toyPOWER to the People!

The Future of Alternative Fuel Options for General Aviation

By Jim Cavanagh

What will YOU be using to keep your plane flying?

Things seem to have mellowed out over the last couple of years regarding the expected demise of avgas. Three years ago you couldn’t pick up an aviation magazine without reading something about alternative fuels. Today, you can go a few months without reading anything about the development of new fuels. Well, you’re reading one now because the subject, while not the darling of editors these days, is still very important to aviation and its future. After all, if we cannot power up, we can’t fly! And in a much longer perspective, the same concept holds true for our ground-bound vehicles as well. Between limited supplies and government policies, we’re in the early stages of ushering fossil fuels to a back burner.

When I was a kid, I had a toy airplane. You’d spin the propeller with your finger and twist a rubber band until it started growing appendages. Of course, mine would take off and do an instant loop into the ground. Still, technologically speaking, that was a good, albeit primitive, sort of power—at least it was a step beyond simply tossing the airplane as hard as I could. These days, fuel alternatives are similarly shallow steps beyond the original option—the good old gas engine.

Our gas engines are popular because way back in the day, when the auto industry was trying to find a seamless fuel for all of their vehicles, they decided on gasoline. Before that, in 1789, there was a French automobile powered by steam; even that was preceded by an internal combustion engine powered by, of all things, gunpowder! In 1807, the Swiss developed a hydrogen/oxygen-powered engine, and in 1876, Nickolas Otto built the first successful four-stroke engine.

When cars were getting popular in the 1920s, engine designers needed to boost octane from the 20-40 RON rating they were getting. Higher compression engines needed higher octane for power and efficiency. Some researchers found that iodine was an excellent power booster, but a company owned by Standard Oil and GM decided to use Tetra Ethyl Lead (TEL) instead— mainly because the developer of TEL, Kettinger, worked for one of the companies. So, here we are.

Though we seem to have plenty of oil for making avgas, rising costs continue to knock a lot of guys out of aviation. Those who can burn auto fuel do so, but realistically, there are few alternatives. The following is an overview of such options. Will any of them ever make it to the “big show?”

Petroleum fuels

Fuels made from crude oil include mogas, avgas, diesel, and the family of jet A and JP fuels used by turbine-powered, airplanes. From one barrel (42 gallons, not 55) of crude oil, refiners can make about 19 gallons of gasoline, 10 gallons of diesel, and four gallons of jet fuel—oddly, the pricing is inverse as compared to the product!

MoGas: Typical car gasoline, or mogas, is not the viable option it once was. First, it’s difficult to get approved because it is blended seasonally for different locales, so it’s not consistent. It’s also becoming difficult to find mogas that hasn’t been cut with ethanol which can negatively affect the seals and hoses in a fuel system. In fact, the Experimental Aircraft Association quit selling their auto fuel STCs when all of this came about. Still, there are thousands of pilots who truck mogas to the airport.

100LL: In GA we find standard 100LL—aka “blue juice.” Three decades ago with the proliferation of more powerful and turbo-equipped engines, 100LL replaced 80/87 (“red juice”) and 100/130 (“green juice”). However, in smaller engines 100LL can cause lead fouling of spark plugs—and in people, it can cause mental and nervous system problems. In fact, back in the ‘20s, four refinery workers “went crazy,” thus alerting scientists and the public to the toxicity of TEL. Granted, the amount of lead thrown out into the atmosphere is very minute. Still, it’s enough to have gotten the EPA involved and has prompted the two-decades-old “scare” in the demise of 100LL. TEL is only produced by one company, Octel, located in Great Britain. There are rumors that Octel could quit making the product at any time, thus stranding GA aircraft. However, company spokesmen have said that it’s used in other products, and as long as there is a need, they’ll continue to make it.

85UL: A petroleum-based fuel blended for use in ultralights. Owners of Rotax and their ilk may find this fuel at ultralight/light sport airports.

91/96UL: Hjelmco Oil, of Sweden, developed this fuel in the early ‘90s, and Continental and Lycoming have approved it for aircraft in Europe. According to Wikipedia, it’s legal and safe in 90 percent of all aircraft in the world. It also meets the ASTM D910 standard for 91/98 octane. There’s also a leaded version of this fuel only used by the military.

93UL: In 2013, a company called Airworthy AutoGas certified this unleaded, ethanol premium auto fuel under ASTM D4841, and it was approved by Lycoming via SL 1070S. Where can we get it? Not a freakin’ clue!

94UL: This is 100 LL without the TEL. It was tested by Continental in the new IO-550. At the time, Continental said it would be fine for most of their engines. Lycoming, however, did not share Continental’s enthusiasm—then again, Lycoming builds probably the most demanding engine out there; the TIO-540-J2B. Since we already make it and it’s already certified, this would be a readily available, transparent, seamless fuel for most of the world’s airplanes.

G100UL: In development by General Aviation Modifications, Inc. (GAMI), the injector and turbo upgrade people in Ava, OK, this fuel has languished in the test tubes for a year or so now. It was GAMI’s chief engineer, George Braley, had plans to license his formula to refiners around the country, ensuring that the fuel was available wherever it was needed without expensive transportation costs.

