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Bill Rumburg says he found it necessary to install a pilot controlable
throttle for oil cooler air flow in order to raise oil temp to the desired
180-190° range.
Bill, could you tell us a bit about the design of your engine/oil cooling
system?
Angier Ames
Angier -
Please pardon me for taking awhile to respond to this request, I've
just been very busy.
YES, this is a subject I'd like to address for the benefit of those
who haven't yet installed their system...
I used a "9" vane Stewart-Warner oil cooler and installed it in the
location suggested in the construction manual (lower left side of the
firewall), angled slightly from horizontal, given the direction of the
inlet/outlet. For whatever reason, I felt that the NACA inlet should
be located on the opposite side of the cowl and that now appears
to be THE way to go. You can then see that the inlet is angled
slightly upward (approximately 30 deg) when viewed from the front
of the A/C.
The NACA inlet I used is listed on page 101 of the June 1994
issue of LNN. It has a 3" outlet and is available from B&F Aircraft
Supply, Frankfort, Ill. (800) 345-2558. To obtain the proper size
cutout, I enlarged the one provided in the manual to 165%, but
check that yourself to be sure. I located it on the lower right side
of the cowl, far enough forward that the 3" SCAT outlet tube would
clear the gascolator cooling shroud. That will place it near the # 3
cylinder updraft tube, which is of no concern, just ensure that it has
at least a slight clearance for engine motion.
The 3" SCAT tube is then routed across the rear of the engine,
to the oil cooler inlet plenum.
***By the way, someone recently stated that he was now tired of
glasswork and especially did not like the thought of custom shapes
for firewall forward applications. Well, neither did I. So, I made
friends with a sheet metal shop supervisor who could make custom
aluminum shapes from sketches that I worked up. It was surprising
how well they turned out!!! I then had them powder coated locally.
The oil cooler inlet was one of these. I did the same for the filtered
air funnel (installed in the baffling, at the left cooling inlet), the
filtered/ram air selector and the heat muff air intake (also installed
in the baffling, near the left cooling inlet).***
You can mount the oil cooler with about 2" - 3" clearance to the
lower cowl and you SHOULD install an exit air plenum to duct air
to the louvers, which will develop a vacuum to efficiently draw out
the hot exit air. I did fabricate this from resin/fiberglass. It isn't
difficult. With the lower cowl in place, use a suitable piece of
Styrofoam (from an arts and craft shop) to develop the exact
shape. Cover it with clear package tape as a release, then lay-up
glass to form the shape. You will later have to add flanges to it for
attachment to the oil cooler flanges. Fabricate these separately.
Do this and you will have an excellent oil cooling system. On a
typical day of 60 - 70 degrees, my oil temps were running no
more than 140 - 150 degrees, even during repeated touch and go.
I then went back and installed a pilot-controllable butterfly (flapper)
valve in the neck of the oil cooler inlet (make the neck about 3" long
for SCAT attachment and to accommodate this). I made the flapper
approximately 2.75" round, of baffling seal material (cut half-circular)
sandwiched between two thin, round 2" aluminum plates, with a 3/8"
aluminum tube in the center as the actuator shaft. Use rubber
grommets to support the shaft where it penetrates the plenum neck.
Install a heavy aluminum actuator arm (I scavenged air throttle plates
obtained from Ken Brock for some of these components). The results
are now that I can easily set my oil temperature between 180 - 190
degrees, most days with the flapper 1/3 to ½ open. On the hottest
100 degree day, with the flapper wide open during climbout, it only
reaches 180 degrees.
For engine cooling, I used only a standard baffling/seal arrangement.
My CHT never exceeds 400 degrees during climb on the hottest days
and typically averages 350 degrees (sea level) to 370 degrees (8,000 ft.)
with usually no more than 5 degrees max between cylinders.
E-mail me for any additional info or questions !!!
Bill Rumburg
N403WR (Sonic Boom)
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