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Glad to hear that increasing the exit area appears to have
been the magic bullet. Dealing with air flow is a bit like
magic. There are so many factors that can be interacting that its
tough to get a handle on it even with data collection and analysis.
But, your results shows the 1st order
effects.
Sufficient intake area (which you have)
Sufficient core area (which you have)
sufficient exit area (which you now have).
Easy said, sometimes hard to figure out though.
Good work, Dennis
Ed
----- Original Message -----
Sent: Saturday, September 29, 2007 9:20
AM
Subject: [FlyRotary] Re: RV-7A
Cooling
Ed had asked the following:
I still believe you
need to divide you plenum vertically - have you tried that, I know you tried
several things, but I don't recall whether you tried that approach.
Perhaps as you suggested having more exit opening would help as well as your
cowl pressure seemed a bit high near your core
exits.
Ed
You asked if I had divided my inlet plenum to
divert more of the water cooling air into the oil cooler. The attached
picture shows a 1/8 inch thick foam board with a thin layer of glass cloth
covering it. I installed the diverter and flew several times. No
measurable improvement was noted. It probably helped some but I needed
quite a bit more! The picture also shows some white vanes I installed on
the rear half of the oil cooler - left side in plenum. I had thought
that the air flow was having to make too big a direction change at the
radiator face. The vanes did not improve cooling of the oil
significantly either. Bobby H. brought over a spare radiator and we
tested it on our improvised wind-tunnel at 90 deg. to the air stream and 30
deg to the air stream. The duct leading to the radiator was shaped so
that the radiator surface area receiving the air flow was kept the same in
both tests. Using a very sensitive velocity measuring device Bobby
provided we found that the exit velocity was 28.7 mph at 90 deg - in this test
the air went straight through the radiator fins. With the radiator at 30
deg. to the air stream the air had to turn 60 deg to go through the
radiator. The air speed behind the radiator at 30 deg was 28.0
mph. This test proved my suspicion that the radiator fins were causing
turbulent flow at the surface of the radiator was WRONG! This was
Good News to me because it meant my oil/water cooling system
probably could be made to cool without major redesign.
I have made 3
flights recently with static pressure, dynamic pressure and temperature probes
under the cowl. After reviewing the data, I made a change to the cowl
outlet area and flew again. The cooling was GREAT. My oil/water
cooling system will work. I'll post pictures and results soon.
I need to do some more flight tests to determine if I will need any sort of
cowl flap or not. My water was much cooler and the oil stayed
below 210 deg. F. while climbing at 25 in MP. to 6500 ft. Also
additional tests may show that I can blank off some of the water radiator
surface to force more air into the oil cooler. Only testing will
tell!
Some time ago I modified the James cowl by cutting the upper
inlet hole just below the spinner. This opening provides combustion air
to the engine. A fiberglass plate was installed to separate this
combustion air inlet from the oil/water plenum. This increased my
manifold pressure in cruise significantly.
Ed Anderson wrote:
Ed
.JPG)
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