Food for thought on Fuels


Below are four observations on fuels, a subject that rarely sees opinions based on numbers and reason. The topic of fuels draws out emotional responses ranging from compulsive cheapness to conspiracy theories, neither of which serve the serious builder. Feel free to use the comments section, keeping in mind I reserve the right to delete any comment which doesn’t have a human name attached to it.



(1) Yes, high octane unleaded fuel exists. Above is a can of 110 Octane unleaded fuel in my hangar. We use it for dyno tests and other research. The detonation resistance of this fuel meets or exceeds 100LL.  I buy it in our little town, off the shelf, it is about $8 a gallon, a price which includes a healthy profit and the container. It is sold at a little golf cart repair shop near our town’s drag strip. If ordered in a 55 gallon drum, it is substantially less than $5/gallon. Every year I hear “Experts” at Oshkosh talk about how having unleaded fuel with an octane higher than 94 would require a scientific breakthrough.  Reality: it already exists, no one need ask for a federal grant to re-invent it. I strongly suspect that if it were manufactured in the volume of 100LL, it might even be cheaper. Even if it wasn’t, aircraft engines would live a lot longer without lead in them. Extending the life of a motor 20% would offset a substantial price differential. Think it over.


(2) Fuel cost is a much smaller cost of aircraft ownership than people think. When the price of fuel goes up by a dollar, several people in every EAA chapter will pontificate that “flying just became unaffordable.” Try this at your next meeting: Poll ten people who have a hangar at the airport on how much their hangar rent was last month, and then ask them how many dollars they spent on fuel the same month. 9 of 10 will have bought less fuel than rent, yet they don’t complain with the same venom. Picture this: A lower cost homebuilt which took $25,000 to build, not to mention years of labor, which costs $1,000 a year to insure and $250 a month to store. The builder has an AARP card and may have only 10 or 15 good flying seasons left. If he flies 100 hours a year at 5 gallons an hour, he will spend $1,500 on $3/gallon fuel or $2,000 on $4/gallon fuel.  Only a fool would choose to fly a lot less because his annual operating cost went from $5,500 to $6,000/year. Reality says the sand is running out of the hour glass and you built the plane to fly it, not to protest the price of hydrocarbons.



(3) Aviation Gasoline is not expensive and apparently here to stay.  Above Is a photo I took at the Palatka Florida airport the day Paul Salters Panther flew. Notice the $3.29 100LL price. This isn’t accurate today, as the price has come down 9 cents in the last 2 weeks. I have worked in aviation basically every day since 1989. In that time I have heard several dozen experts and magazine editors citing “new laws” , “Federal standards”, “lead being outlawed” all predict that 100LL would disappear in 1990. 1992. 1996, 2001, 2002, 2008, 2012, and 2016. Lord knows, there will be people saying it is being outlawed in 2017, and people will believe them, in spite of the fact they have never been right. On the price of 100LL, people like to quote the price at the signature FBO at Miami International Airport, because it justifies their statement “I would fly all the time, but no one can afford to anymore.”  The actual local price of 100LL is a small fraction of this distorted number..


(4) There is a very ‘popular’ internet forward that states “Gas was $1.89 the day President Obama took office, and it is a record high today at $3.69” People like this, it gets passed around in aviation circles all the time, it just doesn’t happen to be true. The record peak gas price in the US was August 2008, when  George Bush was president, and it was $4.11/gallon. The change to $1.89 in 5 months reflects the economic collapse in the fall, and it says nothing about either president.  The $3.69 was July 2014, the actual national average today is $2.13 a gallon. essentially unchanged in eight years. There are a lot of people who think the price of gas is set in the oval office, and there are even more who decide if they can enjoy their life based solely on which party is occupying the public housing at 1600 Pennsylvania avenue. My personal love of airplanes goes so far back in my life, it certainly predates my awareness of politics. Given an chance to go flying or argue partisan debates with misleading data, I confess to being in the minority, the people who would rather build and fly.




