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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