The Monosoupape (French for single-valve), was a rotary engine design first introduced in 1913 by Gnome Engine Company (renamed Gnome et Rhรดne in 1915). It used a clever arrangement of internal transfer ports and a single pushrod-operated exhaust valve to replace the many moving parts found on more conventional rotary engines, and made the Monosoupape engines some of the most reliable of the era. British aircraft designer Thomas Sopwith described the Monosoupape as “one of the greatest single advances in aviation”.[1]
Produced under license in both seven and nine-cylinder versions in large numbers in most industrialized countries including Germany (by Oberursel), Russia, Italy, Britain and the US. Two differing nine-cylinder versions were produced, the 100 hp (75 kW) 9B-2 and 160 hp (120 kW) 9N, with differing displacements giving the larger displacement 9N version a nearly-cylindrical shaped crankcase, with the 9N also adopting a dual ignition system for increased flight safety.
2,188 units were produced under license in Britain, with an uprated 120 hp (89 kW) version later built in Russia and the Soviet Union, two of which flew the Soviet TsAGI-1EA single lift-rotor helicopter in 1931-32.
Source: Wikipedia
Check out how these rotary engines were assembled with this video.
Video Credit: Pierre Jansen