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Aviation History
1948
1948 - 1633.PDF
SEPTEMBER 30TH, 1948 FLIGHT 411 Fuel Pumps for Gas Turbines Successful 500 Hour Non-stop Test Run Made on Petrol ^ REFERENCE was made in Flight, September 9th, to thepossibility that, with the increasing use of gas turbinesin aircraft, the demand for aviation kerosene may out- strip the production of this fuel. This possibility has led toinvestigations of fuel pumps capable of running on straight petrol so that, if the necessity should arise, gas turbines couldbe switched over to run on the same fuel as piston -engined aircraft or motor transport. The experience of Dowty Equipment, Ltd., of Cheltenham,in the manufacture of hydraulic pumps of various types is well known, and this company has, for some years been at workon the special problems of fuel pumps. The announcement that the Fuel Pump Division of the Company, under the super-vision of Mr. F. Carey, had recently succeeded in carrying out a successful 500 hour non-stop test run with a pump deliveringstraight petrol was made shortly before the S.B.A.C. show at Farnborough Flight, August 19th). The achievement of the Dowty fuel pump, Type 260Y MarkIV, in passing such a rigorous test, completed under A.I.D. supervision is principally remarkable in that no lubricantwhatsoever was used either in the fuel or in the pump. The production of such a component is not only highly creditabletechnically but is also an important step in the advancement of gas turbine development. The actual performance figuresof the petrol pump are of interest when assessing the merit of this official test-run. Throughout the trials the pump was runcontinuously at 3,500 r.p.m. for a period of three weeks de- A cut-away view of the Dowty Fuel Pump, Type A260Y. The splined drive-shaft, retained by a circlip, is readily detachable without dismantling the pump, in the event of it being damaged. livering fuel at a pressure of 1,000 lb per sq in and at a rateof 650 gallons per hour. The pump incorporates seven radial pistons which recipro-cate through a stroke of 0.58m in cylinders of 0.594m bore. The reciprocating action is produced by a stationary circulartrack ring, eccentric from the cylinder block, the latter being rotated by the drive shaft. Unlike the well-known live-linehydraulic pump, the track ring of the fuel pump cannot pivot about a knife edge or hinge, but is fixed so that its degreeof eccentricity does not vary; thus the unit is a fixed rather than a variable delivery pump. Valving is by means of acentral shaft or hub on which the cylinder block or star member rotates, containing ports through which liquid enters and leavesthe cylinders. The dry weight of the complete unit is 11 1b. Comparative figures for the A260Y fuel pump running onstraight petrol and aviation kerosene respectively, show that the output on the latter fuel is slightly higher than on theformer; these also show the delivery figures of the pump at different speeds;Using 87-octane petrol, specification R.D.E/F/22, with no added lubricants, inlet pressure 3 to 5 lb / sq in; outlet pressure1,000 lb/sq in. Speed (r.p.m. Delivery (g.p.h.)~~~ At 3.500 650 At 1,000 .. .. .. .. ,. 180 At 300 60With a pump inlet depression of I2in of mercury, the delivery at 3,500 r.p.m. and 1,000 lb/sq in, is 580 g.p.h. Using aviation kerosene, specification R.D.E/F/KER, inletpressure of 3 to 5 lb/sq in; outlet pressure 1,000 lb/sq in. Speed (r.p.m.) Delivery (g.p.h.) At 3,500 .. ..*.- _ - i. <. At 1,000 .. .\ At 300With a pump inlet depression of I2in of mercury, the de- livery at 3,500 r.p.m. and 1,000 lb/sq in, is 700 g.p.h. Further evidence of the reliability of Dowty fuel pumps wasshown in the pump which was fitted to the de Havilland Goblin Mk. V during the military endurance trials successfullycompleted recently, reported in earlier issues of Flight. During this 500-hour test run the pump delivered a total of 136,000gallons of kerosene at a pressure of 1,000 lb/sq in. The pump was calibrated for delivery both before and after the test,and the delivery was found to have dropped only 0.2 per cent from its original figure. This indication of how little theunit had worn was further substantiated when the pump was dismantled for inspection, the only sign of wear being minutescores on the thrust side of the valve member due to slight impurities in the fuel; the condition of cylinder and boreswas virtually as new, as could be seen at the Dowty stand at the Farnborough display. A further advance in the range of Dowty fuel pumps is acomponent which incorporates an overspeed governor and pres- sure control by-pass valve. Above predetermined speed centri-lugal oil pressure generated by the rotation of the cylinder block deflects a diaphragm which opens a release valve; thisoperates a by-pass, thus reducing delivery to the engine. 1 "L'' 770 220 68 HERMES IV (Continued from page 408) most important change is in cutting down the basic emptyweight by 2,000 lb, thus making this weight available for additional payload. Improved materials and the refinementof structural detail design are the methods by which this weight saving will be achieved. At present an all-up weightof 82,000 lb is envisaged for the Mk VI but, if Bristols can make extra power available from the engines, it is likely thatthe take-off weight will be increased to 84,000 lb. In com- parison with those fitted to the Mk IV larger-chord shorter-span ailerons, and larger-chord greater-span flaps will be incor- porated in the Mk VI. Shielded Frise-type ailerons will stillbe used, but flaps will be of double-slotted or eyebrow-slotted type. These modifications arc designed to improve the take-offand stalling speed characteristics, and in order to maintain controllability at the lower safety speed derived from thelowered stalling speed, the fin and rudder area will be" in- creased. Thermal de-icing and electric airscrew de-icing willbe embodied as on the second prototype Mk V, but although British Messier disc-type brakes will likewise be used, theiractuation will be hydraulic rather than pneumatic. Naturally enough, all the lessons to be learned from opera-tion of the Mk IV will be put to good use in producing the Mk VI, and although it would be precipitous to prophesywondrous things for the Mk VI, it is, quite patently, a good aircraft and, moreover, an evidently sound, purposeful designwhich should go a long way toward silencing the too numerous traducers of our civil aviation capacity. PILOTS' AND NAVIGATORS' LICENCES AS from the date of introduction of the new I.C.A.O. licenceexaminations, the concession at present in force for the first and second class navigators' licence examinations, inwhich candidates are allowed six months to qualify, will be discontinued. Candidates for Flight Navigator, Airline Trans-port Pilot and Senior Commercial Pilot licences will be required to obtain not less than 60 per cent in each subject excludingsignalling, 70 per cent of the total marks for all subjects, excluding signalling, and in signalling not Jess than 90 percent. For full conversion all subjects must be taken in one examination.
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