In the early 1930s, Daimler-benz set out to develop a diesel engine for use in airships... lighter-than-air craft sometimes called dirigibles and, incorrectly, blimps. Daimler Benz based the new diesel on their recently designed 1,000 horsepower model F-2 aircraft engine, V12 gasser. Called the OF-2, the first diesel variant shared the same 3,288 cubic inch displacement (6.60 x 8.27-in. bore and stroke) as the F2. It was a very advanced engine with dual overhead cams and four valves per cylinder. With a 16:1 compression ratio, the OF-2 cranked out a max of 750 horses at 1790 rpm. The OF-2 had passed all it’s certification tests by 1932 but the German airship industry was moving towards bigger airships and needed bigger powerplants. Enter the LOF-6.
The LOF-6 (designated DB-602 by the German Air Ministry) was a whole new design and a 50 degree V-16 that displaced 5,401 cubic inches from a 6.89 x 9.05 bore and stroke. It had an aluminum alloy block, so despite it being a monstrous engine (8.8 x 3.4 feet), it weighed only 4320 pounds. Unlike the OF-2, it used a single camshaft with pushrods and rockers. Maximum output was 1,200 horsepower at 1600 rpm (900 hp @ 1480 rpm) but the engine could be run for five minute intervals at 1320 horses.
The LOF-6 was a four stroke, direct injected engine that started on compressed air. It was unusual for a four-stroke by being direct reversing, meaning it could run in both directions. Direct reversing two-stroke engine were easy and common. Four-strokes less so. It was accomplished in the LOF-6 by a camshaft with two sets of lobes and the cam was moved forward or back pneumatically. Another fascinating feature of the LOF-6 was its ability to run on only eight cylinders at speeds below 300 rpm. One bank was cut off by disabling the injection pumps. The LOF-6 were complicated engines but proved to be reliable.
Not many LOF-6 engines were built. Some of the earliest production engines powered the famous Hindenburg, launched in 1936, and the Graf Zeppelin, launched in 1938. The hydrogen explosion of Hindenburg at Lakehurst, New Jersey, put a damper on German airship development, so the LOF-6 line of diesels ended in the late ‘30s. The design was adapted for marine use and concurrent with the LOF-6 was a separate marine design, the MB-501, that followed many of the same design cues of but were very different. The MB-501 are better known than the LOF-6 and had a notable career powering Germany’s deadly E-boats. Their production and evolution continued after the war... but that’s another story.