No Lead Aviation Fuel

Discussion in 'Flight Following' started by brien23, Dec 8, 2020.

  1. nrpetersen

    nrpetersen Line Up and Wait

    Joined:
    Jan 4, 2013
    Messages:
    550
    Location:
    Minnetonka MN
    Display Name:

    Display name:
    nrpetersen
    Unrelated.
     
  2. bnt83

    bnt83 Final Approach

    Joined:
    Dec 31, 2012
    Messages:
    9,408
    Location:
    Lincoln NE
    Display Name:

    Display name:
    Brian
    That's just it, a whole pile of engines could safely burn mogas by lowing the compression, a lot of those could be done using FAA/PMA parts that exist today.

    I'm not aware of any existing FAA approvals to install these FAA approved parts in aircraft that were originally certified with higher comps to lower with the intent of burning mogas.

    There are anti-detonation injection STC, the system takes some labor to install and kits are pricey, but that's another path to MOGAS for some.
     
  3. midwestpa24

    midwestpa24 En-Route

    Joined:
    Mar 4, 2016
    Messages:
    2,972
    Display Name:

    Display name:
    midwestpa24
    Yeah they pretty much do these days. Either that, or they have to have the tanks totally cleaned after loads to avoid contamination. I don't believe any pipelines will carry leaded fuel anymore either, its all being trucked.

    Thats where I keep saying, the QA/QC in the supply chain for aviation fuels, both Avgas and Jet-A, are much different than your regular auto fuels. Every step of the way the fuels are tested for contamination. There is careful consideration of what trucks are carrying it, it is not allowed to intermix with other fuels. Your auto gas gets mixed all the time. Regular/premium, ethanol/no ethanol, all come from the same place same truck, and not a lot of concern about mixing. Thats why even gas labelled no ethanol at the pump may easily have 1-5% ethanol just because they didn't get it all out from the previous load. That is not tolerable in aviation.
     
  4. GRG55

    GRG55 Final Approach

    Joined:
    Dec 29, 2015
    Messages:
    8,910
    Display Name:

    Display name:
    Aztec Flyer
    Second comment first - In our region, at least, the transporters are not legally allowed to use a tanker that has carried leaded aviation gasoline to carry any unleaded product unless it is first "de-contaminated" - an expensive cleaning process. So the tankers used for aviation gasoline are typically dedicated solely to that purpose as there isn't any other leaded fuel being delivered any more.

    To the question: In the northern Rockies and western Canada it is at the refinery. Our two main regional supply points are Phillips 66 at Billings and Exxon/Imperial at Strathcona/Edmonton, Alberta, Canada. Lots of fuel crosses the border both ways as these two refineries do not produce avgas continuously. Product is trucked some significant distances here in the mountainous terrain. Don't know if any of the west coast refineries in WA produce aviation gasoline any more. I believe BP Cherry Point only produces aviation jet fuel.

    Exxon Strathcona is the only refinery in Canada still producing aviation gasoline. Eastern Canada imports all of its leaded aviation gasoline from the USA. As I said earlier, aviation gasoline is transported quite large distances now.

    I would be surprised if ANY refiner allows a jobber to mix additives of any sort into aviation gasoline. As an example, one of the test standards aviation gasoline refiners must meet is a conductivity test. This is for the capacitance fuel indicator probes such as Cirrus uses. A couple of years ago the Strathcona refinery ran a whole batch that failed that test and for several months it supplied no aviation gasoline to the market while it got that problem sorted out.
     
  5. bnt83

    bnt83 Final Approach

    Joined:
    Dec 31, 2012
    Messages:
    9,408
    Location:
    Lincoln NE
    Display Name:

    Display name:
    Brian
    I've always wondered how the quality of AVGAS (100LL) changes over time, Some of these storage tanks at airports are huge and I cant imagine most of them are filled more than once a year.

    While the distribution of AVGAS meets standards does the gas you actually buy at podunk? Airplanes are falling out of the sky everywhere?


