Diesel Engines Go Mainstream...Finally

Cessna and Thielert officially announced at the annual AOPA Expo last week that the C-172S Skyhawk will now be offered equipped with a Thielert Centurion 2.0 turbodiesel engine as the C-172TD.

This engine has proven very efficient on Diamond's DA-42 Twin Star. Thielert had already obtained an STC allowing a retrofit of the engines on old Skyhawks...making it very easy for Cessna to offer the engines as a factory option.

The engines burn Jet-A (currently cheaper than 100LL) and, according to Cessna, they burn 30% less fuel per hour than current engines. They have a 2400 hour TBR (Time Before Replacement), they employ full authority digital engine control (FADEC) and single lever power control (SLPC), and they run at a lower RPM (meaning slightly reduced cabin noise.) The engines are only 155 hp, but they are turbocharged and turn 3-bladed constant speed propellers.

I think the only questions remaining are: why didn't this happen a long time ago, and how long will it be before diesel engines completely replace current models?

As a student of human factors, I feel that FADEC with SLPC constitutes the most useful advance in aircraft controls since pitch trim. I hate to admit it, but computers are better than us at some things. Managing RPM, manifold pressure and fuel mixture all at the same time is one of those things. I'm a little hesitant to give up direct control of aircraft systems, but after a few hundred hours of flying FADEC aircraft I'll give up that control based on experienced reliability and the fuel savings.

I think a constant speed prop on front of a turbocharged engine will give performance and safety increases that make this engine the best choice. When flying in Colorado on days with the density altitude over 10,000 ft, I would have gladly traded the fixed-pitch, 180hp, O-360s I flew with for a constant-speed, turbocharged, 155hp Thielert in a heartbeat.

I expect that sales of non-diesel Skyhawks drop drastically while C-172TD sales skyrocket, and that we'll see every major aircraft manufacturer offering turbodiesel engines within a year. I hope it isn't that long.