by: Stephen T. Lawson [ ]
HistoryIn 1913, Louis Seguin and his brother Laurent (engineers who founded the Société Des Moteurs Gnome [the Gnome motor company] in 1905) introduced the new Monosoupape (Mono-soo-pap) series, which eliminated the inlet valve, replacing it with piston-controlled transfer ports similar to those found in a two-stroke engine. . .The overhead valve exhausted directly into the slipstream since there was no exhaust manifold in order to save weight.
The charge was an overly rich mixture of air, which was acquired through the hollow crankshaft, and fuel that was continuously injected by a fuel nozzle on the end of a fuel line. . .
On the early B 2 100hp version the single park plug was installed horizontally into the rear of the cylinder at the top. But had no connecting high-voltage wire. The stationary magneto mounted on the firewall, whose high-voltage output terminal was in close proximity to the spark plug terminals as they passed by. This arrangement eliminated the need for points, distributor, high-voltage wiring and capacitors found in conventional mechanically timed ignition systems. But this necessitated use with tractor design with a firewall behind the motor. Pusher aircraft had none, so a type with external wiring leads had to be developed. . . On later B, M and N types the Monosoupape the spark plugs were connected to high voltage wiring.
The Monosoupape had no carburetor or throttle, and since most of its air supply was taken in through the inlet /exhaust valve, it could not be controlled by adjusting the air supply to the crankcase like other rotaries. Early Monosoupape had a single petrol regulating control used for a limited degree of speed regulation. In early examples, engine speed could be controlled by varying the opening time and extent of the exhaust valves using levers acting on the valve tappet rollers, but this was later abandoned as it caused burning of the valves. Instead, a blip switch was developed.
The Copper State Models Ltd, 1/48 resin Gnome MonosoupapeIs a good representation of the late “B 2” used on pusher type aircraft. It could physically pass for the tractor type “N” if you added a second spark plug. To pull off a tractor early type “B 2” you would have to move the single sparkplug 15 degrees back toward the rear face of the cylinder. About the 4-5 O'clock position when viewed from above. (Remember no wiring for this version). I can highly recommend this resin motor.
applicationsThe complete list of allied aircraft that used this engine is extensive. Here are some of them.
Coventry Ordnance Works Biplane No 2
F.B.A. C Flying boat
Royal Aircraft Factory B.E.8
Royal Aircraft Factory F.E.8
Short Type C
Sopwith Circuit Seaplane
Sopwith (Admiralty Type ) 807 Folder Seaplane
Sopwith Two-Seat Scout
Vickers Gunbus (FB.2, 3, 5, 6 and 7)
Vickers E.S.1 Bullet
Vickers F.B 19 Bullet
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