The Drome Demon was an English-made 6 cc spark ignition engine which was manufactured by the Model Aerodrome of 141 Stratford Road, Birmingham, England, hence the unit’s name. Several previous commentators have given the engine's date of production as 1941 or earlier, but this is highly unlikely to be true. Both the manufacture of model engines and their use for flying purposes were prohibited during the WW2 years due to wartime production priorities and security concerns. The sole advertisement for the engine appeared in the February 1946 issue of "Aeromodeller" magazine.
The Drome Demon is mainly notable as having been the sole British-made representative of the infamous class of “slag” engines which originated primarily in the USA. The term “slag engine” implies a design having no cylinder liner, with the piston therefore running in an untreated aluminium alloy cylinder bore (no chrome plating in those days!).
Most of the American slag engines such as the well-known Thor models added insult to injury by also featuring an aluminium piston to go with the aluminium bore. Amazingly enough, some of these engines were capable of running reasonably well over a limited working life, to the extent that SAM used to offer a free flight competition class for models powered by unmodified slag engines. The main requirement was the use of a fuel containing a lot of oil – 50% was the usual recommendation.
The Drome Demon didn’t go quite as far as the all-aluminium piston/cylinder combination of the American products. Instead, it featured a pressed steel piston running (probably briefly) in an aluminium bore. The engine was sold both ready to run and as a kit. Consequently, examples may be encountered which have been significantly modified by their home builders. Based upon a comparison with the advertising image, the illustrated example of the engine appears to be substantially original.
The paragraph in O. F. W. Fisher’s book describing the engine makes mention of a latter-day reproduction of the Drome Demon made especially for collectors. If so, these are even more rare than the originals, as I have been unable to make contact with anyone who has so much as heard of one, let alone seen one! If any reader has such a reproduction, some details and/or a photograph would be most welcome.
These engines are somewhat rarer than a mixture of hen’s teeth and rocking horse droppings, so finding one would be a case of lightning striking. And if you do find one, don't expect it to run for long, if at all! Still, the engine holds a unique place as Britain’s only genuine slag engine. Further details of the Drome Demon may be found here in the “Whatzit?!” section of Ron Chernich’s “Model Engine News” (MEN) website - scroll down the page to find it.