Build a mock rotary engine

Model Airplane News, Jan 1999 by Irvine, Martin

NEEDED TO build a 1/5-scale dummy 80hp LeRhone for a 1915 Nieuport 12, but nothing commercially available would do the job. Every idea I came up with to build the finned cylinders seemed to be a tremendous amount of repetitive work or was likely to achieve a second-rate result-until this one. This basic method can be used for other scales and engines. The big plus is that although the fins are very thin, the structure is pretty sturdy.

The dummy crankcase is a piece of a mailing or drafting tube. If you can't find a suitable tube, make one by rolling brown packing paper, and use glue sparingly.

The "cylinders" are red cardboard tubes cut to length (as long as the cylinder is high-from crankcase to cylinder head). Cap the cylinder ends of the tubes with 3/16-inch sheet balsa and sand them to match the crankcase curve using sandpaper wrapped around the large tube.

Cut the fins out of a manila file folder. Cut the outer circle first. On the LeRhone, the outer diameter of the fins changes, so about a third of the circles should be slightly larger than the rest. Now cut out the inner circle. This has to be slip-fit over the cylinder, so take your time to get it right. If it's too tight, the fin will become distorted when you put the cylinder on; if it's too loose, it will be difficult to glue into place.

Place the fins on the cylinder one or two at a time (align them using the plastic cap), and glue them into place with a drop or two of CA. Continue this process until you reach the top of the cylinder. Make the rest of the cylinders in the same way.

The front of the crankcase is balsa. I added another piece of 1/4-inch balsa to the front and sanded it to a conic section to simulate the front of the LeRhone. I spaced the cylinders 40 degrees apart because the real LeRhone has nine cylinders (only six show). Be careful when you place the cylinders; the human eye can pick up even small discrepancies.

I mounted the finished project in the Nieuport cowl. The cylinder heads can be made out of l/32- or 1/64-inch plywood disks with 1/32-inch plywood fins. The valves and pushrods are dowels, and the other bits are basswood. The intakes are modified parts left over from another kit, but you could easily carve or mold them.

I painted the dummy engine with a mixture of silver and black and painted the intakes copper. The next step is very important: go over everything with a wash of brown/gray thinner. I used the muck left over from cleaning my brushes.

When you're faced with a task like this, regard it as a model in itself. Breaking it down into its component parts turns it into a less daunting task. An evening in front of the TV will get the cylinders finished; it will take another evening to finish the structure, followed by an hour's painting; then it will be ready for mounting.