DAVIS DIESEL
A chat with the father of modern micro diesel engines

Bob Davis was inducted into the AMA Hall of Fame in Fall 2008. Sponsored by Stewart L. Richmond (see the January 2009 issue of Model Aviation), he was cited for significant contributions in three arenas: conversion of engines to diesel power, model muffler design and CO² engine conversions. Bob has run Davis Diesel Development since 1975—over 33 years. I caught up with him to get a personal view of over three decades contributing to the hobby.

Fly RC: How did your involvement in RC modeling get started?

Bob Davis: I was very fortunate to be able to speak to the “big guys” who started the hobby. People like Carl Goldberg, John Broadbeck—who started K&B—Don Anderson— who founded Great Planes in the 1970s and who was interested in Davis Diesel products—and many others. Goldberg was so forward looking; he said the hobby needed quieter mufflers. I later worked with Minivox, a German company, to develop SoundMaster mufflers. The breakthrough technology was that the muffler spun the gasses from stage to stage, which effectively lengthened the muffler. Baffles inside diminished the sound by reflecting sound into sound, and the mufflers also added power.

Peter Chinn, the famous engine writer, really rocketed us onto the scene by writing reviews in a foreign magazine column on me, an American. In the 1960s, the American Fox .15, with high nitro, pretty much ate the European diesel market for lunch. By the time we got there in the mid-’70s, diesel had pretty much died away. Control-line combat was the hot thing even as RC was just emerging. Then we brought in the first conversion for a volume-produced engine, the Cox .049, and it really took off. They were selling millions, and we got a piece of that market. We brought out heads for the O.S. .40, the SuperTigre .35 and .60 and essentially all the main engines—Webra, Enya, the new K&B Schnuerles; you name it. Peter Chinn said it “extended the useful purpose of the model engine.” We carry a very long list of heads and conversion kits to this day, and we produce them in the U.S. We also produce the fuel—a special diesel blend that’s distributed through Great Planes.

In CO², I realized I should be doing the same thing. We made conversions for the Cox .049, .020 and.010. We made twin versions of the last two, physically making the engines from the Cox cylinders while making our own crankcases and crankshafts.

Fly: Tell us about your work in the UAV market and the future.

Bob: I had the privilege of working at the Lockheed Skunkworks, Boeing Phantom Works and the Navy’s Swamp Works—all advanced work projects in cutting-edge aerospace, producing diesel technology for UAV programs. One of our diesel-powered UAVs carried a gallon of fuel and could fly for 24 hours while generating its own onboard electricity and surveilling with video. We did 150 of those, and there were many other projects.

I produced Cox .010 conversions with generator drives for 6-inch-span micro-UAVs. These had twin-ball-bearing rear output shafts driving micro-generators to power the radio. The front shaft spun the prop. We did work for Redstone Arsenal in Alabama evaluating engines for UAVs. We worked with 1.6ci O.S. FXs. At one point, a Skunkworks representative asked me incredulously, “You mean you have variable-geometry combustion chambers in your micro diesels?” I said “Sure.” I had the pleasure of the being the world expert in this very narrow market, and I credit this to the hobby.

We will be here and are not going away, and we are proud to be an American manufacturer. The hobby will become more electric, but the love of engines will never go away, and diesels will continue as an option that performs better and costs less than nitro. The largest diesel conversion we now carry is the O.S. 35cc BGX-1; it puts out over 5hp, and that’s a model airplane engine with fewer vibration issues than comparable gassers. We offer the most horsepower per pound of engine and the biggest prop per cubic inch. It has been an exciting career.

Fly: Bob, thanks for the interview, and congrats on the induction.

Bob: My pleasure, thank you.