I tried to find people that were doing research into using any ethanol based fuel in aircraft, and managed to exchange some e-mails with a few of them and collect a few references and notes along the way.
Any mistakes, omissions, errors, etc are my own, and anything presented on this web site is not guaranteed to be safe or practical for aviation use. The comments below should not be considered an endorsement from myself or any of the names presented. Any use of this information is AT YOUR OWN RISK.
FAA Special Airworthiness Information Bulletin concerning alcohol in fuel
Petersen Aviation Testing Fuel for Ethanol
Here is a summary of the e-mail exchanges:
From James Behnken, South Dakota State University:
(08/28/2007)
Dear Dj,
Compatibility with ethanol by itself is a relatively straight forward process. However, in your list of potential fuels you have opened the possibility for a wide range of petroleum components. You will therefore need to consider both the individual components and the potential combinations if you want to have true multi-fuel capability.
Back when the FAA decreed that it was acceptable to replace 100/130 with the then new 100LL, several interesting things happened. Despite the complete alignment with the ASTM specification (D-910), the two fuels did not exactly perform the same. Most significant was a series of seal and fuel system material failures. This was primarily blamed on the higher content of toluene in 100LL, so the FAA then decreed that all fuel wetted components had to withstand a toluene soak test. This was very fortunate for us in that for the most part, if a material is compatible with toluene, there is a high probability it will withstand ethanol. So, as long as you use new manufactured aircraft materials, you should be in pretty good shape as far as the ethanol goes. What is harder to plan for is the automotive gasoline. There are several materials that they have had difficulty with when using automotive gasoline, and when you blend ethanol with a non-compatible gasoline, the degradation process is typically accelerated. What happens is the ethanol works as a solvent, constantly flushing any loose material away and thereby exposing a greater material area to the non-compatible gasoline. I would recommend using fluorosilicone seals whenever possible, and Teflon lined hoses. Nitrile rubber works well if you plan to use fuel bladders, otherwise a good polysulfide sealant like Pro-Seal (used in RVs) would work for a sealed aluminum tank.
Something else you should keep in mind is fuel flow and potential for vapor lock. Under certification standards a fuel system must flow 125% of the maximum engine requirement if a fuel pump is used, or 150% if it is a gravity feed system. This test is to be performed at the most adverse aircraft angle for fuel delivery as opposed to a level aircraft position. As a rule of thumb, figure the maximum fuel required for the engine to be 1/10th the horsepower in gallons per hour (200 horsepower = 20 gallons per hour at takeoff). If you figure this for ethanol, figure 1.33 times the gasoline amount. In terms of vapor lock, you should know that there are serious issues using automotive gasoline, and blending ethanol with automotive gasoline makes it worse. One of the issues is that automotive gasoline may contain butane (butane is not permitted in aviation gasoline). One interesting characteristic of butane is that it vaporizes with decompression. So, a rapid climb can create a potential for vapor lock that you would never experience in a car. I like to use carbonated water in a clear bottle for demonstrations. Just open the bottle and watch how decompression can cause the water to generate bubbles. If you think about it, what is happening is the water is boiling, and well below 100C. at that. If you mix ethanol with a high butane content gasoline, the vapor generation is enhanced, and vapor lock is even more likely.
We have spent a lot of time looking at formulations of ethanol and petroleum products. The big issue with automotive gasoline is not that something bad will happen, but that something bad could happen if a particular compound is blended on a given day. Interestingly, this is not an issue with 100LL since we know what can and cant be used. Therefore, my recommendation would be to run 100LL, ethanol, a specifically formulated blend like AGE, or any blend or combination of the above. I would next consider operating on automotive gasoline, but without ethanol. The least desirable fuels for aircraft use would be an ethanol blended automotive gasoline or an automotive E-85 with an unknown blend. Again, I am not saying any of these will not work, I am simply listing these in the order of potential problems.
If you can, I would also recommend going with fuel injection. Nothing wrong with a carburetor, but we see a lot more consistency and tuneability with the fuel injection. We use the Airflow Performance system, but just about any of the others should also work well. Finally, if you do run on automotive gasoline, you will need to run with a low compression piston (7.2:1 maximum). If you stay with 100LL, ethanol, or AGE, you can run a higher compression piston (like 10:1). The higher compression piston will give you more power and fuel economy than the low compression piston.
