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.