Diesel in the Sky: How Compression Ignition Is Rewriting Aviation

From The Drag Stip to the Runway

When you think diesel, you probably picture a lifted (or lowered, we love ‘em all) pickup, a tuned tow rig, or maybe a piece of heavy equipment working away on a job site. What you don’t usually picture is a Cessna 172 cruising along with a motor that has more in common with your truck than it does a Boeing or Airbus. Yet, that is exactly what is happening in some corners of aviation, and it is finally starting to grab people and make an impact.

The appeal is pretty easy to understand. Jet-A fuel is available almost anywhere an airplane can land. It is cheaper than aviation gas (avgas), carries more energy per gallon, and is far less volatile. With leaded avgas on the way out, the idea of burning a cleaner, more available fuel has clear benefits. One of the cooler qualities is the way a diesel-powered airplane actually flies. Pilots who have flown one describe the initial climb as steady and confident, with a feel that is closer to rolling into boost in a tuned diesel pickup than ripping a gas engine out to redline.

Thielert, a German company, was one of the first to really push piston-diesel conversions back in the early 2000s. Today, Continental Aerospace Technologies and SMA Aero Engines are leading the charge. Their engines claim to sip fuel at rates up to 20-30% less than their avgas counterparts. Numbers such as those make avgas engines look wasteful, and knowing you can stretch your range and cut costs is especially exciting for flight school operators. When trainers are in the air all day, every day, fuel and maintenance savings add up fast. So having the ability to cut back on that can be huge.

Of course, aviation is never that simple. Certification costs are sky high, and early diesel aircraft engines have had their share of teething problems. Reliability, parts support, and the need for airframe modifications scared off plenty of owners in the beginning. No one ever wants to be the guinea pig in the aerospace industry, but thankfully, the technology and safety have matured. The latest diesels feature electronic fuel injection, liquid cooling, and turbocharging. If that sounds familiar, it should. Diesel truck owners have relied on those same technologies for years. Seeing them bolted into an airplane engine bay feels like two distinct paths slamming together—kind of like the Fairly OddParents meets Jimmy Neutron crossover.

The experimental crowd has also been busy. Guys building their own planes at home have tinkered with everything from Mazda rotary conversions to automotive-based turbo-diesels. For some, it is about fuel economy, but in many cases, it is about practicality. In regions like Africa or South America, where avgas supply is hit-or-miss, being able to fuel up with Jet-A or even kerosene can be the difference between completing a mission or staying grounded. For bush pilots, missionary operators, and long-distance flyers, that kind of reliability is something you just can’t put a price on.

Will diesel take over general aviation the way it dominates the truck world? Probably not. Big ole turbines still run the airline industry, and piston gasoline engines have had a hundred-year head start. But the momentum is shifting. Environmental pressures are building, and more pilots are asking for efficiency without giving up usable power. To us, that sentiment is the opening diesel has been waiting for.

For those of us who love compression ignition down here on the ground, it is hard not to cheer it on in the sky. Hearing the familiar hum of a diesel engine pulling a load down the interstate is satisfying enough. Hearing it rip down the runway straight into the clouds takes it to another level. Torque and turbo whistle do not stop at the edge of the runway. They take off and fly around a bit now.