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I probably have used the wrong phrase in saying that the fuel 'loses
octane'. Old gas definitely causes a loss of RPM in the spring though - I
usually gain a few hundred RPM after my first fill up in the spring. This
year was a bit more of a fight then usual to get the bike running again
because I couldn't ride it at all last summer, it wouldn't run at all
without at least 1/2 choke and even then it was pretty rough until I topped
the tank with premium.
While we're walking down memory lane, I faintly remember that the octane
rating was originally a measurement of the percentage of the fuel which was
Octane molecules (a relatively round hydrocarbon molecule with very low
knock tendencies) as opposed to another specific molecule (a linear shaped
molecule with very high knock tendencies). Ratings at/over 100 are a result
of additives with lower knock tendencies then even Octane.
I re-state that the above is a rather dim memory and might even be a
complete fantasy :) The only point from this direction is that old,
untreated fuel WILL have poorer performance then new out of the pump. Even
flying 1 tank a month will probably be enough that you won't notice the
difference.
Back to lurking....
Andrew
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Bryan
Sent: May 11, 2004 12:55 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Mogas issues
Correct me if I'm wrong but as I recall, octane is a rating based on the
stability of fuel (i.e.. resistance to detonation). The problem with
storing fuel is evaporation and water buildup due to condensation. Actually
the higher the octane the lower the energy potential of the fuel. It is
recommended for cars to use the lowest octane fuel available without getting
detonation.
Just some stuff I seem to remember reading.
Bryan
----- Original Message -----
From: "Andrew Stagg" <kastagg@shaw.ca>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, May 10, 2004 11:07 PM
Subject: [FlyRotary] Re: Mogas issues
> From up north: Ask any 'bike rider about using last falls' gas up in
> the spring and you'll have no doubt about mogas losing octane. If you
> know
that
> the plane will be sitting, you can always add a fuel stabilizer to
> prevent the evaporation (most riders add it as part of the fall
> 'winterization' prior to storage but others simply drain the tanks).
>
> Also, if the fuel is allowed to sit for awhile (usually 1 to 2 months
> is long enough) the float bowls and carburetors can get a coating
> build up.
It
> will rinse out as fresh fuel flows through. Based on the performance
> of
my
> old Suzuki, I'd guess that an airplane's carbs would be clean by the
> time you've finished a run-up.
>
> Andrew
>
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
> On Behalf Of echristley@nc.rr.com
> Sent: May 10, 2004 5:43 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Mogas issues
>
>
> I was asking someone very knowledgeable in the area
> of epoxy systems about gas tank sealants for
> composite tanks that can stand up to mogas. His
> response is below, and he brings up some issues that
> I've never considered. Transport will not be an
> issue for me, but what do those of you who've been
> flying with mogas think about the issue of smell and
> loss of octane?
>
> Could the latter be the reason that Rusty is seeing
> such poor static performance? The gas has been
> sitting to long and gotten a little rusty?
>
>
> > Jeffco makes a coating (tank lining system )
> specific for Avgas. It is
> > used in Lancairs. I don't know the number so
> you'll have to contact them.
> > Mogas stinks - literally. You'll have an
> airplane and a hanger that
> > smells like a jet ski . It makes passengers sick
> real fast. You will get
> > tired of the transporting hassles too. I've
> never seen any data on
> > storage stability, but I know the makers never
> plan on it being around much
> > longer that a few days. If you wind up not
> flying on a regular basis,
> > I'll bet dollars to donuts that it looses octane
> units with time - say 30
> > days or so.
>
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
>
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
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