Plane & Pilot
Tuesday, March 26, 2013

Diesel With A Jet Heart

Cessna introduces a turbo diesel for the popular Skylane

Thielert of Germany and SMA of France produced the first general aviation aircraft diesels in 2001. By now, practically everyone knows the story of Thielert. Despite developing what seemed a viable engine for the single-engine Diamond DA-40 Star and DA-42 Twin Star, Thielert went bankrupt in 2008, leaving Diamond holding the bag on hundreds of diesel-powered airplanes and an uncertain future for its two primary products. As a result, Diamond was forced to develop its own partner engine company. Diamond created Austro Engines and built the new manufacturing facility next door to the company's production facility in Weiner Neustadt, Austria.

Though Cessna's initial interest in diesels was in the Thielert/Mercedes product, the German Thielert company's bankruptcy caused Cessna to take a closer look at the French SMA engine. The 305 cubic inch/230 hp SMA mill had been fitted to older Skylanes under an STC in 2001, and since then, SMA has continued to develop the engine.

I flew one of those aftermarket Skylane diesels for this magazine in 2006 (see our April 2006 issue), when the predicted avgas shortage was still far in the future (we thought). Today, 100LL is becoming scarce in Europe, the Middle East, Indonesia, Africa, the Far East and other parts of the world. North America is one of the few places with adequate supplies of avgas at the moment, but 100LL isn't a high-volume fuel, and volume is everything in the fuel business.

Like its avgas equivalent, the diesel Skylane's JT-A power plant offers 230 hp, but fuel efficiency on Jet A is roughly 30% better. That means you can fly farther on the same fuel and convert more useful load to payload. 
These days, few refiners are willing to dedicate the resources necessary to produce avgas. In addition, the American Environmental Protection Agency has been trying to shut down avgas production for years because of its minuscule lead content. If the EPA ever gets its way, we'll have to turn to alternative fuels. Some of those show promise, and several are under development, but no one can guess when they might be ready for mass distribution and universal application.

Unlike the early SMA effort, the installation on the Skylane JT-A is a dramatic improvement over the old engine, with an estimated 40% new parts. The C1 version features a huge turbocharger and an equally impressive intercooler, the latter designed to keep the diesel cool while pulling as much as 90 inches of manifold pressure. Yes, you read that correctly, 90 inches. No one expects a Skylane JT-A to run against the Mustangs and Bearcats at Reno, but that's the kind of power they pull from their Merlins and Pratts, at least numerically.

As we went to press, Cessna was anticipating an FAA type certificate for the Skylane JT-A by April. I flew a pre-production model with flight-test equipment in the aft fuselage, but the design had been frozen for production, so there should be no differences in performance or specifications between the prototype and the completed airplanes.

The Skylane JT-A is virtually identical to the Turbo Skylane from the firewall aft. Weights and CG are the same. All the changes (except for diesel instrumentation on the G1000) are confined to the power section and prop of the aircraft. Even the cowling is recognizable. It fits in the original footprint, though its configuration does boast two large intakes out front, one for intercooler and the second for oil cooler. Other than that, you could easily mistake a JT-A for an older Lycoming-powered Skylane.

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