Diesels In The Sky: The Marriage of Light Aircraft and Diesel Technology

Diesel engines are all around us. Some in places we don't ordinarily expect. For example, I recently watched some railroad workers perform an oil change on a railroad car. No, it wasn't a railroad engine. It was a passenger car who lights, kitchen appliances and other needs were diesel powered. I never knew that. 

A day later I received an email with a link to an article about diesel engines in aviation. This, too, had some interesting surprises. The intriguing article by Trevor Anderson appeared on the Engine Labs site in December 2015. 

Anderson began by noting all the familiar places we find diesel to be the engine of choice. Heavy equipment, tractors, earth movers and their ilk depend on compression ignition power for a range of good reasons. But what about the other end of the spectrum, he asks. That is, what about the light weight, more delicate forms found in the aviation community?

Many of us might be surprised when we learn of the inroads of diesel in small aircraft. This article explains part of the reason this has been happening.

A little history is in order here. It's been less than 120 years since the Wright brothers took flight at Kitty Hawk. Diesel power has only been used in aircraft for a little over 80 years. It's hard to image the Wright brothers getting off the ground with those first monstrous diesels, though the reason diesel engines have been second string power sources for planes has more to do with the fuel than the engine.

This latter issue is actually what has incentivized the choice of diesel engines in more light aircraft today, the two primary reasons being lower cost and more widespread availability.

Anderson notes how light aircraft have historically run on Avgas, which is a gasoline-based fuel specially designed for aviation. Avgas chemistry is akin to racing fuel. It's available at U.S airports, but for aviators flying into remote areas of South America or other places off the beaten path -- places where pilots fly humanitarian missions in the Third World or remote parts of Australia -- it is not always available.

Diesel, on the other hand, is really available nearly everywhere. When you fly, your topmost concern is reliability. It's not like driving a car where you can just pull over and see what that sound is that your engine is making.

What's more is the simplicity of a diesel engine's design. With half as many moving part in a two-stroke diesel, you have half as many things that can go wrong.

There are, however, a few drawbacks to diesel, the author reminds us. He's not trying to sell us. He's just her to inform us of our options and why diesel in aircraft has been growing.

Avgas is designed for "the specific needs of aviation," especially in high altitudes. One of its properties is the ability to avoid vapor lock. That is, it's designed to resist becoming vapor in the lines, cutting off the flow of fuel to the engine. Diesel is subject to gelling, icing and the problem of microbial growth in the fuel.

The Arctic regions and dense tropical rainforests will present problems for diesel planes that Avgas-powered engines will shrug off.

Naming Names

There is only one left. Diesel-powered Junkers 
took to the air during WWII

In the latter part of this article the author begins by taking us back to the first diesel-powered aircraft, the German-engineered Junkers JU-86. The plane was produced specifically for the Luftwaffe initially. It had a variety of looks and was the first to have diesel engines. It was a twin engine bomber and transport craft. 

A unique feature of these engines is that they had vertically opposed six-cylinder, 12-piston, liquid cooled, supercharged engines that generated 868 hp each. It could climb 900 feet per minutes and carry 11,000 pounds. Not too shabby.

Nowadays there are a number of aircraft builders who use diesel power in some of their planes including Diamond Aircraft Industries, which is discussed in detail. Diesel engine suppliers are also noted, including unique engines like Superior Gemini, DeltaHawk and Centurion. The big two engine builders, Lycoming and Continental, primarily make Avgas powered engines, but have also produced some diesel engines on a limited scale.

The article has lots of photo and goes into more depth on the diesel engine builders near the end. You can find the full story here at EngineLabs.