    Lets not forget there have been lyconisour powered RVs flying on ethanol for at least a decade now. Not 5 or 10% but 100%

    http://vanguardsquadron.com/Aircraft.aspx

    I understand the cross contamination argument but I think its a bit over blown. If the tanker is actually empty and you put 500, 1000, or 5000 gallons of AVGAS in it, it won't matter which petroleum was in it before, in practice operationally. Regulatory wise is another matter.

    Aircraft fuel tanks have all kinds of other chemicals in them that contaminate fuel like rubber, primers, sealants, lubricant, even biologicals all such tinny amounts it doesn't matter.
     
    Last edited: Dec 9, 2020
  6. Snowmass

    Snowmass Line Up and Wait

    Joined:
    Oct 31, 2019
    Messages:
    513
    Location:
    S.E. Arizona highlands
    Display Name:

    Display name:
    Arturo
    Yes! There is no rational need for unleaded AVGAS. All fuel was leaded until the 70s and the species survived. AVGAS use is utterly trivial and most is burned far away from people as opposed to MOGAS. I suspect the FAA was struck by a bolt of common sense and shelved the idea.
     
    kyleb likes this.
  7. midwestpa24

    midwestpa24 En-Route

    Joined:
    Mar 4, 2016
    Messages:
    2,972
    Display Name:

    Display name:
    midwestpa24
    A lot of smoke and mirrors there...trust me :thumbsup:
     
    nrpetersen likes this.
  8. DaleB

    DaleB En-Route

    Joined:
    Aug 24, 2011
    Messages:
    4,747
    Location:
    Omaha, NE
    Display Name:

    Display name:
    DaleB
    What smoke and mirrors, specifically? Their claim is pretty straightforward... is it not true?
     
  9. midwestpa24

    midwestpa24 En-Route

    Joined:
    Mar 4, 2016
    Messages:
    2,972
    Display Name:

    Display name:
    midwestpa24
    They do use 100% ethanol, but it's far from bullet proof. They have a header tank of 100LL they switch to when needed.
     
  10. Spacedoc

    Spacedoc Pre-Flight

    Joined:
    Dec 11, 2019
    Messages:
    38
    Display Name:

    Display name:
    Spacedoc
    That may be true if it all got distributed homogenously across the planet as it burned. But there are a lot of neighborhoods around airports that have higher lead contamination levels. IIRC this is one of the arguments that the people trying to close Reid-Hillview are making.
     
  11. DaleB

    DaleB En-Route

    Joined:
    Aug 24, 2011
    Messages:
    4,747
    Location:
    Omaha, NE
    Display Name:

    Display name:
    DaleB
    Interesting. When would it be needed?
     
  12. 40YearDream

    40YearDream Pre-Flight

    Joined:
    Jan 23, 2020
    Messages:
    49
    Display Name:

    Display name:
    40YearDream
  13. midwestpa24

    midwestpa24 En-Route

    Joined:
    Mar 4, 2016
    Messages:
    2,972
    Display Name:

    Display name:
    midwestpa24
    If they encounter vapor lock in flight, or sometimes in starting from what I've seen.
     
  14. Doug Reid

    Doug Reid Line Up and Wait

    Joined:
    Dec 29, 2013
    Messages:
    546
    Location:
    North Carolina
    Display Name:

    Display name:
    Doug Reid
    Seems to me those folks need to be more concerned with drunk drivers around Reid-Hillview.
     
  15. Snowmass

    Snowmass Line Up and Wait

    Joined:
    Oct 31, 2019
    Messages:
    513
    Location:
    S.E. Arizona highlands
    Display Name:

    Display name:
    Arturo
    Yet the amount of lead is miniscule compared to the preceding 60 years when you were bathed in lead every day by millions of automobiles surrounding us. And we we advanced enormously in science and most scientists were living in that TEL pool and driving their own cars. I am not giving up flying nor driving based on this. But one could move to Antarctica and finally be safe.
     
