Overhead Cam Engines
The Afridi and the Maori
The Afridi was Coatalen's second 12 cylinder, overhead cam aircraft engine and was conceived as a replacement for the sidevalve Crusader and Zulu.. It was very different to the Cossack, which was the first V12 in the series. The engine was very much smaller and had a 92mm bore and 135mm stroke, giving a capacity of 11.476 litres. The two banks of cylinders were set at 60 degrees and had two overhead camshafts per block, which operated 4 valves per cylinder. The engine had two Claudel-Hobson carburettors and 4 magnetos. It delivered 200h.p. at 2,000r.p.m. The first two engines were delivered in July 1916 and production built up slowly. By January 1917, fifity five engines were produced per month. Development continued and the bore was increased from 92mm to 100mm, to produce a power output of 250/260h.p. The new version was called the Maori, and 100 of the 299 Afridis, that had already been built, were converted to Maoris before despatch. The Maori superceded the Afridi and production of the Afridi ceased in June 1917. The Maoris were initially unreliable and the problem was overcome by using dual ignition, with two sparking plugs per cylinder. The Maori II soon appeared with a power output of 260h.p., and this was followed by the Maori III, which could deliver 275h.p. The Maori III had the exhaust valves moved to the outside of the cylinder banks and carburettors inside the 'V'. Throughout 1917 and 1918, large numbers of the engine were produced and after the war a Maori IV was produced for use in the R.33 and R.34 airships. Each airship was powered by five Maoris and they were the most successful British airships ever built.
Aircraft Fitted with the Afridi
Aircraft Fitted with the Maori
There is a Maori II preserved at the Imperial War Museum, Duxford, another at the Musée de l'Air, Le Bourget, Paris, and a third at Straight 8 Restorations, in Hamilton, New Zealand.