John,
Diesel engines are not new to aviation.
In 1929, the one and only Charles A. Lindbergh piloted a Stinson SM-1DX powered by a new Diesel type oil-burning motor manufactured by Packard Motor Car. The model was a DR-980. It weighted around five hundred pounds, had a 16:1 compression ratio, and used "furnace oil".
Additionally, I believe Waco (open cockpit plane) was testing one of their own diesel engines during the same era.
Nevertheless, more recently, a diesel engine has been developed in Germany and installed in a Cessna 172 and an Austrian airframe. Check out this article,
Throw out the textbooks, diesel airplanes are here for more information.
Matt,
The idea of a water-cooled engine for aviation has too been around since the late 20s, early 30s.
In the state of your previous residence, the Hendee Manufacturing Company (Indian Motorcycles) built an eight cylinder water-cooled “V” type engine.
I believe Kawasaki was doing some testing in the late 90s with a V-8 liquid cooled engine.
Good stuff, thanx 4 the story.
Joe