FLYING DIESELS

Whether you’ve seen them in person or not, you know there are diesel in ships and boats, road vehicles of all types, off road vehicles of all types and in every conceivable stationary use. If you are a long time reader of this column, you will also know there were, and still are, diesels in the air.

In the January, 2018 issue, we covered the Guiberson aircraft diesel story. In the September 2018 issue, we covered the earlier Packard diesel (see it online at www.dieselworldmag.com/diesel-engines/first-in-flight/). Those were the two main American contributions but the Europeans had many more. Let’s round up some of the other more important aircraft diesels we found and tell you a little bit about them. Along the way, you’ll learn what was good about them and what wasn’t.

1933-46 Junkers Jumo

Dr. Hugo Junkers, 1859-1935, may be one of the most unrecognized diesel geniuses of all time. A German, he was the first to develop a diesel engine specifically for aircraft in 1913 but his genius did not end at engines. He was also an aeronautical engineer, visionary and pioneer in the development of aircraft. He proved to be a good man as well, taking a stand against Fascism and refusing to develop aircraft for the Nazi regime. As a result, was threatened with prison for treason and died under house arrest in 1935. His company and patents were all effectively nationalized.

His first experimental aircraft engines came in 1913-15 and shared a recurring technical theme for Junkers, opposed pistons. That’s two crankshafts connected together and two pistons facing a central combustion chamber. When the cylinder fires, two pistons react. The first Junkers engines were technically oil engines and even had spark ignition to assist combustion but later engines were true compression ignition. All were two strokes. Opposed piston engines are an idea that delivered mixed results over the years but did see notable success by Fairbanks-Morse as a submarine diesel.

The early Junkers test engines culminated in the FO-3 5-cylinder in 1926 that made 830 horsepower and was a true diesel. This engine became the basis for what would become the legendary Jumo line. The final push to production started in 1928 with the FO-4 six-cylinder that made about 750 horsepower and these would be the first in the series to actually fly in 1929. The development progressed rapidly through several other test engines (that also flew) and culminated in the Jumo 205 that debuted in 1932, was approved for aviation and went into production.

Even after the Jumo 205 went into production, experimentation continued. The most spectacular prototypes were the Jumo 223 and 224, both 24 cylinder engines, the 223 displacing 1,767 cubic inches and the 224 making 4,150 cubic inches. The 223 cranked out a maximum of 2,380 horsepower at 4200 rpm. The 224 made 6400 horsepower at 3000 rpm from 4150 cubic inches. Because the Dessau, Germany, Junkers factory fell into the Soviet Zone, the Russians captured the factory at the end of World War II and conscripted some of the Junkers engineers to continue with the 224 development. That ceased in the summer of 1948 but some 205 variants were produced during that time.

Though the Jumo diesels are legendary and mythical, they didn’t see a great deal of service in aircraft. A small number of different German aircraft used them, mostly seaplanes, but some of those were later converted to conventional gasoline engines. During World War II, a shortage of diesels led certain small patrol boats to be built with marineized Jumo engines. Jumo engines were used postwar into the ‘60s by the East German Navy to power small patrol boats as well.