Quarter-Scale Merlin

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1/5-scale Merlin: Work is proceeding on the design of a 1/5-scale Merlin. Present thinking is to try to keep it simpler than the Quarter-scale Merlin, particularly in the supercharger area. One design goal is to try to keep it light, so that flying a 1/5-scale airplane with it may be possible. There is a minimum recommended wall thickness in investment casting, so it's difficult to reduce the weight in proper proportion to the scale. Besides finishing the design, all the wax molds have to be made, so it's going to be a while.

1/5-scale Allison: The Allison, of course, was the U.S. counterpart to the Merlin. Never as glamorous, it still contributed tremendously to the war effort. The Flying Tigers' P-40s did pretty well with them, the Russians liked the P-39 for tank-busting, and the P-38 did extremely well in the Pacific. The original idea here was to design an engine which could be machined completely from bar stock, so that plans could be sold. The Allison was selected for this because its shape is much less complex than that of the Merlin, so machining a fairly scale model of it from bar stock is easier. A fair amount of work has also been put in on designing castings for a much more scale (and lighter) version.

1/5-scale Griffon: While working on the Allison design, it was noted that a 1/5-scale Griffon cylinder block would fit in the exact same length as the Allison block, which is quite a bit longer than the Merlin's. A 1/5-scale Merlin's displacement is 216cc, while the Griffon would be 294cc. Quite a bit more displacement, and not that much more weight. A 1/4-scale Griffon would be 574cc, compared to the Merlin's 422cc. Like the Allison, the Griffon doesn't have the cachet of the Merlin, but 36% more displacement might be handy.

1/4-scale Ferrari 250 V-12 engine: This was the first V-12 engine that was built in the process that lead to the Quarter-scale Merlin. Machined mostly out of bar stock, but with investment-cast valve covers and carburetors, it's pretty impressive.

If you're interested in these projects, please email