Autogas

[Flyboy66]

The Rotax engine is designed to run in auto gas and I think 91 octane is the recommended octane. I live in Colorado, well above sea level. I normally put regular in my tank so I don’t remember the octane rating of “premium”, but I think it is 89 out here, and regular is 85 if I recall correctly. It also contains ethanol. What do all of you Rotax owners(who are well above sea level) use in your Rotax engines?

Steve

[Dave S]

The term "premium" is purely a marketing term....which is best off ignored in favor of facts.

Depends on which engine you have and how octane is labeled in your locale.

The 80 hp 912 is a lower compression engine and can use 87 octane

The 100 hp 912ULS requires a minimum of 91 octane

With the octane being determined by the average value of the two methods of determining octane - research and motor, which you should see on the dispensing pump as R + M/2 = 87 or 91 (be aware there is other labeling which uses only one of the methods and the numbers come out differently)

OK now the corn gas thing - Rotax permits up to 10% ethanol as far as the engine is concerned; however, you have to consider the entire fuel system. Kitfoxes use fiberglass tanks and I believe the consensus is fiberglass tanks can degrade with the use of ethanol. I have a friend with a different plane which has poly fuel tanks and he runs 91 octane corn gas all the time because the entire system is compatible up to 10% ethanol.

Having a 912ULS in our kitfox, I use 91 corn free autogas, occasionally 100LL when on a trip when that is all a person can get. The autogas is also procured from a site which has a dedicated tank and pump for that product.

One word to the wise - some (getting to be more all the time) auto fuel stations do not have a dedicated 91 octane pumps; but, use blend valves drawing from different grades of fuel all going through one hose and pump - this means the first gallon, even if you select 91 corn free, has a pretty good chance of being diluted wItith lower grade or ethanol contaminated junk. I have no idea how often blend valves can fail but I am not at all in favor of getting airplane fuel from any place which uses multiple tanks and a blend valve. One gallon of 87 in a 5 gallon container of gas (or a gallon of E85) which you want 91 octane in could very well inspire detonation in a 912ULS as the 91 is a hard minimum. I do know of folks who squirt the first couple gallons in their car then fill their aircraft cans.

[Esser]

Shell V Power 91. It’s almost the only ethanol free gas I can get. I haven’t run it in my Rotax yet cause I’m not flying but put it in the Cherokee for years.

[Flyboy66]

As far as I know, we don’t have corn free gas as an option. I am headed down the hill in an hour to drop off daughter and then to the gas station to see what we have available. At Denver altitude, we don’t get full power out of any engine (car or otherwise) that isn’t turbo charged, so the available octane ratings are lower because we don’t need the higher numbers necessary at sea level to make most cars run as designed.

And being so close to the smog laws in Denver, I believe ethanol is in all the gas, at least in the winter, when inversions trap the smog down low.

I just hate the idea of running 100LL due to fuel cost and maintenance cost (time and money) for the engine.

Maybe I should just hang a PT-6 on the front. :)

[avidflyer]

Here is a link to a site that will tell you where you can get ethanol free gas in every state. Not garunteed to be accurate, as people can add gas stations to it if they wish, but it's a start. JImChuk
https://www.pure-gas.org/

[jiott]

Maybe CO has an airport or two with clear Mogas on site? Oregon has two. Generally airport fuel tanks and dispensing equipment are cleaner and better maintained.

[Av8r3400]

Hopefully this will all be academic soon. With the introduction of lead free aircraft fuel we won't have to worry about carting fuel from questionable auto-gas stations.

There's a couple airports in my area that dispense Swift fuel. This is an excellent, if not widely available yet option.

[jrevens]

Steve,

We do have enthanol-free gas here in the Denver area, but not a lot. There is a station in Lakewood that carries “premium”... I’m not sure of the exact octane yet. The Longmont airport (KLMO) carries it also. I’m like you, and don’t much like the prospect of using 100LL, but I will if necessary. I’ve been thinking seriously of buying a 30 or 40 gal. aluminum transfer tank to mount in the bed of my pickup under the tonneau cover, and using that to fuel my airplane with the “farm gas”. I find it ironic that many farmers need/prefer the alcohol-free stuff for their “off-road” vehicles. I’m hoping that in a year or 2 Swiftfuel or Shell will start to have their unleaded alcohol-free products (both are 100 octane or better) all over the country. I believe that Swiftfuel is available at a few airports in the midwest and Eastern parts of the country now. I know that Portage, WI (one of my favorite stops going into OSH) has it. Anyway, it’s going to get better... 100LL is definitely going away.