  16. I Flied

    I Flied Filing Flight Plan

    Joined:
    Sep 7, 2020
    Messages:
    1
    Display Name:

    Display name:
    rr
    I am rusted out by 35 years but I recall the fuel truck had two grades of fuel in the 80's (80 and 100) and it seems reasonable (to me anyway) to have two grades now: unleaded and leaded.
    As I slowly make my way back to the sky, it seems there have been more than a few problems getting the lead out- the domestic engine manufacturers not being interested marketing new designs (co$t issues I guess), FAA not interested in new ideas, consolidation in the FBO fueling business- trying to wring out some profit by minimizing variables- fewest number of fuel types, reducing equipment and training expenses all come to mind.

    Wouldn't it be better for the many piston aircraft that can safely use unleaded do so? From the reading I have been doing the maintenance costs are reduced with fewer oil and spark plug changes and cleaner engine innards in general. Plus there's that slightly cleaner environment angle.

    What is odd is here in clean and green California unleaded is only available at San Carlos and its the new Swift stuff.

    Is there really not enough interest or is it willingness in adding unleaded as a fuel choice in the areas that have the volume of traffic to support it?
     
  17. CharlieD3

    CharlieD3 Pattern Altitude

    Joined:
    Jun 17, 2019
    Messages:
    1,759
    Location:
    Tennessee
    Display Name:

    Display name:
    CharlieD3
    The quickest, easiest solution to this is to make flying our "religion." The AIM is our "Bible." A flight is a religious "service" during which we commune with Sky (god).

    We (pilots in general and GA pilots in particular) are a minority population. We are ethnically and gender diverse.

    We even have annual pilgrimages to the "Mecca" of our faith, KOSH. To say nothing of minor pilgrimages to various other venues, some of which even provide "communion" consisting of pancakes and coffee on weekend mornings.

    In light of today's social norms, we DESERVE to be a "Protected Class," allowed to practice our faith with whatever vehicle we may have at our disposal with no constraints on what is required to fuel it.

    Additionally, all AMU$ spent in the practice of our religion should be untaxed.

    "Thus sayeth the prophet."

    AMUN!

    Jocularity folks, jocularity!
     
    ETres, Palmpilot, DenverDave and 6 others like this.
  18. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,133
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    Amen and Amen, lol.
     
  19. Jim K

    Jim K Cleared for Takeoff PoA Supporter

    Joined:
    Mar 31, 2019
    Messages:
    1,068
    Location:
    CMI
    Display Name:

    Display name:
    Jim
    Does this mean I don't have to pay tax on my airplane?
     
    aterry1067 likes this.
  20. CharlieD3

    CharlieD3 Pattern Altitude

    Joined:
    Jun 17, 2019
    Messages:
    1,759
    Location:
    Tennessee
    Display Name:

    Display name:
    CharlieD3
    Petition your congress critter... Get them to sponsor the Bill... Once passed by House and Senate, and enacted...

    You sir, will not have to pay taxes on your AC or anything expended for aviation!

    Beauty, right?
     
  21. Jim K

    Jim K Cleared for Takeoff PoA Supporter

    Joined:
    Mar 31, 2019
    Messages:
    1,068
    Location:
    CMI
    Display Name:

    Display name:
    Jim
    That sounds like too much trouble. I'm just going to call it a protest. Against gravity.
     
    CharlieD3 likes this.
  22. CharlieD3

    CharlieD3 Pattern Altitude

    Joined:
    Jun 17, 2019
    Messages:
    1,759
    Location:
    Tennessee
    Display Name:

    Display name:
    CharlieD3
    A flying autonomous zone? I like it!
     
    Jim K likes this.
  23. clear_prop

    clear_prop Pre-takeoff checklist

    Joined:
    Jul 5, 2012
    Messages:
    102
    Location:
    San Jose, CA
    Display Name:

    Display name:
    John
    Airnav and Skyvector let you search for Mogas.
     
    MarkH likes this.
  24. Computerjim

    Computerjim Pre-takeoff checklist

    Joined:
    Oct 3, 2013
    Messages:
    102
    Location:
    Pine Shadows Airpark - N Ft Myers, FL
    Display Name:

    Display name:
    JimISC2452
    It is current and accurate. Big bore Lycomings (IO540’s) and Continentals require 100 Octane because they run higher compression ratios. I own and operate three of them! Nothing to do with radials.
     
