I adapted (and installed) eye-ball style fresh air vents several years ago (23.04.16) and it was finally time to devise a way to supply them with air. To 'feed' vents in this location, most Rebel builders have been using under-wing scoops. Adding drag-inducing scoops on an already 'dirty' airframe never sat well with me, so I decided to try and test an alternative intake solution. I selected this ABS polymer NACA-shaped vent ($15 ea) because it's just wide enough to clear the gap between the fuselage and the wing root on a Rebel. It also has a 1.25" hose fitting, which was close enough in size to be hooked up to the 1" flange I installed on the wing root (with a DIY adapted ring).
NACA inlets work on the premise that fast flowing air over a surface will 'depressurize' into the uniquely shaped opening and get funnelled down to the exit. This, supposedly with less drag than a scoop sitting in the airstream. However, I'm not entirely sure of the aerodynamics at the wing/fuselage/windscreen junction. A high-pressure zone (and a slow-moving boundary layer) is more likely here than highspeed free-flowing air. However, I'm banking on the the fact that 1) the vents are at slight angle v. relative wind in flight and 2) that the cabin is at a lower pressure than the high-pressure zone outside, which should still see some air coming in simply due to the pressure differential. The question is: how much? Only flight testing will tell, but I've told myself that I can always add a traditional 'scoop' to drive more air into these openings if my theory fails.
I had fabricated and fitted the wing-root fairings last year, so it was a simple matter of creating a pattern of thevent opening and cutting it into the fairing.