OK back from Florida, Shady Bend  and Tracy's cooling test.

I am here to say that the difficulty of cooling a Mazda rotary engine
in an airplane has been greatly exaggerated. Its a myth for sure.
People are not paying enough attention to getting the air out of
the cowl. Making the inlets larger and larger will do absolutely
no good at all unless the outlets have two or three times more area
than the inlets. All you would be doing is adding drag.

In effect Tracy has been cooling his engine with only one of his
two radiators for the past five years despite a huge inlet on the
right side of his cowl.

Here is the last set of several sets of pressure data we measured on
his cooling set up. The hole behind the prop spinner was taped up in
an attempt to seal it. This made the pressure in the cowl about
a 1/2 inch of water higher pressure confirming what Jim Mosure discovered.
Apparently the spinner backing plate and prop bolts and nuts are function
somewhat like a centrifugal pump lowering the pressure in the cowl.

All numbers are in inches of water at 120 MPH

Front of oil radiator _______________6.36
Front of right radiator _____________5.11
Front of left radiator ______________8.36
In cowl behind radiators ____________3.61
Under fuselage behind cowl opening __0.86

The dynamic pressure at this 120 MPH speed is 7.6 inches of water.
The slip stream from the prop is increasing the pressure in
front of the left radiator apparently.

As you can see the pressure difference across the right radiator
is 5.11 - 3.61 is only 1.5 inches of water or about .055 psi
which is hardly enough to generate a gentle evening breeze.
In effect this radiator is not functioning. Well hardly at all.

In general the cowl pressure is much higher than it need be
judging by the near ambient pressure under the fuselage near
the cowl outlet opening. Tracy's airplane is in dire need
of a cowl flap down there. If Tracy installed a proper cowl
flap the engine would cool much better and probably with
smaller water radiators and cowl openings.

In the picture of the left cowl opening below one can clearly
see the static pressure tap using porous kitchen foam hot glued to
the end of the drip irrigation tubing.

For more pictures on the test see Tracy web site at:
http://www.rotaryaviation.com/

click on "What's new at RWS cooling Test."

Paul Lamar

I have lurked on here for over a year and I saw Tracy's airplane
at OshKosh last summer. When I saw the butchery on his RV4 cowl
I thought it must be real hard to cool a Mazda. I am not sure I want
to get into all that so I am sitting on the fence. From a business
point of view Tracy is sending a negative message. No telling how
many gear boxes and fuel injection systems he would have sold if
the cowl was more conventional looking.

Charles Wright

Who says he wants to sell more? You should have heard him complaining after
orders started rolling in after Paul's article in Sport Aviation :)

Finn

 
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