[Av8r3400]

I believe that the mandate for unleaded aviation fuel is this year (2018).

[Danzer1]

Steve,

We do have enthanol-free gas here in the Denver area, but not a lot. There is a station in Lakewood that carries “premium”... I’m not sure of the exact octane yet. The Longmont airport (KLMO) carries it also. I’m like you, and don’t much like the prospect of using 100LL, but I will if necessary. I’ve been thinking seriously of buying a 30 or 40 gal. aluminum transfer tank to mount in the bed of my pickup under the tonneau cover, and using that to fuel my airplane with the “farm gas”. I find it ironic that many farmers need/prefer the alcohol-free stuff for their “off-road” vehicles. I’m hoping that in a year or 2 Swiftfuel or Shell will start to have their unleaded alcohol-free products (both are 100 octane or better) all over the country. I believe that Swiftfuel is available at a few airports in the midwest and Eastern parts of the country now. I know that Portage, WI (one of my favorite stops going into OSH) has it. Anyway, it’s going to get better... 100LL is definitely going away.

As far as I know KLMO is the only airport within say 3 or 400 miles of Denver that sells mogas onsite. Really a PITA if you are considering mogas out here in the wild west!


I believe that the mandate for unleaded aviation fuel is this year (2018).

Don't hold your breath! Once Phase 2 testing is done there is a "6 month" period for the FAA and ASTM to write it up and then someone has to decide on the transition phase in and how it will be implemented. Knowing how "fast" these guys work, I'd suspect either neither the Swift or Shell products will be available any time soon.

YMMV, Greg

[Flybyjim]

I ordered a tote of Swift fuel this past summer after talking with them at Oshkosh. The tote was shipped to me by a freight hauler, delivered to my business. The truck had a lift gate, the tote holds 350 gal, I transferred the fuel into our own tanks, 2-100 gal tanks on a trailer that I bought from Tractor Supply, the balance of the fuel was put into 55gal drums that my flying buddies used to take their share of the purchase. With freight charges, fuel charges, state tax charges the fuel was still less than the local airports 100LL.
Give Swift a call, you can order fuel in 55gal drums also. I was their first delivery in Pa.

[Flyboy66]

Thanks John, I was planning on calling you to see what your plan for fuel was. I did a search on ethanol free gas and was shocked at how many places sold it. I already own several 5 gallon gas jugs, so I have dropped down from panic level 5, to about 0.5. Fuel will not be causing me anxiety for now.

I spent 3 hours last night watching some YouTube videos featuring a Rotax expert at an airshow. After listening to him speak about what 100LL does in a Rotax, I didn’t want to be using it. More $/gallon to possibly quadruple my oil change costs and time required to clean out the oil tank. No thanks.

[Esser]

I ordered a tote of Swift fuel this past summer after talking with them at Oshkosh. The tote was shipped to me by a freight hauler, delivered to my business. The truck had a lift gate, the tote holds 350 gal, I transferred the fuel into our own tanks, 2-100 gal tanks on a trailer that I bought from Tractor Supply, the balance of the fuel was put into 55gal drums that my flying buddies used to take their share of the purchase. With freight charges, fuel charges, state tax charges the fuel was still less than the local airports 100LL.
Give Swift a call, you can order fuel in 55gal drums also. I was their first delivery in Pa.

Really interesting to hear. Awesome that essentially you cut out the middle man since no refineries would ship you fuel if you weren’t going through a distributor

[neville]

For information: the rotax 912iS operators manual stipulates 92 oct. minimum.
There are 4 listed airports in Wa. that offer MOGAS (92 oct no ethanol). The fuel tanks used in the SS7 are made from material which is resistant to ethanol.
I believe (????) they can be identified by having serial numbers etched into the inboard face. The fuel at my home airport (KOKH) has mogas however, the supplier also has the same fuel available at two of their auto fuel stations in the area which carry all three grades of no ehtanol.