13 Replies to “Food for thought on Fuels”

  1. Most of my flying used fuels blended with nitromethane and anhydrous methanol. My concept of the most exciting airplane I could build would look something like a Cri-Cri with a 650ci V8 running a black and decker air pump. I would not care at all about the cost of gas, just about my likely ability to land in the remaining runway. Budgets and life events prevent going flying for just the cost of gas, for the last 5 years. I’m not dead yet, I still look up multiple times a day and wish I could get my wish. My dream airplane would fly from my yard, low, slow, and quiet; not exciting; satisfying, bringing contentment. I also, still, would not care about the cost of gas. Please keep telling the truth that those who would listen, might hear, be encouraged, and think.

  2. William,
    I’m glad to see this subject addressed a bit and for the record I have done all the math that you have suggested. While our price is over a dollar more than yours here, I choose to fly with 100ll exclusively as you witnessed yourself at Barnwell several years ago my plane does not like auto fuel. (probably more to do with the Aerocarb) I choose to buy my fuel at my home FBO to support it. I also have done testing that shows that lead is not the best for the inside of the engine. About 8 years ago i removed my heads after about 110 hours and found the lead build up to be able to be measured at nearly 1/8″ thick. I cleaned the heads and ran another full year and withinn several hours of the same time using marvel mystery oil which i was told could scavenge lead and exhaust it. For me it did and does. The lead build up was only maybe .020″ after the second year. I have the real numbers and times recorded somewhere. The only comment i might challenge is the 20% increase in engine life. Is there evidence to support that or was is a supposition? I would gladly change to a no lead alternative if it were readily available. BTW… I am hoping to attend OSH next summer with the 1000 hour on corvair power stickers displayed on my plane.
    Joe Horton, N357CJ

    1. Joe, thank you for your insights from your experience. I also have had good experience with Marvel oil added to gasoline. Many other Corvair pilots have had good success with Decalin used at the maximum recommended level. My comment on 20% was a guess, but I have seen a lot of repair stations guess the same number on Lycomings, and the Swift fuel people have data that implies the same idea. I would be very surprised if it made no difference in the life of an average valve. In the end, I think you have a rational proven plan, buy good fuel, add something to remove lead build up, fly a lot, enjoy without worry. We have had far more people damage engines by using low octane car gas because they were cheap than we have ever had hurt by lead build up. Looking forward to shaking your hand next to the 1,000 hour sticker. ww.

  3. Isn’t the lead used to control flame front propagation rate, anti-knocking, etc? Also, protection of valves? I really don’t know, would like to know.

    1. Michael. Lead primarily provides detonation resistance. If the engine detonates, it breaks, period. So one way or another, the available octane of the fuel must exceed the octane requirements of the engine. This said, the lead in fuel is actually bad for valves in the long run. Lead build up causes a number of issues, the primary one being the byproducts of combustion of leaded fuels being very corrosive in the presence of moisture. That pits valve and seat faces when in contact with humidity when the engine is parked for a few weeks. There is a lot too it, but given the choice of lead or no lead, you would choose the latter, IF and ONLY IF, the unleaded fuel meets the octane requirements of the engine.

  4. You got some mighty good critical thinking skills for a “troglodyte mechanic”. I don’t know if it’s that easy to fool some of the people all the time or if they just don’t want to go to the trouble of thinking for themselves. As usual, you’re spot on with your thinking. Keep up the good work!

  5. We had a LOP issue with our soaring club tug, and my understanding is that it had to do with a sticky valve from excessive lead buildup. Just something to stay on top of.

    As far as partisan debates about fuel costs, at $4/gal and 5g/hr – $20/hr of flying – I’m with you can’t we all stop whining about who is in office and just go flying? 😉

    1. The label gives 4 ounces per 10 gallons. That’s what I’ve been using. Really does seem to help. I also add Decalin at 1/2 ounce per 10 gallons.

