Randy,
My large sharp
edged NACA duct is poorly placed on the left rearward side
of cowling. It enters a short flexible 3" smooth rubber sleeve
(plumber's sleeve) and then to a plenum above the small SW oil cooler
mounted to the fire wall. The bottom is open to the lower
cowl. I climb at about 135 KIAS and see cylinders occasional
reach 400 degrees on a hot day while the oil stays at 180. In
cruise in 30-40F temps, I must at least partially close the door
between the NACA and the cooler. Recently, in 10C temps, I had
to completely close the door to keep the oil temps about 180. In the
pattern at 100 KIAS I will see the oil go 190F or even 200F on hot
days because of lack of air thru the cooler.
It wasn't always that
way.
When I had high oil temps,
I tried a special cooler air exit to assist, no
help..
Another was to try exiting
thru shark gills on the side of the cowl, no help.
I temporarily attached a
scoop to force more air in the duct, no help.
I finally discovered that
the air was backed up in the NACA duct plenum (or chamber), thus
cutting off air flow. I used Micro to smoothly shape the
chamber, thus directing the air into its 3" outlet (no more dead
corners) with the results detailed above.
Good Luck,
Scott Krueger AKA Grayhawk
Lancair N92EX IO320
SB 89/96
Aurora, IL (KARR)
In a message dated 3/9/2009
12:41:32 P.M. Central Daylight Time, marv@lancair.net
writes:
Posted for randy snarr
<randylsnarr@yahoo.com>:
All,
Thanks for
the good suggestions on the oil cooler.
I flew again today
and my oil temps are at 208 F flying in 35 f air.
They will
be 215 or 220 this summer.
I will try a few solutions that
do not need to cut the cowl. I will most
likely make a duct to
carry the exhaust air from the oil cooler down to the
lower aft
part of the cowl. I have also heard that the aft vertical edge of
the naca opening should be shaped like an air foil. Mine is flat
and fairly
sharp. The easiest way to test will to be construct a
piece to give it a
little airfoil made from balsa or foam taped
in place and flight tested. If
that does not work, I will make a
duct from the cooler to the low pressure
area on the bottom of
the cowl and lastly would be a small lip on the bottom
of the
cowl aft.
every producton airplane I have seen with an
opening on the bottom of the
cowl has 45 deg lip to create a low
pressure area. I should have done that
before I
painted....
I will post my findings
when I get them.
Randy
Snarr
N694RS
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