Gnome Monosoupape B
Gnome Monosoupape B
  • Date of Manufacture: 1914
  • Country: France, Britian, U.S.A, Russia
  • Type: Rotary
  • Cylinders: 9
  • Horsepower: 90
  • Diameter: 98 cm
  • Depth: 101 cm
  • Weight:115 Kg (dry)
  • Aircraft Example: Sopwith Pup

The Gnome Monosoupape

The Monosoupape (French for single-valve), was an engine design used by Gnome et Rhône's later rotary engines, and first introduced in 1913. It used a clever arrangement of internal transfer ports and a single valve to replace a large number of 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".


Earlier Gnôme (as opposed to Le Rhône) designs used a unique arrangement of valves in order to avoid needing pushrods and other complex devices that operated during the inlet phase of the combustion cycle on more conventional engines. Instead, a single exhaust valve on the cylinder head was operated by a pushrod that opened the valve when the pressure dropped at the end of the power stroke. The inlet valve, which was operated by a counterweight, was placed in the centre of the piston crown, where it opened to allow the fuel–air charge to enter from the engine's central crankcase.

Although ingenious, the system had several drawbacks: the cylinder heads had to be removed for both maintenance of the intake valve, which could easily become jammed, and in order to get the timing and pressures right for the rod-less operation; and the Gnômes exhibited even poorer fuel economy than other rotaries because the inlet valves opened at times that were not efficient.