I hope this was helpful.
Hi James,
This was VERY helpful, thank you! My intent at present is to use an
Eggenfellner H-6 Subaru automotive conversion for the powerplant. I
know this engine runs fine on autofuel with ethanol in an automobile,
and is fuel injected with the appropriate knock sensors, etc. Firewall
Forward, I believe the parts used should all be ethanol compatible. The
rest of the airframe is where I am not sure. I believe I am basically
going to have to trace every part used to ensure it is compatible, and
replace with an alternate if not.
The tanks in the Sportsman are a welded aluminum tank separate from
the wings themselves. I've read that any aluminum parts in the fuel
system should be alodized to prevent a corrosive reaction with the
ethanol. Do you have any recommendations/comments on this?
My ultimate goal is to build a floatplane. Most of my flying is
generally below 5000 feet. I'd like the option of refueling at a boat
marina if necessary, or bringing fuel to the plane in cans if needed.
I'm sorta stuck with autofuel containing ethanol for the immediate
future, unless there is a change in what we use at the pumps for
cars/boats. I'd like to do all that I can to make my airplane as
compatible as possible with this fuel. At airports, I will most likely
be using 100LL with a TCP additive. I definitely would like to consider
using AGE85 or other ethanol based fuels if they become available in my
area (Durham, NC).
My two wing tanks will be gravity feed into a 4 gallon tank located
behind the seats. Two electric high pressure fuel pumps will feed from
two ports at the bottom of the 4 gal tank, and will be located directly
under the tank with a very short line (maybe 2-3 inches). This should
help to alleviate vapor lock issues. The Subaru uses a full cycle fuel
injection system (fuel is pumped to the fuel rail in the engine
compartment, and returned to the 4 gal tank), which should also help
prevent vapor lock since there is a constant flow and the fuel is cooled
once it returns to the 4 gal tank.
Any comments that you might have, web references of research that I
should read, or other recommendations that I should consider are greatly
appreciated!
Thanks!
-Dj
(08/28/2007)
Given you multi-fuel quest, I would alodine your tanks and system. This
will offer some protection in the event of water contamination too. In
our studies, we use a corrosion inhibitor. I like 0.75% corn or soy
biodiesel, but there are commercial products also available that are
very good (Corrpro for one). But, given a purchased fuel with the
ethanol already blended, you won't know if the corrosion inhibitor was
used or not.
Using a high pressure fuel injection should alleviate much of the vapor
lock issues, but careful fuel line routing is still prudent.
Just a thought. When using a standard automotive fuel injection, the
issue of redundancy sometimes comes into play. I always thought that a
basic carburetor equipped with a throttle position sensor could be
utilized as the throttle body. In the event of a power failure, open a
valve to supply the carburetor with fuel and fly home. The carburetor
wouldn't have to be perfect, just good enough to keep the fan turning if
needed.
Jim
Todd Schaufenbuel of Team Ethanol
(08/28/2007)
Hey Dj,
This is Todd Schaufenbuel of Team Ethanol. Congrats on building a glastar!
We fly airshows with four RV-3's powered by 100% ethanol. The only thing you have to do to burn ethanol is send the fuel servo to Rocky Mountain Aircraft Accessories to have the fuel curve re-calibrated to burn ethanol.
We sometimes have to burn avgas when we travel to and from airshows. To do this, we have to adjust the mixture in the cockpit slightly leaner to burn avgas. We do this on the engine runup prior to every takeoff. Sometimes we have a mixture of avgas and ethanol in the fuel tank. Again, we just do an engine runup and adjust the mixture for smooth operation. Above 3000 ft msl we begin to adjust the mixture leaner as you do in all recips.
Good luck on your glastar!
Todd
www.ethanolairshows.com
Hi Todd,
Thanks for the feedback! Did you have to do anything special to the
aluminum parts in the fuel system for corrosion protection or check any
rubber seals, O-rings, etc for compatibility with ethanol? I've been
told that some rubber parts used in aircraft fuel systems degrade
quickly when using ethanol.
