Ethanol Fuel

[Bill3558]

I’ve been using ethanol free 93 octane fuel for years with zero problems. My local station has discontinued it and the only 93 octane I can find is “ up to 10% ethanol”. The last time I used ethanol fuel was during the Colonial Pipeline debacle and it made my gas caps swell so much I had to replace them. I know the engine doesn’t care, but I bet the rubber parts do.  
What do you guys use?

[Tommy Mc]

UL91

[Madhatter]

I've used 93 ethanol for 12 years with no issues. 

[Anticept]

It could be other additives that cause issues. Especially if you live in a state with poor inspections and controls.

I've had issues dealing with different gas station gas, but it's really evident if you have a bad batch.

[CTB]

I mix 50:50  of 93 ethanol with 90 non ethanol rec fuel in my 50 gals portable tank and add Marine Fuel Stabil. I hope I don't do anything wrong. No previous experience with Rotax. I fly a few times a week so the fuel doesn't sit for long in the tank(s). 

2023 F2 with 912i.  75 hours no issues. 

[FlyingMonkey]

17 hours ago, Madhatter said:

I've used 93 ethanol for 12 years with no issues. 

Same until very recently...

[Towner]

About 350 hours with 91 w/ethanol and no problems 

[GrassStripFlyBoy]

20 hours ago, CTB said:

I mix 50:50  of 93 ethanol with 90 non ethanol

That's a good option, I often bring up 90 rec fuel with 10% addition of 100LL, or 93 at higher mix as you're doing.  There are a couple airports nearby with 91 Rec and Swift fuel that I'll fill up at.  I do try to avoid ethanol, but I also see a lot of guys running 93 and zero issues.  RunToEat (Dick) and Phil Wade are near me, both run 93.  Probably 3000+ hours between both those guys (Phil just installed new 912), and zero issues.  They just stopped in for lunch last week and we talked fuels a bit, here's a pic:

[EricB]

As you say, the engine and the rubber parts (and fittings) are different beasts.  SO, I checked and both Rotax and FD authorize fuel with "up to" 10% ethanol.  Even if there's a minor effect, doing the 5 year rubber replacement should mitigate any issues.  Using replacement hoses rated for ethanol also eliminates any issues but if you wanted to maintain S-LSA you'd have to be careful there.  

[FlyingMonkey]

2 hours ago, Roger Lee said:

You guys need to quit worrying about ethanol.

I never did, until I had multiple instances of power loss on takeoff that were completely resolved with 100LL.  Whether due to my particular fuel system, the local winter blends, or a combo... I can't say.

It's usually not a problem, but vapor lock can happen and it's a pucker factor.  BTW I did wrap my exhaust and got a noticeable CHT and oil temp reduction.  With that done I might try reducing the 100LL amount to 30% and see if I get vapor issues again.

[FredG]

Ethanol blended fuel has a higher vapor pressure than non-ethanol blended fuel and, consequently, a greater tendency to vapor lock.  Sounds like a reason to pay attention to it, especially when winter blend fuel may still be in the storage tanks at the local mogas station. 

[Madhatter]

I've been flying at 8 to 10 thousand for the last 12 years and have never had an issue like many thousands of others have with a 912. Something else is going on. 

[Anticept]

Different regions have different fuel standards. https://www.epa.gov/gasoline-standards/gasoline-reid-vapor-pressure

Ohio for example, only requires 9.0 psi RVP with a +1 psi allowance if blended with 10% ethanol.

Also, how did altitude get into this? You're not going to run into RVP issues until quite a bit higher due to cold temps.

[Madhatter]

9 minutes ago, Anticept said:

Different regions have different fuel standards. https://www.epa.gov/gasoline-standards/gasoline-reid-vapor-pressure

Ohio for example, only requires 9.0 psi RVP with a +1 psi allowance if blended with 10% ethanol.

Also, how did altitude get into this? You're not going to run into RVP issues until quite a bit higher due to cold temps.

I also climb to 1000 feet in 98 degree heat with no issue.

[Anticept]

Do you live in ohio or georgia?

I can't speak for georgia, but aside from the lax RVP requirements, the "testing" requirements here are trash.

