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Scale Airplane Tips: Installing a Dummy Rotary Engine

Scale Airplane Tips: Installing a Dummy Rotary Engine

If you’ve been following my online Build-Along Series on the MAN website for my Sopwith Camel, then you know I have been featuring little mini projects as they pop up in the construction. Well, as Dave Platt, master scale modeler has said numerous times, “A scale model is never truly finished–you simply stop working in it.” Here as well, I first test flew the Sopwith Camel back in June and have flown it several times over the summer. All the while with my Zenoah G38 engine fully exposed in that big radial cowling. So, to help dress up the Camel, I have begun to install a dummy rotary engine. I hope you find the techniques involved interesting as they can be used on any similar round nosed airplane you might be building.

Starting point

Balsa USA is a great source for all things WW1 and they have been offering nice molded fiberglass dummy engines for a long time. I picked up a 9-cylinder molding at the recent Rhinebeck Jamboree and wasted no time in getting it detailed out and ready to add the Camel’s engine compartment.


Nicely molded from several layers of fiberglass cloth, the BUSA molding is nicely detailed. You would spend a lot more time trying to make your own. This is an older photo, the one I just picked up has a nice gel coat finish on the front.


The first thing to do with any molded fiberglass part is to use a grinding wheel and a Moto-tool and remove any sharp edges or areas starved of resin. After this, throw it in the kitchen sink and scrub it with dish washing detergent so you can remove any left over parting agent that might still be on the surfaces.


Here you see the open end of the cowling, it is important to use a molded engine that will fit properly. The 1/4-scale BUSA rotary engine is 7 3/4 inches in diameter, a perfect fit.


With the cowling removed you will notice I installed a ballast box filled with lead shot and resin right over the engine. I made it’s dimensions with the use of a dummy engine in mind.


Here’s the front end of the G38 with it flywheel and magnet for the magneto ignition showing proudly in front of the cylinder head. The engine is installed upside-down with the cylinder and muffler both pointing downward. The first thing to do is to open up the molded engine to clear the ignition block. But more importantly, the opening is also for cooling airflow to enter the engine compartment.


Making the opening is easy with a cutoff disc and a Dremel. I simply removed one of the cylinders and opened up the area between the other cylinders as shown here. Also, the center opening for the crankcase, has to be big enough to fit over the G-38’s propeller hub.


Here I am test fitting the molding over the G-38. The opening should provide about 1/8 inch of clearance all around so vibration won’t cause any chaffing of parts. You can also see that cylinder is right in the line of fire for airflow.


So the molding fits nicely centered over the G38 while contacting the front of the ballast box. Another good thing about the box structure is that it helps channel airflow down toward and around the engine and not up in the empty space about the engine.


Before painting, I drilled holes and added nuts and screws to add detail to the engine case. Also, I drilled offset holes in the engine case for the bushing (from short sections of brass tubes), for the pushrods which will be added later. Medium and Thick ZAP CA glue is used throughout. Be light with the kicker as it can cause the glue to foam up, which will not help the finish.


You might also have noticed the lite-ply guide/supports I glued to the engine molding. These have 1/16 inch holes in them set at the proper spacing to hold the pushrod wires. Here is the simple cut job loaded into my laser cutter.


Using my 40W Full Spectrum Laser Hobby Laser I was able to import some simple CAD drawing and cut out the eight are required for the dummy engine. You can see the lite-ply guide plates in detail here below.



To begin the paint job, I start with a coat of metallic silver from Décor. This paint is fast drying and it gives a real metallic almost chrome look to the part. I like using this bright coat as the first layer which I will build the weathering coats onto later in the process.


The paint really makes all the bits and pieces come together for a scale appearance. The 16 pushrods are made from pieces of 1/16 inch welding wire.


So here the cylinders, and the back webbing have been spray painted flat black. I have found that there is no need to carefully mask off the engine case while spraying the cylinders. Again here I use Decor spray paint which dries very quickly and is gasoline proof when dry.


As you can see, there is a slight amount of over spray on the edges of the crankcase, and that’s what we want. Additional detailing and weathering will be added to the engine to help bring out the finer detail and overall realism a scale model requires.


The next part will be highlighting the cylinders’ cooling fins and adding the pushrods. So stay tuned. This project is only half done.

See part 2 here: http://www.modelairplanenews.com/blog/2015/09/15/installing-a-dummy-rotary-engine-dressing-up-my-camel-part-2/




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  1. What size nuts/bolts did you use?

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