Gnome Monosoupape 9 Type B-2
| Monosoupape | |
|---|---|
 |
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| A 1917 Gnome 9N 160 hp Monosoupape rotary engine, with dual ignition provision (twin spark plugs per cylinder) | |
| Type | Rotary aero engine |
| National origin | France |
| Manufacturer | Gnome et Rhône |
| First run | 1913 |
| Major applications |
Avro 504 Sopwith Camel |
The Monosoupape (French for single-valve), was a rotary engine design first introduced in 1913 by Gnome Engine Company (renamed Gnome et Rhône in 1915). It used a clever arrangement of internal transfer ports and a single pushrod-operated exhaust 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".
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 CV 9B-2 and 160 CV 9N, with differing displacements and a dual ignition system on the later 9N version.
Contrary to the Le Rhône designs, the early Gnome engines like the Gnome Omega, Lambda and Delta 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. A pressure-operated inlet valve, which was balanced by a counterweight to equalize the centrifugal forces, 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 both in order to perform maintenance of the intake valve, which could easily become jammed, and in order to adjust the timing and pressures correctly for the rod-less operation; and the Gnomes exhibited poorer fuel economy than other rotaries because the inlet valves could not be opened and closed at the ideal times.
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