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Aviation History
1957
1957 - 0108.PDF
108 FLIGHT, 25 January 1957 "Comet 3£A" Powerplant ONE of the numerous changes being made to the Comet 3prototype in order to bring it up to Comet 4 and 4A standard is die replacement of its Rolls-Royce Avon RA.26sby the higher-powered (10,500 lb st. thrust) Avon RA.29s. This change has involved extensive re-engineering of theengine bays and—in particular—of the air intakes. The converted Comet 3 (nicknamed Comet 3|A) shouldfly in three or four weeks' time with its new engines, and with other changes which will make the aeroplane as repre-sentative of the 4 and 4A as possible. These include: (1) the fitting of detachable outer-wing panels, to permit flight-testevaluation of the 7ft-shorter-span Comet 4A; (2) the instal- lation of an automatic pressurization and air conditioningsystem (see Flight for July 6, page 29), and noise-reducing refinements to the distribution and recirculation; (3) modi-fication of the electrics so that power is distributed by split bus-bars (July 6, page 29); (4) structural provision on theengine jet-pipes for reverse-thrust and engine silencing; (5) the embodiment of q-feel in the elevator control circuit. With the "Comet 3£A" de Havilland intend to completea large part of the flying programme for A.R.B. and American C.A.A. certification before the first production Comet 4 flieslater this year. On the engineering and technical side A.R.B.'s requirements have, the company states, been met: C.A.A.requirements—at least those so far made final—appear to present "no insurmountable problems." (Above) One of the brand-new Avon RA.29s is hoisted into the refashioned engine bay (No. 3) of the Comet 3. An important modification is the replace- ment—in line with modern practice—of stainless steel fire-walls by titanium. The outlet pipe near the man's hands supplies hot compressed air for the airframe de-icing. (Right) The first photograph to be published of a production RA.29 Avon. Points of interest include the large de-icing air pipes (kinked to avoid the front mounting points) and the cabin-air manifold at the rear. Full-size tunnel testing established the optimum shape of these re-styled and enlarged air intakes (below). They have been enlarged to match the greater power of the Avon RA.29 engines. Note the central intake: as before, the upper aperture blast-cools the rectifiers, and the lower aperture cools the primary heat exchanger of the cabin air conditioning system.
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