David Carter wrote:

Ed Anderson wrote (in "Dumping radiator hot air into the cowling" 22 Feb 99)

 "I place louvers on the side of the cowling which helped me . . .
eventually I built exit ducts routing the radiator 
hot air to the louvers.  That solved
the problem and I have had no problem with the radiator temperature since."

Now I have info that 2 of the 3 RV's with 13Bs uses louvers as an
integral part of their solution:  Ed Anderson, and Dave Atkins.

Ed,
 1)  Is the louver some off-the-shelf thing?  Source, price, &
description: length, width, and description of openings (louver lips):
Angle of inner lips (scoops), angle of outer lips (exit "flaps", spacing
between lips (measured fore-aft), spacing between each louver's "wall"
(measured perpendicular to louver's "ducting" surface, angle of a thin
straight piece held horizontally in a louver opening, with outside end
angled aft until rod in contacting an inner lip (forward) and an outer
lip (aft of that).

 2)  How would you describe or estimate the "directions changes"
imparted to the exiting air?  90 degrees outboard, then 90 degrees aft?
45 each way?  Less? (related to the "thin straight piece's angle"
above).

 3)  Attachment to cowling:  Riveted?  Bonded?  Reinforcing doublers
around the hole cut in cowling?  Where installed on cowling (I'm not at
that stage of building so don't know if the cowling separates into "top"
and "bottom" halves:  If two halves split halfway up, is the louver on
top or bottom half?  How far from edges (location)?

 4)  What did I forget to ask?

In both these cases, louvers have been "final solutions" to cooling
problems, one for engine coolant, other for oil cooling.

In terms of fluid dynamics theory, I'm curious about how much direction
change these two louvers are imparting to the hot exit air.  I suspect
the louver lips aim somewhat forward and somewhat aft, with gap of some
unknown amount at this point.  The louvers are providing a "turning"
function, like a duct would.  Angles of turning, if selectable by type
of louver bought, ought to be selected carefully to avoid the "dreaded 2
90 degree turns".  Also, we know that the air should ideally exit
parallel to side of airplane/parallel to free stream airflow.  I'd think
that anything under 30 degrees off of "straight aft" would be practical.
  It would also seem that the outside lip, if not pointing straight aft,
but being at 10 to 30 degrees angle to the airstream, would be providing
a low pressure effect like an open exit flap on a P-51 style cooling
system.

In general, it seems from these two experiences that ducting to a nearby
louver is better than just dumping hot air into the "cowl plenum" and
letting it find its way out of the factory designed exit at bottom of RV
cowl at the firewall.

David Carter

What ever you do guys plan ahead for all the stuff you are trying
to cram into the cowl.

Paul
 
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