Because aside from my own, there is also another with an eprop also having issues here. There are two more with sensenich props, and one with a neuform, that get alarms but thankfully don't quit. They can get a stumble if they do long runups though. They don't climb at the rediculous attitude that our eprop equipped aircraft do.

We've been climbing out at higher airspeeds on the eprop aircraft and it makes a difference. This is hint #1 that fuel might be having trouble reaching the fuel pump.

A LONG runup, with the engine cooking, and then attempting a takeoff will trigger the fuel pressure alarm. I abort, go back to the hangar, start investigating, can't find anything, go back out and do a high speed test... no alarm. I had on a separate occasion, a lengthy wait due to multiple arriving and departing aircraft and got quite warm too. Took off, alarms blaring, emergency landing in the remaining runway length (thankfully OSUs runway is so long). The only thing I did was land, do a couple run tests, then taxi all the way to the beginning of the runway again for takeoff, and I noticed the temps were reading quite a bit cooler than on first takeoff (have to watch this because sometimes, too long of an idle can push the engine coolant into the yellow). Hint #2.

Adding a little bit of avgas clears the issue right up. Not even a peep from the pressure sensor. Hint #3

Not sure what's so hard to grasp about a concept that we might be right on the edge of what's tolerable for vapor issues. Boiling it down to "everyone uses ethanol and doesn't have problems" as your answer to every time this issue is brought up is an ignorant as hell position to take in the face of people that have already been trying other approaches, ESPECIALLY if you handwave the AVGAS demonstrations. We have told you time and time again we do NOT have fuel pressure loss or delivery issues with AVGAS/AVGAS blend.

I even posted my story and observations when I flew down to south carolina at the beginning of spring, i had pressure alarms and erratic fuel flow on the morning when I planned to fly back, and still had over half tanks of ohio fuel. I went from a very cold place to a very warm one. Everything was going nuts. All I did was add 3 gallons of avgas a side and it cleared up, and that afternoon I was coming back to ohio.

When you do a search for rotax fuel pressure loss, you get quite a lot of posts here and there about various people having periodic issues. Some do find a fuel system issue, others have gone on unresolved.

I don't know if you realize, but you have had a real cantankerous tone on this forum lately too. You give a lot of good knowledge, but lately it just feels like you're irritated at everyone. You aren't the only person in the world who experiences problems, or has the answers, and it's really getting on my nerves how you take that tone. I feel like that tone is casting shade at us as either incompetent, or hasn't tried some other solution.

You think I WANT to pay several hundred hundred dollars in parts, a dozen hours of my time, on top of arguing back and forth with several people making my case about trying a fuel pump, without doing something like checking the fuel system and replacing any suspect parts? Which I did already, including the fuel pump. Didn't solve it. Flow test is good too.

I won't claim that I have undeniable proof that it's vapor or that there isn't something more that could be done, but I am very confident given all the observations I have made with my own, as well as other CTs I fly here. I am waiting for flight design'a final blessing for this pump before putting it to the test. Only reason it hasn't been done a year ago is that I had been flying for someone all over the country and never had the time to get the effort done.

[Duane Jefts]

2013 CTLSi in Arizona. 100% ethanol and flying at high altitudes and high outside temps with 0% problems. It does have positive fuel pressure from the two fuel pumps associated with the fuel injected engine.All factory original equipment.  Life is good here.

[FlyingMonkey]

On 5/11/2024 at 8:47 AM, Anticept said:

I won't claim that I have undeniable proof that it's vapor or that there isn't something more that could be done, but I am very confident given all the observations I have made with my own, as well as other CTs I fly here. I am waiting for flight design'a final blessing for this pump before putting it to the test. Only reason it hasn't been done a year ago is that I had been flying for someone all over the country and never had the time to get the effort done.

My guess is the CTs are pretty close to the edge in terms of temperatures, strength of the factory pump, climb angle, etc.  Change just a couple of aspects of the fuel system or have a poor blend for conditions, and vapor issues start to crop up.

