from Wikipedia, the free encyclopedia
Gnôme 9N monosoupape
Section through a cylinder

Monosoupape (French as much as Einventiler ) is the name for a type of four-stroke - rotary engines have that no more intake valves, but in each cylinder only a controlled variable exhaust stroke. The fuel - air mixture is passed through the hollow crankshaft in the crankcase, from where it passes through openings in the liner enters the cylinder.


This aircraft engine from the Société des Moteurs Gnôme was first shown at the Paris Salon in 1913. Like his predecessors, he was also granted licenses in various countries, including the German Reich , where he was manufactured by the Oberursel engine factory . So it came about that during the First World War this widespread engine and its derivatives were used by both warring parties.

The US patent for the crankshaft was filed June 12, 1909 and granted May 24, 1910. The U.S. patent for the exhaust valve mechanism was filed July 1, 1913 and granted May 21, 1918.


The individual, rather large-sized valves in the crests of the combustion chambers were operated by a camshaft mounted on the crankshaft and running at half speed opposite the crankcase via roller tappets , push rods and rocker arms. Towards the end of the work cycle the valve was opened, the burned gases could escape directly into the ambient air without an exhaust manifold and were pushed out with the subsequent upward movement of the piston. Fresh air first flowed in from the outside through the valve, which was still open during the subsequent intake stroke, which meant that the valve was well cooled. It was only closed during the downward movement of the piston, so that a negative pressure formed in the cylinder as the piston continued to move. In the previous engines, a relatively complicated, freely moving inlet valve was built into the piston crown, the mass of which had to be balanced by counterweights in order to neutralize the centrifugal force. As a result of the negative pressure in the cylinder, it had opened shortly before the bottom dead center was reached and allowed the fuel-air mixture from the crankcase, which was still too rich, to flow into the cylinder. This valve had now been omitted in the monosoupape engines and replaced by a series of inlet bores, which were now exposed by the piston in the last part of its way and thus enabled the access of the fuel spray. It was only through the mixing with the fresh air that had flowed into the cylinder that an ignitable mixture was created during the compression stroke, which was ignited by the spark plug when the top dead center was reached. The work cycle followed and the process began again. The petrol-insoluble castor oil had to be used to lubricate these engines , so that the pilot had to endure not only the smell of the combustion gases but also that of the oil.


The engine had neither a carburetor nor a throttle valve . Instead, the fuel was fed under pressure by a pipe through the hollow rear section of the stationary crankshaft to the crankcase, where it was atomized via a nozzle. Fresh air also came in through the hollow shaft. The power could now be largely regulated, unlike the previous engines. The stroke of the valves could be adjusted with the help of a small handwheel in the driver's cab. This enabled the ratio of fuel to air to be adapted to the flight altitude or the power to be reduced by a lean mixture. For the first time, a rotary engine could be regulated within limits. Before that, the pilot had to temporarily interrupt the ignition - for example when landing - in order to reduce the power, as he did not have a throttle. The engine was switched off simply by closing the fuel cock.

By eliminating the intake valves, fuel and, above all, oil consumption have been reduced significantly.

Maintenance was also easier. The automatic intake valves on the early Gnome engines were difficult to adjust and only accessible after removing the cylinder heads. In addition to their performance, which is limited by the engine speed and the resulting poor degree of filling of the cylinders, the internal intake valves quickly tended to malfunction, became stiff and did not work properly at great heights. The inlet valves were the cause of constant maintenance problems and were responsible for the very short times between engine overhauls (TBO).


  • Fritz Huth: Engines for airplanes and airships. Richard Carl Schmidt publishing house, Berlin 1914.
  • Flugsport magazine, years 1913 and 1914.

Web links

Commons : Monosoupape  - collection of images, videos and audio files

Single receipts

  3. Archived copy ( memento of the original dated July 6, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 465 kB) Kimble D. McCutcheon: Gnome Monosoupape Type N Rotary. P. 2. @1@ 2Template: Webachiv / IABot /