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Aviation History
1945
1945 - 2285.PDF
552 FLIGHT NOVEMBER 22ND, 1945 NAPIER SABRE VII boost control unit and charge temperature correction of the fuel/air ratio. The Sabre VA passed its type test at the first attempt and is now being delivered installed in the Tempest VI. Developing 2,600 b.h.p. for a weight of 2,460 lb., its specific weight is 0.94 lb./h.p. Maximum r.p.m. has been in- creased to 3,850 and the maximum boost pressure to 15 lb., the unit output being equal to 71 b.h.p./litre. Following a development programme that paid special attention to installation problems, the Sabre VI emerged. This was basically a VA with modifications to suit an annular radiator and an engine-driven cooling fan. Very successful flights have been carried out with this installa- tion and the performance is quite promising. However, this particular form of installation is dependent upon employment in an aircraft especially designed for it if the best use is to be made of the increased performance. The latest stage in Sabre development has come with the Mk. VII in which the physical capacity of the blower NAPIER SABRE VII DATA Bore Sin. (127 mm.). Stroke ... 4£in_ (121 mm.). . Compression ratio 7.0 : ! Total swept volume 2,238 cu. in. (36.7 litres). Reduction gear ratio ... ... 0.2742 : I Reduction gear type ... Spur gear through four layshafts. A/S shaft rotation ... ... ... Left-hand tractor. Supercharger drive ratios :— M.S : ... 4.68:1 F.S 5.83 : I Net dry weight 2,540 Ib. (1,152 kilos). Rated power ;— M.S 2,235 b.h.p. at 3,700 r.p.m. at 8,500ft. F.S 1,960 b.h.p. at 3.700 r.p.m. at f8,250ft. Maximum power (combat) rating—5 minute limit :— M.S 3,055 b.h.p. at 3,850 r.p.m. at 2,250ft. F.S 2,760 b.h.p. at 3,850 r.p.m. at 12,450ft. Maximum take-off power :— M.S 3,000 b.h.p. at 3,850 r.p.m. at sea level. Continuous cruising (weak mixture) :— M.S 1,610 b.h.p. at 3,250 r.p.m. and +7 Ib./sq.in. T.V. dive maximum ... ... ... 4,050 r.p.m. and + I7J Ib./sq.in. Fue, ._ CONSUMPTIONS Max. take-off conditions 235 gallons/hour. Max. climbing conditions at altitude :— M.S 2|4 gallons/hour. F.S 204 gallons/hour. Max. combat conditions at altitude :— M.S 239 galloni/hour. F.S 241 gallons/hour. Max. continuous cruising conditions at altitude :— M.S 117 gallons/hour. F.S 2 gallons/hour. Water/Methanol :— Max. take-offjconditions... ... ... 65 gallons/hour. Max. combat conditions at altitude :— M.S. ... ... ... ... 66 gallons/hour. FS . 102 gallons hour. Oil :— At maximum cruising conditions ... ... ... 47 pints/hour. At maximum climbing conditions 67 pints/hour. At maximum combat conditions ... ... ... 7i pints/hour. On the test bed. The surplus power output from Napier's engine test beds goesto augment Willesden's electricity supply. The idea of utilising power developed on test beds—and normally going to waste—was advanced by Flight and Aircraft Production in 1942. The Sabre with annular radiator installed in a Hawker .Typhoon. The fan can be seen immediately behind the airscrew boss. impeller has been further increased in conjunction with water/methanol injection equipment. The purpose of water / methanol injection is to enable higher boost pressures to be used with consequent increase in power output; water has an extremely high anti-detonation value when introduced with the fuel and enhances the effective volu- metric efficiency by virtue of charge cooling effect. Methanol, although a fuel, is embodied to prevent the water freezing at high altitudes, 60 per cent, methanol additive offering protection for heights up to 40,000 ft. In the Mk. VII the percentage of water/methanol to fuel is of the order of 35 per cent, in M.S. gear and 70 per cent, in F.S. gear, and it is, of course, necessary to arrange proportionate automatic stricture of the fuel passed by the fuel injector if over-rich mixtures are to be avoided. An interesting point is that with the removal of a few gallons of fuel from an aircraft and its replacement with water / methanol—which is of greater weight—the range of the aircraft is quite considerably increased, this being due to the higher power output obtained. Various components in the Sabre VII have been strengthened in order to cope with the increased loads, and the controls have been modified to suit the altered boost pressures and speeds and, further, to ensure that the water/ methanol cannot be used except under appropriate con- ditions. In addition to the water / methanol unit, which is fitted on top of the supercharger bend at the rear of the engine, an ignition control over-ride valve is embodied to vary the effective pressure acting on the capsule in the ignition contiol unit when water/methanol is being used, and thus to alter the ignition timing accordingly. Two safety micro-switches are fitted to ensure that the water/ .methanol pump cannot function if engine conditions are not suitable, and a boost-restriction servo- valve is incorporated to prevent combat or take-off boost being used unless water / methanol is being supplied. In addition, the cylinder head form has been re- designed to allow two compression rings to be fitted between the head and the sleeve instead of the single ring used on previous engines. It should be noted that at maximum combat conditions the
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