Cessna 172TD: Skyhawk With a Bang
We fly the Cessna 172TD and find out how the most popular airplane of all time translates into diesel.
By Robert Goyer
Photographed by Robert Goyer
April 2008
The fuel filler caps on the new Cessna Skyhawk 172TD aren’t your garden-variety flip-lid 100LL caps like I’d pried (or twisted) open countless times before. These babies are industrial, overbuilt Teutonic-looking things, placarded in bold letters to make it clear what kind of fuel to use: “Jet-A Only.” They seem emblematic of this new breed of Skyhawk, and I was looking forward to climbing aboard and seeing how one of my all-time favorite pair of wings would do with a new approach to power.
Cessna’s test pilots were still wringing the airplane out under its Experimental type certificate when I made my visit to Cessna’s Pawnee engineering facility in Wichita in November to sniff a little kerosene, but it was already sitting pretty, with what could pass for a production interior and panel and paint scheme and all. The airplane isn’t scheduled for certification until the middle of this year, but it sure looked ready for a customer to climb in and fly away.
Despite its business-only fuel caps, it looked pretty much like any other Skyhawk, so much so, in fact, that an inexperienced eye might not notice the three-bladed prop and walk right on by.
But make no mistake: This is no ordinary Skyhawk, not by a long shot. In some ways it represents a whole new path for the light airplane industry, a path that might lead to places that have been very lightly trod before. It’s noteworthy that the latest word on small airplane engineering would find a home in the most prolific airplane design in aviation history. It tells you all you need to know about today’s Cessna.
Now, diesel technology comes to the drafting table with its own set of issues—heavier fuel, additional engine weight, a tendency to be a bit shaky, all while carrying with it a reputation for being blue collar to a fault, no doubt due to their long association with trucks and trains and black smoke.
But that was back in the bad old days, and today’s diesel engines are technological marvels. The strengths that modern diesel engines embody—turbocharging, easy start-up, full authority digital engine control (fadec) and one more biggie—the fact that they burn the most widely available fuels on the planet—are so compelling that nearly every light airplane manufacturer has taken notice. The question was never, “Is diesel technology desirable?” but, rather, “Is the technology ready yet?” The answer finally seems to be, “yes.”
That’s largely thanks to Frank Thielert, the visionary designer who decided that what the aviation world really needed was a diesel engine done right and then decided to be the one to do it.
The engine that his company has arrived at today, the Thielert Centurion 2.0, is the culmination of that quest, at least the current culmination. Derived from a production Mercedes automotive engine, the 2.0 is a 155 hp, 2.0 liter, fadec-controlled turbodiesel swinging a three-blade composite MT prop.
Is it ready for prime time? That’s a tough call for even an experienced observer to make, and the future of auto conversion engines is a complex subject, to say the least. But it does speak volumes that Cessna is sold on the engine.
The company is not alone in its interest. Piper, Socata, Diamond and others have already worked on, or certified, Thielert-powered airplanes. But Cessna is far from a latecomer. It has been following the development of Thielert engines for nearly 10 years, and while it was intrigued by the previous model engine, the 135 hp 1.7 liter model, it wasn’t until the launch of the 2.0 (a development necessitated by a model change by Mercedes) that the engine developed enough power to get Cessna’s attention. The company began exploring the 2.0 in early 2007, and by early November it made the launch announcement of the diesel-powered 172.
The availability of the 2.0 was critical, in part because it allowed Cessna to get 155 horsepower out of the engine, as compared to 135 for the 1.7. And because of its larger displacement, the 2.0 has to work less hard to achieve 155 horses than the 1.7 did to develop 135.
It’s important to point out that the primary weights and the flight envelope for the 172 have not changed with the addition of the Thielert engine. The engine does weigh slightly more than the Lycoming engines in the 180 hp 172SP and the 160 hp 172R, but the max takeoff weight (often referred to as “gross weight”) is the same, at 2,552 pounds.
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