Ryan, my understanding after checking the Petersen website it that the O-540 has been tested with auto fuel, but that the PA-32 airframe itself is not approved. The Petersen website has two routes to check, one for the engine, and one for the airframe. Did not check the EAA (who also sell Auto Fuel STC) for approved compatability with a PA-32 with an O-540.

Petersen website here- http://www.autofuelstc.com/autofuels...nAviation.html


This is an interesting subject to me, mainly for the reason that Avgas in Juneau is horrendously expensive the last few years. It's above $5 a gallon there right now, and a couple of summers ago it was near $7 a gallon. Pretty painful in a Beaver burning about 25 gph. Had a very negative effect on my employer at the time.

I've got a PA-11 (C-90-8F) which I purchased the Auto Fuel STC for, and a friend has a C-172D (O-300C) who also did the same. Our problem is ethanol. The 11 has enough "soft" parts in the fuel system that I have never even been tempted to violate the STCs prohibition of fuel containing ethanol, and I hope my friend will avoid it also, as the old 172 has plenty of parts that I have concern about too. Things like fuel selector seals and o-rings. Those get goofed up and there might be a problem.

The concerns about future availability and price of 100LL and ethanol free auto fuel are big ones.

 

What would be the problem with burning ethanol so long as you burned it all right away? I hear that the main problems come from sitting in the tanks while in the hangar.

What about a mix of avgas and ethanol fuel?

Replacing a few O-rings is most likely cheaper than spending $3 a gallon more for 100LL. I read a story about a guy who had to replace all his rubber components after 1000 hours of flying on Ethanol. It sounds like a good deal to me. Why not fly the bad gas until things begin to leak then fix it? It seems like a cheaper way to go. Are new O-rings made to be Ethanol resistant?

Is there a simple way to chemically separate the ethanol out of the gas?


Skyhigh

 

All good questions Sky,
I'm sure you've seen that there's plenty of debate on all sides about these issues.
Most of the people I know using auto fuel use a mixture of it (ethanol free) and 100LL and seem to have good results.

My concerns about using auto fuel have been documented ad nauseum elsewhere- cleanliness, storage, effects on "modern" aircraft propulsion systems- but I have no qualms about using auto fuel in my Cub as its engine originally ran on that type of stuff.

Ethanol, however, is kind of unproven territory to me based on everything I've read, and the fact that the STC specifically prohibits it. I'm not sure the prohibition is based solely on the effects of ethanol on parts of the fuel system. Some of the evidence seems to point towards ill effects of fuel containing ethanol on engines. I'll leave that to the experts.

I'm not sure ethanol is a huge concern in non aviation settings, but most vehicles now have systems which adjust ignition timing based on data gathered by electronic systems- our aircraft do not, and have fixed magneto timing. There seems to be lots of evidence for fuel containing ethanol to provide lower mpg versus old school "straight" unleaded too. I wonder how that translates in an aviation setting where we push our engines pretty hard, they are air cooled, are expensive, and we demand utmost reliability and full power in many situations from them.

I would NOT use auto fuel containing ethanol in any aircraft system where I was not 100% sure that the entire engine and airframe system could handle it with no ill effects. How does one determine that on their own? My answer is that legally in a non-experimental aircraft- they can't. I'll stick to that.

 

In my much younger days I was not as careful when purchasing mogas. I am sure that some ethanol got by. I never did see any ill effects other than a lot of water in the fuel. Does Ethanol absorb water?

I just can not see any clear negatives for using gas with ethanol. Even if it would burn your engine up in 1000 hours it still seems like a financially advantageous way to go. Where I live Avgas is much more costly than auto fuel.

I wish we had a clear future to depend upon. Currently it seems as thought ht powers that be are going to do away with 100LL and leave us to deal with ethanol auto fuel.

Skyhigh

 

That brings up a good point Sky. I can't remember- was ethanol commonly added to fuel during our younger days?

It seems to me it's only been around a few years, and that it was pushed as a way to reduce the amount of foreign oil we use.

There's an interesting article on wikipedia about ethanol, a lot of the chemistry went over my head, but check it out.

Ethanol fuel - Wikipedia, the free encyclopedia

Maybe an interesting experiment (with no concern for the possible long term effects of fuel with ethanol)- what if we get two identical Super Cubs, both with the same Lycoming up front, both weighing the same, with equal weight pilots. Then we top the tanks. Now say one is "theoretically" Experimental so we can run auto fuel containing 10% ethanol in it- (There's plenty of Experimental Super Cubs nowadays, but lots of them are quite a bit lighter than a stock one) The other Super Cub in our test will run standard auto fuel with no ethanol.

Which one will get out of the shorter strip, which one will outclimb the other, and which one will go farthest at the same cruise speed?

Will there be any difference?

I don't know, but I'd like to see it done.

 

Where I live it has been added to gas for a long time now in the city as a way to reduce emissions. I am sure that there has already been a lot of ethanol laced fuel burned in airplanes that few are admitting to. I suspect that it is not as bad as others would like us to believe. In any case if we don't get a replacement for 100LL the alternative will be to be grounded. I would rather take the risk with ethanol poisoned fuel.

Maybe someone should finance a program where you and I get identical new Supercubs from cubcrafters and free fuel. Each of us could then be paid to fly the cubs for 1000 hours to see the results. One of us could be the control and the other the test subject.

Skyhigh

 

Sounds good Sky.
You get to be the guinea pig.

The only ethanol in my Cub is gonna be in the six pack nestled in amongst the tent, sleeping bags, rifle, and fishing gear.

 

Most of you are missing the point - if it is $$ - go experimental and make your fuel system compatible with all the fuels - not as simple as changing a few seals - there have been several inflight fires due to fuel leaks caused by alcohol - and mysterious engine failures - because damaged seals in fuel selectors caused air to be ingested into the fuel system. As far as the 0-320 - 160 hp models go - Lycoming did extensive testing - much more than Petersen - and found that while using 91 oct mogas - there was a area of detonation over 7500 when the engine was leaned - 75% power or less. Are you sure that your timing is right on, the fuel mixture is rich enough, and the carb is set up properly ? If everything is exactly correct and the mixture is kept rich enough - maybe no problem with 91 mogas (this is how Petersen tested it - everything exactly correct) - I have used it in the past in cruise only and that seemed to work well. EPA says lead in the air has increased - of course it has - no more 80 oct avgas which had 1/4 the lead that the 100LL does - about 70% of the GA planes can still use 80 oct av gas - yet we are forced to use the 100LL with 4 times the lead ?? GO figure this out ?? GO back to 80/87 fuel and the problems with the engines and the lead will be much less. Yes - it is possible to build or modify the engine and airframe to work with just about any fuel - if enough people are willing to spend the $$ to get it approved. Problem is - to many different planes and not enough people willing to spend the big bucks $$ to do it !

 

That website was very interesting.. especially to see the airframes that didn't make it through the tests. I recently saw a 6 getting an annual which the owner claimed to have an STC for the -540. The outboard tanks were pulled and... wow! Fuel has everywhere inside the wing, the tanks were cracked and bubbled.

 

I wondered if new planes are certified for auto fuel with ethanol. The Remos GX only lists "Premium" auto fuel as a requirement. So far I have not found a restriction against ethanol laced gas.

Skyhigh