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Rotax auto fuel

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dick seiders

Well Known Member
I believe this may have been discussed already, but can't find it, sorry.
Madison Airport (52A) only 19 mi. from my home base (9A1) has installed a tank and is going to start selling car gas that is rated for aircraft. It is (guarenteed) 90 octane with NO ethanol, and is called Recreational Aviation Fuel. The airport is run by the county so will add only 15 to 20 cts. more than 91-93 sold at gas stations that does include ethanol of course. My question: is the 90 octane rating sufficient for the Rotax 912 ULS? All the info I have seen usually calls for 91-93 oct. Don't know if this is due to fact that is the state (Fed?) gas station rating for cars, or is it because it is the min. for the 912 when referred to for our engines? I'd like to be certain as I don't want to use an octane that may detonate in the engine.
This issue becomes more important down the road as I hear that our omnipotent Gov/EPA is planning on boosting the ethanol from 10 to 15%, or maybe even 20% in the not too distant future. Interested in comments please, and thanks.
Dick Seiders
 
Rotax says 91 only!

The minimum Octane is 91 per the Rotax Manual. Anything less could cause problems. The information you have received from the airport management does not seem accurate. Here in Texas in smaller counties where non-ethanoll fuel can be found there is no octane rating of 90. Flying to OSH twice in the last 2 years I have never seen mogas at an airport with a 90 octane rating. Only 87 or 91 for non-ethanol fuel. Maybe some one with more experience in Mogas can speck to this matter.
 
I've seen some mo-gas locally that is only rated at 90% octane and some at 91% octane. That's with ethanol of course. Thankfully you can run mo-gas with ethanol (up to 15%) in the Rotax.

Bob
 
Given that it's billed as an aviation fuel, I'd be curious if it's 90 MON or AKI. 90 MON is closer to 94 AKI (which is what you get at the regular gas pump).
 
Have done much reading in research on web about recreational fuel for LSA's. More confused than ever. There are a lot of data out there, but no guarantee that the info is supported by scientific fact as near as I can determine. Some are referred to as 92 to 97 octane E0 fuel, some are stated to be 91 octane E0 fuel, some are 90 octane E0. Seems to me a lot of data is available as a wish list, but can find no hard evidence as to why all the spread in octane on the ethanol free Rec. fuel. At this point I choose not to experiment with my fine running and expensive Rotax engine. I will conduct further inquiries of airport manager at 52A as to why the new fuel is 90 instead of 91 to try to find a fact based answer. Failing that will make an effort to contact the producer/supplier to seek an answer.
Until I am totally satisfied I will continue to go to the gas station for my 91-93 premium motor fuel. If and when I learn anything of substance I will post the findings.
Dick Seiders
 
If the fuel is being accurately identified as "Recreation Fuel" it is undoubtedly a product of Marathon Oil that markets 90 AKI Recreation Fuel for marine and off road use in many states in the face of the ethanol onslaught. Here is an announcement about it on the Petersen Aviation web site. Marathon Oil does not want its ethanol free fuel used in aircraft and they state that emphatically on their web site. It turns out that 90 AKI mogas satisfies practically all marine and off road uses, but does NOT meet the needs of the Petersen high compression STC's nor the Rotax 912. It will be perfectly legal for the EAA and Petersen low compression STCs.

It is unfortunate that any airport would select this product for sale to the aviation community, because it does not meet every pilot's needs and because of the attitude of the producer towards aviation. If I was a pilot in the vicinity of this airport, I would urge them to find a different distributor that will deliver ethanol free 91 AKI gasoline. I wouldn't be surprised that if Marathon finds out about this they will lean on the distributor to cease delivery to an airport, even though it would be illegal restraint of trade. I am only aware of one airport that ever stood up to an oil company and their distributor and put in mogas over a distributors objection.
 
Without trying to muddy the waters (Oh! why not?), I went to Repairman's School with Jim Scott in Arlington, Wash. Jim is a VERY experienced Rotax user and mechanic.

We had quite a discussion about fuels - Auto vs Avgas. I'm paraphrasing his comments and hope I do this accurately - but I wrote it all down clearly and reconfirmed.

What he said was that - on teardown - engines that had run MoGas were CLEAN; engines that had run 100LL were DIRTY, and engines that had run about 50/50 MoGas/AvGas were EXCEPTIONALLY CLEAN, i.e. CLEANER than those which had run just MoGas. He ascribed this to the higher octane in the 100LL allowing for a hotter, better fuel burn than possible with just the MoGas, while the MoGas reduced the overall lead content to a level below which the lead was contaminating the engine with deposits.