It is great to see your team using an alternative fuel in a very
public venue. Please keep up the great work!
Thanks,
-Dj
No we didn't. What you're referring to is outdated information. In the early 80's companies used a cheaper, less resistant type of rubber when producing rubber products. Since the mid 80's rubber products have been built with compounds that better resist wear, fatigue, etc. The fuel hoses on our rv-3's were replaced last annual after being used in the airplanes since 1993.
To put that old information into perspective, sometimes at an airshow I will get a person who will tell me that we can't possibly be using ethanol in our planes because the alcohol would rot away the seals in the fuel tanks, destroy the rubber hoses, etc. I've actually told somebody standing directly in front of me that we are burning ethanol and they have responded with "you can't be". At that point I don't know what to say to somebody like that. The point is that trying to get people to accept change is a very hard thing to accomplish. Even when the evidence is directly in front of them they will still deny that ethanol can be used in airplanes.
Unbelievable, right?
It happens at nearly every airshow we do.
:)
Hi Todd,
I am honestly not surprised at all. Glass panels and alternative
engines always get similar reactions whenever I bring it up, too, yet
there are many flying with both of these.
It is good to know that at least the Van's kit uses good quality
rubber components, and I'm betting the Sportsman kit does as well. I'm
going to attempt to make a list of all the fuel components in the kit,
and verify with the respective manufacturers that they are compatible.
I think you are right in that I will find they are all okay. The slight
difference is that I may be using autofuel with 10% ethanol, which might
be different than using pure ethanol. Less work to check it now than
after it is built... :-)
-Dj
EAA
(10/19/2007)
Hi,
In your recent article on legislation in Michigan to require ethanol in
autofuel
(http://www.eaa.org/communications/eaanews/071018_ethanol.html), you
state (in part):
------
(cut)
* Ethanol is not compatible with rubber seals, fiberglass fuel
tanks, and other aircraft fuel system components.
(cut)
Extensive studies by EAA, the FAA, Cessna, and others all came to the
same conclusion: A 10 percent ethanol blend in auto gasoline is not
compatible with aircraft use.
------
I am building a Glastar Sportsman aircraft, and will be installing an
Eggenfellner Subaru auto-conversion engine. For the past few months, I
have been attempting to research the use of autofuel containing 10%
ethanol for use in my aircraft.
I do not have the resources of the EAA or the FAA, but from what I have
been able to find, it appears that aircraft fuel components made within
the last 20 years or so should be compatible with ethanol. I have
received communication from both the "Team Ethanol" group that flies
Van's RVs powered by E85 and pure ethanol, and from James Behnken, an
ethanol researcher at South Dakota State University, and both have
reported no issues with ethanol compatibility in multiple airplanes with
fuel system components made in the past 20 years. Prior to that, there
is a potential for incompatibility due to the materials used in the
"rubberized" components of the fuel system.
I am very interested in any research that you may have on using ethanol
in airplanes. If at all possible, I am trying to design the fuel system
in my Sportsman so that I will be able to use autofuel obtained from
boat marinas, which may contain some ethanol.
Thank you very much for any information that you might be able to share!
-Dj
DJ
Thank you for your questions.
First since you have an experimental aircraft you may experiment to find
what works best for your aircraft.
You ask about specific studies and you mention experience from Team
Ethanol and the E85 project. Let me state a few points that I think may
help with my explanation.
100% ethanol IS an FAA approved fuel and an aircraft appropriately
configured for that fuel should not be a problem.
The E85 fuel is not the same as 100% ethanol or automotive gasoline with
10% ethanol
From a chemical corrosion point of view 10-20% Ethanol and autogas with
a little water absorbed from a vent line is about as bad of a mixture
you can get in an aircraft.
EAA is not aware of any composite epoxy that is resistant to Ethanol.
There are "sloshing" compounds that are marketed as resistant to
Ethanol.
The most recent aircraft component tests with fuels have been the tests
done by Cessna and the E85 development team. As I noted the E85 fuel is
NOT the same as autogas with ethanol or 100% ethanol. The Cessna test
report gave the fuel a failing grade and the E85 development team says
it passed the tests. The FAA was to settle the tie but EAA has not seen
any results from an FAA test.
