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Aviation History
1918
1918 - 0746.PDF
U JULY 4, 1918. REPORT ON ALUMINIUM PISTONS FROM 230 H.P. BENZ ENGINES.* A 230 h.p. Benz engine, No. 31,560, taken from the Aviatik biplane, G. 130, captured on February 12th, 1918, was found to be fitted with aluminium pistorrs. As these are the first aluminium pistons to be found in a captured enemy aero engine in service, a detailed report of their design, together with a chemical analysis of the alloy, should be of interest. which these pistons were fitted. The design of the standardcast-iron Benz piston, which is fitted with a conical steel support, riveted to the inside of the piston crown, and whichbears upon the centre portion of the gudgeon pin through a slot cut in the connecting-rod small end, is well known.Unlike the standard cast-iron piston, the domed head of the m Fig. 1 Left :Inside view of 230 h.p. Benz cast - aluminium piston. Fig. 2.—R i g h t :Sectional view of piston showingformation of ribs. vThe pistons weigh 4 lbs. 8£ ozs, each, without rings, whichweigh 1.5 ozs. each. The total weight of the complete piston, with rings and gudgeon pin set screw, is 4 lbs. 14J ozs.,as compared with the standard cast-iron piston, which weighs 6 lbs. 11J ozs. The gudgeon pins and connecting-rods are ofstandard Benz design, as also is the rest of the engine to * A report by the Technical Department, Aircraft Production, Ministry of Munitions. sand-cast aluminium piston is supported and stengthenedby eight webs radiating from a central boss in the piston crown. The formation and shape of the webs is clearly shownin the photographs and sectional drawings of the piston. Three cast-iron rings are fitted above the gudgeon pin,and one scraper ring is provided below the gudgeon pin. All rings are concentric and are machine hammered on theinside. It will be noticed that the rings are all exceptionally deep in section, being 5.25 mm. deep and only 3 mm. widevertically. The piston ring gap measured in position in a Fig. 3.—Details of aluminium pistons now used in 230 b.p. Benz engines. 744
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