While I was at the Sebring show today I found the air cam cooling
system to be rather odd but interesting. It's a twin pusher with the
radiators on the top of the wing and a NACA duct feeding from the bottom
of the wing. My question is this a efficient or good way of ducting air
and getting real good cooling results?

Tom/norpro

If I have to use a NACA duct the bottom of the wing is a good place
for it as it is a high pressure area. It all depends on the rad core
size.
Obviously it works for this airplane.

Paul Lamar


Airflow over the aircraft skin creates drag.
Airflow over the surfaces of the radiator creates drag.
If we could find a way to use the skin as a radiator then
could we get rid of the radiator drag?

Jeffrey John Martin

It's been done several times before. The Schneider cup racers used
it. You need so much surface area it rapidly becomes impractical
to cover the entire airplane with a double skin. The early P38's had a leading
edge double skin used as an intercooler. It was not enough so they
went to conventional intercoolers.

Paul Lamar


One problem is that these radiators are subject to damage.  A number of
early aircraft put copper cooling tubes back along the fuselage, and
they would leak because of the flexing of the structure in flight.  They
were also dented, dinged and punctured by such stuff as gravel kicked up
while taxiing.  The only solution was to make the tubing thicker, thus
heavier.

The next problem was that an ENORMOUS amount of area is needed to cool
this way -- more than in a normal heat exchanger -- because there are
fewer air molecules to transfer the heat into along the exterior
surfaces.  A 6-fin radiator, 12" x 12" x 2" thick, has 3456 square
inches of radiating area (not counting holes for tubes), or 288 square
feet!  Even if there were no loss of efficiency, imagine the built-in
penalty weight you'd add to the design by making so much of the surface
"wet" . . .and once they boosted horsepower beyond those earliest
engines, there just wasn't enough space, while a hit from a single
bullet would open the cooling system to the outside world.

The ONLY advantages they found in running the cooling system back along
the fuselage were that it would warm the cockpit and it allowed them to
move a significant portion of the FWF weight back, so when
high-performance, liquid-cooled planes came along, they moved stand heat
exchangers to other parts of the plane, putting scoops in the fuselage
(P-51), tail boom (P-38) or high-pressure area under the wing (Spitfire).

In fact, the unique sound which spawned the nickname "Whistling Death"
for the Corsair came from heat exchangers in the wing root which cooled
engine oil.

Keith W