R.A.T.O., Mr. Bod- ington recalled that the need for a rocket with a burning time of 4 sec resulted in the development of the present 5in motor about 4ft long and weighing 65 lb. Nozzle sizes were chosen to suit Arctic, temperate and tropical condi- tions. The limits of burning time were 3.7 to 4.7 sec, de- pending on temperature, and the total impulse about 4,600 lb/sec. The cone of the jet included an angle of 26 deg and in general all airframe parts should he outside this boundary. . , , In operation the pilot started his run in the normal way and at a speed of about 24 knots (interpreted to him in terms of distance) the rockets were fired It was imperative that the rockets should not fade out before take- off speed was reached. In contrast to a normal free take- off run the pilot made no attempt to get the tail up, and a better take-off resulted if the tail were kept down Introducing his remarks on arrester gear, the lecturer said that the design requirements remained at 1.5 g re- tardation until recently, when the figure was increased to 2 g to meet the needs of higher-performance aircraft, since the deck space would not permit an increase in the arresting distance. Entry speeds had not yet changed. Arrester wires, made of 6/37'extra-flexible steel ropes. were connected to the main reeving by pin couplings. The rope supports could be collapsed by an aircraft wheel and would reset immediately; they could be held permanently collapsed by an air piston and cylinder. British and Ameri- can carriers were similar in the deck equipment and its layout. Concerning arrester hooks, Mr. Boddington said that design conditions now required the hook installation to take working retardations of 2 g under the maximum weight conditions. Various types of installation were illus- trated; but it was impossible to put them in any order of preference, though it was generally true to say that the hook suspension for tail-wheel aircraft should be as far aft as possible. Hook Design There were two forms of installation. • The first, re- ferred to as A- or V-frame, WBS restrained io swing in the vertical plane only. Side loads were eii!i-. 1 taken through the frame or transferred directly to the fuselage ii a snap gear was used. The second form embodied a single shaft free to swing sideways as well as vertically, and to .ilitin itself with the forces exerted by the arrester win-, li varied in detail and to keep the suspension point as far aft as possible might introduce forward stowing, telescopic stowing or complete, or partial, retraction. In general the layout of British and American under-deck arrester equipment was the same, but the methods of developing the resistance differed. The main problem in the design of this equipment was to cater for the wide range of aircraft weights and speeds. The British method had the advantage, from the airframe aspect, that practically the full stroke of the gear was used whatever the engaging speed. Mr. Boddington went on to discuss in some detail arrester gear performance, the mechanics of pick-up, aircraft motion, hook bounce, hook design, barrier operation anil requirements, and barrier engagement. The barrier, he said, divided the flight deck into two parts and was de- signed to arrest an aircraft which had failed to engage the wires. The operation of the barrier in the normal landing cycle was- as follows: — (a) Aircraft lands-on, barrier up. (b) Barrier down immediately aircraft engages miarrester wire. (c) Aircraft arrested, released and moves forward to theforward park or to be struck down. (d) Barrier up, aircraft signalled on. (e) Aircraft lands-on, and so on. Barriers were designed to receive aircraft at entry speeds of up to 40 knots, and present-day American equipment catered for speeds up to 60 knots with a pay-out up to 100ft. The British barrier had a considerable advantage over the American in that resistance was offered immediately on engagement. Little information was available on the per- formance of the safety barrier, but retardations up to 10 g had been recorded. Concluding his Paper, Mr. Boddington said that it was his opinion that the operation of aircraft from carrier decks could be turned into an advantage over land-based air- craft. (Report of discussion will be published next week) FORTHCOMING EVENTS May 16th to 19th.—Royal Netherlands Aero Club. Aerial rally at Ypen- burg, The Hague. May 16th to 24th.—Coupe Montana for iet propelled aircraft. May 17th.—Air League of British Empire : Display at Whitchurch airfield, Bristol. May 17th.—Wolverhampton Aero Club : At Home. May 18th.—Southern Area Model Flying Championship. A.S.T. airfield. Hamble, Hants, 2 p.m.—6 p.m. May 20th.—R.Ae.S. (Graduates and Students) : " Operation of Civil Aircraft in the Tropics," Capt. G U. Allen May 24th.—Cannes Air Rally. May 24th and 26th.—Isle of Man Air Races. Ronaldsway Airport. May. 29th.—Royal Aeronautical Soc. : Thirty-fifth Wilbur Wright Memorial Lecture " The Development of All-wing Aircraft." To be read by J, K. Northrop. O
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