You know the old adage, right? “If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.” This year marks the 30th anniversary since the FAA approved the first STC for the use of autogas in aircraft. Since then, it has enjoyed an excellent track record as a safe, affordable, lead-free alternative to avgas that can power 70%-80% of the current piston-engine fleet. This includes numerous warbirds, many vintage aircraft, most auto-engine conversions as well as many next-gen piston engines from Rotax, Jabiru, ULPower, Continental, and Lycoming.
Nevertheless, there are still those who refuse to admit that autogas is an aviation fuel, simply because it was not created solely for the use of aviation (although we all know of the popularity of 100LL in antique and race cars). Do we buy “marine fuel” for our boats, “home & garden fuel” for our lawn mowers, chainsaws and power generators, or “recreational fuel” for our snowmobiles and ATVs? Of course not. Manufacturers have designed their products to operate on gasoline that meets ASTM D4814 standard, and it’s in the interest of oil companies to deliver high-quality fuel that meets this standard if they want to stay in business.
Aviation-specific fuels have not always been common. In the pre-World War II era, most piston aircraft operated on vehicle fuels, as this image of an airplane topping off at a gas station clearly demonstrates. It was the need for high octane fuels to power military aircraft during the war that led to the development of high-octane fuels containing lead, as well as to “water” injection systems, which are now available for light aircraft from Air Plains of Wellington, Kan.
As different grades of cheap avgas became generally available, autogas slowly disappeared from our airports. Times have changed, with the triple pressures of environmental concerns over lead emissions, the continued transition towards jets and turboprops reducing the consumption of avgas, and a rapid increase in the price of avgas relative to autogas in recent years making autogas more attractive than ever.
Manufacturers have long recognized the legitimacy of autogas as a fuel, evidenced by autogas STCs for 150-plus aircraft from Petersen Aviation and the EAA, by its inclusion in the list of approved fuels for most next-gen aircraft engines, and in specifications from many aircraft component manufacturers. For instance, Aeroquip, makers of fuel lines and components, states the following in the first paragraph of its Service Bulletin SA24-18091:
TO OWNERS/OPERATORS OF ALL GENERAL AVIATION AIRCRAFT USING AIRCRAFT GASOLINES (E.G., INCLUDING, BUT NOT LIMITED TO 100 OCTANE LOW LEAD, HIGH OCTANE AUTOMOTIVE UNLEADED, ETC., HEREINAFTER REFERRED TO AS “AVIATION GASOLINE”).
There you have it: Autogas clearly passes the quack test as an aviation fuel.
The GAfuels Blog is written by two private pilots concerned about the future availability of fuels for piston-engine aircraft: Dean Billing, Sisters, Ore., a pilot, homebuilder and expert on autogas and ethanol, and Kent Misegades, Cary, N.C., an aerospace engineer, aviation sales rep for U-Fuel, and president of EAA1114.
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Rich. Times have changed. Today’s gasoline is comparable to Jet-A and gasoline in terms of quality, and has a 6-12 month ‘shelf life’, provided ethanol is not present. Many also do not know that autogas has 3% more BTUs per gallon than 100LL. One does have to check for ethanol when buying at gas stations, but we’d always recommend having it delivered directly from a fuel terminal (where ethanol is added to the ‘clear’ gas coming from a pipeline) to an airport with the MSDS documentation certifying that the fuel has the correct octane and contains no ethanol. Outside the US, Canada and parts of Europe, there is no 100LL today. Autogas and Jet-A are the only aviation fuels you’ll find, which is why airplane/engine manufacturers now certify their latest products to run on autogas. This includes Continental and Lycoming. Many pilots in the US are living in the past.
Unfortunately, the number one reason for engine failure “back then” was fuel contamination/poor fuel. Contamination comes from it not being treated as well cautiously by everyone in the supply chain and poor comes from its short shelf life. Neither of these will kill you in a boat or a car but in an flying machine you usually want to keep flying. There is also the problem with airplanes sitting for longer periods. “Back then” people who owned airplanes actually flew them. They weren’t tied down at some airport just so some schmuck could tell everyone he owned an airplane. And of course there is the ongoing issue of getting fuel or an airplane that can be guaranteed to have no alcohol or never had it in its system. I would love to use auto fuel but I know that a large percentage of the pilot population doesn’t use it just because they think “it’s auto fuel”. They use avgas for its known track record and avoid auto-fuel for its track record.
The smell and the ugly brown dye are added to the fuel for highway use. If someone were to sell it solely for off-highway use, it would smell better and could be any color, but smart would be simply clear, or “white” as people used to call high-octane gasoline.
When I was flying my own Skyhawk  for four years (between 2002 & 2005) and 800 hours I burned more than 4,000 gallons of auto fuel.  The only thing I didn’t like about it was the smell.  I also saved about $1.00 per gallon back then.
Good article! Thirty years! Let’s hope that reason finally prevails on the issue of autogas as aviation fuel.
FYI:Â The weblink for “Air Plains of Wellington, Kan” in the article triggered my antivirus software.