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Overhead Cam Engines During the early years of the war, the Admiralty was demanding more powerful aircraft engines that would enable aircraft to bomb the German fleet, or bomb the industrial factories that supplied the fleet. Such an engine would have to be capable of delivering at least 300h.p. and because of this challenge, Rolls-Royce developed its first aircraft engine. Coatalen's response was to design a new type of aircraft engine that would fulfil the Admiralty's requirements. The existing side valve engines, had one disadvantage, the side valves ran very hot and tended to warp, as the engine cooled down, after use. The problem could be so bad that an engine would have to be removed from the aircraft for an overhaul after each flight. The larger engines could also be difficult to start, often the plugs would have to be heated before the engine fired. Coatalen decided to overcome these problems by developing an overhead cam engine, that was based on the existing racing car engines. The Cossack The first of the new engines was the V12, 310/320h.p. Cossack, which was one of the most powerful engines that was available at the time. The engine had a 110mm bore and 160mm stroke. It had an overhead cam which operated four valves for each cylinder and had articulated connecting rods. The engine was fitted with four Claudel-Hobson carburettors and had a 2:1 gear ratio for the propeller. When running, the engine weighed 1372.5lbs. The Cossack would become one of Sunbeam's most successful engines. Production started early in 1916 and the engine was initially hand-built in small numbers, but as the Gurkha engine was phased out, production of the Cossack rapidly increased. Development work on the engine continued, and before the year was out the Cossack II had been produced. The new engine could deliver 320h.p. at 2,000r.p.m. and was fitted with four magnetos, and an air and hand starter.
Aircraft Fitted with the Cossack
The Nubian Harris Booth, of the Admiralty's War Department, designed the AD biplane flying boat, which was to be built by Supermarine. In response to this, Louis Coatalen designed the Nubian engine and work on the project began in March 1916. The new engine was based on the one used in the 1913 Peugeot racing car. It was a V8 engine with cylinder banks set at an angle of 60 degrees. The cylinders had a bore of 95mm and 135mm stroke, giving a capacity of 7.685 litres. The engine had twin overhead camshafts, weighed 684lbs and delivered 155h.p. An order for 50 Nubians was soon received for use in the AD biplane, but there were a large number of problems with the design and it was sometime before any could be delivered. Due to this the War Department decided to use the 150h.p. Hispano-Suiza engine instead. A complete redesign was necessary in order to overcome the problems, and in the end, the same configuration as the original Crusader was used, and the engine was known as the Nubian II. The delay meant that the first 4 of the 50 engines that had been ordered for the AD biplane were not delivered until October 1917, by which time the engine was superceded by Sunbeam's own Arab and the 150h.p. Hispano-Suiza. 36 engines were actually delivered and the last 14 were cancelled. Its probable that none of the 36 engines were actually used. Ironically one of them still survives in London Science Museum's store, at Wroughton. The only aircraft which is definitely known to have been powered by a Nubian, was the Saunders T.I. Special. Only one of which was built.
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