OK, aero-rotary engine newbie question!

As I am reviewing numerous websites about the rotary engine applicability to
aircraft, it seems that more and more the issue of proper lubrication for
the rotor seals is one of, if not the, paramount concern.  At www.wankel.org
under the Aircraft Rotary Engine Best Practises the 3 options of

    a.    retaining the stock crankcase oil injection system,
    b.    mixing 2 stroke oil with the fuel, and
    c.    replacing the stock metering pump with one to inject 2
stroke oil

are reviewed and the advantages/disadvantages of each are summarized.

    Clearly retaining the stock crankcase oil injection system is at
best problematic and should not be part of any responsible and effective
aero-installation.
    While mixing the two stroke oil with the fuel during aircraft
refuelling would seem to be the most simple and straight forward solution I
have substantial concerns about keeping the oil properly and even
distributed throughout the fuel so that the fuel/oil ratio being sent to the
engine remains constant independent of how much fuel is in the tank.  (If
the oil has a tendency to separate and settle onto the bottom of the fuel
tanks then the mixture would start out oil rich and then become increasingly
oil-lean as oil/fuel is used.)   Problems could also occur when only
partially filling fuel tanks or "topping up" partially empty tanks - since
the proper amount of oil is a function of fuel added it seems the potential
to have too much or too little oil is quite high with resultant oil-rich or
oil-lean mixtures adversely affecting engine operation/reliability.
    Metering pump injection of 2-stroke oil would seem to be the best
solution but the best practises site cautions that this retains the "single
point of injection" problem of the stock system.  When reviewing a general
engine layout drawing of a 13B I notice two oil injectors per rotor, one in
the intake port runner and one directly into the rotor chamber.  I would
have expected that the intake air flow turbulence and fine oil misting
provided by the oil injector would have resulted in sufficiently thorough
mixing that the fuel/air/2-stroke oil mixture would effectively accomplish
adequate seal lubrication and that the chamber injected oil would serve to
provide an excess of oil thus erring on the side of safety.

    So, are my concerns about keeping the oil properly mixed and evenly
distributed in the fuel valid and if so what is being done to maintain
proper mixing?  Secondly how are people ensuring that the proper 2-stroke
oil/fuel mix ratio is maintained as fuel tanks are partially filled,
partially emptied and refilled in the course of normal aircraft operation?
(I would think that you would want to put the oil into the fuel tanks before
fuelling so that fuel "in-rush turbulence" would assist in mixing and
distributing the oil throughout the fuel volume, but at that point you don't
"know" how much fuel you will be adding and hence there is no "factual"
basis to determine how much oil to put into the tanks first.)
    Secondly, is there really a problem in distributing the oil evenly
over the rotor seal faces when using a metering pump that draws 2-stroke
oil.  At first review a replacement metering pump really seems to be the
ideal solution with the advantages of properly proportioned oil/fuel
mixture, constant mixture control independent of fuel reserves on board, use
of a 2-stroke oil tank for oil cleanliness, ease of adding oil when required
and the ability to carry sufficient oil in case of supply problems where
airports might not have 2-stroke oil readily or inexpensively available
when/where re-fuelling.  (No doubt there are other advantages of which I am
not yet aware.)

Comments, advise, suggestions please.

Thanks and Cheers
Good Building and Flying

Carl

Carl P. Lindon  B.Eng., CD.
Lieutenant (Navy)
DGIIP/DIRAP



I prefer mixing the two stroke oil with the fuel.
There is enough sloshing around in flight so keeping
it mixed is no problem. It lubes the seals better than injecting
oil.

Paul Lamar

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