Based upon that, I do not fear running 100LL as much as when I started down this road. Actually, I am seriously considering running the 50/50 blend as the normal and preferred fuel load.

Bob Bogash
N737G
 
Dick -

There are many "octanes" in the fuel world, Iso, MON, RON and a couple of others. But when it comes to auto gasoline, octane is not used, Anti-Knock Index is used, AKI. AKI is the average of the MON and RON spec for the particular gasoline. That is why you see a label on the side of every gas pump in the U.S. which must list the minimum AKI and under it it will say something like (RON + MON) / 2.

There is a difference between "octane" and AKI. Avgas specs refer to MON octane only, 100 LL has a 100 MON octane lean rating, and an unexpressed 115 octane rich rating, hence the old 100/115 rating years ago, when we also had 80/87 and 91/96 and 115/145, etc. Today we only use the lean octane rating when designating avgas, hence we have 100LL, 82UL, 87UL, 91UL and 94UL today, although none of the UL versions of avgas are in production in the U.S.

When you see an "octane" spread on auto gasoline it is usually referring to the RON octane which is always higher than the MON octane rating for gasoline, so it looks better. Auto gasoline in most of the rest of the world is reported as RON.

All aviation STC's list the minimum AKI necessary and the LSA engines do also for mogas operation in the U.S.
 
Thanks all for the feedback thus far. I am interested ion the 50 - 50 mix of mogas and 100ll. Sounds logical. Raises a question: If burning half 100ll and half mogas I suspect the 90 octane E0 Rec Fuel would be ok to use in that the overall Octane (and AKI) would be sufficiently raised to meet the Rotax minimums?? Question 2: How about half&half with 87 mogas? Does anyone out there have the answers? Sure would like to know. Has anyone with a rotax in a 12 tried the 50-50 mix yet, and if so let's hear from you. Of course mixing the fuel is even more of a hassle than going to gas station and hand pumping from portable bottles in that after filling 1/2 tank one would have to take the bottles (or the 12) to the 100ll pump, etc etc. Then there is the increase in fuel costs as well. Very interesting idea tho.
I plan to call the City Mgr at 52A and ask why they aren't insisting on 91 octane Rec Fuel. I suspect they aren't aware of the difference. I hope to find out if they are interested or even care a whit. We'll see.
Dick Seiders
 
Running a mixture of 87 octane and 100ll works fine. I would tend to use less of the 100ll though, the 912 does not like the lead. A 25% 100ll and 75% 87octane works well.

Earlier, a post talked about a very clean engine running a mixture and that make sense to me. Good info BTW. ;)

Stay away from continually 100ll use no matter what the manual says. Fying cross country burning 100ll is fine, but mix it with non leaded as much and as often as you can. Change oil every 25 hours for two or three times after that to clean out the lead. Get back to a diet of non leaded fuel as soon as you can.
 
Octane Calculator

Search on octane calculators and many are available on the net. This calculator says that mixing 20 Gal. 87 regular with 10 Gal. 100 LL will result in 91.3 Octane.

http://www.serioussolutions.com/evo/octcalc.htm

I have read that there are no magic additives that somehow chemically react to increase octane, rather it is strictly a matter of ratios of the fuels that are mixed.
 
I would think that lead in the avgas would kick the octane level higher than the arithmatic average. Any thoughts?

Doug Dahl
 
It would seem that production and marketing of UL 91 (100LL without the lead) would solve all of our Avgas/MoGas/Octane/Ethanol problems in one fell swoop. This fuel is beginning to appear in Europe.

Maybe Lycoming's recent actions will act to spur activity in this country - but don't count on it.

Announcement here:

http://www.aopa.org/aircraft/articl...s-ul-91.html?WT.mc_id=&wtmcid;&WT.mc_sect=gan

and a good discussion of the technicals and problems here:

http://www.generalaviationnews.com/2012/04/09/ul91-explained/

Bob Bogash
N737G
 
Bob et al, thanks for the info. Referring to your (Bob's) comment about importing ul91 to the states I just read in Aviation News that the FAA is demanding fuelers come up with an unleaded avfuel promptly and they're only getting till 2018 to do it. Wow! What pressure. Given the fact fuel creators have been alledgedly working on that goal for yrs already I am underwhelmed with the target date.
I discussed as I said I would earlier the 90ul ethanol free fuel at Madison (ga) with the City Mgr. He was very interested and stated he would look into it. I informed him that I, nor any other rotax100 drivers could use the stuff, and also mentioned the fact that Marathon Oil says the fuel is NOT to be used in aircraft. I suspect that got his attention as it did mine given the position of Marathon the use of the fuel in aircraft suggests a transfer of liability in the event of fuel issues arising. So that's it for now. I will follow up in a few weeks to see if any conclusions and/or changes are made as to what fuel would be offered. It doesn't appear that anything else (other than 100ll) will be available, but I am still curious to see whether the 90 E0 Rec. Fuel will be offered. When I learn more I will post it here.
Dick Seiders
 