There are obviously fuel components that are resistant to Ethanol and in
choosing the components you use in your aircraft check with the
manufacturer of the materials as they will list the specific
environments that the components are made to survive in.
Now for the real issue.
Airplane fuel systems are not the same as cars or other vehicles the big
difference is our systems are open to the environment. Cars have closed
and pressurized fuel systems today. Because aircraft fuel systems are
open vented, because we change altitudes quickly, fuel in aircraft
absorb water then this water reacts with the fuel.
With 100% ethanol the water that mixes in does not create a corrosion
issue the only bad effect is loss of range do to less BTU's available in
the fuel.
With autogas and 10% ethanol in an open vent system the fuel absorbs the
water in the air and forms a corrosive mix that is a different than is
worse than ethanol alone, petroleum fuel alone, or water alone. The mix
of all three makes creates a particular corrosion problem that is
unique, it effects, steel, aluminum, rubber, epoxies and just about
everything else. Ironically this problem is at its worse with the 10%
ethanol mix as the level of ethanol increases or decreases the problem
is less prevalent. This is a problem that is also much worse for
aircraft than cars as aircraft tend to sit around for long periods of
time letting this mix of components do its damage. Even if a car had an
open vent system we tend to drive them everyday which prevents the
accumulation of the water in the fuel and for the phase separation of
the corrosive mix to come out of the fuel.
This in short is why aircraft have not been approved for the 10% mix of
ethanol and autogas.
If you like ethanol, my suggestion is do what the "team Ethanol" does
run either 100% ethanol or 100% 100LL.
If you want to use autogas with ethanol in it use as many ethanol safe
components you can a drain the fuel from your tanks or add 100LL
whenever the aircraft sits for more than a week or so.
Also attached is a note from a Ethanol aircraft operator in Brazil it
outlines what they have done to use the fuel.
Sorry we do not have more recent testing for you. If you want a copy of
the Cessna test of the E85 I only have it in hard copy so send you
address and I will make a copy for you.
----------
Henri and all,
I just received the following mail from James Waterhouse in Brazil:
"We have around 15.000 h with ethanol in reciprocating engines,
including radial engines, mainly Lycomibg and Continental engines; and
we had a lot of corrosion problems into the fuel systems.
The ethanol is very corrosive, so all the aluminum, brass, magnesium
parts need to be protected or changed to any resistent metal (like some
stainless steel). There are several problems with protective coatings,
but is possible to achieve good and certifiable results.
All the elastomers need to be replaced, and all the fuel pumps need to
be replaced also.
In order to comply with FAR23/33 requiriments, all the fuel system need
to be converted, and sometimes redesigned due the fuel flow increase.
Our company is working on the development of a fadec multi fuel system
for aircraft, unfortunatly our government refuses to help us, so it is
taking longer than we planned, but we hope to have in the future several
STC for small aicraft to use any fuel around ethanol/avgas.
For composites aircraft the problem is worst, just because ethanol
reacts with 99% of the epoxies used on the fuel tanks, but there are
some posible solutions possible.
There are some aditives against corrosion, but those aditives may solve
metal problems, not elastimers or fuel flow problems.
Best regards
James Waterhouse
----------
So, from what I can make of it, we have three choices:
1. Unless we change our fuel system to address the corrosion and rubber
incompatibility issue fuel with alcohol is a no-no.
2. We have to convince the distributors to deliver autofuel with no
alcohol, since that is the way it comes from the refinery.
3. Use 100LL with TCP.
Earl Lawrence
EAA, VP Industry and Regulatory Affairs
(10/24/2007)
Dj, as a side note to your question - aviation and boaters in the state
of Hawaii are up in arms because of ethanol in autofuel - seems the 10%
ethanol in autogas at marinas are destroying boat engines = destroying
their part of the tourist industry. Feel free to contact EAA Chapter
1182 President Terri Thomas at terri ---at--- airservicehawaii.com to learn more
about the problems boaters are having with ethanol-blended fuels.
