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Aviation History
1954
1954 - 1304.PDF
FLIGHT, 1 May 1954 581 Wetland. W2B/23 passed its 100-hr type-test in April 1943, and was given the name Welland; in June 1943 two were fitted in the Gloster F.9/40 (prototype of the Meteor), and by May 1944 Wellands were being regularly delivered for R.A.F. Meteors. The Welland had a reverse-flow combustion system, a maxi mum diameter of 43 in and could develop 1,700 lb, although for the F.9/40 it was at first derated to 1,450 lb. casing and front air intake, and the wheelcase. To the rear the main structure comprises the rear air intake, the cooling-air casing and the centre and rear bearing-housings, which successively lead to the nozzle-box assembly. This last takes the gas flow from the combustion chambers and distributes it to the annulus of stationary nozzle-guide vanes; it also carries the auxiliary cooling- air ducts leading from the region of the turbine disc and rear-bearing housing. Centrally runs the main rotating assembly, and disposed round the engine, between the compressor casing outlet elbows and the nozzle-box, are the nine combustion chambers. So carefully balanced is the rotating assembly that as much as a minute-and-a- half elapses before it comes to rest after the engine is shut down. At maximum static thrust the characteristic double-sided impeller deals with 62 lb of air per second, with an efficiency of 80 per cent and a compression ratio of 4:1. For this task it needs about 8,000 h.p., which is transmitted from the turbine through the coupling. The impeller is 24in in diameter and has 29 vanes on each side. Guide vanes convert axial to radial flow. Maximum thrust of the Derwent 8 is 3,600 lb at 14,700 r.p.m., and the specific fuel consumption is 1.01 lb/hr/lb. Experimental Derwents included the RD.9. which had a 15 per cent increase in mass flow, and the RD.10—a scaled-up version utilizing the rotating parts of the Nene. The RD.ll was another scaled-up development. Derwent 8. THE DERWENT While work on the Welland was in hand Rolls-Royce were already proceeding with a new design to utilize experience gained from their development work. The project was to be of the same maximum diameter, in order that it might be installed in standard Meteor nacelles, but it was to develop 2,000 lb thrust. Drawings were started in April 1943 and by July the new unit was ready for test. In November of that year it passed its 100-hr type-test at die full 2,000 lb rating and in April die following year it went through its first flight tests in a Meteor, with a Service rating of 1,800 lb and a weight of 920 lb. It was known by its experimental designation B.37 or, in conformity widi the "River" nomenclature, as the Derwent I. The Derwent II gave a tiirust of 2,200 lb, and the III was a special unit to provide suction for boundary-layer removal; die Derwent IV was rated at 2,400 lb dirust. The Derwent 5 was an entirely new engine—still of 43in diameter, but developing twice die thrust of die original Derwent I. It was, in effect, a scaled-down version of the Nene, and its development was motivated by die promise shown by the Nene and the knowledge that die Meteor could utilize thrust gready in excess of die original estimates. The Derwent 5 was superseded by die Derwent 8 and 9. The 8 incorporated two outlets to feed compressor-air dirough piping to heater muffs on die exhaust unit; tappings were taken from these muffs to heat die cabin and die guns and/or camera. The 9 used the same mediod of heating, but had in addition larger combustion chamber-inter-connectors and high-energy ignition to give more consistent relighting in flight as well as to increase the altitude at which relighting was possible. The body of a typical Derwent is built up on the compressor rear casing which, tiiough immensely strong, is very light and is considered by Rolls-Royce to be a fine example of dieir foundry technique. On the front face are die diffuser ring, the front Nene 10. Designed to a Ministry of Aircraft Production specification of 1944, calling for a turbojet having a maximum diameter of 55in, a minimum static thrust of 4,000 lb and a weight not exceeding 2,200 lb, die Nene, as has already been explained, is the "big brother" of the later Derwents. Consideration was given in die early project stage to the scaling-up of a Derwent to meet die specification, but as this would have entailed increasing the diameter to nearly 60in a new design was put in hand and was completed in 5i months. In diis die diameter was kept down to 49£in and a thrust of 5,000 lb was attained. The design of the nine combustion chambers follows Derwent practice. Each consists of a cast expansion chamber attached to an outer air-casing containing a flame tube. About 15 per cent of the air entering each chamber is directed by per forated baffles and swirl-vanes in the flame tube into die com bustion zone around die burner head. In this zone, where die air is turbulent and moving slowly, die primary air flow, togedier with a small reverse flow round die flame tube, mixes with die fuel sprayed from die burners and burns at a flame temperature of 1,600-2,000 deg C. To prevent distortion of die flame tube due to local overheating caused by flames impinging on the walls, a min layer of air is admitted round die inside periphery of the tube through a circular "window piece." The remaining air flows between die flame tube and air casing, and communicates widi die combustion zone dirough rows of holes in the flame tube. This diluting air is consequendy expanded and accelerated rear wards, but it also cools the products of combustion to die tempera ture required at the turbine inlet. Current marks of Nene include die 3, widi electric starter motor and two torch-igniter units (diis powers the Supermarine Attacker F.l); die Mk 10, which is similar to the Mk 102 later mentioned but has a larger wheelcase of accessories (this is die engine of the Canadair Silver Star); the Mk 101, specially adapted for the Sea Hawk and having a horizontal gear-box drive, Plessey turbo-starter and divided jet-pipe; and die 102, which is inter changeable with the III but has various design changes, includ ing two high-energy igniters. This last powers die Supermarine Attacker F.B.2. Nenes have also been installed in die Gloster E.l/44, an experimental Lockheed Shooting Star and the Dassault Ouragan.
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