Gnome Monosoupape 9B
One of the best engines of the early years of aviation was built by French designer-engineer Laurent Seguin in 1913. Seguin had already had five years' experience of building aero engines; however, his 5- and 7-cylinder 'Gnomes' had structural weaknesses (the automatic intake valves were too often out of balance, springs failed etc). To eradicate these problems, Seguin decided to completely remove the induction valves, instead using a clever arrangement of intake ports around the cylinders this involved the role of the valve being played by the piston itself.
The new engine appeared to be successful enough and gained its full name of Gnome Monosoupape (translated from the French, 'single valve'). Sir Thomas Sopwith, the outstanding British aircraft designer, later called the Monosoupape "one of the greatest single advances in aviation". Mass production of Monosoupapes began in 1914. Most widespread were two basic types: the 7-cylinder Gnome Lambda, and the 9-cylinder Gnome Delta. The 7-cylinder version very quickly showed limited suitability for the greater and greater demands placed on engines in the conditions of a rapidly growing air force; however, the more successful Delta version became an impetus for the much improved Gnome Monosoupape 9N, which had an increased capacity and an increased RPM (up to 1350). The power of the Gnome Monosoupape 9N grew to 160 h.p.
As with all other rotary engines of the time, the Gnome Monosoupape had a substantial drawback: its production was very expensive, as all the separate parts had to be made by precision machining. The cost of the engine in 1914 was equivalent to approximately 75 thousand of today's dollars. On the other hand, the Gnome Monosoupape weighed somewhat less than comparable engines of its class, and was not too fussy about the quality of its fuel. The Gnome Monosoupape was used in many types of airplane, such as the Airco DH2, Vickers FB5 Gunbus, RAF F.E.8, and the Nieuport 28.

Type Air-cooled rotary engine
Cylinders 9
Displacement 11.76L
Bore 110mm
Stroke 150mm
Dry weight 118kg
Power output 75kW
R.P.M. 1230
Fuel consumption 0.353kg/(hp·h)