  6. About gasoline, supply, demand and politics, here’s a message sent to me back in 2004 by one of my very best friends, a Purdue engineer with absolutely no agenda other than recounting his experience:

    > True story —
    During the summer of 1973 I worked on a tow boat on the Mississippi
    > River. Every 10-14 days or so we’d load our barges on the Gulf Coast
    > and deliver petroleum products to some place in the midwest. During
    > the time Congress was holding the Watergate hearings. When we’d be in
    > range of a TV station it would be the only thing we could tune in.
    > That was the summer of the big gasoline shortages. As we would travel
    > up and down the Mississippi, we’d pass an Exxon tow. It would have 8
    > barges (a double unit) fully loaded, or about 10M gallons of
    > gasoline. The tow wouldn’t be moving, it would be tied up in a quiet
    > spot on the river. Each trip we find more tows tied up. Shell,
    > Texaco, Exxon, Amoco were all doing it. One day they announced in the
    > news how much gasoline would be used in the USA in a single day. I
    > made some quick calculations and realized we had passed a month’s
    > supply on our last trip.
    > By mid summer the river depth was lower than normal. In a few places
    > the channel would become impassable. For a few days we had to wait
    > near Greenville MS until the Corps of Engineers cleared the channel.
    > It was nice because we were within range of a TV station. The good
    > folks of Greenville were having problems with the gas shortage. It
    > dominated their local news. If they had only known there was about
    > 60M gallons of refined, ready to use gasoline only 10 miles away, I
    > wonder how they would have reacted.
    > For most of the summer we hauled No 6 fuel oil to Arkansas Power &
    > Light’s power plants. (Nasty stuff, that No 6) When we were at a
    > Gulf Coast refinery, I remember how we’d be rushed in and out. During
    > that period, dock time was at a premium. There would be lots of
    > barges and ships waiting for dock space. No 6 is hard to pump. A
    > couple times they couldn’t wait until we had a full load, so they sent
    > us on our way with a partial load. This really upset the folks at the
    > power plant who were expecting more fuel than we brought. There was
    > no shortage of petroleum or production capacity along the Gulf Coast
    > that summer. They just conveniently didn’t deliver it to the
    > distributers.

  7. Mr. Wynne,
    Being a Corvair owner for 46 years I have always been interested in anything Corvair. I have followed your web site for several years and enjoy it very much. The latest post on fuels brought back memories from my four years (1970-1974) at Milwaukee School of Engineering. My
    associate degree was in Internal Combustion Engine Engineering. One of the classes was Fuels and Lubricants. In our thermodynamics lab was a Waukesha CFR (Cooperative Fuel Research) engine. It is a motor driven water cooled engine with a variable compression ratio mechanism and various ways to control the inlet air temperature and water jacket temperature. This allows for measuring the knock sensitivity of different fuels to the two standard octane rating systems. They are RON which is the Research Octane Number and the MON or Motor Octane Number. This is where the R+M/2 math comes from on today’s gasoline dispensers. This average is called the AKI or Anti Knock Index. American automotive companies as well as American Petroleum companies pretty much have always used the RON when telling customers what grade of fuel to use. For our labs we always tested to RON. Our base line reference fuel was always AMOCO white gas. It is almost pure iso-octane and completely lead free AND has an RON octane number of 100. Amoco started selling their lead-free gas back in the 1920’s. If you can believe what you read in Wikipedia modern gasoline sold in the USA with an AKI of 90-94 which is equivlane to a RON rating of 95-99. Seems pretty close to 100 if you ask me.
    Just my two cents

    Phil Spainhour

    1. Phil, Very interesting experience. Dan and I both spent some time at the Swift Fuel booth at the DeLand showcase, and they had long discussions about how they used the same CFR engine to develop their data. -ww.

  8. Mr. Wynne,

    One more pennys worth.
    Low octane fuel and high octane fuel ALL have the same amount of energy. It’s approximately 18,500 BTUs per pound of fuel. What the higher octane rating does is reduce the fuel air mixture inside the cylinder to explode spontaneously. Some people say doesn’t it always explode? The answer is NO. It is a controlled burn. The flame front in normal combustion starts out from the spark plug at about 5000 feet per second. When you have detonation (ping, knock) the unburned fuel air mixture explodes. In this explosion the flame front is traveling at about 25,000 to 35,000 feet per second. Now, you can’t hear this explosion but the results of the explosion. At this super high velocity the pressure wave created starts reflecting back and forth inside the cylinder. At this velocity this reflecting happens very rapidly. What we all hear is the cylinder head, the cylinder, and the top of piston flexing under the enormous pressure caused by the explosion. Since non-ferrous alloys, aluminum, have no endurance limit this flexing ultimately results in piston and/or cylinder head failure.


    Phil Spainhour

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