good, i made my point. for a while i thought i was being too obscure.Originally Posted by martymayes
good, i made my point. for a while i thought i was being too obscure.
There is no 91 "octane" auto gasoline. There is 91 AKI auto gasoline and higher in some areas of the country, 89 AKI auto gasoline or 87 AKI auto gasoline. In the Rockies there is even some 85 AKI auto gasoline. All auto gasoline, regardless of the AKI rating is made to ASTM D4814. Auto gasoline is not rated in octane like avgas. AKI stands for Anti Knock Index and is the average of a MON rating and a RON rating for the gasoline. That is why you see a label on every auto gas pump that says AKI = (MON + RON) / 2. The MON and RON ratings in this case are determined by very specific tests as outlined by ASTM and may have no relationship to the two MON numbers used for avgas. RON is never used in avgas ratings.
All avgas ratings are actually two MON octane numbers, for rich setting and lean setting, which as of late have been truncated to the lower "rich" MON octane rating. 100 LL is actually 100/130 avgas with 2 grams of TEL / gallon instead of 4+ grams of TEL / gallon for the older version, which is still sold as 100/130 avgas in a few locations in the world. All avgas, regardless of the amount of TEL and octane rating is made to ASTM D910. To add to the confusion there is also an 82 UL avgas specification which also includes 87UL (ASTM D6227), a 91 UL avgas specification (ASTM D7547) and a 94 UL avgas specification (ASTM D7592), none of which are produced commercially in the US.
So if you are going to put a placard on your gas tank, you need list the quantity that the tank will hold and all of the various fuels that you as the designer have determined will work properly in your homebuilt. If you are talking about auto gas, it needs to say 87 AKI min or 89 AKI min or 91 AKI min auto gasoline, or gasoline made to ASTM D4814, but not octane. If your engine will tolerate 100 LL and run OK on 91 AKI auto gas, you might want to include 94 UL avgas on the label, as it will probably become available in the future, especially when TEL disappears. 94 UL avgas is essentially 100 LL without TEL. (91 UL avgas is really a specification for DOD drones using the Rotax 914 engine and will probably never be found on a commercial field, even if the drones are operating there.) If you have determined that your airplane will run on swamp gas, you need to list that too.
The lack of desire to put a cluttered placard on my aircraft is why I'm glad my placards will simply read (depending upon the design):
"JET-A or JET-A1 only _______ gallons"
or
"100LL only _____ gallons" (or whatever equivalent is developed to replace it as a proper aviation fuel)
Unfortunately in science what you believe is irrelevant.
"I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.
i couldn't find a reference for that requirement. only the minimum fuel, not a requirement to list ALL the fuels. which is how we ended up with aircraft certificated for 80/87 using 100LL without fresh certification testing. where did you come up with that one?
maybe not, but i can get 91 AKI unleaded fuel at over a hundred marinas and nearby gas stations across Florida. 87 AKI at hundreds more. they taught the principle backwards in econ 101. it should be, demand = supply.
FAA AC 20-116
FAA AC 91-33A
Last edited by Mike M; 01-30-2012 at 04:03 PM.
Too bad I can't come up with one that will run on methane there seems to be an endless supply.
A label that reads, 80/87 Min, implies any avgas made to ASTM D910 with an equal or higher octane rating is permissible, unless the manufacturers know of some reason that 100 LL wouldn't work in an engine TC'd for 80/87, which they should have, because 100 LL with four times more TEL than 80/87 causes many problems in the old low compression engines. I would maintain 100 LL should never have been approved in those engines. However 80/87 Min avgas does not imply 87 AKI mogas which is made to ASTM D4814 and has no TEL, nor does it imply 94UL avgas which is made to ASTM D7592 because it doesn't have any TEL in it either. If you as the manufacturer determine that those fuels will work in your homebuilt you must specify them. If you as the builder design a cool replica with an old round engine of very low compression that was certified on 80/87 avgas, you might not be able to specify 87 AKI mogas, because your old round engine may require TEL for the valve seats.
As I explained in my previous entry 91 AKI mogas does not equal 91 UL avgas. One is Anti Knock Index which has a single MON rating corresponding to one test specified by ASTM that is probably around 88-89 MON and 91 UL has a minimum 91 MON at a different test specified by ASTM, but the MON is not lower than 91. You don't know what the MON is for mogas, it could be 87 or lower, as long as the RON is 95 or higher.maybe not, but i can get 91 AKI unleaded fuel at over a hundred marinas and nearby gas stations across Florida. 87 AKI at hundreds more. they taught the principle backwards in econ 101. it should be, demand = supply.
oh. learning is a wonderful thing, it helps me not appear so stupid and inflexible. these also helped me:
http://www.lycoming.com/support/tips...els/index.html
http://www.lycoming.com/support/publ...fs/SI1070Q.pdf
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