EAA does have a autofuel STC web page that can answer most of your
questions - http://www.aviationfuel.org/ or the FAQ page -
http://www.aviationfuel.org/faqs/
I guess the key document in our defense is the FAA SAIB CE-07-06 that
talks about ethanol use for aircraft using autogas -
http://www.aviationfuel.org/saibs/10_27_06%20-%20CE-07-06.pdf - in it
the FAA says that ethanol-blended autogas should not be used in aircraft
engines. In this FAA SAIB, they do not say that if your aircraft was
build within the past 20 years it is ok to use ethanol-blended autogas -
they just say that ethanol-blended autogas is not to be used period.
Keep in mind that Team Ethanol and the South Dakota State University
groups fly aircraft at or near 100% ethanol - which is ok. But 10%
ethanol-blended autogas can and does cause harm to even today's modern
aircraft engines and unpressurized fuel systems.
Randy Hansen
EAA Government Relations Director
Hi Randy,
Thank you for the information. I've been reading through the links that
you sent, and am trying to learn as much as I can about autofuel with
ethanol.
Under the FAQs page that you sent, there is a pdf file called
"ethanol_blends.pdf" under the link name "What is the history of state
exemptions for aircraft that need ethanol-free autofuel?
6. Will EAA be doing further auto fuel STC studies to add
ethanol-blended gasoline to the STC in the future?
Answer:
o No. EAA, the FAA, Cessna, and others conducted studies they have all
determined that a 10% ethanol and gasoline mix is not compatible with
aircraft use. Further testing will not change the basic fact that to use
ethanol-blended autofuel in your aircraft will require a total fuel system
re-design costing well over $10,000 per aircraft.
In particular, I am interested in "to use ethanol-blended autofuel in
your aircraft will require a total fuel system re-design costing well
over $10,000 per aircraft." Since I am currently building my
experimental aircraft, my hope is to design and build the total fuel
system to be compatible with ethanol-blended autofuel from the start. Do
you have any idea where I might find information on how to do this?
Thanks!
-Dj
(10/29/2007)
Hi Earl and Randy,
Thank you for taking the time to respond to my inquiry. The
information you both sent is very useful, and adds to the collection of
knowledge I am gathering concerning autofuel containing ethanol.
The biggest challenge I am facing currently is that I can't seem to
find any specifics on finding fuel system components that are safe to
use with this fuel, and/or finding a way to treat the existing fuel
components to make them safe (ie, in the case of an aluminum part such
as the fuel tank, is a simple alodine corrosion treatment adequate?).
If either of you know of someone doing any research into what it
would take to make an airplane fuel system safe for autofuel containing
ethanol, I would greatly appreciate it. In the references that you
send, and the web pages that you referred, I find places where it is
mentioned that it should be possible, but I am having a hard time
finding anywhere that describes what would actually need to be done.
Earl, by any chance do you have e-mail contact information for the
gentleman James Waterhouse in Brzail that you quoted in your reply to me?
Thanks,
-Dj
(11/03/2007)
DJ
The note from the James Waterhouse came from the Stinson yahoo group
(Stinson@yahoogroups.com). I do not have the email for James
Waterhouse. I included his note as you asked about Brazil and James
note was consistent with what I have had verbally reported to me by
others at fuels meetings.
If you want the list of engineering criteria to deal with to run a
machine on a 10% ethanol blend then please give me a call and I can run
down the list for you. It will be much easier than email and I can
answer your questions/concerns as I share the information. Yes, there
is a way but it is very complicated and expensive.
I will be out of the office on Monday (visiting the EPA about aviation
gasoline, they are being sued for not banning lead in aviation gasoline)
and Tuesday ( I am visiting with FAA and NTSB on LSA and amateur-built
aircraft safety).
The office number is 920 426 6522. A toll free number is also listed on
you membership card or look in your last edition of SportAviaiton.
Earl
Notes from various builders that responded to my inquiries:
DeWitt Whittington
(08/27/2007)
Take a look, if you haven't already, at http://www.baylor.edu/pr/news.php?action=story&story=3089
Then email or call Maxwell Shauck, I bet he can answer ALL you ethanol fuel system related questions. And when you get them answered, let me know too!
