With the recent dramatic rise in fuel prices nationwide, I have been looking again at using Autogas in my Long-EZ.
The main issue (which has led to more discussion threads than I care to remember on the Canard forums) is that while there is a national standard for 100LL in the USA, no such standard exists for auto fuels. Instead there is a complex patchwork quilt of Federal and State regulations, which means that everything from octane ratings to additives can be different from town to town, city to city and state to state. As a result, refineries generally pump out a limited number of grades of generic gasoline that meet basic "lowest common denominator" standards, and leave it up to local distributors and filling station brand owners to supplement the fuel with required local additives and special additives for brand differentiation. You can see this system at work down the road from where I work, in Euless. There is a major gasoline distribution depot that supplies fuel all over the D/FW metroplex. When I drive past that depot, you can see fuel trucks from all sorts of filling station chains - Mobil, Chevron, RaceTrak, Joes Garage etc. all waiting in line to be filled. Clearly they are all being filled with the same basic fuel, and then the individual operators are adding whatever extras they deem necessary for branding purposes.
The differences in auto fuel specifications start with the displayed octane number at filling stations, which is actually the average of 2 different measurements - the RON (Research Octane Number) and the MON (Motor Octane Number). The technical abbreviation for the formula used is (R+M)/2. The difference between RON and MON is not supposed to exceed 10. So a fuel with a displayed value of 87 could have a RON of up to 92 and a MON of down to 82.
However, the differences that lead to the most trouble are the special standards implemented for fuel sold in major urban areas whose pollution levels exceed certain EPA and state standards. Fuel in those areas has to meet different standards (the Reformulated Gasoline standards), which place strict limits on levels of sulphur, levels of oxygenates etc. In order to meet those standards, fuel refiners, distributors and filling station owners add all sorts of chemicals to gasoline. Some of the additives (such as detergents and fuel system cleaners, which are usually added by the filling station chains) are fairly benign. However, other permitted additives - oxygenators such as ethanol and methanol, are nothing but trouble for aircraft use.
Historically, gasoline distributors used MTBE as an oxygenating additive; however, emerging evidence about the long-term toxicity of MTBE (including its appearance in local groundwater supplies) has led many states to enact MTBE bans. So far, Texas has not yet gotten around to banning MTBE (what else could we expect from a state with such a laissez-faire approach to environmental protection generally?), but a number of fuel suppliers, conscious of the bad PR from the continued use of MTBE, are already phasing it out in favour of ethanol.
Ethanol is a double-whammy no-no for aircraft - it attacks fuel system seals, gaskets etc. and also absorbs water, which can lead to significant operational issues (like the replay of "The Sound of Silence" at altitude).
Another variation is that some states (including Texas) mandate that fuel sold in the Summer (1st May to 1st October) in a list of 90+ counties has a lower Reed Vapor Pressure (RVP) to reduce vapor lock issues. This is actually good from an aviation standpoint.
Here where I live in the D/FW metroplex, fuel additives can include ethanol, and the 3 counties (Dallas, Collin and Tarrant) that largely comprise the geographical area appear to be exempt from the lower Summer RVP requirement. this is probably because adding ethanol to gasoline increases the RVP by at least 1 psi, reducing the chance of this blended gasoline passing the wider RVP Summer pressure standard.
This is bad news for pilots on 2 counts - not only could your autogas contain ethanol, but it may have too high an RVP in the Summer for safe aircraft use.
My tentative conclusion is that if you live in D/FW, and buy auto fuel in Dallas, Collin or Tarrant Counties for use in aircraft, you would be well advised to test if before use to make sure it does not contain ethanol, and that its RVP is safe for aircraft use. It might be better to buy fuel outside of those 3 counties altogether.
One positive advantage of using autogas for aviation use is that you can reclaim the state tax on it, if you save the receipts and get a special form from the Texas State Comptroller's office. Unfortunately it appears that you cannot reclaim the Federal tax on the autogas, unless you can prove that the fuel was used for charitable activities.

Link: http://alexisparkinn.com/fuel_truck.htm

Jay Honeck, who owns a plane that happily runs on autogas, and does not like 100LL, built his own fuel truck that he uses to fuel it at his home airport. With Avgas prices once more heading towards the stratosphere, here's the link to his story of how he built it, for those entrepreneurial types...

This is a posting that I wrote on the Canard Aviators Forum in the Summer of 2003, as part of what is a regular series of debates about Auto vs. Aero engines for experimentals:

Here are the key factors that I think we all have to consider when
evaluating our powerplant decisions:

1. Operational Data
I think that a major factor in the debate between Aviation and
automotive powerplant proponents is operational data.
A large amount of operational data exists for aviation powerplants in
aviation use.
A very large amount of data exists for automotive powerplants in
automotive use.
A (relatively) limited amount of data exists for automotive engines in
aviation use.
Given the different operating regimes of aviation powerplants
compared to most road car powerplants, not all operational road use
data is relevant to aviation and vice versa.

