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

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Paul-regarding the pros and con's of adding oil to wing tanks, that is what
we did with the RV-4 from 1988 to almost 1998 with two different prototype
rotary engines of varying configuration. Ditto the RV-3 which Alan flew with
our Mk II Superlight engine for five years from from 91-96 and the Mazda
conversion engine in 96& 97.  Often there were extended down times for both
aircraft at different times. In all those years we never had any operational
problems related to mixing oil with fuel in the wing tanks.

At first we assidiously mixed the oil with fuel when refueling but as time
went by, simply poured in the oil when fueling.  At one point the RV-4 was
sitting for over a year when a new engine was being produced.  We didn't
even periodically rock the wings when it sat in the hangar then or any other
for prolonged periods.

We never experienced a problem except when the driver was tired, lazy or
both flying from Little Rock, Oshkosh or some other such long haul to Oregon
in one day.  On those hot summer days or on other multi-state hauls, I
bitched about having to futz around with pulling the oil out of the baggage
compartment, dip the tanks to determine the correct amount of oil  for each;
decant the correct amount of oil for each then put everything away.  It was
not normally a big deal unless it was 105 degrees under a hot sun and trying
to keep the refueling stop time to a minimum.  Everett always maintained
completely tongue-in-cheek that it wasn't a problem for him (he would drive
the air conditioned motorhome to the destination airport of Oshkosh,
Lakeland, Arlington, etc. so we had a nice handy HQ and bunk).  The
convienence factor appears to be the one major argument in favor of some
type of metering pump and remote tank.  That is, unless, you forget to fill
up the oil tank and don't have a warning light or other device that reminds
the knothead behind the stick. But again, a metering pump, tank, lines, etc.
simply adds to the weight, complexity and failure modes of the installation.

Steve Beckham

Something for everyone to consider. On the last of the Kawasaki road-going two strokes they injected oil directly into the carb float bowl. Earlier they had it going to the carb inlets. Point being the thought was that mixed into the fuel was best. Once synthetic oil was available we took the throttle cable off the pure and ran on revs alone. Very lean mixtures were OK. They never stopped changing the oil injection set up. Lastly, they never ran oil injection on ANY roadracer. ALWAYS ran pre-mix. On your plane just record the gallons from the pump into each tank. That is plenty accurate for the mix.
Bill Jepson