Overhead Cam Engines
In 1916, British manufacturers were hard pressed to meet the demand for aircraft engines and so to ease the problem, the War Office decided, in 1917, to standardise on engines of about 200h.p. At this time Sunbeam was in the process of designing the 200h.p. Arab, and the War Office looked at 4 engines, including the new Sunbeam.
The V8 Arab had cast aluminium cylinder heads and blocks, and die-cast aluminium pistons. It weighed only 550lbs. The bore was 120mm and the stroke was 130mm, giving a capacity of 11.771 litres. The engine had one Claudel-Hobson carburettor, two Dixie magnetos and delivered 208h.p. at 2,000r.p.m. The first engine was bench-tested, late in 1916, and by the end of the year four or five had also been built and tested.
Early in 1917 the design was submitted to the Internal Combustion Engine Committee of the National Advisory Committee for Aeronautics. In March Sunbeam received an order for 1,000 Arabs, which was increased to 2,000 in June. Deliveries had to be completed by March 1918 and no alterations were to be made to the design of the first 500. Eight weeks notice was to be given of any changes in subsequent engines. Contracts were also placed, for the production of a total of 2,160 Arabs, with Austin Motors, Lanchester, Napier and Willys Overland, in the United States. Sunbeam immediately began to produce production drawings for the engine.
By the time the initial order had been received, problems were found with the engines under test, which would require modifications to the design. It took until August for this to be resolved and when production started, problems arose with the cylinder castings. By the end of the year only 83 Arabs had been delivered. The engine soon got a bad reputation as it suffered from vibrations and was unreliable. In the meantime, large numbers of new aircraft were in store, waiting for the engines and something had to be done to resolve the problems. In response to this, the Arab II was produced, with an ungeared propeller, but problems still arose when the engine was tested in flight. Things got so bad that the Air Council sent Captain Verney to Sunbeam, to try and sort things out. The other manufacturers were experiencing the same problems as Sunbeam, and very few engines were being delivered. By the end of the war, the total number of Arabs produced by all of the manufacturers, was only 1,026. The Arab had been one of the worst engines produced during the war. A number were produced after the war, some of which were sold abroad.
Aircraft Fitted with the Arab