Plane & Pilot
Tuesday, March 26, 2013

Diesel With A Jet Heart


Cessna introduces a turbo diesel for the popular Skylane


There's something almost hypnotic about flying behind turbines. There's extra power, of course, and if you're standing outside, you experience that characteristic shriek of jet combustion that only a pilot can love.

Perhaps more than that, however, at least for aviators with most of their hours in avgas airplanes, there's the phenomenal smoothness of one or more turbine engines. Whether your turbine is driving a propeller or blasting you forward with pure jet thrust, the experience is akin to riding on velvet.

The new Cessna Skylane JT-A may not be quite that smooth, but it's close, and the airplane's power plant isn't even a turbine. As the designation implies, this 182 runs on jet fuel, but it's not driven by a jet engine. It's a turbo diesel, designed to operate on conventional Jet A, and the four-cylinder diesel is smoother than any six-cylinder avgas engine you've flown. (No, in perhaps the ultimate irony, the diesel Skylane isn't certified to burn diesel fuel, even if you were willing to drain some out of your Mercedes. You'd certainly never find any at local airports.)

For 2013, Cessna elected to retire the not-so-old avgas-powered Turbo Skylane T182T and replace it with a turbo diesel. Diesels have had a checkered career in aviation, though their heritage stretches way back to the 1920s. In the United States, Packard diesels were used on rigid airships starting in 1928, and German Jumo and Daimler-Benz diesels were employed on the famous Zeppelins (including the ill-fated Hindenburg) of the same period.

The major advantage of diesels in all applications was/is a comparatively low fuel consumption.

Piston aircraft engines experience an average specific fuel consumption of .43 lbs./hp/hr., whereas diesel engines record an sfc (specific fuel consumption) of more like .37 lbs./hp/hr. burning jet fuel. That's about a 12% improvement in efficiency. A second advantage is that avgas availability outside the U.S. is a sometime thing, whereas jet fuel is plentiful practically everywhere. Since American GA aircraft manufacturers sell roughly half their products overseas, the near-universal availability of jet fuel outside the U.S. and Canada makes a diesel engine more attractive.

Finally, jet fuel is almost universally cheaper abroad. To use an extreme example, when I flew through Narsarsuaq, Greenland, about a year ago, avgas cost $16/gallon while Jet A was priced at $5.89/gallon. Luckily for Americans, the delta between the two fuels on domestic soil is barely noticeable, but jet fuel is obviously far more attractive on the other side of either pond.



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