Dee
PS. Also, take a look at http://www.age85.org/ActiveProjects.htm
Chris Lowery
(08/28/2007)
Dj,
I used to be of the opinion that vapor lock was the problem with ethanol, implying that ethanol is more volatile than autogas, but on further reading and research I have changed my mind. In fact, the reverse is true, ethanol is less volatile. The Reid Vapor Pressure (psi @ 100 deg F) of ethanol is 2.0 and gasoline is 4.5. The higher the number, the more volatile it is.
The real drawbacks to using ethanol are that:
1. It has a lower energy content than gasoline, only 73% of that of gasoline. This means less power per gallon.
Ethanol has 84,000 BTU/gallon and gasoline 115,000 BTU/gallon. So, 10% ethanol in gasoline means 111,900 BTU/gallon, 97.3% of the power.
2. It can attack seals and O-rings in the fuel system, unless they have been changed to a material resistant to it.
3. Ethanol is happier dissolving in water than gasoline. Any water in the fuel system will be a magnet for the ethanol and will suck it out of the gasoline.
All auto engines built after about 1995 are made to handle ethanol.
In your modern, computer controlled, fuel injected engine with knock sensors and sophistication up the wazoo, the computer will simply increase the fuel flow and advance the ignition timing until it sees knock and then back it off. Your system "learns", so then it will then continue that way. Net result, you use a bit more fuel.
On a side note, butanol is a much better fuel than ethanol. It has almost the same energy content as gasoline (110K BTU/gal), is less volatile, and does not suck up water like ethanol does. A small modification to the ethanol fermentation process will give butanol, so I see this as a fuel of the future.
Just my two cents worth...
Chris L.
Dj,
Well, let me see if I can contribute something extra.
Firstly, the best elastomeric sealing material that I've been able to find is Viton. But Viton comes in a lot of grades, so it still leaves some unanswered questions.
Viton is a Dow product, see:
http://www.dupontelastomers.com/Products/Viton/techInfo.asp
What I did was soak various elastomers in autogas and measure the swelling (increase in thickness) using a vernier caliper every day for 15 days. Viton (grade not known) was by far the best, with less than 15% swelling. Ordinary rubber doubled in thickness and went sticky, Buna N swelled about 50% and went soft. Neoprene was about the same as ordinary rubber.
Aluminum is unaffected by pure ethanol. But if water is dissolved in it, and chloride ions are present, then you can get corrosion. But with only water and chlorides you get the same corrosion, so the presence of the ethanol is not an accelerant.
It is virtually impossible to anodise the inside of an aluminum tube because of the way the anodising is done. (I spent years in the metal finishing industry.)
I also found that high pressure fuel injection hose is unaffected by autogas, but the low pressure fuel hose is.
The big car companies have thoroughly investigated this issue and they have upgraded their fuel systems using the right grade of Viton.
Chris L.
Dj,
I did my tests when they were changing over from MTBE to ethanol, so I can't be certain that it was with ethanol but I'm fairly sure it was.
I do know that autogas was far more aggressive to elastomers than 100LL since I did the tests in parallel.
I recommend you do your own tests, just get some clean jam jars with screw lids and various samples of elastomers: rubber, buna N, viton, neoprene. Most of the swelling was over in about 3 days.
I think it is pointless to try to anodise tanks or lines since they are relatively impervious to fuel.
Anodizing (American spelling) Anodising (British spelling) is the process of creating a thick (relative to the thin native oxide) uniform layer of aluminum oxide on the aluminum surface. Any aluminum alloy has a native oxide on the surface. I have measured the rate of formation of this oxide on fresh aluminum surfaces and it is completely oxidised in about ten seconds. Commercial oxidation of this thin surface to a thick one takes about 15-30 minutes, depending on the type of anodising.
Any similar name is a commercial variety of the same thing. Note that some processes incorporate dyes, pigments or other stuff into the surface. It depends on the process used as to how they do that, but the bottom line is that they are all aluminum oxides.
Chris L.
Andrew Stagg
(08/28/2007)
Make certain that you use Viton (or similar material) seals and not rubber, ensure that you won't have problems with fuel pump suction causing fuel to vaporize in the feed lines, and pay attention to the potential for the fuel to corrode the metal tanks/fuel lines:
http://www.tegger.com/hondafaq/gas-line-af.html
http://www.chevron.com/products/prodserv/fuels/bulletin/oxy-nona/concerns.shtml
http://www.chevron.com/products/prodserv/fuels/bulletin/oxy-nona/
One of the recent articles in the RAA Canada magazine indicated that gasoline containing ethanol (GCE) is corrosive to aluminium.
