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