If You’re Going To Make A Model Engine, You Might As Well Make It A Merlin

It has been remarked before in more than one Hackaday post, that here are many communities like our own that exist in isolation and contain within them an astonishing level of hardware and engineering ability. We simply don’t see all the work done by the more engineering-driven and less accessory-driven end of the car modification scene, for example, because by and large we do not move in the same circles as them.

One such community in which projects displaying incredible levels of skill are the norm is the model making world. We may all have glued together a plastic kit of a Spitfire or a Mustang in our youth, but at the opposite end of the dial when it comes to models you will find craftsmanship that goes well beyond that you’d find in many high-end machine shops.

A project that demonstrates this in spades is [mayhugh1]’s quarter-scale model of a vintage Rolls-Royce Merlin V12 piston aero engine. This was the power plant that you would have found in many iconic Allied aircraft of the WW2 era, including the real-life Spitfires and all but the earliest of those Mustangs. And what makes the quarter-scale Merlin just that little bit more special, is that it runs. Just add fuel.

The build took place over a few years and many pages of a forum thread, and includes multiple blow-by-blow accounts, photos, and videos. It started with a set of commercial castings for the engine block, but their finishing and the manufacture of all other engine parts is done in the shop. In the final page or so we see the video we’ve placed below the break, of the finished engine in a test frame being run up on the bench, with a somewhat frightening unguarded airscrew attached to its front and waiting to decapitate an unwary cameraman. Sit down with a cup of your favourite beverage, and read the build from start to finish. We don’t think you’ll be disappointed.

If this Merlin has whetted your appetite, you’ll be pleased to hear that the HMEM site it’s hosted on has been going for quite a while.

Thanks [nfk] for the tip.

42 thoughts on “If You’re Going To Make A Model Engine, You Might As Well Make It A Merlin

      1. Original design was for an Allison V12, but the British put a Rolls Merlin V12 in it to get high-altitude performance. Later ones were powered by Packard’s version of the Merlin with two-speed supercharger.

        1. Quote from somewhere on the web:

          “I still do it, it’s habit from driving over-carbed V8s when I was young. If you didn’t pop the motor after idling for a while, the plugs would load up and make it hard to start the next time.”

          1. “clearing the engine” @TGT “blow out the carbon”

            Car Talk on the subject.
            Tom: In the ’70s, cars had carburetors. Carburetors let gasoline slosh into the cylinders. And with all that excess gasoline, a buildup of carbon was a much commoner problem.

            Ray: There was a school of thought that suggested that running the car at high speed would help clean the caked-on carbon off the valves and pistons.

            Tom: But by “running the car at high speed,” they meant taking it on the highway for a long, high-speed drive – not stomping on the gas at a stoplight and leaving a lime-green AMC Pacer in the dust.


  1. The guys and gals that pull this stuff off blow my mind.

    The attention to detail and patience is awe inspiring, not to mention the physics of making a scale engine just run. It’s not just the challenge of copying a scale but then making the adjustments to compensate for the flow of fuel and air,

    1. “Normal” production Merlins (not racing engines) came in a lot of variants, ranging from about 1000 to 2000 horsepower. Assuming the same power/displacement ratio, a quarter-scale engine with 1/64 the displacement would be in the 15-30 hp range. (I would assume this naive scaling is an overestimate, because an optimal design at one scale would not be optimized for a different scale, but I really don’t have any experience with model engines.)

      1. Holy hell. 500 horses at 330 pounds. That’s not a bad thrust to weight ratio, is it? I bet merely touching the throttle on that bike launches it to the moon, dropping the rider off at a police station or hospital along the way. I want it.

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