When Continental announced in May that it planned to develop a diesel engine for the light aircraft market, it was boldly going where many have gone before. Unfortunately, the many have had their diesel entries ground to a bloody pulp by a fickle market more interested in speed than economy and unconvinced that diesels supposed longevity is worth the higher purchase price. A historical fact: Depending on how you define commercial success, there has never been a commercially successful diesel engine for aircraft. The Thielert/Centurion line launched in 2005 comes closest, but the company went belly-up and although its building engines again, it remains insolvent. Our idea of success is defined by having enough engines in the market to represent a sustainable economic bloc and/or a company thats still viable. In that regard, Pratt & Whitneys round engines might qualify as a continuing success while Centurion remains in the iffy column. So what is it about diesels? They seem like such a terrific idea in theory. But in practice, theyve consistently failed to deliver. Theyre usually heavier than gas engines, have poorer power density and have proven substantially more expensive to build. That much hasnt changed since Packard tried the Dr-980 radial diesel in 1928. So what possible market trend could rewrite the equation? Only one: fuel availability.
Failure to Launch
History has a way of repeating itself and that certainly seems to be true in the diesel market. The first serious effort in aircraft diesel was launched by Packard in 1928 in the form of the Dr-980, a nine-cylinder radial intended to compete with the IO-550 of the day, Wrights 225-HP Whirlwind J-5. Although the Whirlwind gained indelible fame for reliability by powering Lindberghs flight across the Atlantic, it had terrible fuel specifics. At 0.6 pounds of fuel per horsepower hour, its thirst was closer to a turbine than a modern, relatively efficient gasoline engine. Designers using the J-5 had to find a lot of room for fuel and even then, gasoline-powered aircraft were range challenged. Further, in 1928, just as now, the world was worried about running out of oil, since discoveries of new major fields-especially the Black Giant in East Texas-were still in the future.
Even by modern standards, the Dr-980 was an impressive effort. According to Robert Meyers The First Airplane Diesel, the Dr-980 matched the Whirlwind on weight, power density and overall size, something that no modern diesel can claim. It crushed the J-5 on efficiency, running at 0.40 BSFC, a 50 percent improvement in fuel economy. No modern diesel can claim that kind of improvement over the gasoline competition, either.