[Esser]

The min octane on the 912iS is 91

[Flyboy66]

For information: the rotax 912iS operators manual stipulates 92 oct. minimum.
There are 4 listed airports in Wa. that offer MOGAS (92 oct no ethanol). The fuel tanks used in the SS7 are made from material which is resistant to ethanol.
I believe (????) they can be identified by having serial numbers etched into the inboard face. The fuel at my home airport (KOKH) has mogas however, the supplier also has the same fuel available at two of their auto fuel stations in the area which carry all three grades of no ehtanol.


I thought I had seen somewhere that the fiberglass fuel tanks were susceptible to degradation due to ethanol and that is why it should be avoided. (Kitfox, not Rotax). Rotax seems to be concerned about ethanol because it can off gas and change the AKI or can come out of solution due to water in the fuel, which also can change the AKI. Both Kitfox and Rotax are concerned about the stability of auto gas that sits for even short periods of time. This is where 100LL shines. It is very stable over time and far less likely to varnish the carb bowl...

Does anyone have documentation regarding the use of ethanol auto gas on the Kitfox being recommended/not recommended.

Here is a link to part 1 of Rotax stuff. There is some discussion about fuel 100LL in there somewhere. https://youtu.be/DFfxHbaU_Bs

[Esser]

There are old legacy tanks that are not ethanol resistant. All kitfox tanks now are ethanol resistant

[Flyboy66]

John,

Where do you get that information. I don’t have the kit yet, so no Flight Handbook etc.

Steve

[airlina]

I ordered a tote of Swift fuel this past summer after talking with them at Oshkosh. The tote was shipped to me by a freight hauler, delivered to my business. The truck had a lift gate, the tote holds 350 gal, I transferred the fuel into our own tanks, 2-100 gal tanks on a trailer that I bought from Tractor Supply, the balance of the fuel was put into 55gal drums that my flying buddies used to take their share of the purchase. With freight charges, fuel charges, state tax charges the fuel was still less than the local airports 100LL.
Give Swift a call, you can order fuel in 55gal drums also. I was their first delivery in Pa.
Very interesting Jim, do you remember what the pricing came out to per gallon. Thanks Bruce N199CL

[Esser]

John,

Where do you get that information. I don’t have the kit yet, so no Flight Handbook etc.

Steve

It’s not really written anywhere that I know of. It’s just common knowledge after bring on this forum for a while. I think on my packing slip the tanks were labelled ethanol resistant. Either way here is a quote from 10 years ago from John:

“We have done some changes over that past 6 months... although I do not think our tanks as of 1996 to 2007 have had any specific issues. (no reported issues)

As of this year we are using a new resin. To date.. we have put some pretty harsh materials in them with no effect. For the last several months they have had both 10% and 85% ethanol fuels in them and no effect.

I will not go into the details of the resins as it is proprietary information.

Fly Safe !!“

You can always call the factory too

[jrevens]

Hi Josh,

On your post #15 of this thread, the attached image refering to minimum octane for the 912is shows just a little bit of a statement at the bottom that starts out saying that “AVGAS 100LL places greater stress on the valve seats due to its...”

What is the rest of that statement?

Thanks.

[Esser]

AVGAS 100LL places greater stress on the valve seats due to its high lead content and forms increased deposits in the combustion chamber and lead sediments in the oil system

[Bud Davidson]

My 912 has water cooled heads. My ford v6 was water cooled...including the heads. After 100 hrs the ford had damaging lead deposits in the exhaust chamber of the heads. I was using 100 LL. The machinist, an A&P, removed the deposits and suggested I use non-alcohol auto fuel since the water cooled heads did not reach temperatures high enough to purge the lead. Spark plugs gave a clear indication of the lead buildup. 300 hrs later plugs did not show lead. Cost is less than 100 LL or at least similar. Incidentally, it stores well also in my mower and pressure washer. But, on cross countries use of 100LL cannot be avoided. A 23 hr flight from AZ to FL did not seem to be a problem. My view of this question is to use auto fuel as much as possible at least in water cooled engines.

[Flybyjim]

I will look for the receipt from Swift, but I believe it worked out to $4.65 gal.

[neville]

Hi Esser, I stand corrected. 91 octane is correct. My supplier buys fuel at a local refinery and blends it themselves to 92 and no ethanol so I guess I always have 92 lurking in my brain.