  25. Computerjim

    Computerjim Pre-takeoff checklist

    Joined:
    Oct 3, 2013
    Messages:
    102
    Location:
    Pine Shadows Airpark - N Ft Myers, FL
    Display Name:

    Display name:
    JimISC2452
    It is added at the refinery. Av gas is shipped by truck and barge is a fuel only containers. Dedicated trucks and barges. It is not sent through pipelines. That is part of the reason is is much more expensive the mogas.
     
  26. kyleb

    kyleb Final Approach

    Joined:
    Jun 13, 2008
    Messages:
    5,771
    Location:
    Marietta, GA
    Display Name:

    Display name:
    Drake the Outlaw
    No doubt the high compression engines need hi-test. The aircraft which used a lot of 100LL, and needed it (the radial engined freighters, fire fighting aircraft, and ag aircraft) are no longer in commercial service. Those were the ones which drove the "70% of 100 LL goes into the small % of aircraft which must have it." statistic.

    Most of the freight, firefighting, and ag stuff is turbine powered today.
     
  27. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,133
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    But does that mean they won't run just fine on 94UL? At what load/rpm do they start to suffer from detonation? If they start to detonate at max rpm, would planning a limitation of 100-150 rpm less make the aircraft useless or undesirable? These are the kind of things that the 94UL testing is supposed to sort out. Not a flat out "100LL is what was specified by manufacturer so that's all that can be used".
     
  28. hindsight2020

    hindsight2020 Final Approach

    Joined:
    Apr 3, 2010
    Messages:
    5,047
    Display Name:

    Display name:
    hindsight2020
    8.5 CR NA doesn't need 100 octane in my anecdotal experience. The issue with low wing spam/negative pressure spam cans was their plumbing wasn't resilient to mogas vapor pressures aft of the firewall. Avgas blend doesn't have that problem. It's not a detonation issue for the recreational players (turbo-supercharged notwithstanding).

    I continue to challenge the "20 burns 80" trope in this decade.
     
  29. kyleb

    kyleb Final Approach

    Joined:
    Jun 13, 2008
    Messages:
    5,771
    Location:
    Marietta, GA
    Display Name:

    Display name:
    Drake the Outlaw
    Read the report I linked earlier in the thread. Combustion chamber size and compression ratio are the biggest drivers. Higher RPM actually helps. That's why you see bikes with tiny cylinder volumes and 12:1 compression do OK at 10,000+ rpm on pump gas.

    To make the high compression (higher than roughly 8.5:1), big bore engines happy on 94 octane would mean reducing compression ratio, which hurts efficiency and power.
     
  30. OneCharlieTango

    OneCharlieTango Pre-takeoff checklist

    Joined:
    Dec 21, 2018
    Messages:
    242
    Display Name:

    Display name:
    OneCharlieTango
    ISTM this is more true than ever. Every year, more pre-1976 airplanes become scrap, and Cirruses, etc become a higher percentage of the total fleet.
     
  31. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,133
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    I understand that the big bore engines will need higher octane at an earlier point than a small bore. That isn't the point. It's that you're assuming the octane needed to operate an IO-540 is above the 94UL currently offered. Has there been definitive proof of that, or are you just speculating? Absence of an STC isn't evidence, either.
     
  32. kyleb

    kyleb Final Approach

    Joined:
    Jun 13, 2008
    Messages:
    5,771
    Location:
    Marietta, GA
    Display Name:

    Display name:
    Drake the Outlaw
    Go look at the report I posted. The curves are all in there. You will not find better information than that report.

    Anecdotally, the RV crowd is largely in agreement that you're gonna need 100LL to be happy running a C/R of >8.5:1. And the hardcore RV guys are a bunch of cheap gearheads, so if they thought it was OK, they'd happily use pump gas in hopped up engines.
     