Larry,

You gotta come talk to the engine in New Blue and tell it that it doesn't like 100LL. It doesn't know.

The engine has over 600 hours on it, the last 410 has been nothing but 100LL with decaline. I have seen no ill effects. I maintain the engine as per the maintenance schedules and it's just a purring right along.

On second thought, please don't come and tell it. Apparently what it doesn't know won't hurt it. :)
 
As an additional note, next week New Blue is going down for annual. We'll be changing oil, plugs, wiping out the oil tank, rebuilding the carbs, changing coolant, and everything our Rotax mechanic out here says we need to do.

Believe me, if I see something that can attributed to the steady diet of 100LL it gets, I'll be certain to let everyone know.
 
How about this one!

Well, there is that one thing. "rebuilding the carbs". Would you have to do this if you were running pure Unleaded? Could you share what the cost is to send them off to get them rebuilt?:confused: Just finished another set of happy trainees.Thanks
 
John. I believe carb rebuild is a Rotax requirement at 500 hours.

Mitch , sounds like you are doing fine on 100ll. Please keep us posted on what you find. Thanks.
Dick Seiders
 
There are only two maint. interval differences, caused by the (majority of the time) use of 100LL that I am aware of.

1. Plug replacement is supposed to be done every 100 hrs instead of every 200.

2. The first gear box internal inspection is due at 600 hours instead of 800 hours (This is from memory, someone correct me if I have it wrong).
 
rvbuilder2002 said:
There are only two maint. interval differences, caused by the (majority of the time) use of 100LL that I am aware of.

1. Plug replacement is supposed to be done every 100 hrs instead of every 200.

2. The first gear box internal inspection is due at 600 hours instead of 800 hours (This is from memory, someone correct me if I have it wrong).
Click to expand...

3. Change oil every 25 hours instead of 50.
 
BigJohn said:
3. Change oil every 25 hours instead of 50.
Click to expand...

It figures that someone would catch me on the obvious one.

But it is actually 50 hrs instead of 100, with the most recent revision of the approved fluids service bulletin recommending that with heavy or exclusive use of 100LL, that you do it every 25 hrs (but this is not listed as a requirement in the service schedule).
 
MLock said:
As an additional note, next week New Blue is going down for annual. We'll be changing oil, plugs, wiping out the oil tank, rebuilding the carbs, changing coolant, and everything our Rotax mechanic out here says we need to do.

Believe me, if I see something that can attributed to the steady diet of 100LL it gets, I'll be certain to let everyone know.
Click to expand...

Mitch, it is the $3000 sprague clutch (shop replacement cost) that is very susceptable to loading up with lead. Talk to the guys that overhaul them, don't take my word for it. I had to replace one in a 912 10 years ago or so. A major PITA, and expensive. ;)


When you clean out the oil tank you will find lead has settled in the bottom like mud. This is the same lead that collects and coats the sprage clutch and loads up the springs and "bearings" that grab the crank when starting. If it starts slipping (or the engine kicks back) it can ruin the sprage clutch.

The lead also collects in the piston rings as the tolerances are extremely tight. Some rings have been stuck due to lead fouling.

My experience comes from the school of hard knocks and costly replacement. Your milage may vary. ;)
 
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I don't doubt you one little bit , Larry. Known you too long for that. I'm just sharing my experience as you have yours. Hopefully I'll be spared the troubles you had. But no matter what I go through, I'm going to share it here.:)
 
One difference in Mitch's operating with 100LL exclusively, that may get a different result from past experiences, is that he has been using Decalin from the very beginning. It goes a long way in savaging the lead out of the inside of the engine and it's related systems. I look fwd to hearing what amount of lead he finds in the bottom of the oil tank. <Mitch, will you try and get a good quality photo?>

BTW, Mitch's Blue RV-12 and the red demonstrator (N412RV) have been purposely being operated completely opposite, as far as fuel usage goes, to gain some first hand experience.

