Chris W wrote:

Corky Scott wrote:

Chris, what's a reverse NACA duct? My understanding is that they were
designed to work in one direction only, to bring in air with a minimum
of drag.

They don't work well, or at all, when placed on the fuselage or cowl
in a negative pressure area.

I had heard once that on some planes, a reverse or backwards NACA duct would
be installed in the aft part of the cockpit to improve ventilation by helping
suck air out of the plane. I also think I remember something about the
design being somewhat different.

--
Chris W

"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania

About all that I can remember is that the NACA (or NASA, I don't recall) exit
ducts were essentially rectangular and that the exit ramp maintained a basically
constant width and faired smoothly into the larger surface.

I believe, but am not at all certain, that the exit lip protruded slightly and
was fairly sharp, as compared to the submerged inlet lip which was rounded.

There was considerable discussion of these duct entrances and exits from the
late 1960s until the early 1980s, and numerous examples appeared on
automobiles. Generally, the ones on real factory facing cars were well
designed, and the ones on street machines intended to look fast (such as some
Mustang models) were atrocious.

I couldn't find a solid reference to the exit ports of the submerged ducts, but
considerable work (originally classified, but now unrestricted access) appears
to have been done during the period from late in WWII through the end of the
1940s; and reports are referenced in 1945, 1497, and 1948.

I am not sufficiently motivated at this time to read through even the titles,
but further information is available at: http://naca.larc.nasa.gov/ and
http://naca.larc.nasa.gov/cit.html Reports made after 1958 are in another
directory.