Autogas for everyone: Part I

The GAfuels Blog is written by two private pilots concerned about the future availability of fuels for piston-engine aircraft: Dean Billing, Sisters, Ore., an expert on autogas and ethanol, and Kent Misegades, Cary, N.C., an aerospace engineer, aviation sales rep for U-Fuel, and president of EAA1114.

Judging from the reaction to the Aviation Fuel Club, interest at airports and among pilots regarding the “other” aviation fuel, autogas, has never been stronger, especially with avgas prices exceeding a stunning $9 a gallon at some FBOs. Many pilots are now asking if autogas is a legal and safe alternative for their aircraft. This three-part series of articles seeks to answer this question. In Part I, we’ll review the history of the autogas Supplemental Type Certificates (STCs) that allow us to use the fuel in hundreds of different legacy aircraft and engines. Part II will describe efforts to modify higher compression ratio engines that are currently not covered by these STCs. In Part III, we’ll describe the growing list of new aircraft and aircraft powerplants designed from the outset to operate on autogas.

New Jersey pilot Stuart Brown is a big advocate for autogas, which he uses in his Bonanza.

To understand the history of autogas STCs, start by reading this summary article that appeared in EAA’s Sport Aviation in 1982. It describes how, in the aftermath of the oil crisis of the early 1970s, the 80/87 octane grade of avgas started disappearing from airports. Thankfully, Paul Poberezny, Dick Roemer, Harold Zeisloft, and other EAA leaders embarked on an effort to gain approval for autogas, despite fierce resistance from the FAA and industry. Their tenaciousness, and a near-perfect record of safe operation in test aircraft, led to the FAA’s issuance of the first STC to the EAA on Aug. 5, 1982. This was followed by numerous additional STCs, all for 87 octane AKI unleaded autogas, that are available today from the EAA. In the author’s opinion, the autogas STC ranks among the top three or four achivemenents in the illustrious 58-year history of the EAA, right up there with homebuilding in general, the establishment of nearly 1,000 local EAA chapters around the world, the Young Eagles program, and the Sport Pilot Certificate and Light Sport Airplane category.

For those who incorrectly assume that an autogas STC involves its owner doing little more than submitting paperwork and money to the FAA, the following comments made last year by my recently departed friend Jack Cox, former editor of the EAA’s Sport Aviation, provide evidence that gaining the original STCs was a Herculean effort: “With no one left at the EAA today who was there when we were working with the FAA to get the STCs, I don’t know how much you know about the effort that went into the program. Harry Zeisloft, who had been a research engineer with General Motors for most of his career, conducted the program. He had to work with the FAA office in Chicago and they really put him through the wringer, requiring proof testing of everything. I remember one time when — with FAA personnel observing — we heated a big can of mogas to a required temperature by dipping it into a 50 gallon drum filled with hot water, then quickly poured the gas into a big Stinson Jr. and climbed to a specified altitude (and temperature) to see if vapor lock would result. (It didn’t.) Reid vapor pressure and attendant vapor lock took up most of the time during the program. Alcohol (ethyl and methyl) were extensively tested. Harry and his assistants had containers of the stuff all over the Weeks Hangar with samples of all the materials used in aircraft fuel systems to see what sort of deterioration would result — and that included materials used in airplanes from the 1930s that were no longer in use in currently produced planes. There was deterioration and that was why the EAA STCs do not allow the use of fuel containing ethanol. Of course Harry had to document everything, but I have no idea if the EAA retains any of it today. Having been a part of the EAA program to get STCs for the use of mogas, of course I know it can be safely used in the aircraft for which those STCs were obtained . . . and I know that myths still persist regarding its use. Every problem that occurs in engines that have been burning mogas is blamed on the fuel — by people who have never been involved in any sort of testing. And, sadly, the coming of ethanol by politically influenced government fiat has just added to the confusion.”

Among those who followed the EAA’s autogas initiative closely was Charles O. Petersen and his son Todd, crop dusters based in Minden, Neb. Todd, still heavily involved in autogas-related research at his Petersen Aviation and a founding director of the Aviation Fuel Club, describes how they got started: “Flying a fleet of six Grumman AgCats in the early 1980s, we knew that our planes’ Pratt & Whitney R-985 radials would probably run just fine on autogas. With advice from Harry Zeisloft and Dick Roemer, we established the same testing methods used by the EAA and embarked on an effort to gain FAA approval for the R-985. Once this was achieved, we started testing many other airplanes and have to date sold over 34,000 autogas STCs around the world.”

One of the most critical and expensive aspects of obtaining a new autogas STC is determining if vapor lock will occur using autogas. Petersen describes the procedure: “Each model of airplane had to be flight tested. Differences in fuel systems had to be taken into account so that if you tested an early model but the fuel system was altered in any way two or three model years later, that model had to be flight tested again if we expected the STC to include the later models. We are required to take winter blend gas (RVP 12.5 or higher), keep it 52F or colder until we tested, then put it in the airplane cold, on a day that’s at least 85F (hotter is better because the tests are more valid), then we would heat it in the airplane to 85F. As soon as it hit 85F, we would hop in and fly to 12,500 at Vmc. If it missed, surged or quit, or if the fuel pressure fell below 1 psi, then it was considered a failure. If it passed, we would do it all over again, but this time heating the fuel to 110F. Once you pass both sets of tests, the FAA runs the same tests all over again and if it passed the FAA tests, then you had the airframe STC.”