Mitch's engine has operated exclusively on 100LL (except the first 200 hrs which was about 50/50 between auto fuel and 100LL)

N412RV has been operated 600+ hrs, exclusively on auto fuel, except for the occasional long cross country (maybe 20 hrs per year, average)
 
I'll try to get as good a picture as I can, but I'm not expecting to find much as we wipe the cannister everytime we change the oil. Our Rotax guy out here, Ed Johnson, does most of the engine maintenance and has never expressed a concern about a large amount of lead in the tank.

And for you John (and everyone), Ed will be doing the rebuild on the carbs so we won't be sending them out. I bought a two carb rebuild kit from Leading Edge Airfoils for $147.00 which consisted of gaskets and some small screws.
 
Geico266 said:
Mitch, it is the $3000 sprague clutch (shop replacement cost) that is very susceptable to loading up with lead. Talk to the guys that overhaul them, don't take my word for it. I had to replace one in a 912 10 years ago or so. A major PITA, and expensive. ;)

Larry interesting about the spague clutch, my hangar mate has a 912S in a Kitfox and he had his sprague clutch replaced at around 450hrs and then it failed big time at 800 hours (on downwind the engine bucked, apparantly locked up the starter, spun it up till it melted and then disintegrated the sprague into the running engine internals), to the 912's credit it kept running till shutdown, figured out there was a real problem when it wouldn't re-start. Bottom line engine worth only core value and had to buy a new one. Although in his case the engines diet was probably 80%mogas/20%leaded with 25 hr oil changes. I didn't realize other folks were seeing sprague problems, the Rotax guys didn't allude to any of that when he talked to them. Wonder if it's a weak spot in the design?
Click to expand...
 
fly3g said:
Geico266 said:
Mitch, it is the $3000 sprague clutch (shop replacement cost) that is very susceptable to loading up with lead. Talk to the guys that overhaul them, don't take my word for it. I had to replace one in a 912 10 years ago or so. A major PITA, and expensive. ;)

Larry interesting about the spague clutch, my hangar mate has a 912S in a Kitfox and he had his sprague clutch replaced at around 450hrs and then it failed big time at 800 hours (on downwind the engine bucked, apparantly locked up the starter, spun it up till it melted and then disintegrated the sprague into the running engine internals), to the 912's credit it kept running till shutdown, figured out there was a real problem when it wouldn't re-start. Bottom line engine worth only core value and had to buy a new one. Although in his case the engines diet was probably 80%mogas/20%leaded with 25 hr oil changes. I didn't realize other folks were seeing sprague problems, the Rotax guys didn't allude to any of that when he talked to them. Wonder if it's a weak spot in the design?
Click to expand...

I think you are talking about a different sprague clutch . There is one in the main PSRU gear box and there is a small one just for the starter motor.
Click to expand...
 
Geez, down to just a core due to a clutch failure (2x in 800 hrs) with 80% mogas and 25 hour oil changes. Geez.....

Bob Bogash
N737G
 
octane ...

I located a gas station that sells non ethanol gas for "recreational vehicles" that is a bit more expensive but has only 90 octane.The Rotax site says 91 octane minimum should be used. Is one AKI and the other RON ... I'm confused.
 
dick seiders said:
Sorry all, I am wrong about 500 hr carb oh . It's 200 hrs
Dick Seiders
Click to expand...

Dick,
I wasn't going to correct you because I don't have access to documentation at home, and couldn't remember if there was a 500 hr overhaul.

But I do know that the 200 hr interval isn't a requirement for an overhaul.
It is a very thorough inspection though, but only requires replacement of parts "on condition".
The full blown overhaul kit retails for about $500, but it shouldn't be needed until the engine has a lot of time and years on it. I think Rotax recommends that you need a service parts kit (about $150) to do the carb. inspection. With care, you can disassemble and reassemble the carbs. without it (many Rotax techs do so).

My experience has shown that the highest wear item in the carbs is the float arms, as a result of the float pins rubbing on them because of engine vibration. Fortunately the are not super expensive.
I believe a dynamic prop balance goes a long way towards minimizing this wear.
 
Prop Balancing

I have been wondering about dynamic prop balancing. With the geared engine and the prop turning at different speeds in seems that the relative position of the engine parts and the prop would be constantly changing. Does the dynamic balancing still work? Are different systems available to do the balancing and which works best? Thanks for mentioning this, Scott.

