Plane & Pilot
Tuesday, March 26, 2013

Diesel With A Jet Heart


Cessna introduces a turbo diesel for the popular Skylane


Previous diesel cycle engines have suffered from significant weight increases over avgas mills. That's a function of the fact that diesels need to be stronger to endure the extreme compression ratios and temperatures of ignition without spark plugs or magnetos. Most aircraft avgas piston engines employ compression ratios of 7:1 or 8:1, diesels compress their fuel/air load to 17:1 or more.

The JT-A avoids part of the weight problem by mounting a lightweight three-blade Hartzell carbon-fiber propeller behind the spinner. As a result of that and other economies, the total weight increase forward of the firewall is only 15 pounds.

As mentioned above, the JT-A uses the same fuel tanks as the avgas model— 87 gallons. That means if you fill the tanks, you'll be carrying an extra 70 pounds of fuel, since Jet A weighs an extra .8 pound per gallon more than avgas.

Theoretically, that increases the delta to 85 pounds, but the good news is that the airplane's range is so exemplary with the lower-Jet A sfc, you may not need to fill the tanks on some flights, a characteristic common to turbines. Cessna doesn't mount sight gauges on the JT-A's high wings, so you may not be able to trust the line boy to hit your exact fuel requirement, but the company claims the fuel gauges on the Garmin G1000 are extremely accurate. Still, payload is only 400 pounds, so you may need to mind the weight and balance if you need to carry a full fuel.

(Cessna recognized the distinct possibility of line personnel misfueling the JT-A, and accordingly, the fuel tanks are designed to accept the duck-billed "jet only" filler nozzles. This makes it extremely difficult—nothing is impossible—for anyone to pump avgas into the tanks.)

Since horsepower hasn't changed, aerodynamics are identical and airframe weight is essentially the same, it's no big surprise that the Skylane JT-A flies basically the same as last year's avgas-powered T182T, only better. I flew with Cessna demo pilot Charles Wilcox out of the company's Wichita Mid-Continent facility. Wilcox did much of the test work on the JT-A and probably knows the airplane better than anyone. He had worked out a standard demo routine that showed the JT-A to maximum advantage.

Predictably, the new Skylane demonstrated the manners we've all come to expect from a 182. Climb is simply a matter of pushing the single power lever (you're almost tempted to call it a thrust lever) full forward, and letting the ECU computer set power. There's no waste gate on the engine, so all intake air goes through the turbo. As a result, you'll see something you've probably never seen before on a Cessna: 90 inches of manifold pressure during climb. This turbo is indeed stout.





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