[azrv6]

Nice brief article on the origins and how they work: http://www.buildingspeed.org/blog/2012/12/whats-a-naca-duct/
The NACA also did work on speed rings and bump cowls for radial engines back in the day.

 

[terrye]

NACA duct

I'd be surprised if the NACA ducts as shown on the rear window of a NASCAR are very effective. They are operating in a very turbulent area, in the aft part of the car body, behind the driver's open window covered by a net.

The original NACA research papers recommend that they be placed in an area with a positive pressure gradient, that is on the forward part of the body (forward fuselage, forward part of engine nacelles). Any NACA ducts I have seen on the aft body have to have raised strakes on the inlet opening to try to penetrate the thick boundary layer. I think to work on an aft body location, the air outlet would have to be in a very low pressure area, such as the engine cooling air exit on a canard.

 

[Flying Scotsman]

I can't help but notice that everyone calls them "NACA ducts" or "NACA scoops", pronounced "nakah"...but the correct pronunciation is EN-AY-SEE-AY", each letter pronounced individually.

It's always bugged me that we all (and I do it, too) call the "nacka" scoops LOL! I guess it's because NACA became NASA.

Just idle thoughts after a long day in the hangar

 

[Ironflight]

I can't help but notice that everyone calls them "NACA ducts" or "NACA scoops", pronounced "nakah"...but the correct pronunciation is EN-AY-SEE-AY", each letter pronounced individually.

It's always bugged me that we all (and I do it, too) call the "nacka" scoops LOL! I guess it's because NACA became NASA.

Just idle thoughts after a long day in the hangar

Bingo! I got very funny looks (like "rookie".....) when I joined NASA and pronounced the "previous agency" the same way in front of the old timers. For the old agency - every letter individually. Except when it comes to that danged scoop....