[Dave S]

After reviewing Josh's post and others on the octane rating for gasoline; figured I better update my post (#2 on this thread) because the references I was using for the acronyms we commonly used in antiquity - (like the 1970's) where I mentioned the octane rating of 91 for the rotax requirement is an average of two methods for determining octane i.e. R + M /2 which you normally find labeled on the fuel pump.


Josh's post referencing the Rotax octane requirements indicates 95 Octane RON also indicates that is equivalent to 91 Octane AKI.

Apparently "AKI", "RON" and "MON" are the more commonly used acronyms in some places

so: AKI = Anti Knock Index = R+M/2 or RON (Research Octane Number) + MON (Motor Octane Number) divided by 2

"R" or "RON is an octane rating determined via analysis of the fuel; while "M" or "MON" is an octane rating determined by actually running he fuel in a standard engine to determine when it starts to knock.

Sheesh!..:confused:..almost as bad as the alphabet soup of acronyms the FAA puts on us

AKI, RON, M, R, MON, R+M/2, RON+MON/2

What can be really confusing is seeing two numbers in the Rotax book 91 and 95, and without associating the units, or how the units are determined, pretty difficult to recognize that 95 and 91 are the same number.

[Esser]

And I think only the US and Canada use AKI. Of course we couldn’t use something the rest of the world uses:rolleyes:

[zadwit]

I worked on a 160hp SUperCub in Alaska that belonged to an outlaw trapper guy. He never got annuals, no pilot license and he has over 11,000 flying in a Alaska. He insisted on using unleade car gas in his 160 high compression engine so I had a fuel blender at a local refinery help me and we determined that you only have to add 10% 100 LL to unleaded car gas and it raises the anti know index over 100. Before we did that , the trapper burned a couple of pistons in the summer on a hot day (80) low level full throttle....after we came up with the mix , no more problems.... TEL was used because it only takes a very small amount to raise the anti know indext right up there... So I am guessing in a Rotax little 100 LL wont hurt and will likely help prevent detonation or pings....The problem with a full diet of 100 LL is it will coat the inside of the combustion chamber and raise the effective compression ratio. Then if you put some cheap car gas in the same engine later, you might get into detonation area,especially at low altitude and full throttle on a hot day..
Car gas has butane and other aeromatic fuels added to raise the antiknow index but it these things that cause problems with rubber hoses and gaskets.
Alcohol is a another problem but pure alcohol has an antiknok index of 100 so it helps raise the antiknow index number.
exthane, methane, propane , butane , pentane, ?,?,iso octane.... Iso octane has a knock index of 100 and that is what was historically used in a test engine and then the ratio was compared to regular car gas as to what pressure it could take before pinging.....Alkand parafin series of hydrocarbons are what is in the fuel...
SO in summary, adding 10% avgas 100 will raise the anti knock index and provide some protection against detonation. Avgas is stable and will store for several years. I have used some gas that it over 5 yrs old....The real problem is the EPA was sued by friend of the earth and so there is a deadline to remove the lead from the fuel....so far, there have been limited results. The test engine is the Lycoming TSIO 540 J2BD engine with is turbo supercharged and makes 350 hp at 41" MAP so the thinking is if an unleaded avgas can be made to run in this engine, it will run in the rest because this engine has a fairly narrow detonation threshold.I was lucky to have a petroleum engineer who designed and built the refinery at North Pole, Alaska and another flyer who was a fuel blender at the refinery so they taught me a lot about fuels. The petroleum companies will tell you nothing because of potential liability...

[zadwit]

List of straight-chain alkanes

The members of the series (in terms of number of carbon atoms) are named as follows:
methane, CH4 – one carbon and four hydrogen
ethane, C2H6 – two carbon and six hydrogen
propane, C3H8 – three carbon and 8 hydrogen
butane, C4H10 – four carbon and 10 hydrogen
pentane, C5H12 – five carbon and 12 hydrogen
hexane, C6H14 – six carbon and 14 hydrogen
heptane, C7H16; octane, C8H18;
There are more but iso octane has an antiknock index of 100 and that is what gasolines are compared to. If octane pings at 100, 91 car gas pings at 91% fo the pressure required to make octane ping...