Plane & Pilot
Tuesday, March 25, 2014

What’s Up With Diesel?

Diesel power was once touted as the savior from the threatened avgas shortage. Is that still true?

Diesel engines have been around for flying machines since the German rigid airships of the early 20th century. These aircraft used several diesels to provide both forward and reverse thrust, and in fact, diesel-powered Zeppelins were the first aircraft to offer formal, revenue-producing passenger transport.

Diesels fell from favor before World War II, but three-quarters of a century later, diesel power has once again been proffered as a solution for economical air travel, this time for fixed-wing, general aviation aircraft burning jet fuel. As nearly anyone who hasn't been living on the dark side of the moon has probably heard, avgas is becoming scarce and more expensive, though not so much inside the U.S.

Traditional wisdom is that refineries are backing away from high-octane avgas because of poor volume. Mobil is out of the avgas business altogether, and companies such as Chevron, Shell and Exxon are becoming concerned that the relatively low volume of avgas simply isn't an appropriate allocation of resources.

Similarly, many manufacturers have taken a wait-and-see attitude about certifying models to fly behind diesel power. Austria/Canada's Diamond Aircraft is the only company to embrace diesel wholeheartedly with a progression of engines: first, the flawed Thielerts, then the follow-on, improved Centurions and most recently, Diamond's own Austro diesels, produced in a new manufacturing facility next door to the main Diamond plant in Wiener-Neustadt, Austria.

Even Cessna Aircraft jumped in with a French engine, the SMA SR305-230 turbo diesel, mounted on the venerable 182. Cessna went so far as to cancel production of the standard, normally aspirated avgas-model Skylane, a leap of faith for one of the most trusted Cessna models in the company's 87-year history. That's all the more surprising, considering that prior to the Skylane JT-A's introduction, the standard 182 consistently outsold the turbocharged avgas model by two to one.

But now what? Interest in diesel technology hovers somewhere between stalled and jump-started. Though Dia-mond continues to produce the Star and Twin Star with their captive Austro diesel power plants, even they seem to be hedging their bets by offering either airplane with a conven­tional Lycoming avgas option. Still, Diamond has over 1,000 diesel-powered singles and twins flying, so there must be some significant demand, especially overseas.


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