> What is the best size NACA duct for the 320/360 oil cooler? It will be
> mounted on my firewall. What is the best location on the cowling for the
> duct? Is the pressure highest on the bottom?
>
> Bill Kennedy
> N42BK 90/90


Hello Bill,

We put our NACA duct on the left side of the cowling. We used the pattern in
the manual for the cabin air and blew it up to 2X on a copier. Behind the
NACA scoop, we have a gradually expanding plenum ending in a flange for 3"
scat tubing.  The scat tubing only bridges about a 3/4" gap to the plenum on
the oil cooler. Taking off the small piece of connecting scat tube allows
removal of the lower cowling while leaving the rest of the oil cooler
plumbing in place. We have the cooler (small 5 vane) mounted on the firewall
and it's plenum  gradually opens up to cover the entire face of the cooler.
It's sealed on with RTV so that no air escapes, every molecule that enters
the NACA scoop comes out the back side of the cooler.  No seperate exhaust,
it just dumps into the lower cowling area.

It works good...too good. I've never seen oil temperatures reach 180. Summer
climb is about 170 and summer cruise is 160 or so. If I were doing it again,
I'd make it the same except instead of blowing the pattern up to 2X, I'd
probably use 1 1/2 - 1 3/4X.  Let me know if you'd like pictures.

Bill
harrelson@erols.com
N5ZQ  LNC2  O-320  VA42  Fredericksburg, VA