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Mogas Octane

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We are starting to plan for our trip to Page from PA. http://www.flyunleaded.com/airports.php has the airports that sell Mogas by State. But, most of the airports are offering less than 91 octane. It's been discussed that you can mix 87 and 100LL at a 50/50 ratio and be OK. If the airport is selling 89 octane or even 90 octane, what would be a safe mixture?

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We are starting to plan for our trip to Page from PA. http://www.flyunleaded.com/airports.php has the airports that sell Mogas by State. But, most of the airports are offering less than 91 octane. It's been discussed that you can mix 87 and 100LL at a 50/50 ratio and be OK. If the airport is selling 89 octane or even 90 octane, what would be a safe mixture?

 

I'd plan based on airports you want to visit, not fuel available.  Bring some Decalin to treat it, and run 100LL.  It won't hurt anything to run 100LL for a few days out of the year.  That's what I did going to/from Oshkosh.

 

Just IMO of course, freedom of choice is a grand thing!  :)

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I'd be reluctant to use anything other than 91 or 100LL. I believe that car gas degrades overtime, loosing octane and therefore useless you can be sure of fresh gas, like from a gas station that is busy, you might be calculating octane with erroneous data. The risk of detonation outweighs the risk of lead build up which can be mitigated by more frequent oil changes and or use of scavenging agents.

I'll be interested in seeing what the Rotax guru's have to say.

See you in Page!

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It's basically math for final blended octane.  ROAN has a paper on it: http://www.rotax-owner.com/pdf/AvgasAutogasMixing.pdf

 

 

Method: -100LL has a minimum motor octane of 104 -Regular automotive gasoline (87 AKI) has a minimum MON (motor octane number) of 82.5 You can get a fairly close guess of the octane number by multiplying the MON by the percentage of that fuel in the mixture. EXAMPLE 1: 50% 100LL and 50% Regular (104 x .5) + (82.5 x .5) = 93.25 MON (rough approximation)

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I have 91 no ethanol fuel at my airport. I don't sell it, but you can have some if you reimburse me for my cost. I also have jugs and a courtesy car if you would rather go that route. I likely could find a empty hangar if you wanted to make a overnight stop too.

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Tip,

 

I use Decalin whenever I travel to combat the lead deposits caused by the 100LL.

The Decalin changes the by product of lead oxide to lead phosphate after combustion, which will do no harm to the valves or seats.

 

I used it when I had my challenger. After using the Decalin for awhile, I took the exhaust manifold apart to look at the piston crowns. There were no lead deposits there or on the spark plugs. It works as advertized.

 

It acts like TCP but can be carried inside the aircraft. I believe the mix ratio is 1oz to 10 gal fuel.

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Hi Tip,

 

I wouldn't loose any sleep over the small amount of 100LL for just that trip. In the life of the engine it won't make any real difference.

use the Decalin.

 

p.s.

You can mix 87 with 100LL at a 50-50 blend  and be just fine.

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1) "Shandy" is a new one on me.

 

2) Using MOGAS when able, then 100LL when unable, often mixing appreciable amounts of each, is such a common practice that if mixing MOGAS and 100LL had deleterious effects I think we'd know about them by now.

 

Has anyone heard of a single incident/accident caused by mixing fuel types?

 

Sounds bogus if you ask me.

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I do not know the answer to your question. For an alternative perspective, see http://jabiru.net.au/Manuals/Engine/JSL007-5_Fuel_Guidance.pdf

 

Look at page 5, section 2.3, regarding mixing motor fuel with aviation fuel. I have no idea if they are correct on this point, but it gave me pause.

 

I've heard that before and it's a crock of shit. Both AVGAS and MOGAS are controlled standards, and they are required to be compatible with other blends under their own categories. If there was a problem with "Shandys", it would affect all fuel mixing between the categories, not just a couple.

 

What's more likely to happen is the octane number drifting a bit. We use 93 primarily because it's what is available around here, but also because it gives us 2-3 points of buffer.

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1) "Shandy" is a new one on me.

 

 

 

Pop into a pub and ask for a pint of shandy - you get half a pint of bitter and half a pint of lemonade - very refreshing on a hot summer's day (and of course we get lots of those  :giggle-3307: )

 

But I've never seen "shandy" used for a fuel mixture before, must be an Aussie thing?

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Morden is correct on this one.  You can mix them, but why chance a lower octane?  Just buy some Decalin and use 100LL. 

 

Mogas does not degrade any faster than Avgas.  And you can use 91E10 right out of the pump...no need to look for or use non ethanol gas.  The most important issue is to be sure to do a fuel check before each flight looking for dirt/water and adequate reserves.

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Pop into a pub and ask for a pint of shandy - you get half a pint of bitter and half a pint of lemonade - very refreshing on a hot summer's day (and of course we get lots of those  :giggle-3307: )

 

But I've never seen "shandy" used for a fuel mixture before, must be an Aussie thing?

Then there's the old lager and lime which is quite refreshing. If you add lime to taste rather than drown.

 

Down in the southern parts of UK (where they don't say ya'll) they have a pint of 'bitter top' which unlike shandy has the lemonade poured on top of the beer. Only a narrow layer to taste the beer through. 50/50 is quite a large ratio, many prefer a 30/70 mix.

 

Not unlike adding decal in to 100LL…but more refreshing, for the pilot that is!

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"Mogas does not degrade any faster than Avgas. And you can use 91E10 right out of the pump...no need to look for or use non ethanol gas. The most important issue is to be sure to do a fuel check before each flight looking for dirt/water and adequate reserves."

 

If I have mogas in the tank and there's only 100LL available then I'm happy to mix the two. I add Decalin in proportion to the amount of 100LL added.

 

I'm fortunate to have a field not far away with 93 non-ethanol on the pump and a gas station nearby that sells 93 non-ethanol at $2.99 gallon.

 

For me if non-ethanol isn't available then I'll add 100LL before I'll add an ethanol mogas blend. For me the corrosive aspects of ethanol are potentially worse than the lead from the small amounts of 100LL I use. So far this calendar year I've only added 2.5 gallons of 100LL the rest has been 93 non-ethanol.

 

I anticipate a longer trip to the northeast this Fall where 93 non-ethanol is scarce so I anticipate a couple of tankfuls of 100LL.

 

I just completed the annual and the mechanic found only a trace of lead at the bottom of the oil tank. Initailly, I used 100LL exclusively for the first few months of ownership adding Decalin and I've had excellent results with the Rotax operation.

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back on the subject

having half tank of Mogas and putting half tank of Avgaz ..with the recommended ratio of Decalin.

This will make the total fuel dilute the Decalin by half the ratio.

should I put more Decalin ?  I think NOT,,,,, but i want an expert advise

thanks

 

 

B0B571D5-0336-4851-AB91-E26884355ABA.jpeg

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50.2 liters is 13.2 gallons.   Whether you put in 1/4 oz of Decalin or the 1/2 oz Decalin is fine. Putting in the full 1/2 oz won't hurt a thing. Both the Decalin and auto fuel will help delete the leading affects of the 100LL.

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I would stick with Decalin.

TCP has harsher chemicals and is not supposed to be carried in the cockpit. Decalin is a better choice and a newer product compared to TCP.

TCP can ruin your paint if not wiped up.

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I will cycle through the brand new can of TCP first... and for now on will order Decalin.  Thank you for all of your valuable posts... helps a new owner like me a ton. 

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