http://www.aopa.org/aircraft/articles/2008/080319avgas.html

What thinks ye?

I read that the highest octane rating refiners can currently achieve
without using lead as an additive is 97. I wonder what the
percentage spread would be then? (i.e., what percentage of the
GA fleet could run/operate safely on 97 octane).

There would no doubt be some airplanes that simply couldn't
(warbirds like the P-51 Mustang, and high compression,
turbo-charged and/or supercharged, high horsepower GA
airplanes).

One thing that bothers me about the article is the following comment:

“The majority of the CRC’s work has been on testing an unleaded
fuel that can provide the same octane level as 100LL.”

That doesn't help the (current) 70% of us out here who don't need
100LL, and in fact, don't want 100LL (too much lead!).

On another board (or was it here?) I saw a comment about how
at refineries, ethanol is the last ingredient added before they
pump mogas into transport trucks for delivery. In theory then at
least, there should be an "ample supply" of ethanol-free Mogas
available at your local refinery which can be transported / delivered
to airports for use in STC'd aircraft that don't require 100 octane
fuel.... (naturally, theory often times doesn't equate to reality
in the typical, so-called "market driven dynamics" we have in place
these days....

Bela-

I read that too, somewhere, hell I may have even written it here after reading about the refining process out on the interwebz, I can't remember. My next questions will show that I've forgotten anything I knew.

How long before we see an alternative mogas-based fuel pop up at an airport-based pump? Currently many states require the addition of ethanol for emmissions, for automotive usage, but why can't the fuel distributors who are peddling 100LL avgas work something out where untainted automotive fuel can be used at the airport pump?

Is ethanol the reason for instability of mogas? Is the evaporation of ethanol the reason mogas loses octane over time? Or is 100LL stabilized during its refining process, and that's one of the reasons it's more expensive?

1954C180 wrote:On another board (or was it here?) I saw a comment about how
at refineries, ethanol is the last ingredient added before they
pump mogas into transport trucks for delivery. In theory then at
least, there should be an "ample supply" of ethanol-free Mogas
available at your local refinery which can be transported / delivered
to airports for use in STC'd aircraft that don't require 100 octane
fuel.... (naturally, theory often times doesn't equate to reality
in the typical, so-called "market driven dynamics" we have in place
these days....

The article stated that 70% of the fuel sold is to GA airplanes that require 100LL even though they make up a small percentage of the GA fleet due to the fact they have a high fuel burn rate.

So, an airport looking at stocking MoGas or Stocking 100LL is going to stock what they sell most of, especially since it can be used in other airplanes in spite of problems. Since selling just MoGas could mean a 70% reduction in fuel sales, I doubt we'll be seeing a big push to make MoGas available soon. Hopefully I'm wrong here. I'd love to see more airports stocking Mogas.

FAA is proposing rule changes to the Experimental category regarding "builder assistance". I'll try to post some more on that soon. One longer term solution piece would be to make it easier for GA airplanes to swap engines without the expensive STC process.

Craig

There are a number of reasons why 100LL is more expensive. Perhaps the biggest is the distribution system, it cannot share the same system with automotive fuel. It must use it's own dedicated system which is small and not heavily used. Consequently, more expensive.

Another reason is that 100LL is cracked in very small amounts. There are only a few refineries that gear up for it's production and then for only a short duration. Unlike regular automotive fuel which is produced year-round by most refineries.

On the positive side, that is the reason that while 100LL may be expensive, it is not sensitive to constant price changes. Whatever the cost is when it is made is what it remains at until it is produced again.

In truth, when I think about it, if it were not for the very small population of GA aircraft and how slow the turnover rate is (compared to the life of cars) we should all be flying aircraft equipped with small, efficient jet engines!

Then we could be using Jet A and there would be no problem.

Skystrider wrote:In truth, when I think about it, if it were not for the very small population of GA aircraft and how slow the turnover rate is (compared to the life of cars) we should all be flying aircraft equipped with small, efficient jet engines!

Then we could be using Jet A and there would be no problem.

Or SMA or Thielert diesels running Jet A.

I don't think you will ever see a true replacement for 100LL. I think you may see some kind of 90 Octane fuel and a bunch of STC's that will lower the compression, limit boost or manifold pressure or something that will allow it's use in most aircraft. I don't think you can compare auto gas octane to octane with Avgas. Auto gas octane rating is derived by an average of research and methanol comparison, I believe whereas I think Avgas is research, but done as both a lean and a rich mixture. Not sure about the research part, but I'm sure about the lean and rich part.
I also think there are some significant vapor pressure differences between auto gas and Avgas. I run auto gas in a little C-85 in a C-140 that I have with no problems, but I would think there would be some major issue with what happens to car gas over time in a vented container for some airplane owners.
If there is ever a replacement, I bet the same thing happens price wise to it as has happened to this ultra low sulphur diesel. I mean who are they kidding ULSD costs more than JetA+ ?

Other than putting TEL into 100LL there must be differences in the vapor pressure etc.

If there are no differences other than the lead then there should not be a problem. The older engines probably would require some type of lubricant to take the place of the lead, but 97 octane is pretty decent.

Any petroleum product expertise would be welcome.

I know there is a placard on my O-540J1A5D that specs the minimum octane, but I cannot remember right now if it is 98 or 100 octane.

TD

The only FBOs that will carry Mogas in the US are ones that are not associated with fuel brands. Mogas is refined to such a lower standard than 100ll, that it should not be used in aircraft, period. Fuel suppliers recognize the excess liability, and don't want to take the added risk. It just doesn't make sense for them to do so. The benefits of being branded to FBOs are so great, that they will do just about anything to stay in the good graces of their supplier.