Gasohol: Rotax allows the use of ethanol-enhanced auto fuel in their engines—if there is no more than 10% ethanol. This is basically any gas you buy at a pump these days.

Diesel: With Cessna now providing the Continental/SMA engine in the 182 and another diesel in the 172, it looks like diesel is here to stay—albeit in very, very small numbers. Cessna also claims they will begin phasing out gas engines in the 2014 model year 182 in favor of this engine. The new 182 is listed at $515K, so you won’t see many of them around for a while, and conversions will be quite expensive—probably $100K+.

Benefits of diesel include its (and its derivative’s) availability worldwide, no need for mags and spark plugs, single-lever operation with automatic mixture, and an engine that already sports a turbo so you can cruise at FL20. Plus, diesel provides exceptional range. NOTE: The new Cessna T182JT-A offers a 1,360-nm range and fuel burn drops to 11 gph. While it’s called a diesel engine, the SMA mill is certified for Jet A, which you can get at most airports.

Along with SMA, Thielert is still in the diesel business with no fewer than eight other companies around the world who are all working on both two- and four-stroke diesel aircraft engines.


Biofuels have been the rage for the past couple of decades. It started with corn (you call it maize), but technologies have also developed ethanol and derivatives from things like tree bark, saw grass, and pond scum—really, about anything that grows in dirt or water! Though it’s considered a “renewable” fuel, there are huge problems. First, even though it has been around for a while, it’s still an emerging technology. Ergo, there are dozens of uncoordinated efforts to create the ultimate fuel source from a myriad of substances. Corn and sugar beets would never work in the long run because of the infrastructure required to grow, cultivate, and transport useable amounts. Without government subsidies and with requirements for most states to include up to 10 percent ethanol in almost all gasoline (pure lobbying and farm PR), there probably wouldn’t be any ethanol in our gas pumps.

Still, ethanol will burn; and if it burns, it can be made to burn in airplane engines. Biodiesel has enormous potential and, as mentioned above, diesel engines continue to be developed around the world.

AGE-85: Developed by the University of South Dakota (USD) as a fuel their corn growers could provide, this is a specially-blended ethanol that has improved cold start dependability. Texas Skyways and USD worked together to develop a few STCs for some Cessna models. Owner Jack Johnson says that the STC requires different jets in the carb, but the AGE-85 actually produces more horsepower—the downside being a heavier fuel flow. An American through and through, Johnson embraces the idea that with AGE-85 we would not have to depend on foreign oil. In addition to a cleaner-running engine, Johnson estimates that engines using AGE-85 get nine percent more horsepower and run 30 percent cooler. Because of this, he also expects increased engine life. All of his engine conversions can be readily converted to AGE-85.

100SF: Swift Fuels, based in West Lafayette, IN, is developing a 100 octane biofuel using biomass sources that are not starch-based, like corn. Their goal is to develop a replacement for both avgas and jet fuels. Swift was going hot and heavy for a while, but seems to have slowed down their efforts over the last couple of years. Enthusiasm soon gets overtaken by expense in this business.

A plug-in “fix?”

Yep, pun intended. There are no fewer than 12 companies throughout the world working on electric airplanes. At least one has flown each of the last three years at Oshkosh. One of the leaders is Bye Aerospace, a company started by forward thinking George Bye. Based in Colorado, Bye has a new little two-seater as a test bed airplane. The company had also retrofitted a Cessna 172 with an electric motor and batteries for flight testing.

In California, Chip Yates modified and flew a Rutan Long-Eze to a record 202.6 mph. A French Cri-Cri, much smaller and lighter, had flown 175 mph with its electric rig.

Now THIS is an emerging technology. Using vastly improved batteries and motors, companies around the world are looking at fast-charging electric power for the next generation of small airplanes. The machines are exceptionally quiet and the torque coming from an electric motor is the same throughout the RPM range, i.e. no power spool up required.

An airplane at Oshkosh a couple of years ago had a motor and battery pack that weighed just 54 lbs., and if flown like a motor glider (climb then glide) it could remain in the air for well over an hour carrying two people. The batteries recharged in an hour.

There is still a long way to go for electric power, but the next amazing breakthrough could be around the next bend.

And way, way out there…

There have been theoretical engines that use hydrogen pellets or the “fuel cell” power pack. The only byproduct is water. A good friend wrote his Master’s thesis on hydrogen powered airplanes a few years ago. Toyota is introducing a hydrogen powered car in 2015. I can’t even get a T-Mobile signal in my living room!

So, there we have it. How we are currently (or could be) powering our airplanes—and I didn’t even get into dilithium crystals, beryllium spheres, or fairy dust! All joking aside, everything you read has validity and potential. Yet, all of them depend on a myriad of factors including development, certification, technology, and economics. Plus, all these factors need to intersect at the same time with a viable infrastructure. The latter, above all, is the expensive part. Even if a fuel is supposed to be capable of a seamless insertion into the system, lobbyists and bureaucratic agencies won’t let it happen without incredible expense.