Ethanol Fuel

[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.

[Madhatter]

Blaming an E-Prop makes absolutely no common sense. What do people think occurs during a full power stall demonstration,  very high angle of attack. 

This is the kind of issue that interests me. I can't pass up a challenge when someone says it can't be done. My wife says I need to learn to say NO but after 49 years she gave up. When I was in college I built a plane in my room and several hundred said it would never fly. When I did fly it I flew over the campus at 500 feet, went to idle and yelled out a statement that I can't say here. Never give up.

[Anticept]

It's not the e-prop alone, but if you want to continue to ignore that I have said it's a contributions of other factors in addition to the eprop, you do you.

It's not hard to grasp that an efficient prop would lead to a higher pitch. Add a fuel pump all the way out on the front of the engine being elevated higher, you get a smaller vertical column component, so lower pressure at the inlet side. Add in heat from run up, a sudden call for a lot more fuel... if we're already questionably close to vapor issues, the extra pitch pushes us even closer or even past the point of no return.
 

EDIT: Also, to respond to the "high angle of attack on power on stalls bit": you're cycling gallons of fuel through the system in flight and have airflow under the cowl. Try doing it when you have little fuel demand and a hot engine.

I can get fuel pressure alarms if I have a long period of climb following some level flight. But none so bad as the initial takeoff.

[Madhatter]

I give up

[Skunkworks85]

19 hours ago, Madhatter said:

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.

My CTSW has the same issues/ symptoms/ remedies.

There are ≈185 CTSW registered with the FAA as of 5/14 - I know of at least 6 that have similar symptoms. Best case is you can say that 97% of them may or may not have the same symptoms. Also, If you do not have the Dynon EMS ( or similar) I suspect you would never know this issue to occur.  

I have also narrowed it down to fuel only in the early to middle spring with "10% ethanol" I do regularly test my ethanol content and it varies from 6% to 11% There are some outliers on the content correlation but it seams to happen more often when the content is higher than 8%. I have never had this be an issue with some percentage of 100LL or non ethanol fuels. 

 

19 hours ago, Madhatter said:

I am assuming you have an SW. What is the difference between my engine and yours? There IS something different.

 

I think one of the things that you are not considering is that the auto fuel used in the different parts of the country/manufactures are significantly different formulations. If you can agree on that, this may be a variable in your comparison. 

[FlyingMonkey]

I tend to agree with Corey on this, it's just an intersection of factors...deck angle on climb, fuel blend, temperature, fuel pressure, etc.  I will say that the last time I had the issue it was VERY bad (power drops to 4000rpm or so every few seconds), and on that flight I was in the process of testing some fixes and consciously climbed out very shallow.  For that reason I'm leaning toward fuel formulation and temperature being the two biggest factors.

Now that I've wrapped my exhaust and the winter blends should be out of the tanks, I'm going to increase my percentage of mogas and see how it goes.  The wrap did make a noticeable difference to oil and CH temps as I mentioned previously, so I suspect overall under cowl temps must be greatly reduced.  If I had 91+ ethanol-free in my area I might try that as a test to confirm ethanol as the overall culprit.  But we only have 90 ethanol-free here, it's not convenient to get to from the airport, and it's almost as expensive as 100LL...so the juice ain't worth the squeeze to run that all the time.

I also still think the braided hoses retaining more heat than rubber could be a factor, that's the only major change to my fuel system. Though Madhatter has similar hoses in his airplane. Hatter, is your exhaust wrapped?

 

[FlyingMonkey]

1 hour ago, Skunkworks85 said:

My CTSW has the same issues/ symptoms/ remedies.

There are ≈185 CTSW registered with the FAA as of 5/14 - I know of at least 6 that have similar symptoms. Best case is you can say that 97% of them may or may not have the same symptoms. Also, If you do not have the Dynon EMS ( or similar) I suspect you would never know this issue to occur.  

I have also narrowed it down to fuel only in the early to middle spring with "10% ethanol" I do regularly test my ethanol content and it varies from 6% to 11% There are some outliers on the content correlation but it seams to happen more often when the content is higher than 8%. I have never had this be an issue with some percentage of 100LL or non ethanol fuels.

I think one of the things that you are not considering is that the auto fuel used in the different parts of the country/manufactures are significantly different formulations. If you can agree on that, this may be a variable in your comparison. 

Good points.  I tested my fuel when I first started running it and it was 5-5.5% ethanol, but I haven't tested it in the years since because "it just worked."  There's definite regional variation, and when I'm traveling I only will use 100LL or ethanol free mogas on the airport (if available) from now on.  Cheap insurance.

It's a definite challenge to see problems before they have physical symptoms in my airplane.  No fuel flow or pressure, no EGT or other indications make it a guessing game. If I ever do an avionics refresh I will add some of that.

[shiny.ice]

1 hour ago, Skunkworks85 said:

 

I have also narrowed it down to fuel only in the early to middle spring with "10% ethanol" I do regularly test my ethanol content and it varies from 6% to 11% There are some outliers on the content correlation but it seams to happen more often when the content is higher than 8%. I have never had this be an issue with some percentage of 100LL or non ethanol fuels. 

Do you run non ethanol gas in the spring? This sounds like a winter gas issue more than an ethanol issue- no matter where you live, the RVP of winter gas is higher. That isn’t an ethanol thing.

 

By comparison, Arizona has ethanol in its gas year round but obviously has a much lower RVP.

[Skunkworks85]

5 minutes ago, shiny.ice said:

Do you run non ethanol gas in the spring? This sounds like a winter gas issue more than an ethanol issue- no matter where you live, the RVP of winter gas is higher. That isn’t an ethanol thing.

 

By comparison, Arizona has ethanol in its gas year round but obviously has a much lower RVP.

