Name Dragonfly Designer unknown
Type Compression Ignition, RRV Capacity 0.1cc, 0.2cc
Production run unknown/small Country of Origin England
Photo by various Year of manufacture 1961



This engine was never advertised as such, although because of its small size, it did attract some model press attention in British Model Aircraft magazine of January 1961 and American Modeller of March 1961. The actual designer and constructor of the Dragonfly is unknown (at this time), the engine being sold by word-of-mouth through the fameous HJ Nichols model shop in London.

Neither is it known how many were made, although it is apparent that enough were built for some to remain in the hands of collectors today, and for there to have been "prototype" engines, and "production" variants. The photo and accompanying text here appeared in the "Dope Can" feature (love the name) of March 1961 American Modeller. It is similar to that appearing in Model Aircraft as it describes the engine, both clearly stating that front bearing as being separate from the main crankcase. This requires that four tiny holes be drilled and tapped, and another fou be drilled to exactly register with the tapped ones. Quite a procedure.

The engine appears in Clanford's A-Z of Model Engines with three pictires as seen here. Clanford reports that there were three sizes: 0.1, 0.2 and 0.3 cc. Each photo clearly shows the front bearing being integral with the crankcase--a much simplier and more practical arrangement. But Clanford's book, valuable reference that is is, is litered with mistakes and errors.

A sketch I received from Ken Croft in the UK (prepared by Tom Crompton, I believe), allowed the engine to be drawn in CAD (and rendered in 3D for the pic at the top of this page). As sketched, the engine is indeed of 0.1cc capacity. While it would not be practical to increase the bore to make give 0.2cc capacity, neither bore nor stroke can be increased to make it 0.3cc, and as neither the Aeromodeller, nor AM articles mention a 0.3cc version, I'm going to call horse-pucky on Clanford until proven wrong by an actual owner of such a beast.

The Rear Rotary Valce (RRV) configuration makes good sense for an engine this size. It can provide generous induction timing with just a little more complexity than the more conventional Front Rotary Valve (where the permissable diameter of the induction hole in the crankshaft would be a limitation), and permits higher top RPM than a Side Port configuration (which, due to symetrical timing and the small flywheel effect of the small prop, would make starting more hit and miss as regards direction of rotation).




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