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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