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Aviation History
1946
1946 - 0239.PDF
7TH, 194b FLIGHT 133 "RIVER CLASS" EVOLUTION special deep-grooved type, which was developed for the supercharger of the Griffon piston engine. The two roller bearings are located forward of the rotor and impellor. The compressor impeller and the turbine rotor are each dynamically balanced, and then finally balanced as a complete rotating assembly. It was found, however, that balance is likely to be upset if rotors are unbolted and reassembled. This constitutes an im- portant .reason for the division of the drive shaft from turbine to compres- sor. The shaft connection comprises a quickly-detachable toothed coupling, which transfers all the power from the turbine to the compressor shaft, and a grooved ball joint on the axis which incorporates a lock of the bayonet type. The sequence of operations re- quired to remove the turbine rotor and shaft is as follows: —Insert hand through an access hole in the interme- diary casing; disengage two spring de- tents and slide back the lock ring which they locate ; withdraw the outer toothed coupling; turn the shaft through 30 deg. to break the bayonet interlock of the ball coupling; with- draw rotor and shaft rearwards. Cooling- of Bearings As the plain type bearings used on the Derwent I have been replaced by roller bearings on the Derwent V, no oil cooler is fitted. A triple gear-type pressure pump supplies oil through a filter to the various bearings, and two scavenge pumps return the oil tp the pressure side. As two tons of air are delivered each minute by the main compressor, the provision of a separate centrifugal fan to provide cooling air for the centre and rear bearings and the turbine disc seems at first sight superfluous. It DIFFUSER AUXILIARY BLOWER FOR COOLING REAR BEARING FORWARD BEARING The main air flow from the double-sided compressor to the combustion chambers. Note also the cooling fan. (Left) The rear half of the compressorcasing with diffuser in position, and Right) the complete compressor cas-ing and assembly. is, however, well justified in that the air leaving the main compres- sor normally has a temperature of about 200 deg. C, whereas the auxiliary blower can supply the air at about 30 deg. C. The extra rotor is a die casting, cheap to pro- duce, and requiring only 18 h.p. to supply the requisite volume of air, while it is estimated that to by-pass the air from the main com- pressor would involve an expendi- ture of about 50 h.p. Another con- sideration is that air for cabin pressurising is taken from the main supply, and there is an under- standable reluctance to reduce further the output of the main compressor. Another apparent difference in 800 |600 5500 CtU. '00 0 [s* B23 37MK1 y J37M J f BB37MK2 1943 1944 1945 1946 An increase in thrust per square footof frontal area from 150 lb. for the Welland to 350 lb. for the Derwent Vwas shown in a period of two years. 065 0-60 yjO'55 30-50 *0-40 iQ-35 0 50 0-25 V \ 37 MK \ j 1 337M KD \ PMKV 1943 1944 1945 1946 The specific weight per lb. of thrusthas improved from 0.57 for the Welland in 1943 to 0.36 for therecord-breaking Derwent V in 1945 Ql X 2 CONSUMPTIO N I o g \ °Bi 37 MK \ V (B37^ KO - VN N \ V943 1944 1945 1946 The Welland gave a specific fuel con-sumption of almost 1.15. The figure for the Derwent I was 1.07, while theDerwent V has reached unity.
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