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Aviation History
1952
1952 - 0274.PDF
ii4 FLIGHT REFUELLING THE COMET Transferring 21 Tons of Kerosine in 20 Minutes by the Under-wing Pressure System The new Dorset refueller has been put through comprehensive trials with Xhe Comet preparatory to operational service. AS the mean block-speed of an airline's equipment is /% increased, so does the time that each airliner spends on the ground assume progressively greater importance. The de Havilland Comet, which promises to earn revenue more rapidly than any other transport in production, has shown beyond doubt that the speed with which it can be serviced must influence, to a great extent, the ultimate economy of its operation. This lesson has been demon strated frequently during the comprehensive proving trials conducted by B.O.A.C. On a scheduled service, the period that must be spent at a staging point is often governed by the time required to complete refuelling; this will usually be the longest continuous servicing item, other tasks being of a more incidental nature. It thus becomes of primary importance to provide a tanker capable of a very high delivery rate and further, to enable the aircraft to take on fuel at that rate. Shell are now in the process of stationing at the appropriate airfields the new 3,000-gall Dorset refueller, built by Thompson Bros. (Bilston) Ltd., which was designed specifically to meet the exacting demands of Comet services. It may not be generally realized just how much kerosine the Comet can take on board. The later series 1 aircraft have a capacity of 7,000 gal (31,850 litres). The first Comets—the early Series 1—had a total tankage of 6,030 gal, and it is to this type that the following description refers. All fuel is carried in the wing, there being bag tanks in the centre-section—a 2,020-gal tank under the cabin floor and 785-gal tanks just outboard of the power plants—and integral outer-wing tanks, each with a capacity of 1,220 gal. The system is designed not only for pressure refuelling from the underside of the wing, but also for conventional replen ishment from the wing upper surface. Waymouth capacity-type contents gauges are employed, together with withdrawable * drip- sticks" in the tank under-surfaces for visual checking on the ground. A drip-stick is shown in use in one of the accompanying photographs. Initial fuel-feed to the power units is by S.P.E. immersion booster-pumps, two of which are fitted in each tank; provision is also made for suction feed as a stand-by. Each pump may be removed from the underside of the wing without draining the tank concerned. Venting air is drawn from an intake in the wing leading-edge; should jettisoning become necessary, the ram pressure from this intake is employed to blow out the fuel from the three centre-section tanks. Access to all tanks is via inspection covers in the under surface of the wing. The under-wing pressure-fuelling system employs only two under-wing refuelling points. The connection under the port wing is piped to the large central tank and the inner and outer wing tanks on the port side, while the starboard fuelling-point supplies only the inner and outer wing tanks on the starboard side. Each of these external connections consists of a standard Lock heed Avery screw-coupling, situated at about 50 per cent chord just outboard of the main-bogie well on each side. During refuel ling, each coupling is only some six feet from the ground—a most convenient working height. From these points the fuel is led to the appropriate tanks through large-diameter pipes in which are situated electrically operated refuelling valves. As each tank becomes full, a float-operated cut-off switch automatically closes the appropriate refuelling valve and shuts off the supply to that tank. As a safeguard against excessive pressure caused by over filling all tanks are provided with blow-off relief valves. In each of the main undercarriage wells is situated a refuelling control panel (see illustration) which includes a three-position switch for each tank, reading "refuel," "off," and "off-load." These switches are normally restricted to the two former posi tions by a hinged flap, which must be raised before they can be moved to the "off-load" position. Each panel also has a dial con tents gauge and red warning light for each of the tanks it serves. The amount by which the tubular drip-stick (left, below) has to be withdrawn from the tank before fuel can escape down it is a direct measure of the fuel contained in the tank. The action of screwing home the Lockheed Avery coupling—as shown in the right-hand photograph—automatically opens self-seating valves in both the tank and the hose union. It will be noted that the operation can easily be performed from ground level.
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