and with a wingspan of 22.5 m (73 ft 10 in), was powered by a single engine. The first large multi-engined aircraft was Igor Sikorsky's Bolshoi Baltisky, first flown in May 1913 with two engines and later equipped with four. Engine development Early aircraft development was heavily reliant on the development of the internal combustion engine, and the problem of staying in the air was largely a matter of having an engine which was not only sufficiently powerful but was also lightweight and reliable. Most early engines were neither powerful nor reliable enough for practical use, and the development of improved engines went hand-in-hand with improvements in the airframes themselves. The Wright Brothers had been unable to find a satisfactory engine and, with the help of their mechanic, had manufactured their own. They used a single flight engine, a 12 hp water-cooled four-cylinder inline type with five main bearings and fuel injection. The first internal combustion piston engine design to be widely used for powering aircraft was the Antoinette water-cooled V8 engine, believed to be the very first V-form eight-cylinder internal combustion engine ever placed in production, designed by the Frenchman Léon Levavasseur. The Antoinette 8V incorporated direct fuel injection, evaporative water cooling and other advanced features, weighed 95 kg (209 lb) and produced 37 kW (50 hp). Introduced in 1906, these engines were used by, among others, Santos Dumont, the early Voisin aircraft and Samuel Cody. American aviation engine designers quickly picked up on the V-8 engine concept from 1906 onwards as the era progressed, with both Glenn Curtiss' firm designing a series of liquid-cooled V-8 aviation engines culminating in the Curtiss OX-5 by the early years of World War I—another major American engine manufacturer, Hall-Scott, had their A-2 and A-3 overhead valve, liquid-cooled V-8s in production as early as 1908. The British Green C.4 of 1908 followed the Wright's pattern of a four-cylinder inline water-cooled design but produced 52 hp (38 kW). It powered many successful pioneer aircraft including those of A.V. Roe. Horizontally opposed designs were also used with some success. Santos-Dumont's Santos-Dumont Demoiselle No. 20 monoplane used first the 18 kW (24-hp output Dutheil et Chalmers liquid-cooled opposed twin engine, later replaced by a 22 kW (30 hp) Darracq-built engine of the same layout. The four-cylinder water-cooled de Havilland Iris achieved 45 hp but was little used, while the successful two-cylinder Nieuport design achieved in 1910.