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This may be of interest, from S.D. Heron's "History of the aircraft piston engine" (Ethyl Corporation, 1961):
"The Hispano-Suiza V-8...initial rating of 150 horsepower...had a light and weak crankcase which was stiffened very materially by two very stiff aluminum cylinder blocks. Although aluminum was used as a cylinder material, it did not contribute to cylinder cooling. In fact, the cooling was equivalent to that of a badly cooled steel cylinder...The engine had totally enclosed valve gear lubricated with engine crankcase oil...The design was exceedingly clever but showed little knowledge of either cylinder or valve cooling. However, none of us knew very much about these subjects in 1915...The durability of the European built Hispano engines was very poor, the major items of difficulty being the connecting rods, the exhaust valves, and the reduction gear where used...The late Henry Crane was responsible for introducing a greatly improved connecting rod design, but the exhaust valve durability of the American [Wright-Martin] engines was about as bad as that of the European design...Subsequent to the end of the war, a considerable number of direct-drive models were built by Wright Aeronautical (successor to Wright-Martin)...The engine had an unpleasant high-frequency vibration that put the pilots' feet to sleep." p.15-16
Bletchley
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