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Aviation History
1948
1948 - 1221.PDF
AUGUST jTH, 1948 FLIGHT 157 Power for the Giants alternator associated with the "master" Proteus, together with that of the^uiiit under control. This motor trims the setting of the constant-speed unit which, in turn, corrects airscrew pitch by ^n appropriate blade angle change. Concerning the air intake system, an important feature is the full use made of the airscrew slipstream ram. A pair of intake ducts is arranged (one duct each side of the main power cell) with their inlets in the leading edge, directly in line with the most effective part of the airscrew blades. These ducts extend to a point level with the com- pressor air inlets, where the flow is reversed through the fire walls towards plenum chambers which completely en- Engine . Servicing*^ Trolley Easy Inhibition of Engines While in Store circle the compressor air inlets of both units. The main air-intake ducts are of such a design that adequate precau- tions may be taken against icing troubles ard the ingress of foreign bodies. As a further protection against icing, a "sheltered " intake is proposed, in the form of louvres or slots in the power plant access door. In order to maintain the temperature of the power cell at a level consistent with requirements for best efficiency, and at the same time to avoid dangerously high temperatures, an air bleed is arranged from the main air intake ducts. A great deal of development lies ahead of the Proteus and of the various components which go to make up the coupled installation. Major alteration of the foregoing account, however, is not likely to be called for by the time the S.R.45 Ind Mark II Brabazon are airborne. WHEN an engine is not performingits designed function, but is leftstatic for anything much beyond a purely nominal period, it becomes sus- ceptible to corrosion. During the war, when engines were put into duty almost as fast as they left the manufacturers, the bugbear of corrosion did not obtrude unduly, and even in engines stored at Main- tenance Units, the period of storage was usually so short that the incidence of corrosion was negligible. To-day, however, it is entirely possible that, after delivery from the manufac- turers, an engine may be stored for a year before being in- stalled in an aircraft, and this has necessitated the most elaborate ritual of defence measures. It 1s, of course, quite simple to protect the exterior surfaces of an engine, but to give adequate protection to the more vital and vulnerable interior surfaces is a vastly more complicated problem. For some time now, a committee on which the Ser- vices and manufacturers are represented, has made an exhaus- tive study of corrosion and has issued mandatory requirements for engine protection. These requirements call for the elabor- ate use of desiccants such as silica gel, applied both to the engine itself and to the interior of the enclosing case. Some time ago, the Napier company devoted their attention to the effects of corrosion in engines and possible means whereby the aggravation could be lessened. As a result of their investi- gations, they have developed an apparatus that goes quite some way toward putting the anti-corrosive treatment of air- craft engines on a production-line basis. The apparatus is a compact, self-contained trolley unit which incorporates all the equipment required for dynamically inhibiting engines and which, furthermore, enables this to be done with the minimum amount of dislocation to the engine store or maintenance shop. Whilst the trolley, as designed, is principally intended for the treatment of Sabre engines, it is capable of being used for the treatment of any type of engine with little more adaptation than the provision of suitable couplings. Trolley Layout On the top tier of the trolley are four 20-gallon tanks, two of which contain lead-free fuel, a third contains fuel plus inhibitor fluid, whilst the remaining tank contains storage oil., A further tank beneath the last-named unit accommodates two gallons of cylinder-priming fluid. The tanks have large filler caps, and each carries direct-sight level gauges, whilst shut-off and change-over cocks are fitted to the control panel on the trolley. This also incorporates an oil-temperature gauge, cylin- der and carburettor priming pumps, starter button, booster and ignition switch, etc. From the control panel, the tank pipe- lines are run to a grouped onion panel at one end of the trolley. The Napier trolley is here shown ready for the inhibition of a Sabre engine. Each union is clearly labelled and, in addition to a simple colour-identification scheme, the ends of the various coupling hoses are provided with metal tags indicating the particular service. The centre and lower tiers form tool and equipment racks and provide convenient space for stowing the drain trays, temporary exhausts, flexible connecting hoses, etc., when trans- ferring the trolley from one site to another. The lowermost tier carries the two 12-volt batteries that supply the electrical services, such as built-in boost coils, cartridge-starter firing, etc. As all the operating controls are grouped in the central panel, it is easy for the trolley to be so positioned relative to the engine that one man may comfortably perform the entire running operation. A small portable auxiliary panel is sup- plied for attachment to the engine; it provides the requisite engine controls and carries a tachometer, together with oil and coolant pressure and temperature gauges. The method employed is not only effective but is also very simple. Where a Sabre engine is concerned, the smooth run- ning characteristics and high dynamic inertia make it quite possible to run the engine without an airscrew or alternative flywheel mass, and thus the engine can be run as and where it stands in its packing case on the floor. After removal o\ the packing case, the engine is run on the fuel and oil supplied from the trolley tanks. After running lor a sufficient time tc stabilize the operating conditions at the optimum for inhibit- ing, the cocks are turned over to the inhibitor mix and the engine allowed to run for about frwe minutes, after which the cocks are shut off and the engine allowed to die by fuel starva- tion. Thus the fuel and oil become vehicles for carrying the inhibitor into direct contact with the whole of the engine interior, the fuel being used in the process of combustion to leave a protective film. The various supply hoses are then disconnected and the blanking covers replaced on the engine. This method has the merit that, not only does it facilitate the inhibiting of an engine going into storage, but also has the added quality that, when an engine is withdrawn periodi- cally for a proving run, the same operation also automatically re-inhibits it. As an additional safeguard to the internal in- hibiting, if small plugs of silica gel were incorporated in the blanking covers, this should serve quite adequately to cope with any condensation consequent upon large temperature changes whilst the engine is stored, without the provision of large amounts of desiccant as at present called for.
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