In my case, I suspect several things converging.  I flew all last Summer with no issues after a short stint last Spring with the issue just as I finished my new Teflon fuel lines.  I thought I resolved it by flattening the routing of one of the fuel lines to remove a potential vapor trap.  While that might have helped, in hindsight the problem was helped but not solved.  Then last October 28 the problem recurred in Florida on one flight.  I suspected a fuel blend difference with Georgia, pumped in some 100LL and flew home with no issues.  When I got home I reverted to 93 octane with ethanol, and flew that way from November through March with zero issues, then the problem began happening and worsening on every flight.  I now suspect Winter blend fuel as it warmed up for that one.  But since then I have been 100% 100LL and zero issues.

So I think my airplane is just close to the edge and it doesn't take much to push it over.  I feel like short of adding a boost pump I have done everything I can. The fuel pump is new, I was careful with line routing.  I just last week wrapped my exhaust and it made a very noticeable 10-15°F difference in CHTs and oil temps.  At this point I might start scaling back the amount to 100LL to try to find the point where it's a problem for me.  I'd like to get to less than 30% avgas so that I can keep to the longer maintenance intervals, but we'll see.  My engine is past mid-time and if I have to run 100LL to keep it happy then so be it.     

[Madhatter]

My opinion, there is something else going on. I've been doing this stuff for a long time. When I was testing engines for GE and Lycoming if this kind of thing ever happened it would have the CEO or equivalent calling the engineer. ( guess how I know that). If this was a common issue all hell would break loose at Rotax. This has to be analyzed methodically. Putting in a boost pump would be extremely risky. You will eventually find the problem and it will be something you never considered. 

[Anticept]

It's already in their installation manual to recommend an aux electric pump. It's been a recommendation for years. For as long as I can remember.

 

 

SB-912-063-UL also mentions fuel pressure with the new style pumps is an issue but should stabilize.

 

 

Arian told me on the phone that these reported issues with fuel pressure are increasing. I've been asked to do some testing and measurements with the fuel pump as part of the process for data points, so I have to wait for all that to come in. I'll take some pressure samples at various parts of the system.

One thing that got me thinking a factor is that the fuel pump housing also gets VERY WARM with a long run up. Uncomfortably so.

Suddenly calling for full power, which would operate the fuel pump at over 2100 RPM, that's REALLY RAPID for a diaphragm type pump, and although the movement is pretty small, warm housing, warm hoses high nose attitude, it's all a nasty combination. Expecting fuel to flow in rapidly enough to keep up with the displacement the retracting diaphragm would be a lot to ask. Plus, the OUTLET is on the BOTTOM, NOT THE TOP of the fuel pump. So it's potentially air entrapment issue as well.

 

 

Finally, you would think such an issue would have people up in arms..... But Cirrus and their SR22T is another funny one.

It is recommended to just keep the fuel boost pump on with SR22Ts even though the checklists and manual doesn't require it. Level flight, shutting down the boost pump sometimes results in engine sputter regardless of mixture lever setting.

I had asked several people about it and all say the same thing: Cirrus training and experience with pilots and field maintenance facilities all say "just leave the pump on!"

[FlyingMonkey]

This would definitely be easier for me to diagnose if my airplane had fuel pressure/flow indication.  I have the little analog engine gauges.

[FlyingMonkey]

57 minutes ago, Anticept said:

It's already in their installation manual to recommend an aux electric pump. It's been a recommendation for years. For as long as I can remember.

 

Thing that got me thinking a factor is that the fuel pump housing also gets VERY WARM with a long run up. Uncomfortably so.

Suddenly calling for full power, which would operate the fuel pump at over 2100 RPM, that's REALLY RAPID for a diaphragm type pump, and although the movement is pretty small, warm housing, warm hoses high nose attitude, it's all a nasty combination. Expecting fuel to flow in rapidly enough to keep up with the displacement the retracting diaphragm would be a lot to ask. Plus, the OUTLET is on the BOTTOM, NOT THE TOP of the fuel pump. So it's potentially air entrapment issue as well.

 

It is recommended to just keep the fuel boost pump on with SR22Ts even though the checklists and manual doesn't require it. Level flight, shutting down the boost pump sometimes results in engine sputter regardless of mixture lever setting.

I had asked several people about it and all say the same thing: Cirrus training and experience with pilots and field maintenance facilities all say "just leave the pump on!"

Two things:

1) Do you think the rapid action of the diaphram causes cavitation that forms vapor in the pump?