Now, I can tell you that there is one fuel supplier actively working on a Mogas supplement that can be FAA certified, but no one knows how far off it is.

Before someone says the greedy fuel suppliers should support Mogas because it is cheap, don't forget they are running a business.

If they are running a business, they should be subject to
the same laws of supply and demand as any other business.

Monopolizing the aviation fuel supply (by forcing suppliers
to sell 100LL only) doesn't exactly equate to a free, supply and
demand-driven market to me.... (just my personal opinion,
of course...).

I would be interested to learn how the old 80/87 fuel my airplane
was designed to use spec'd out compared to the current "brew" of
100LL, and also compared to ethanol-free 97 octane mogas.

On another board, it was commented that perhaps 1/3 of the
airports east of the rockies currently have mogas available for sale
on the field. Don't know what the number is for airports west of
the rockies, but I suspect it is somewhat lower....

I don't begrudge anyone running a business and making money
until they take active steps to remove the availability of Mogas
at a given airport in an attempt to artificially drive up demand for
100LL there (recently happened at an airport near me....).

Acouple of things that I have heard in regards to mogas, and in particular with ethanol.

Ethanol seems to attract moisture, so that is one bad thing.

Auto gas has a lower vaporization rate. Not sure if this is because of the ethanol or not. I don't think it is such a big deal with gravity feed engines. I have had problems running mogas in a different plane, with a fuel pump mounted to the engine. I got vapor luck with it on a hot summer day.

I run MMO in my gas. I think this may help to stabilize it. In fact I put a little oil in everything that I have that runs on gas. The theory behind this is: My chainsaw gas doesn't seem to ever go bad, and that's the only difference I can see, is that it has a little oil in it.

Gary

Read the label on the two stroke oil. Almost without exception the better ones contain a fuel stabilizer. One recognized brand name is sta-bil. I don't have a clue how it works, but it seems to.
I too add MMO to my airplane fuel, both 100LL and car gas. Probably snake oil, but it makes me feel better.
I can't get TCP and the MMO does seem to inhibit lead fouling. Probably the placebo effect though.

I believe that the only airport in California to offer Mogas is Modesto. http://www.airnav.com/airport/KMOD Well if they don't, they used to. It can be done if they want to do the extra work.

I think that a small FBO could generate a bit of extra business if they had MOGAS.

Oregon has ethanol free gas at the pump for now. Pretty soon it will be required statewide unless they come to their senses and realize what a waste it is. Just look at the high prices of food on the shelf.

Tim

An FBO that had Mogas would be able to make a little bit of money doing it, I tried. I had a tank and separate supplier lined up for it. When I was almost ready, I called my primary supplier to tell them what I was doing. They told me that they would still supply me 100LL and Jet A if I got Mogas, but I would not be covered under their $50,000,000 liability insurance policy. They said they would love to be able to supply it, but it is not worth the liability. The reason behind pulling the insurance is they would no longer allow us to associate their brand with our fuel.

100LL is refined to very specific standards with QC check every step along the way. If the product is not perfect, it does not leave the refinery. Every time the product changes hands, a QC check is done, and if it doesn't pass, the fuel doesn't move. Mogas barely has a standard. The octane can fluctuate about 5 points up or down. In addition to the vapor locking and ethanol issues, you could have a tank half full of water and wouldn't know until you started having engine problems. Engine shops also love it when people use Mogas, you will almost never reach TBO.

Sorry if I come off a little curt, but I listen to old cheap bastards piss and moan all day long about how I should have a tank of mogas just for them to use, make no profit on it, when they don't even have the proper STC to use it. It's hard to get people to understand that there is a lot more to the situation than an oil company that wants to sell more 100ll.

1/3 of all airports in the east carrying Mogas is a gross overstatement. Here in Ohio, I think we might have 4 public airports that sell Mogas, and there are over 100 public airports in the state. Back in the 80s a lot more airports carried it, but then insurance took over the industry.

1954C180 wrote:
One thing that bothers me about the article is the following comment:

“The majority of the CRC’s work has been on testing an unleaded
fuel that can provide the same octane level as 100LL.”

That doesn't help the (current) 70% of us out here who don't need
100LL, and in fact, don't want 100LL (too much lead!).

It would be unleaded, what's the problem?

bigdawg wrote: Engine shops also love it when people use Mogas, you will almost never reach TBO.

You are so full of it. The 182 that my partner bought me out of used Mogas 1/3 of the time and it is at 1500 hrs + and the compressions are high. Lots of folks have gone to TBO on Mogas. All that lead is way worse on an O-470 than is the so called poor quality of the auto fuel.

At 200 hrs after our engine was overhauled (80% run on Mogas) the mechanic, who bo hooed Mogas, could not believe how good the plugs looked. Oh and it was a Melenium Engine. They said that the warranty was void if I used Mogas. I used it anyway.

The new fuel injected engines in the cars of today need a much better fuel than a 7 to 1 O-470. The O-470 is about as high tech as a Ford Flathead.

I will not challenge you on the insurance angle cus I have no experience at that.

Tim

I've mentioned this before, but I've run 90+% auto gas in an O 360. I mix 1/2 high test & 1/2 mid grade. At the over haul, everything looked good.

In other planes that I used auto gas in, I used MMO, but a few years ago I put some (the proper ratio) in a glass- 1 gallon jug and filled with auto gas. Shook it and set it down outside.

A week or so later, there was this slug of stuff on the bottom. It settled out.

Why mix high test and mid grade? Why not run straight premium if you need the octane. I run the cheap stuff in a C-85. It was certified for 73 octane fuel. I've been mixing MMO. I have had some mix in a ball mason jar for a while waiting for it to seperate because I read your earlier post. Was it cold WX when it seperated?