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Flying With Ethanol

By Terri Sipantzi, for Light Plane World

Terri Sipantzi
Terri Sipantzi

There has been a lot of discussion going around the light-sport and ultralight community about alcohol in the fuel. Can we use it? Is it a good idea? What is legal? It’s probably one of the questions I’m most asked. Let me start by addressing this question from a legal point of view, and then I’ll work to the practical side. If you’re flying a special light-sport aircraft (S-LSA), then you must use the fuel specified by the aircraft (not engine) manufacturer. 

That’s right – the aircraft manufacturer is the one that makes the authoritative determination. In making the determination whether to allow alcohol (ethanol is what we’re talking about here, not methanol), manufacturers will typically wait until the engine manufacturer determines the use of ethanol is safe and at what levels. In the case of Rotax engines, the engine manufacturer has stipulated that up to 10 percent ethanol is safe in their engines. (See Rotax service bulletins to determine if your engine has been determined ethanol safe. It will be based on engine serial numbers.)

Once the engine manufacturer has determined the engine is safe for a specified percentage of ethanol, the aircraft manufacturer must then ensure that the fuel system installed in the aircraft is also ethanol safe. If the manufacturer is using fuel lines, a fuel tank, or any other components that haven’t been tested for ethanol, then the manufacturer can’t issue approval to use ethanol until those components are changed out or tested. So check with your manufacturer to determine if your S-LSA is approved for ethanol use. 
By the way, the “approval” can be in one of a few forms. It can either be no specific ethanol restriction or it can be a statement specifically authorizing the use of ethanol. It can even be a deferral to the engine manufacturer (a statement that the aircraft manufacturer authorizes whatever the engine manufacturer authorizes). If you’re flying an experimental light-sport aircraft or ultralight, you can do whatever you want from a legal point of view, but you would be wise to follow the same path the aircraft manufacturers follow in determining whether it is a good idea. Is it a good idea?

I’ve been using ethanol in my plane, off and on, for some time now. However, I always default to ethanol free when I can get it. Why’s that? Last spring, after I had been using ethanol-based gas for several months, I was trying to start my trike. It would start, run, and then die. After three of these false starts, I suspected I was having a fuel problem, and the first thing I checked was the fuel itself by draining a sample. The entire fuel sample cup looked like a filmy, almost jellylike substance. The alcohol in the fuel was completely saturated with moisture and had settled to the bottom. My engine was sucking this filmy, jellified mess into itself. Even if I’d drained the saturated content out, the fuel was still no good because fuel treated with ethanol derives part of its octane rating from the ethanol. Since all the ethanol had separated out with the water, my octane rating was below the safe level. I had to completely drain the tank.

Since then I try to use ethanol-free gas whenever I can find it. It’s more stable, and if moisture gets into the fuel, I can drain it out just as I would if I were using 100LL (the fuel GA aircraft use). With ethanol fuel I have to be much more concerned about how long any of it is sitting around.

Another thing you have to watch for with ethanol-based fuels is corrosion. If I’m going to be storing a plane for more than 30 days, I’ll drain the fuel from the tank and I’ll pop the carb bowls off and drain the fuel out of them. If you store your plane over the winter without emptying the carb bowls, then there’s a good chance that the ethanol will cause some corrosion. If any of the corrosion breaks free, it can foul one of the carb jets causing problems. Corrosion is an even bigger concern with two-stroke engines since the crankcase is open to the environment when the engine is stopped. There are a number of good articles out about protecting your two-stroke from corrosion during the winter storage season, so if you’re using ethanol-based fuel you’ll want to get one of these articles and make sure you protect your engine from the extra risk ethanol poses.

Something else to pay attention to is your fuel filter. This is particularly true if you have bought a used plane that has had one or more fuel lines changed out. If the fuel line going into the fuel filter is being degraded by the ethanol, little bits of that line are going to start clogging the fuel filter. The same thing will happen if the gas tank is being dissolved. A trike pilot here in Virginia had to make an emergency landing a couple of years ago when his engine died. During the subsequent investigation it was determined his fuel filter had clogged up over a period of time, with deteriorating fuel line bits, and finally choked the engine to death.

These are things I don’t have to worry about if I’m using fuel without ethanol. But if ethanol-based fuel is all I can get, then I’ll fly with it – I’m just going to be watching the fuel system a lot more closely.

One of my readers just sent me this cool link for finding ethanol-free gas. Check it out at Pure-Gas.org.

Terri Sipantzi is the owner/operator of Precision Windsports Inc., a full-service weight-shift light-sport aircraft dealer based in Lynchburg, Virginia, and specializing in Airborne trikes. He’s a regular contributor to EAASport Aviation and Light Plane World.

This article was originally published in the Precision Windsports monthly newsletter. You can subscribe to the newsletter, read back issues, and access archives of his published articles at www.PrecisionWindsports.com.


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