Build Stephen Wessell’s


This is an exact model of the Gnome Monosoupape B2 rotary engine in 1:3 scale, based on a number of extant examples together with the Gnome Instruction Book for the engine published in 1913.


No of cylinders                            9

Bore                                           1.42”

Stroke                                        1.97”

Overall engine diameter without cowl                12.8”

Cycle                                        4 stroke

Total capacity                           475cc

Rotation anticlockwise as viewed from front

Weight, incl oil pump & ignition system 14.5lbs

Speed                                        1500 - 2500rpm

Measured static thrust with 36 x 20” prop @ 1900rpm            22lbs

Lubrication by gear pump to all working parts (total loss)

Ignition (single spark plugs): electronic

Fuel:  petrol or petrol/oil mix

There are only two controls, the petrol valve and ignition switch.

There is no carburettor so speed is controlled solely by the petrol supply. Slowest idling speed is about 900rpm and landing is achieved mainly by ‘blipping’ the engine.

Like the originals, the model engine is extremely thirsty for both oil and petrol.

The cycle is 4-stroke but unlike any other, in that there is only one valve (hence the name) which doubles as both exhaust and inlet. A very rich mixture is drawn into the cylinders through transfer ports at the bottom and mixes with fresh air already admitted to produce a combustible mix. Volumetric and thermal efficiencies are therefore low by modern standards. This is, however, a very powerful engine and has flown a scale Sopwith Pup with great success (photo above).

The engine is built without castings mostly in free-cutting steel and Meehanite type cast iron. The crankcase is a silver soldered fabrication. 

Detailed working drawings are available. These have been created in Turbocad 2D and are available in pdf format. There are 35 sheets in A4 size together with Construction Notes and a few photographs. There is no drawing for a propeller. The engine was designed to fly so there are no drawings for bench stand, fuel and oil tanks.

Current (Sept 2012) price: £45. This assumes all files will be sent by email.

Enquiries should be sent to:

Click photos to enlarge.