  33. hindsight2020

    hindsight2020 Final Approach

    Joined:
    Apr 3, 2010
    Messages:
    5,047
    Display Name:

    Display name:
    hindsight2020
    The NA IO-550 is a 8.5 CR though. No different than the O-320-D3G was in my Warrior II. No need for 100LL. And in the case of the Conti it's even better than the Lyco injected offerings, since the former has return fuel lines. Nothing a pair of electric pumps at the wing root couldn't solve anyways, on a million dollar toy mind you.

    The turbo Cirrus otoh, I can see how they can't get the temperature in that compartment to play well below the ASTM D910 standard, so going 100LL is an easier boilerplate answer.

    Still looking for that market survey research data that supports the proverbial Cape Air single handedly steering the piston fuel flowage. Waiting for Godot...
     
    Last edited: Dec 12, 2020
  34. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,133
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    The report does not really allow one to extrapolate what happens with a 94UL fuel mixture in a large bore Aviation engine as best as I can tell. The graphs generally showed no data past 90 octane from what I saw. It also cited the potential variability in cylinder head design, not to mention the fact that the octane calculation method has changed since this report was done back in 1962. Its not that the report isn't relevant, just that I don't believe the data set is large enough to encompass what we're discussing here. 94UL isn't "pump gas" and if the IO 540 (or similar) are 8.5:1, it may be possible to run them without issue as long as you aren't "lugging" the engine.
     
  35. FormerHangie

    FormerHangie En-Route

    Joined:
    Oct 28, 2013
    Messages:
    3,336
    Location:
    Roswell, GA
    Display Name:

    Display name:
    FormerHangie
    I'm looking at the "airborne aircraft by type" page. First on the list, the most common type showing up there, is @Tantalum 's least favorite airplane, the Cessna 172, with 565 airborne The next most common GA type is the Piper Cherokee of the PA-28 persuasion, with 244 flying. Number 3 is the Skylane, with 146. Fourth is the SR-22, with 73, After that, it's the C-150 with 62, C-152 with 46, M20 with 45, Bonanza 36 with 32, and the DA40 with 29. It starts thinning out from there, with a few other types having more than 20, and a number having less. So, yes, I believe there is an 80-20 or thereabouts split, but the 80 and 20 are reversed from what "everybody knows".
     
    clear_prop and hindsight2020 like this.
  36. kyleb

    kyleb Final Approach

    Joined:
    Jun 13, 2008
    Messages:
    5,771
    Location:
    Marietta, GA
    Display Name:

    Display name:
    Drake the Outlaw
    Which is what I've said all along. 8.5:1 or below should be fine on the lower octane (lower than 100 LL) fuel. The STC's alone tell us that.
     
  37. SoonerAviator

    SoonerAviator Final Approach

    Joined:
    Jul 21, 2014
    Messages:
    6,133
    Location:
    Broken Arrow, OK
    Display Name:

    Display name:
    SoonerAviator
    STCs take time and money. They also didn't have the ability to use 94UL until very recently. So, no, the STCs don't tell us anything other than aircraft with an existing STC to use MoGas should likely be fine on 94UL. It doesn't mean that a big bore with no STC for MoGas will not be able to use 94UL.
     
  38. kyleb

    kyleb Final Approach

    Joined:
    Jun 13, 2008
    Messages:
    5,771
    Location:
    Marietta, GA
    Display Name:

    Display name:
    Drake the Outlaw
    Look at the the engines you're talking about. The IO-550's are a good example. Here's Continental's sales brochure. All of the 8.5:1 engines require 100LL. They do have a 7.5:1 version that shows 94UL as approved.

    http://www.continental.aero/uploadedFiles/Content/Engines/Gasoline_engines/550AvGas-SpecSheet.pdf
     
  39. Snowmass

    Snowmass Line Up and Wait

    Joined:
    Oct 31, 2019
    Messages:
    513
    Location:
    S.E. Arizona highlands
    Display Name:

    Display name:
    Arturo
    If you had to use 94 in a 100LL octane engine in an emergency keep the MP low, CHT low and the RPM at redline. Higher RPM has the effect of retarding your fixed spark as the piston will have moved further down the cylinder as the flame front burns across the combustion chamber.
     