2. Vendor/factory support
Liability issues and unfamiliarity will probably prevent Mazda (for
example) from ever properly supporting the use of rotary automotive
engines in aviation. Support is therefore going to end up with the
specialist guys.

3. How Much Do You Want To Be A Pioneering Engineer?
There are engineering challenges that are different for aviation use.
The need for a PSRU is usually one (significant) additional issue.
Another issue is installation packaging. The firewall of experimental
aircraft is often a dimensionally limited CG-sensitive zone (the
latter factor much more so than a road car). For example, while it is
possible to install a Mazda rotary in a Long-EZ (Ron Gowan has one),
I am betting that the packaging is really tight. Gary Spencer has a
neat Ford V8 installation in his Long-EZ, and that is a very fast
plane. However, his installation is also very tightly
packaged. IMHO installing a road car powerplant in a tandem canard
pusher is akin to designing an installation for a single-seater
racing car. For the Cozy and Velocity it is less of a packaging
issue, and more of a general engineering issue of balancing the
installation and matching solution components. However, it is still
experimental engineering as long as we do not have standard
installation configurations, components and packaging.

I am contemplating whether to install an automotive engine in my
future canard pusher (the one I have not started yet, since I'm still
learning about them by flying one). Here are some things that I am
thinking about, and issues that I need to feel more comfortable with:

1. Calculate, don't guess
I was impressed by reading about Greg Richter's Cozy Mazda, mainly
because Greg, being an engineer by training, did the math about the
cooling system instead of guesstimating radiator and cooler sizes. If
you're going to be an engineer, you need to work through stuff.
Guesstimating is not engineering...

2. Test the plane with an aviation engine, then switch to the final
powerplant
I would like to see some sort of universal mounting pattern created to
support installation of both aviation and automotive powerplants
without requiring modification of engine mounting points, or some way
devised of installing mounting points for both types of powerplant on
the firewall.
From the perspective of reducing the number of variables, that allows
for better engineering of ground test and flight test programs. You
flight test the plane with an aviation powerplant (preferably one
that worked well on another aircraft), then switch to an automotive
engine when the plane is debugged.

3. Builder funding of test programs
One thing that I think the experimental community needs to seriously
consider is collaborative funding of test programs. If a bunch of
people could fund a ground test cell for a standard (say) rotary
engine package, and have an aviation rotary expert run a
comprehensive long-duration test program based on a variety of duty
cycles and simulated operational conditions, we could accumulate a
large amount of test data rapidly, and also identify component or
engineering weaknesses in engine installation solutions.
At the moment nearly all of the testing of engines and installations
is occurring "for real", usually above the ground. To use a software
development analogy; that is like testing all of your code changes in
Production (which leads to the old joke that Production is the best
Test environment you have - it is, but only if you don't mind
explaining the failures to the customer...). It also reminds me of
Linda Ronstadt's comment (after one of her LPs went platinum) that
she had finally learned how to sing; it was just too bad that she had
to do all of her practising in public (referring to her previous less
successful LPs).
The number of non-aviation engine units installed in experimental
aircraft in the USA, and the number of different variations, puts us
into the specialist motor racing zone in terms of engineering,
testing and operations. Most successful racing teams working with
custom components spend a significant percentage of their budget and
time testing components before installing them in cars. They also
spend money on testing before racing to ensure that the whole package
works, but they go testing with the expectation that most of the
basic car components are going to work. It's difficult to debug a
race car if the engine keeps failing... Bottom line is that they do
not want surprises in "for real" operating conditions. Neither
do I. "The Sound of Silence" is my least favourite song when applied
to aviation.

Is funding collaborative test programs moving us away from the true
experimental ethos? Well, maybe it is. However, I see flying as an
endeavor involving the assumption of calculated risks, not a daily
trip into the unknown. (I leave it to others to determine if that
makes me a true aviator or a wuss).
We all make decisions about risks every time we fly. The better our
decision inputs (data, experiences etc.) are, the higher the quality
of our decisions ought to be (yes, I know that the NTSB database
shows that some folks are bad at analyzing any sort of input...).
One thing about RAF and Scaled that continues to impress me is that
they are always prepared to collect data, analyze it, continually
challenge technology and solutions, and be very conservative. In view
of the safety records of RAF and Scaled, that is an approach we would
do well to emulate when evaluating, building, installing, testing and
operating powerplants.

See my posting below on the trip to Longmont. The difference of 20 degrees that I have been seeing between #1/#3 and #2/#4 is due to differences in the fuel distribution, not differences in the airflow through the cylinders. I need to work on the cooling to improve it some more, but I also need to see if I can even out the fuel distribution to both sides of the engine.