2) Regarding the "leave the boost pump on" advice...doesn't that depend on the pump design?  Most boost pumps are designed for intermittent operation, not continuous aren't they?  I might be thinking of "aux" pumps.  Just wondering how short the duty life of such pumps might be.

[Madhatter]

If this is such a serious issue why isn't Rotax putting out a service bulletin for a fix. I would think this would be a lawyer's dream case. Doesn't make sense. There are 50,000 of these engines out there. I fly at high temperatures and have an E-PROP and max climb for the first 1000. In 12 years never had any issue, something else is going on. What does Rotax say?

[Anticept]

Madhatter: they say, put in a boost pump. This is the go to response when I ask about it in class after going down the list of checking the lines, checking the filters, checking the restrictor orifice, checking/replacing the pump... It's in the installation manual too...

One other thing to note, is the rotax recommendation is to run the return line to a fuel tank. Running it to the gascolator is allowed, but not preferred.

Flyingmonkey: That's what I am thinking could be a possibility, but not something that happens in normal circumstances. The diaphragm movement isn't very much. Quarter of an inch or so?

I think it's when we get on the edge of issues that the issue compounds itself, but once the nose is lowered and head pressure can displace any vapor, it resolves itself. That's also why avgas blending clearing up pressure and stumbling issues completely really REALLY makes me think vapor.

Re: aux pump: depends on the pump. There's nothing prohibiting continuous operation on the 22T, and the fuel pump I selected is designed for automotive continuous operation. I am paralleling a free flow check valve as a safety precaution, but these facet gold flo pumps are found rebranded on cessnas and pipers, so it's not like I picked something that can't do the job.

[Madhatter]

1 hour ago, Anticept said:

Madhatter: they say, put in a boost pump. This is the go to response when I ask about it in class after going down the list of checking the lines, checking the filters, checking the restrictor orifice, checking/replacing the pump... It's in the installation manual too...

One other thing to note, is the rotax recommendation is to run the return line to a fuel tank. Running it to the gascolator is allowed, but not preferred.

Flyingmonkey: That's what I am thinking could be a possibility, but not something that happens in normal circumstances. The diaphragm movement isn't very much. Quarter of an inch or so?

I think it's when we get on the edge of issues that the issue compounds itself, but once the nose is lowered and head pressure can displace any vapor, it resolves itself. That's also why avgas blending clearing up pressure and stumbling issues completely really REALLY makes me think vapor.

Re: aux pump: depends on the pump. There's nothing prohibiting continuous operation on the 22T, and the fuel pump I selected is designed for automotive continuous operation. I am paralleling a free flow check valve as a safety precaution, but these facet gold flo pumps are found rebranded on cessnas and pipers, so it's not like I picked something that can't do the job.

I am assuming you have an SW. What is the difference between my engine and yours? There IS something different. I would guess that 99.9% of the engines don't have the issue you are having. This could never occur in the certified world, ever. Rotax engineers should know what the problem is or they are not doing their job or just don't care. 

I am only referring to a Flight Design airframe on this issue.

Don't you feel like the lucky one, this kind of stuff happens to me a lot. Maybe when you find the problem you can educate Rotax. Cessna once had a serious propeller problem and had to cancel the program. It took me several months to fix the issue and they reinstated the program. Trust me if you persevere you will find it but you will pretty much live at the airport like me. My wife and dog visit me at the airport.

 

[Anticept]

I have an LS.

Andy has an SW.

The models of aircraft don't seem to matter. There was an SW here that used to be used in flight training too until an instructor cut a student loose in it, who then flipped it over on a runway (it was org policy that students were NOT allowed to solo the SW). It too had fuel pressure alarms and issues.

I haven't done work on the other CTs here in quite some time (91WW the one that got flipped, 26KJ, 178CT, N503NM) but there's been 3 or 4 mechanics since and all hate dealing with this. N178CT experiences engine cutouts and very occasionally engine stutters on takeoff and the only thing changed on it was the install of an e-prop. Same thing, told them to climb out at higher airspeeds, and it curbs the problem significantly.

The consistent variable is the location.

Anyways, not sure what to say other than, I'm doing what rotax recommends: install a boost pump /shrug.