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Aviation History
1932
1932 - 1195.PDF
FLIGHT, NOVEMBER 24, 1932 valve is provided for each cylinder and the sparking plugs are screwed, one on either side, directly into the head, no adaptors being necessary. The valve ports and manifolds are arranged on the right-liand side, so that the slip stream from the airscrew, which is a left-handed tractor, carries any fumes away from the cockpits, and also reduces the noise. The pistons are of the slipper type, cast from D.T.D. specification 131 aluminium alloy ; so designed that the thrust from the crown is taken direct to the gudgeon pin bosses and is not transmitted via the skirt. Three rings are fitted below the gudgeon pin on each piston, that nearest the pin being of the scraper type. Fully floating gudgeon pins, locked at each end by external circlips, have been adopted. The connecting reds are machined from forgings of D.T.D. 130 alloy, a bronze shell, lined with white metal, forms the big end bearing and the big end itself is exceptionally rigid. The crank shaft is made from a nickel-chrome alloy steel forging, machined all over and carried in five plain bearings. A ball journal bearing is provided near the front end to locate the shaft and to take the thrust in either direction from the airscrew. All main bearings are fed continuously with oil under pressure. The airscrew hub is fitted on a carefully designed tapered extension of the crankshaft, pro vided with eight bolts and a quickly detachable spinner. The main boss need not be disturbed on its taper when changing the airscrew. This operation can be performed very easily and quickly by withdrawing the airscrew together with the flanged sleeve which is specially made so as to be an easy lit over the boss proper. The crankcase and top cover are light alloy castings, bolted together in the horizontal plane of the crankshaft centre line. The crankcase is very deep and well webbed iniernally ; each intermediate bearing being supported by a stiff cross mem ber extending right across the crankcase. The main bear ing shells are retained by separate caps, which, being readily accessible by removal of the top cover, facilitate assembly, inspection and overhaul. Appropriate facings are provided on the crankcase for bearer feet, breather, fuel pumps, oil drain pipe and lifting attachments. The camshaft is very rigidly supported by five plain bearings on the left-hand side of the crankcase and operates directly on to hardened steel tappets. Tubular duralumin push rods and steel rockers oscillating on har dened spindles attached to the cylinder head by stout steel brackets serve to actuate the valves. The whole of the valve gear is totally enclosed and is lubricated by splash from the rockers dipping in an oil bath provided in the valve casing covers. Timing gears are housed ir. a separate cover built on to the rear end of the crankcase, and the camshaft is driven by sour gears from the crank shaft. The explosive mixture is provided by a Claude! Hobson A.l 48a Down Hyphenate draught carburetter fitted on the right-hand side of the engine, the vertical lead of which, to the induction manifoid, is jacketed by the exhaust gases. Efficient carburation is thus ensured even in the coldest weather. Bosses can be provided on the induction manifold for connection to a doper system The de Havilland " Giosy Major" (120/130 h.p.). 1117 The de Havilland " Gipsy II " (108/110 h.p.). which, though normally unnecessary, may be used il desired. Mixture control is provided on the carburetter by an " air-bleed " valve, hand operated from the cockpit. Lubricating oil is carried in the fuselage in a separate tank and drawn therefrom through a gear type pump situated on the timing cover. From the pump the oil flows through a Tecalemit felt filter which ensures the removal of even the finest particles of foreign matter before the oil passes into the engine. This filter is so positioned that it can easily be removed for cleaning. The main supply from the filter is taken by an external gallery along the side of the crankcase, where it is con nected by drillings to the five main bearings, thence it passes into the crankshaft through the hollow journals, and so to the crank pins and big ends. Holes are drilled in the big end bearings and connecting rod caps from which oil is thrown on to the cylinder walls and pistons. The lubrication of the cylinders is thus maintained irrespec tive of wear and clearance in the main bearing ; the spray created in the crankcase also serves to lubricate the cam shaft bearings, cams and tappets. The oil ultimately collects in the space formed by the extension of the cylinders into the crankcase whence it is returned by external pipes to the tank. An important point about these engines is the fact that the whole range is designed to run on any good grade of automobile fuel while the lubricating oils recommended are obtainable without trouble at all aerodromes where supplies of the better known brands are held.
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