Andrew Stagg
Jan Eggenfellner
(09/02/2007)
Soft fuel tubing is close to pure aluminum and not nearly as subject to corrosion. It is sold as "Versatubing", I believe, from Spruce.
Yes, we use auto compatible pumps and filters.
Jan
Thanks! :-)
Spruce does have it - lower right on this page:
http://aircraftspruce.com/pdf/2008Individual/Cat08069.pdf
-Dj
David Domeier
(12/06/2005)
Dj,
I've been running on 93 mogas with up to 10% ethanol all year. No problems.
I do check the vapor pressure with each add during the summer. The ethanol has no
apparent affect on vapor pressure. It it checks at 50 kpa's, which it usually does, that's
what it is, with or without ethanol.
Mogas vrs 100LL is not a cut and dried issue. I happen to believe the engine runs better
on mogas but it's just a feeling and there is no data to support it other than the engine
runs fine. I do know 100LL always tests at about 65 kpa's which is a comfort on hot days,
but the mogas I've been using comes in the mid 50's which is just fine also.
The worst time for mogas is late spring when things warm up and the winter blend is in
the tanks. That's a very good time check vapor pressure and maybe a good idea to drain
the tanks and save the fuel for the lawn mower.
dd
(05/25/2006)
re: For those of us who are about to start flying but who weren't really
paying attention last year when all the discussion about fuel testing
was going on, how about a summary?
The kPa of auto fuel can vary from fuel to fuel depending upon blend and time of year (winter fuel in summer ops can be dicey). The other variables are temperature and pressure altitude.
For example, where do we get fuel testers,
Chris Lowery sells the kit and so does Petersen, the 182 conversion guy who also sells STC's.
http://www.webworksltd.com/autofuelstc/pa/HodgesTester.html
What are we looking for when we test fuel,
Vapor pressure. Dr. Hodges, the Aussy who invented the tester, uses kPa of the 6 or 8 different ways to measure atmospheric presssure. There is a conversion chart where by you can determine how high the can go at a specific kPa pressure assuming the temperature is constant - of course it never is, but fortunately it usually gets colder as we climb so the chart is very conservative.
Does octane make a difference in (Hkp?) results,
No.
Summer fuel vs. winter fuel,
Winter fuel can have a lower kPa. One of our guys up in Canada had his engine quit at 8500' a couple years ago, probably due to winter fuel on an 80 degree spring day. As I recall, the kPa of that fuel was not known or reported.
What about AvGas, can we mix Avgas and Mogas.
I've mixed avgas and mogas, engine ran fine. Avgas usually tests at 62 kPa. I can not prove it, but my gut feeling is the H6 loves mogas and just tolerates avgas.
dd
(12/13/2007)
I've been using mogas perhaps 90% of the time, all of it with alcohol. The only unknown at this time is the affect of alcohol and bare aluminum. After more than 4 years, the tanks look good, I find nothing out of the ordinary except some rivets are showing blisters but this is a different issue also occurring with straight 100LL. Perhaps 5% of fuel tanks, many QB, are showing rivet blisters. We really dont know the cause but I am certain it is not mogas and ethanol.
It is my belief that alcohol has no affect on vapor pressure. In fact, Ive checked E85 and it tested almost as well as 100LL. The engine is not set up to burn E85 so dont get any ideas about using it, I was simply interested in its vapor pressure for down the road. Most of the fuel I sample comes in at 40-50 kPa, 34 is the red line on the Hodges meter, 100LL consistently comes in at 62 kPa. The H6 will run fine on 87 mogas but I do not know the long term effects. Ive stopped using it in favor of 93 mogas, all from Walmart. The difference in price is just 20 cents/gallon.
I do not believe there is an issue with the engine fuel system and alcohol compatibility. There may be an issue with the ECU if it is not a stock Subaru. Jan has been recommending a 100LL/mogas mixture with the non OEM ECU now a part of the new engines.
dd
RV-7A H6