"R&R Sherwood" wrote in message
...
Reverse NACA duct ... Bad Idea!
Several years ago I read about someone installing a NACA scoop, pointed
end
aft, to remove air from the cabin. I thought I would do the same for my
plane but first decided to test the idea. I built a NACA scoop and ran
high speed water through it in both forward and reverse directions. In
forward the water flowed as expected. In reverse the water exited at
nearly 90 degrees to the slip stream.
I believe a NACA scoop will just add drag, especially to fast
planes....Better to just use a ramped exit.

Russell Sherwood

I also remember someone else coming to that conclusion.

Try the "bump" or an adjustable "cowl type" flap.
--
Jim in NC