Scale Weathering and Painting — Making a WW1 Rotary Engine Look Old

Jan 22, 2014 7 Comments by

When it comes to really looking scale, it is in the details that we make the most progress in giving our model’s that “used” look. For my Balsa USA Fokker Triplane which I built and flown this past year, I wanted to bring a better scale look to the front so I am installing a resin cast 9-cylinder Oberusel UR 2 rotary engine from Nick Ziroli Plans. This is basically a German built copy of the LeRhone 9J 110hp engine.

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This 1/3-scale kit includes the front of the engine as well as four cylinder back halves as well as induction intake pipes, cylinder heads and valve rocker details all resin casted in white. Overall this kit is nicely detailed with lots to look at but it does need to be painted before installing it in your airplane. Being 33% scale it fits all sorts of Fokker designs including Glenn Torrance Models, Ron Weiss and Balsa USA kits.

Prep work

After removing the engine cowling, I placed the main engine piece over the Zenoah GT-80 to check the fit. It fits nicely over the front housing and propeller hub, and I added some stick on foam strips to make a snug fit. I also painted the bottom of the engine compartment area black to add some depth behind the engine.

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As with all resin cast parts, before you can paint the engine, you have to wash all the parts in warm soapy water. I used dish detergent in an old pot and an worn out toothbrush to really give it a good scrubbing. If you do not do this important step, your paint will easily chip and peel off.

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Be sure to really get into all the nooks and crannies with a good scrubbing to remove any mold release material that may still be on the parts.

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After washing the parts I use a covering heat gun and speed the drying process. Now is a good time to also remove any rough edges and flashing left over from molding the parts. Fine sandpaper and a sharp X-Acto blade does a good job.

To get a good glue joint between the parts, I sand the parts with a belt-sander to produce a smooth flat surface between any mating parts. This includes the front and backs of the cylinders, and the tops of the cylinders and the cylinder heads.

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For this project, I used the new ZAP “Brush-On” CA adhesive and applied the glue with the built-in brush applicator. It is very easy to apply a nice thin layer and avoid drips and excess adhesive dripping over the edges.

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Here the back halves have been glued in place. Some fit perfectly while others need a little trimming to produce a smooth and flat surface. It is important to match up the cooling fins on the sides of the cylinders.

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Once the surfaces have been sanded flat, GLue on the cylinder heads and then the rocker arm details. Medium CA works best for a good bond and for filling in seams.

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Once the cylinder heads have been glued in place. You have to add the induction intake tubes. You can either trim the tubes to fit between the cylinders or you can trim away a little cylinder material to produce the clearance so the tube ends can be glued flat to the backside of the engine case. A Robart grinding bit makes quick work of the job. Here you can also see the foam strips I added to the center opening to fit around the model’s engine.

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After the parts are all glued together I couldn’t help but put the engine in place and see how it would look with the cowl in place. The fit is perfect.

Aging with Paint

The process of making a model part look real, is to detail it layer by layer and do the same thing as is done with scale pilot figures. You start with a base coat, apply highlights and undertones and avoid solid colors. The steps are as follows.

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Since the back of the engine has to painted too, I start with the back and check the coverage of the base flat black paint. I used flat black primer from Krylon applied with a rattle can. Be sure to spray square to the cylinders so you get the black in between and deep into the cooling fins. Also shown here is the lifter tubes I added made from brass wire and glued to the backs of the lifter arm details.

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Once the back is dry, paint the front of the engine as well. be sure to cover all the parts and recesses, you don’t want to see any white.

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Once the base flat black undertone has dried, spray on the silver base coat. Do this at a shallow angle to the engine to minimize the amount of silver that gets in between the cooling fins, then let dry.

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Here’s one of my tricks so to speak. I then apply a light mist of Master Modeler “Burnishing” Aluminum over the Krylon silver. I mist onto all the smooth larger areas and then when dry, I use an old tee shirt to buff the parts to a smooth, new appearance. The is done to the engine case and the bottoms of the induction tubes. The difference is subtle but noticeable.

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Again, I placed the engine on the Triplane to get a feel for how the engine is starting to look. The rest of the detailing is mostly done on the lower 4 cylinders that will be visible below the cowling face plate.

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I now take Master Modeler flat black and thin it with mineral spirits for form a thin wash and I just paint it on and wipe it off over and over until I get the look I am after. You want it to fill recesses and seams and build up slowly with less color on the outer surfaces. This really brings out the fine details like the bold heads around the engine case and the spring details around the lifter arms. You can also add a wash of light brown to add oil residue here and there.

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You really can’t make a mistake. If you apply too much, just wash it away with more mineral spirits before it dries. Next since this is a German rotary engine, it differs from the LeRhone engine in that that the induction tubes were made of steel and not brass or copper. So, they heated up a lot and produced a black and worn look that I reproduce with gloss black, flat black and Rub-N-Buf silver paste. Again, no solid black paint coats. Apply thin washes and scrub the parts with your brush. Flow it on and let it dry then flow on more. In a few areas like around the neck, apply blotches of glossy black to make it look baked on. Also add more black washes around the base of the cylinder and around the bolt heads.

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To add just a bit more detail, I used my Dremel Moto-Tool to make round recesses to the sides of the 4 cylinders. I then added these scale looking spark plugs. They are actually resin cast copies I made of a 1/4×28 mini spark plug from one of my 4-stroke gas engines. Making these copies could be another shop technique posting if the reader interest is there.

So that’s it. I still have a little more detailing to add (Spark Plug Wires) and the final application of “Rust” to pick out some more details. A final application of honey-colored polyurethane will give the engine that, “just run” look so stay tuned for more. Wait till you see it all buttoned up with a Xoar Axial WW1 propeller in place. :^)

Featured News, Gerry Yarrish, Scale

About the author

Senior Technical Editor About Me: I have a lifelong passion for all things scale, and I love to design, build and fly scale RC airplanes. With 20 plus years as part of the Air Age family of magazines, I love producing Model Airplane News and Electric Flight.

7 Responses to “Scale Weathering and Painting — Making a WW1 Rotary Engine Look Old”

  1. Earnest Padgette says:

    Good tips! Thanks for the effort. I’m looking forward to seeing the finished job.

  2. Ron Brownell says:

    Great article, really enjoyed it.

  3. Robert Davidson says:

    Looks great Gerry. For those who want to use acrylic paints, you’ll use some thinned out ‘Future’ floor wax instead of the Mineral Spirits.

  4. Dave Sarfine says:

    Show us the resin technique for the spark plugs please!

  5. jim slaughter says:

    you talk about flat black paint but I don’t see or understand that step as I don’t see it.

    • Gerry Yarrish says:

      the first couple of paint photos show flat black paint sprayed on. What do you not see or understand? flat black reflects the flash from the camera as a light gray, you can see the third photo when the silver is applied that the overspray on the white background is actually black

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