Richard
 
Scott, you are correct in that the carbs are required to be torn down and checked at 200 hrs - not overhauled. Don't know yet if that occurs each 200 hrs, or just at 200 and 600. Manual doesn't help much here. I also cannot find an overhaul event on the schedule. So I have asked a Tech. Instructor at the FL. Rotax Training School to clarify. Will report back on response from them.
Dick Seiders
 
Richard,

Prop balancing made a huge difference in vibration level. Stick doesn't shake anymore! I don't remember the brand of the equipment that was used - I could find out if necessary.

John
 
Ok, got the word from Rotax Tech. at Lockwood on the carbs. Here it is:

The manual stipulates a "Disassembly Inspection" every 200 hours. That has
mostly to do with cleanliness and vibration issues. There is no "overhaul"
required except for when overhaul of the engine takes place or as needed by
other circumstances. If a carburetor has been abused or neglected in some
way, or is showing severe enough performance issues, that's when an overhaul would be wise.

So every 200 hrs insp. with necessary repairs only. No overhaul is scheduled, but if necessary do it.
Now if we could just get UL91.
I will still provide feedback when I get more from Madison on the 90 Rec. Fuel.
Dick Seiders
 
I don't think so!

According to Mr Google.
Swift Fuels LLC was created to pursue the development of 100SF, an unleaded aviation gasoline under Grade UL102 within the ASTM D7719 specification
Click to expand...
I personally wouldn't run this fuel in the Rotax unless Rotax approved it. It sounds like a good product but the Atari computer sounded good to. Maybe if the Swift fuel people could send some to Rotax so they could test it in their engine it could be approved. I'm kind of conservative when it comes to nonstandard products that my affect safety of flight on the airplane.:)
 
I see some answers have already come back but you can find more info here: http://swiftfuels.com/.

I've been following this fuel development for sometime and it looked promising. during testing folks were able to fly over to their facility and fill up (not free) to test it in their aircraft. I never heard anything but good things said about it so I was just curious. If memory servers me correctly the development was started by some Purdue profs and has now been taken over by a local oil/refinery company.

From the website:

'The next generation of aviation fuels.
We are in a new era of energy, and the future will depend on economical and sustainable solutions to our everyday transportation fuel needs.
Swift Fuels is committed to this transition and therefore has developed and patented a process to produce pure synthetic hydrocarbon fuels from biomass sources that mimic the properties of both gasoline and kerosene. The fuels are primarily for the aviation industry; however, they will work in any internal combustion engine and thus all other modes of transportation. Using not only biomass as a feedstock but a variety of other renewable sources of carbon, Swift has created fuels that are matched to the engines of our transportation vehicles without the modifications that were necessary with the first generation of bio-fuels.
Swift Fuels not only have a greater energy density over the current petroleum fuels but also burn more efficiently and create fewer deposits in an engine, prolonging engine life. Additionally, Swift fuels burn more efficiently, thus reducing overall exhaust emissions. Swift has demonstrated a reduction in critical greenhouse gases, such as carbon monoxide (CO), by up to 33%.

The driving force for Swift Fuels is the General Aviation market. The current fuel used in general aviation piston engines is 100LL (100 low lead) aviation gasoline, which contains tetraethyl lead (TEL).'

Bob
 
I've searched every thread about gas and haven't seen this question. My ROTAX operators manual refers to 91 AKI to be used. My RV-12 Pilot Operating Handbook ( rev 1) on page 2-2 agrees with that. But on page 8-2 it says 92 AKI. The pumps I see say 91 AKI for premium. Is everyone assuming that page 8-2 is a typo?
 
Yes!

Yes!;) Ive been running 91 UL Non ethanol here in North Texas without any ill effects. I'm going with the Engine Manual over Vans Manual on this one!:cool:
 
John, are you certain the fuel you reference is 91, not 90? If it is 91 who makes it? I would like to know what their spec sheet says about the product. If it is 90 ditto on who produces it for same reason. I am not doubting your info, but would like to get this recreational fuel I issue clarified for all 12 drivers. Many thanks.
Dick Seiders
 
My decal (received in about March 2012) says "92UL..." (which is a specification discussed earlier in this thread, and not just an "octane" rating), not 91 AKI.
 
dick seiders said:
John, are you certain the fuel you reference is 91, not 90? If it is 91 who makes it? I would like to know what their spec sheet says about the product. If it is 90 ditto on who produces it for same reason. I am not doubting your info, but would like to get this recreational fuel I issue clarified for all 12 drivers. Many thanks.
Dick Seiders
Click to expand...

The mogas I buy and use is from Shell and has 91 octane on the pump sticker.
 
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