The Model Diesel Virus

All right, then. I didn’t let that discourage me and went ahead anyway with building the 3.9 cm² DATZ 4, which a Mr. W. Datz from Frauenfeld offered as a kit in 1947. Part 1 is the crankcase. The assembly instructions state: “This part is available as a clean, light-metal casting at a reasonable price from a specialty model aircraft shop or from the author. It is not advisable to fabricate the housing from individual parts or from solid material.” Great… my local specialty store didn’t have any in stock (what a surprise), and the author has long since passed away. So there was already a second problem—though today we’d call it a challenge. I took it on and told myself that if, more than seventy years ago, such a motor could be replicated “without much difficulty by a reasonably skilled metalworker,” as the instructions state, then it must surely be possible today as well.

So I set out to model all the parts in CAD and bring them to life on the table using 3D printing. That gave me a first impression of the

Size and any tools that might be needed for construction. Except for the cast housing, everything else really seemed feasible. So I decided to go with aluminum casting. To that end, I gathered information from the Internet

To melt the aluminum, I built a melting furnace out of Ytong, into which I placed a gas burner made of

available at the hardware store. As a result, melting the aluminum (approx. 660 °C) in a stainless steel container was surprisingly easy. The first casting, however, was—

It was a deceptive process, and many more attempts and optimizations followed. These involved the design of the casting mold as well as the treatment of the molten metal. The breakthrough came with a special granulate that binds oxides through a flotation process and transports them to the surface as slag, where they can be skimmed off. Once this hurdle had been overcome, a usable crankshaft housing blank was finally on the table. As luck would have it, a DATZ4 was actually for sale at the 2019 model engine collectors’ meet. I purchased it as a reference piece. And at the antique model meet of the

At MG-Bern, where some great colleagues helped me with advice, practical support, and even model fuel, the engine finally started running again after many years of inactivity. After this sense of accomplishment, I was fully motivated to complete my own build.

That same year, we from MG-Grenchen visited the “Faszination Modellbau” trade show in Friedrichshafen. There, “diesel fuel” from England was available for purchase in metal cans, so my second problem was solved for the time being. Construction of the DATZ 4 then proceeded rapidly, and the test run took place on May 1, 2020. After some “practice,” the engine started up; the joy was overwhelming and filled me with great satisfaction. The somewhat arduous journey was more than worth it; I made new acquaintances and was able to gain a lot of practical knowledge. The engine runs at approximately 4,400 ^rpm with a 13" x 6" wooden propeller and, after the break-in period, now starts up happily.

I’d be delighted if this story inspires other hobbyists to take on a project that’s a bit out of the ordinary. “Patience in all things surely leads to success.”