In  eleven years of editing the newsletter nobody has complained about the
oil settling out of the fuel.  There are a couple of reasons for this.
When you start the engine the fuel pickup in the tanks is at the lowest
level generally so you might get an oil rich mixture (as I recall oil
floats on the top of the fuel) but that is soon returned to the tank by the
fuel pressure regulator recirculating the fuel.  At idle it recirculates as
much as 90% of the fuel flowing through the pump.


Paul Lamar


The real question would probably be best answered by those engineers
closely associated with 2 cycle oil and it's miscibility with aviation
or other
fuel.

Oil either mixes with fuel and stays suspended (dissolved for want of a
better word) or floats or sinks. It really can't do all three things.
It is
possible that it falls out of solution and then either one of the
other two
is  possible.  (If my limited knowledge of physics is still in tact.)
If it
floats, it will not collect at the lowest part of the tank (the sump)
yielding  an oil rich mixture. If it sinks it will not float on top of
the fuel
(unless  the various densities of hydrocarbons dissociate with each
other and
based on  their  density relative to water they either float or sink.

It might be an idea to, during your preflight, to vigorously shake the
wings for two purposes. 1, to mix the oil, 2 to check the continuity
of the
spar.

Just a suggestion.

Rich

 I have just tried this, 5 ml 2-stroke oil in 500 ml auto gasoline in a
 glass jar. The oil goes to the bottom. Part does dissolve quickly but
 the bottom half of the jar has all the color. The bottommost layer has
 the darkest color. It takes some shaking to get a uniform color. If not
 shaken, you will get a very oil-rich mix on starting.

 Al Rees

 That is interesting Al. Thanks for doing that. Let it sit for a week and
 see if it settles out on the bottom again.

 If the pump is pumping 20 gallons an hour
 and 90% is recirculated on start up and there is 1 oz per gallon in a 30
 gallon
 tank that means there will be 30 oz in the bottom of the tank. Or.234
 gallon
 of oil. 18 gallons per hour divided by 60 is .300 gallons per minute. The
 oil will
 be sucked up in less than a minute and squirted back into the top of the
 tank.

 Check my arithmetic.

 Paul Lamar

Paul,

A quick real world observation...  My Lancair holds 96 gallons, 47.5
gallons
per tank; I add 1 oz. 2-stroke oil/gallon for a total of 96 oz. oil.  If
the
oil settled to the bottom of the tanks, even a little, I would expect to
see
a cloud of blue smoke on startup. Since this isn't the case, I've
concluded to my personal satisfaction that oil settlement isn't a
problem.  My observation is null and void if you're burning something other
than 2-stroke.

Mark

I was looking at the Lancair web
Site and I did't see 96 gallon tank is this a factory option or
Your own mod.

Clifton.

Clifton,

Extending the fuel bays is a pretty popular mod.  You just add the "mouse
holes" into the next bay and move the fuel cap out an equal amount.  You
don't have to fill it to the rim, but it is nice having the extra range,
especially when you're trying to run only mogas.

Concerning the mixing of the oil, I use a fuel trailer to haul the fuel.  I
add oil to the tank, drive up to the station and get the fuel.  It is
thoroughly mixed by the time I return to the airport.

It is a different story when buying gas from the FBO.  Then I add the oil
first, then the fuel.   I run the fuel pumps for a minute or so before
starting the engine, and by the time I have taxied to the threshold, things
are well mixed.

Mark