I flew the Long-EZ to Longmont, Colorado (ID is 2V2) on 18th August for the Lyons Folk Festival (Marsha was attending songwriting school prior to the festival).
I lifted off from Dallas Executive at 09.15 CST, transitioned directly through the D/FW Class B airspace, and straight-lined it to Colorado, flying at 8500 feet throughout. No weather issues at all. However, I struggled the whole flight with CHT issues, especially #3 cylinder which consistently ran at or above 375 degrees on the CHT monitor. The last hour of the flight was rather bumpy as I hit early afternoon convective turbulence over the plains of Eastern Colorado, and I also found myself running into a headwind, which reduced my ground speeds to the 145-149 knots range.
I touched down at Vance Brand Airport in Longmont. After tying down the plane, I examined the prop and found evidence of a small amount of oil blow-by on one of the prop blades. An oil level check showed that I had 4.5 quarts left, having performed an oil filter and oil change immediately prior to the flight. I had therefore consumed around 1 quart on the flight - not excessive, but not stellar either. However, I am still losing a significant amount of oil in flight out of the breather tube under the wing root (the el cheapo air/oil separator that I installed last year is ineffective because it is too small, and it is currently mounted at the incorrect angle to provide any drain-back into the engine).
I headed back to Dallas on Sunday 21st August. When I arrived at the airport, there was the usual afternoon cumulonimbus build-ups over the high mountains to the North-West. These would probably give some afternoon showers at Longmont, but that did not bother me since I would be gone by then. What did bother me, however, was the unmistakable sign of towering shower clouds to the South and East. A phone call to WXBrief revealed plenty of gaps in the shower activity, so I decided that I would take off and rely on the speed of the Long-EZ to swerve around the weather.
I did not get going until 14.30 MST, which meant taking off at the worst time of the day from a density altitude perspective. I calculated the density altitude was around 7750 feet when I set off down the runway. With myself, luggage and 40 gallons of fuel on board, the takeoff weight was 1485 pounds. Not surprisingly, the plane did not exactly leap off the ground - I lifted off at around 3800 feet. However, once in the air, I was able to climb fairly smartly.
After negotiating the Denver Class B airspace, I initially climbed to 9500 feet. Initially, I realized that I had rain residue on the outside of the canopy that I had forgotten to clean off prior to departure from Longmont. I was concerned about this impeding my visibility; however, a chance encounter with virga as I left the Denver Class B airspace washed off the shower residue, leaving me with a nice clean canopy. (Memo to self - file this trick for possible future use).
Not being happy with being bounced around at 9500 feet, I turned on the oxygen supply and climbed to 11500 feet. 11500 became 13500 as I manouvered around a shower system South-East of Denver.
When I reached 13500 feet, the CHT on #3 cylinder was still around 375 degrees, despite the fact that I was running at low cruise - 2340 rpm. I decided to experiment with more aggressive leaning. My leaning technique had previously consisted of leaning until engine roughness appeared, then moving the mixture knob back around 1/4 inch. This time I leaned until the engine became rough, and then enriched the mixture by increments until the roughness almost disappeared. The results were dramatic. Within 5 minutes, instead of the normal CHT distribution (370, 355, 375, 355) I had a perfectly symmetrical reading on the CHT display, with all cylinders at around 360-365 degrees. Examination of the EGT display showed that #1 and #3 were lean of peak, with #2 and #4 probably slightly rich of peak.
At this mixture setting, the engine was not as smooth as at a richer mixture setting; however, it was not running roughly. More importantly, I was bowling along at 13500 feet, burning 5.4 gallons an hour, with a groundspeed of 162 knots. The lower CHTs allowed me to advance power to 2560 rpm, at which level I was burning 6.4 gallons an hour with a groundspeed of around 170 knots depending on the state of the tailwind, which was varying. The OAT was 42 degrees, but with the sun shining into the cockpit, my body was warm enough. The leaning process showed that the normal 20-25 degree difference I am seeing in CHTs is not due to different cooling on each side of the engine - it is entirely due to poor mixture distribution. The left-hand side of the engine (#1 and #3) is getting less fuel than the right-hand side (#2 and #4). I will be looking at possible causes for this asymmetry and how to address it in the next couple of weeks. I have a stock Marvel Schebler carburetor on the plane, and those are not renowned for even mixture distribution. If I can even out the fuel distribution, then I ought to be able to run the engine to peak EGT or even slightly lean of peak EGT. I doubt I can run any leaner without changing the fuel system to either an Ellison or fuel injection. I have no money for a significant change of that type right now.
I touched down at Dallas Executive 3 hours and 50 minutes after departing Longmont. No sign of blow-by on the prop, and the exhausts were a nice very light gray, except for #2 which was a lot browner. A lot of extra fuel is clearly being fed to #2 with the current inlet tract performance.
On this trip, I ran my new Lightspeed 3G headset for the first time with an aux audio source - a CD player. You need to turn down the CD player volume, but this worked really well, and the sound quality was a lot better than I expected. I was listening to the Pat Metheny Group's live Besancon rough-mix CD for most of the way up to Longmont. Can't get much better than that for in-flight entertainment.