Fred Osborn wrote:

Paul,

One of the items that has us 6.5B people wondering is how to
distribute our excess oil, that is the oil that normally
would be used to cool and lube the second rotor. It would
seem a waste to just let the pressure regulator dump it back
to the oil pan. My choice would be to double the cooling oil
flow to our one rotor. Warm-up should not be extended much
since we will have less thermal mass and total oil volume.
Any wisdom from you and all others would be appreciated.

Fred O.

Sounds like a good idea.

Paul Lamar

If you double the flow of oil to cool the single rotor (I assume by enlarging the spray jet?), you
may actually INCREASE the rotor temperature. Curtiss Wright and Deere studied oil cooling, and
found that there is an optimum flow rate of oil though the spray jet. Too little will obviously
not cool, but too much will result in too much oil trapped in the cavities inside the rotor. The
theory is that a thin film of cooling oil needs to have a very short residence time in the rotor
for effective cooling. A larger volume with a higher residence time may have a somewhat insulating
effect.

I assume Mazda has studied this extensively, which is how they resulted in their rather complex
rotor cooling system. Granted that their objectives for the system are different for an automotive
appliciation than for aviation, and that some changes may be warranted for aviation use.

Why would a larger flow of oil have a longer residence time in the rotor? Because only the oil
delivery rate is controlled by the oil pump and spray jet size. The oil exiting rate is a function
of the instantaneous acceleration vector acting on the oil inside the rotor. This vector sometimes
points outwards and sometimes points inwards, depending on the position within the rotor and the
position of the rotor in its cycle. Yamamoto may have a diagram in the book. Since there is a
fixed time during which the vector will accelerate the oil out of the rotor, a larger supply
volume will lead to an accumulation of oil trapped in the rotor cavities. This may also in an
extreme case lead to a change in the balance of the system.

Jonathan Lauter
Rotary Power Marine Corporation
516-656-5685
www.rotarypowermarine.com

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