You are right and wrong here. 

The "winter gas" has higher RVP, but the lower outside temps counteract this in terms of vapor lock. 

The RVP of "winter gas" is formulated higher, One of the ways they adjust RVP is to vary the ethanol content. I suspect, that for this reason, is why I see the spring fuel (some winter blend still in tanks about 5% ethanol) coupled with higher outside air temps, exacerbate this issue. 

This is all a conjecture based on my observations/ data. 

 

For what its worth, I did quite a bit of research on e85 in college, in Minnesota, they change the ethanol content from about ≈e50 in the winter, to about ≈e75 in the summer. The reason is cars wont start on e75 in the cold Minnesota weather due to the lower RVP. 

[shiny.ice]

27 minutes ago, Skunkworks85 said:

The RVP of "winter gas" is formulated higher, One of the ways they adjust RVP is to vary the ethanol content. I suspect, that for this reason, is why I see the spring fuel (some winter blend still in tanks about 5% ethanol) coupled with higher outside air temps, exacerbate this issue. 

This is all a conjecture based on my observations/ data. 

 

 

Yeah, it’s a cheap way to increase volatility for the winter. This is a decent article for simplifying the issues for my brain to understand:

 

https://www.caranddriver.com/news/a15339380/the-vapor-rub-summer-versus-winter-gasoline-explained/

[Anticept]

The one thing that really convinces me there's a vapor issue that we're running borderline on, is once you introduce avgas or an avgas mix... NO MORE ISSUES AT ALL.

The reason I believe we're seeing this on takeoff, but not really in flight, is because taxi and runup use a low amount of fuel, no airflow under the cowl, and a minimum of 122f on oil before starting the power run.

If anyone hasn't done it yet... try popping the cowling and touching that fuel pump housing after a runup. HOT.

One test I could do is tee a valve in on the outlet side of the fuel pump. Do a runup, get the fuel pressure to alarm (i have to get the engine real hot for this to happen but it DOES happen) and then open the valve for a moment into a container to see if there's much vapor...

[Jim Meade]

Corey,

I recommend you review your previous post and indeed several previous posts and consider modifying language that many men and women consider vulgar and offensive.  Thank you.

[FlyingMonkey]

I recently saw a CT with what looked like a vapor trap (Little metal bulb oriented upwards 90° to the line) coming off of the upper fuel line going into the fuel pump.  Looked like it was designed to let vapor collect at the top of the bulb...Could something like that help?  Seems like a bit of a kludge though.

[Skunkworks85]

16 minutes ago, FlyingMonkey said:

I recently saw a CT with what looked like a vapor trap (Little metal bulb oriented upwards 90° to the line) coming off of the upper fuel line going into the fuel pump.  Looked like it was designed to let vapor collect at the top of the bulb...Could something like that help?  Seems like a bit of a kludge though.

All rotax have those I believe 

[Roger Lee]

What you called a vapor trap is really an fuel pressure dampener for the earlier CT's. Otherwise the fuel pressure would bounce around. Since Dynon upgraded their software and many fuel senders have changed the bulb on top can be removed. I have removed all that have come through my shop.

[renaissanceman]

As a new owner, these threads are so confusing to me. I have access to Swift 94UL at a local airport and will try to go there as much as I can, but practically speaking, I need to decide between 100LL at my home field or 93-E10 from the gas station. (I have only 90 octane UL available near me). It seems like 93-E10 is better for the Rotax than the lead, but I need to avoid winter blend in the spring months to prevent vapor lock. But threads like these make it very difficult to know what's best!

[FlyingMonkey]

30 minutes ago, renaissanceman said:

As a new owner, these threads are so confusing to me. I have access to Swift 94UL at a local airport and will try to go there as much as I can, but practically speaking, I need to decide between 100LL at my home field or 93-E10 from the gas station. (I have only 90 octane UL available near me). It seems like 93-E10 is better for the Rotax than the lead, but I need to avoid winter blend in the spring months to prevent vapor lock. But threads like these make it very difficult to know what's best!

Sounds like you nailed it to me.  Maybe avoid the mogas in March and April and that would probably work for you.

[shiny.ice]

You can also simply use mogas, if you have any issues then do something else. It seems to work for most people. Not all, but some majority seem okay.

[Anticept]

I found that it only takes a gallon in five, if even that, of avgas to clear up pressure issues completely.

[FlyingMonkey]

8 hours ago, Anticept said:

I found that it only takes a gallon in five, if even that, of avgas to clear up pressure issues completely.

Do you think wrapping exhaust helps as well?  I'll go to a 20% mix as you suggest and report back how that works out.

[Anticept]

It might help. I need to take temp readings of the fuel entering and exiting the fuel pump.

The fuel pump's internal construction means that it's conducting heat right from the gearbox to the fuel.

I am curious as to how the vapor pressure changes with temp. That could answer a lot.

[Anticept]

15 hours ago, Jim Meade said:

Corey,

I recommend you review your previous post and indeed several previous posts and consider modifying language that many men and women consider vulgar and offensive.  Thank you.

I've edited out the f-bomb. Not sure what else you are referring to

[Roger Lee]

Many of us fly in Arizona with 100F plus day time heat and most of us use 91 oct. with ethanol and never have an issue.

The only time we see any type of vapor accumulation (not lock) is when we park to go eat somewhere and the heat in the cowl just sitting there heat soaks everything. I've had my start up fuel pressure read 1.5 psi and it runs just fine and while I'm doing my preflight and taxi out to the runway it gets cooler fuel circulated and the pressure goes back to normal. No one out here in Arizona has had any vapor lock in flight that I have heard of. I doubt many of you fly in those temps. That said I also like to fly higher in the summer for the air-conditioning.