    SoonerAviator and kyleb like this.
  40. PaulMillner

    PaulMillner Line Up and Wait

    Joined:
    Jan 14, 2011
    Messages:
    560
    Location:
    Berkeley, CA
    Display Name:

    Display name:
    Paul Millner
    There's a lot of speculation in this thread, even about things that are easy to Google... whatever. Maybe no one wants to see the actual answers, but just in case, here you go.

    [First the disclaimer, I was an engineer at Chevron for 38 years. The last decade plus, I was involved in unleaded avgas development, until Chevron became so frustrated at the FAA's inability to understand science that they walked away (as did many of the majors). I've provided some small consulting to Swift and GAMI since then, but am not privy to their confidential stuff, and am not representing either of them in expressing my observations on the passing scene.

    While the FAA's PAFI (Piston Aviation Fuels Initiative) is stuck, because ignoring science is a bad approach, there are four companies working the issue. In diminishing order of successful probability, IMHO: GAMI, Phillips, Swift, and Shell. Let's look at each approach.

    GAMI has been working on this issue since 2010, and they do observe the science. Their formulation and additives have evolved impressively. The FAA has streamlined (!) the approval process, and GAMI is about ready to begin the final testing, which will hopefully lead to limited approval next year. That will probably result in fleet trials, maybe at a flight school or two, leading to a subsequent AML (approved model list) approval for all 100LL consuming aircraft.

    Phillips came to this game late, announcing at Oshkosh last year and giving a technical seminar. They plan to replace the lead with Methylcyclopentadienyl Manganese Tricarbonyl (MMT). Manganese is much less toxic than lead, although when MMT was used in mogas, principally in Canada, there were issues with spark plug fouling. Phillips thinks they know how to devise a scavenger for the aviation application that will spare our expensive plugs... I'm guessing a molecule that was considered too expensive to be competitive in mogas, but avgas' higher margins make it feasible. Based on last year's update, they're likely a year or two away from fleet trials.

    Swift seems to be struggling a bit, but the underlying science should be workable. I'm not sure they have the resources to get there. Swift is selling an interim 94UL fuel that they plan to discontinue when the 100UL is available. Folks are concerned that the supply logistics on that fuel seems sketchy, and what that might imply about Swift's viability. It may only be a learning curve experience for them. I wish them well.

    Shell was the primary contender in the FAA's PAFI, and that effort was not successful, even after the FAA changed the rules to accommodate them, versus being left with no players after Swift withdrew from PAFI. It's important to note that it's NOT the Shell refining company that's pushing this effort. Instead, it's kind of a speculative effort by their Global Solutions company, which was spun off a few years back. They're hoping to develop a salable solution, rather than developing a solution for the Shell corporation. Don't know if they'll persevere, or succeed, with their heavy-alcohol approach. Paul]

    >> It's not the politics that has held up this change, it's that pesky physics thing. It's got to support the high compression engines which burn most of the 100LL

    [It's a combination of factors... The FAA has to follow the scientific method, but as a federal agency is an inherently political animal. So it tends to be a combination of confounding factors. Paul]

    >> Maybe they need to reduce the compression in those engines. Not a big deal to change pistons. Otherwise unleaded mogas can offer a real solution.

    [The certification burden is enormous for the fleet... each engine/airframe combination would have to be recertified, with new performance tables compiled from flight testing. This is a very expensive effort... and not one popular with aircraft owners, as it will result in reduced gross weight and performance. No one is excited about spending the money to make that happen.]

    >> It's been 25 years since EPA ban on lead in fuel, just how long do you think Kerry and the new administration are going to wait.

