You could try putting a couple of vortex generators in front of the
NACA scoop to trip the boundary layer.
Bill B
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Chris Zavatson
Sent: Saturday, March 28, 2009
9:36 PM
To: lml@lancaironline.net
Subject: [LML] Re: Poor
Slow-flight Cooling
The air coming in from your 3 inch duct may actually be
leaving through the NACA scoop during slow flight. NACA
scoops are somewhat sensitive to orientation to the airstream and while in
slow flight the orientation may be off far enough that the NACA scoop is no
longer effective. Two parallel sources will fight each other if the
pressures aren't well balanced. In this case, if the NACA scoop pressure
drops all of a sudden, you would see a flow reversal.
If you measure the pressure ahead of the cooler as you
slow down, you should be able to see this transition occur.