Thanks to the rigor of such test procedures, autogas has enjoyed an excellent record of safety as an FAA-approved aviation fuel for nearly 30 years since the first STC was issued, and pilots have saved millions in lower fuel and maintenance costs while producing exactly zero lead pollution in the environment. With the end of leaded avgas on the horizon, these STCs are more impotant than ever. Unfortunately, myths about autogas still abound. We tried to dispell some of these in a recent posting, “10 Mogas Myths” Another misconception is that autogas STCs are only available for low-powered planes like Paul Poberezny’s Wag-Aero CUBy and the EAA’s Cessna 150 used in the initial testing. A quick review of the list of aircraft and engines supported by the EAA and Petersen Aviation reveals, however, a wide range of aircraft for which STCs exist. These run the gamut from classic light aircraft (Beech, Cessna, Grumman, Piper) to vintage ones (Fairchild, Funk, Bellanca), warbirds (DC-3/C-47, Be-18, O-1, T-6/SNJ, Stearmans), crop dusters, bush planes (Husky, Maule, SuperCub), aerobatic designs (Citabria, Great Lakes), seaplanes (Goose), and even helicopters (Robinson, Schweizer). Petersen STCs cover many high-performance singles, including 15 different models of the Beech Bonanza/Debonair.

The benefit to pilots who use autogas are significant savings in fuel and maintenance costs related to lead fouling. Take for instance the G35 Bonanza shown here, owned by Stuart Brown of Marlton, N.J., whose autogas-burning plane won “Bragging Rights” distinction in April 2010 from the American Bonanza Society. In cruise at around 150 knots, its fuel-injected Continental E-225-8 engine consumes approximately 10 gph. For this G35 pilot making the annual trek to Oshkosh from his home base, South Jersey Regional Airport (VAY), a distance of 658 nm, one might figure roughly 100 gallons of fuel burned for the round trip. Using the current national average prices for avgas ($5.45) and autogas ($4), an autogas user would save $145 compared to avgas burners flying the same plane over the same distance. That will buy a pilot his nightly beers, an update to his GPS database, and plenty of souvenirs from EAA AirVenture. For a nominal 100 hours of flying annually, the same Bonanza G35 owner might expect to save $1,450 (1,000 gallons X $1.45 fuel price differential) — in essence a free annual or a large portion of the yearly hangar rent. Imagine what the savings would be for the owner of a DC-3, Beech-18 or AirTractor crop duster when using autogas instead of avgas at current prices, especially if your home base is charging $7 a gallon or more for avgas as some are today.

What about the cost of the STC itself? In most instances, you’ll pay a one-time price of a few hundred dollars to the STC’s owner, make a notation in the aircraft and engine logbooks and affix a few fuel-related placards on your airframe. In a few cases, modificatons to fuel pumps and other engine components are required, but these too are modest expenses that will be quickly amortized even for pleasure aircraft. For actual prices and details, contact Petersen Aviation and the EAA.

In the next installment in this three-part series, we’ll describe efforts to modify higher compression ratio engines that are currently not covered by these STCs. As a teaster – they are an extension of Petersen Aviation’s 30 years of research, have already gained FAA approval, and are only a few months from being released. Owners of later model Barons, Bonanzas, Cessnas, Dukes, Mooneys, and other high-performance singles and twins will want to pay particular attention to Part II of “Autogas for Everyone.”


  1. Victor Nazarian says:

    The aviation crowd in general needs to get “in bed” with the boating community on the MoGas issue. Almost everythign airplanes have had to deal with has also cropped up in the boats (and even worse) from composite resin issues to vapor lock to flash point fire issues. As a group, combining the efforts of both airplane and boat owners to get non-alcohol motor gasoline at marinas and airfields as well as lobbying congress and the FAA (and maybe even the Coast Guard) on these issues might get some movement.

    By the way, before someone says something about boats and altitude, I’ve been boating on Lake Tahoe and other high altitude bodies of water. Believe me, boats have more in common with many light planes than most people believe.

  2. Kent Misegades says:

    Tony, since labels describing the level of ethanol at gas stations have disappeared, it is quite possible that you got a batch of E10 – it happened to me when my once-reliable Amoco station started selling E10 with no notice, and I had gotten sloppy about testing every batch. Once ethanol contacts certain compounds, the damage is done, even if you never use a drop of ethanol blend again. Boat manufacturers have switched to new composite formulations and sloshing compounds and seem to be more tolerant of ethanol blends, but not before thousands of boat owners have suffered irreparable damage to their boats and motors. Warranties for some new boat motors today do not cover damage due to ethanol blends, so that about says it all. At U-Fuel, we started our new Sport Fuel brand of autogas to assure that only the highest quality, lead- and ethanol-free autogas is sold at airports.

  3. Tony Bishop says:

    We’ve always used Mogas in our Rotax, but we’ve recently become aware of severe problems when using it in a composite tank (ours is carbon fibre/epoxy with a sloshing compound). We still don’t know whether it’s ethanol or one of the other increased additives, but it’s attacked the resin and now leaks. If you have a composite tank, all is not lost. There are now resins which are far more chemically resistant, but it means a new tank.


  1. [...] Part I of this series, we reviewed the history of the STCs that allow us to use 91+ AKI octane, [...]

Speak Your Mind