    [You overlook that the EPA and FAA duked this one out in Federal Court during the W administration (the White House didn't want to take the heat, I guess). The SCOTUS decided that the FAA is in charge of avgas regulation, so the EPA sits by waiting for the FAA to do their thing. The EPA could make a finding of endangerment, that might adversely motivate the current producers of leaded avgas. But, that didn't happen under 44, and I think Biden et al might be more interested in observing Supreme Court rulings in letter and spirit than running roughshod over them. Paul]

    >> will this lower the price for avgas

    [It's hard to say. The unleaded fuel will probably cost slightly more to make, say another 25 cents per gallon. On the optimistic side, since high-liability lead facilities aren't required, any number of additional blenders might choose to enter the marketplace, introducing more competition than currently exists. My guess is avgas prices will be roughly the same: at wholesale, avgas sells at 80 cents to $1/gallon more than premium unleaded. Paul]

    >> Mogas isn't really a replacement. The vapor pressure is too high. A good chunk of the fleet would have to be retrofitted with in tank boost pumps to keep airframe fuel lines from forming vapors.

    [There's a number of issues with mogas, although in the summertime mogas vapor pressure and avgas vapor pressure are nowadays about the same. Ethanol content and octane are the big show stoppers. Paul]

    >> The mogas you buy at the Texaco station doesn't have the QC/QA that aviation fuels do.

    [That's true.]

    >> Probably would also need to go to electronic ignition with knock sensors and variable timing... more money.

    [There are technical problems with knock sensors in aviation engines; lots of the aerodynamic noise looks like knock to conventional sensors, which is why GAMI tried developing fiberoptic based sensors. But none of that is certified and ready for prime time. And you're right about more money. Paul]

    >> Unleaded avgas can be made to equal the current 100LL... I do not know what the holdup is.

    [There were subtleties when one starts looking at the entire fleet, and then there's the certification process itself. The FAA has very limited experience in certifying fuels, and has made missteps. Paul]

    >> Environmental benefit? The amount of aviation fuel used is microscopic

    [Perhaps, but there's no safe lead exposure... from molecule one the best we understand it, lead exposure to children reduces IQ. Today, 1/3 of the lead entering the ecosystem is from our microscopic avgas use, so it needs to go away as a matter of social policy. There are studies implicating the one remaining tetra-ethyl lead plant in Liverpool, England in adverse impact on children down wind. How does one stand tall about that? Paul]

    >> leaded gas supposedly helps lubricates the valves, but I think that can be addressed in other ways.

    [Leaded gas is actually bad for the valves. There's scholarship and industry papers explaining that the valve problems we saw when lead was phased out of mogas came from the drop in octane, not the lack of lead; and the FAA has done at least one validating study on aircraft. Paul]

    >> Ethanol contamination is a ridiculously easy check. Just add 10% water, shake, & see if the apparent water volume increases.

    [So, what do you do if your airport tank is full of mogas-derived avgas that flunks that test? It's not pretty. It needs to be controlled for upstream, not remedied after the fact. Paul]

    >> high temperature and high humidity reduce horsepower now, yet we accept it. Maybe just reduce the max gross weight?

    [But the impact of temperature and humidity can be calculated in an FAA-approved manner, per the POH and the AIM. To reduce horsepower will require a similar certification effort with flight testing, and that's expensive. Paul]

    >> Not interested in paying for expensive engine modifications to burn lower octane fuel and thereby get less horsepower, less gross weight, less climb performance, less speed?

    [Don't forget, less range too, as fuel efficiency declines when you reduce compression ratio. The lower compression turbo Cirrus burn a gallon an hour more than the more efficient turbonormalized Cirrus with higher compression ratio. Paul]

    >> Kwik Trip has 91, no ethanol.

    [Don't forget the plethora of different octane scales. That Kwik Trip 91 is actually about 86 octane on the aviation octane scale... Paul]

    >> Many of the QuikTrip locations have pure-87.

    [OK, that's about 82 octane on the aviation octane scale. Paul]

    >> You're overestimating the impact of a reduction in compression ratio. It would likely result in less than 5% decrease in peak HP.

    [I don't think that's the issue as much as the certification and modification expense. Paul]

    >> There are more turbo-charged engines in autos today than ever before, and most are running 87 to 91 octane

    [They're accomplishing that today with scheduled direct injection which doesn't seem to work well with very large diameter pistons, say like in aviation engines. And the certification burden would be significant. Paul]