Going Direct: Here‘s An Idea: Drop-In Replacement Diesels

And gasoline was everywhere, so what the heck. Even though diesel technology matured right along that of gas pistons, there was no need for diesel in the light aviation world of the day. And once World War II came about with its ever-increasingly giant piston engines of different configurations (radial, double-row radials, inlines and Vees), the need for a very high-octane fuel was there and there was no turning back. At the time, we knew the dangers of lead in the environment, to a large degree, but as a society, we tended to take such risks in stride. Many of us remember the days of leaded auto gas, 100 octane fully leaded avgas and even more potent lead-filled formulations for super high-performance engines.

Even as the world's unimaginably massive automobile fleet made the switch to unleaded fuel, we were forced to merely cut back on our diet of lead, switching to 100LL in the late 1960s. It was for the minority of engines, true, but they were the most expensive of the engines in the fleet, too, high-performance six-cylinder and four-cylinder turbocharged models, along with geared high-output engines in increasingly capable and power-hungry designs, up through cabin-class piston twins.

We're not entirely stuck with this technology, however. A number of companies are developing diesel engines that do pretty much everything gas piston engines do but better and more efficiently. They're a bit heavy, because their cases need to be built Detroit Diesel-tough to take the very high pressures inherent in the design. But they produce tons of torque, they're a third as efficient as their gas counterparts, and they run on heavy fuel, diesel, Jet-A, surplus salad oil. They're remarkably agnostic in that department.

The thought of a diesel in a high-performance piston single or twin used to be unseemly. Diesels had a greasy, gritty reputation that went along with the big utility vehicles they powered. But diesel technology isn't inherently any of those things. And now that the technology has been popularized in aviation by Diamond, though the use of it originally on its TwinStar piston twin, there's a much wider acceptance of heavy fuel piston engines than ever before.

A couple of Texas companies, Blackhawk and Sierra Industries, do good business in taking run-out engines out of good airframes (Blackhawk with King Airs and Citations, and Sierra with Citations, among others) and replacing them with better, newer more efficient models. The owners pay around the same amount or less to go with new engines than they would have to overhauling their existing ones, and as part of the bargain, they get better performance and lower operating costs.

Such a model will come to pass for our piston engines, as well. It costs a bundle to overhaul an existing big-bore engine, and after you're done, you're left with an old-tech replacement for what you had before. Once suitable diesel engines become available in large numbers for high-performance aircraft, you can bet that companies will arise whose goal it is to pull those 20 gph, 300 hp-class engines out and replace them with 12 gph, 350 hp diesel turbocharged models.

The new owners of those airplanes won't care what you call your 100 octane fuel. They'll be headed right to the Jet-A pump, where they'll find a fuel that has been in ready supply for more than 100 years, doesn't have a trace of lead and can be found anywhere in the world.