NACA vent for oil cooler
 

My neighbor is building a 7A and is going to use a firewall mounted S&W oil cooler. He is thinking of using a 3" Naca vent mounted on the lower cowl with a very short run of Sceet tubing to the oil cooler.

Has anyone tried this method? Can't really see why it wouldn't work.

Darwin N. Barrie
Chandler AZ
RV-7 N717EE (30 hours)

Don't see why it wouldn't work, but also don't see the point. What's he hoping to accomplish that he couldn't do by taking air off the baffles?

Hi Darwin,

I did before in an RV8 with an IO360. I installed the NACA inlet on the right cowling side. It looked very beautiful. I used a 3" NACA and a hose with an Carbon inlet to the oil cooler, which was installed on the firewall.
Test running was a desaster. The oil temperature increased to almost 260?F. My fault: I forgot to install an extra duct for the warm air from the cooler direct to outside. The air pressure under the cowling worked against the incoming air from the inlet. No cooling at all.
Lesson learned: Install a seperate duct only for the oil cooler, that the air in and from the oil cooler will NEVER mix with air from the engine or exhaust.
In the meanwhile, NACA inlet is closed and the oil cooler is in the old fashioned place.

Stephan
RV8
D-EBRV
65 hrs
crankshaft broken

Naca vent
 

Hi Jeff,

The S&W 8432R cooler is larger than standard cooler and will not mount on the baffle in a conventional manner. I mounted mine on the firewall and used tubing from the baffle. I changed the routing of the tubing and have had really good results. He is trying to improve on that.

The way he is planning there will only be approximately a 10" run of 3" tubing with no bends at all. I hadn't thought of making a separate duct for the exit but that is a great idea. With no obstructions and a direct shot to the cooler it should work.

Any other do this?

I still like the idea of attaching it directly to the cowl, mounted over a set of louvers, and then running the scat from either the baffle or a naca duct to the front of it. That way the exit air is taken care of with little or no space wasted. I'll attach a couple of bad pictures in a minute.

Extremely Draggy
 

Refer to Speed with Economy, by Kent Paser
and NASA cooling drag studies.

It'll work from the stand point you'll have acceptable oil temps, but you
are creating massive cooling drag you don't need or want. There is no reason
to do this. You have plenty of air coming thru the existing cowl inlets.

Banner tow planes mount their cooler under the plane outside in the breeze.
That also works, but you would not go very fast in your RV with the cooler
hanging out. Adding an extra NACA scoop and ducting it into the cowl is
like hanging the cooler out in the breeze or worse.


Look at it this way, you are sucking in more air (cooling drag) with an
additional NACA scoop. Plus you have to shove that air out the same cowl
exit. Depending on how you duct the exit air from the cooler, you may
pressurize the lower cowl and reduce the pressure differential across the
cylinders, further reducing cooling efficiency. Unless you isolate the oil
cooler it is going to be fighting with the already over size cowl inlets. Now if
you duct the cooler with its own discrete inlet and outlet than you will avoid
that, but it's still more drag than if you used the typical installation.

One of the biggest problems with firewall mounted oil kits is the crappy
optional parts Van sells. They are just lousy. Search the archives about oil
coolers, ducts and you will find some good info. Bolting the cooler direct to
the baffling aft of the #4 jug works but I don't like it. I guess if you reinforce
the baffle and cooler enough it should be reliable, but more often than not
something will crack. A cooler full of oil and hoses hanging off it is a lot to
support on a shaking engine. I like to mount it just off the baffle on the fixed
engine mount tubing and coupe it to the back of the baffle for air with a flex
duct for air. Van's cooler air-box in his firewall kit is of poor design.
Although 4" duct is the theoretical ideal duct (for the SW 8604R cooler).
Usually 3"-3.5" is all that can fit. I would shoot for the largest duct you can,
may be 3.5". Since most of the off the shelf parts and duct flanges you can
buy are 3" or less, you have to make your own out of fiberglass. Also buy a
SW cooler. Steward Warner/South Wind is worth the cost. Don't be fooled
by SW "Styled" coolers. Most of the above may not be necessary for a O320
flown mostly in the cooler climates. A bigger engine in hot climates needs
more attention to cooler details, especially if you firewall mount it. Don't use
Van's cooler KIT. :eek: Pacific Oil Cooler can give you some advice:
http://www.oilcoolers.com/

My suggestion is follow what is known to work and don't out smart yourself
unless you know all the aerodynamics involved. The inlets of Vans cowl are
already too large, really. The Sam James cowls have approx 1/3rd less inlet
area and you don't hear about cooling problems with SJ cowls with the cooler
internal with no additional cooling scoop. It's not getting MORE air it is using
the air you have most efficiently. Hummmmmmmm :confused:

There is plenty of air with Vans axisymmetric cowl inlets to cool the engine
and provide air to an oil cooler. It is how you duct the cooler is critical.
Check the archives of this site and others.

George