Rolls-Royce RB.41 Nene
Designed to a Ministry of Aircraft Production specification of 1944, calling for a turbojet having a maximum diameter of 55in, and minimum static thrust of 4,000 lb and a weight not exceeding 2,200 lb, the Nene is the "big brother" of the later Derwents. Consideration was given in the early project stage to the scaling-up of a Derwent to meet the specification, but as this would have entailed increasing the diameter to nearly 60in a new design was put in hand and was completed in 5.5 months. In this the diameter was kept down to 49.5in and a thrust of 5,000 lb was attained.
Although based on the "straight-through" version of the basic Whittle-style layout, the Nene used a double-sided centrifugal compressor for improved pressure ratio and thus higher thrust. It was during the design of the Nene that Rolls decided to give their engines numbers as well as names, with the Welland and Derwent keeping their original Rover models, B/23 and B/26. It was later decided that these model numbers looked too much like those for bombers, and "R" was added to the front, the "R" signifying "Rolls" and the original Rover "B" signifying Barnoldswick. The Nene first ran on 27 October 1944.
The design of the nine combustion chambers follows Derwent practice. Each consists of a cast expansion charnber attached to an outer air-casing containing a flame tube. About 15 per cent of the air entering each chamber is directed by perforated baffles and swirl-vanes in the flame tube into the combustion zone around the burner head. In this zone, where the air is turbulent and moving slowly, the primary air flow, together with a small reverse flow round the flame tube, mixes with the fuel sprayed from the burners and burns at a flame temperature of 1,600-2,000 deg C. To prevent distortion of the flame tube due to local overheating caused by flames impinging on the walls, a thin layer of air is admitted round the inside periphery of the tube through a circular "window piece." The remaining air flows between the flame tube and air casing, and communicates with the combustion zone through rows of holes in the flame tube. This diluting air is consequently expanded and accelerated rearwards, but it also cools the products of combustion to the temperature required at the turbine inlet.
Early airborne tests of the Nene were undertaken in an Avro Lancastrian operated by Rolls-Royce from their Hucknall airfield. The two outboard Rolls-Royce Merlins were replaced by the jet engine. The Nene's first flight however was in a modified Lockheed XP-80 Shooting Star.
The Nene doubled the thrust of the earlier generation engines, with early versions providing about 5,000 lbf (22.2 kN), but remained generally similar in most ways. This should have suggested that it would be widely used in various designs, but the Gloster Meteor proved so successful with its Derwents that the Air Ministry felt there was no pressing need to improve upon it. Instead a series of much more capable designs using the Rolls-Royce Avon were studied, and the Nene generally languished.
Marks of Nene include the 3, with electric starter motor and two torch-igniter units (this powers the Supermarine Attacker F.1); the Mk 10, which is similar to the Mk 102 later mentioned but has a larger wheelcase of accessories (this is the 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 the 102, which is interchangeable with the III but has various design changes, including two high-energy igniters. This last powers the Supermarine Attacker F.B.2. Nenes have also been installed in the Gloster E.1/44, an experimental Lockheed Shooting Star and the Dassault Ouragan.
The Nene was used to power the first civil jet aircraft, a modified Vickers Viking, which flew first on 6 April 1948. The design saw relatively little use in British aircraft designs, being passed over in favour of the axial-flow Avon that followed it. Its only widespread use in Great Britain was in the Hawker Sea Hawk and the Supermarine Attacker.
Twenty-five were given to the Soviet Union as a gesture of goodwill - with reservation to not use for military purposes - with the agreement of Stafford Cripps. The Soviets reneged on the deal, and reverse engineered the Nene to develop the Klimov RD-45, and a larger version, the Klimov VK-1, which soon appeared in various Soviet fighters including Mikoyan-Gurevich MiG-15.
It was briefly made under licence in Australia for use in the RAAF de Havilland Vampire fighters. It was also built by Orenda in Canada for use in 656 Canadair CT-133 Silver Star aircraft.
Pratt & Whitney J42