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I cannot speak for all installations, but my fan does very little on the ground. On the other hand, I get a lot of air once I'm flying, so the pressure recovery from the NACA duct must be pretty good. Actually, it is too much when it is below zero outside, until the pressurization kicks in.
On decent, it is easy to tell when the vent pressure exceeds the turbo output and the flapper opens with a pop. If the flapper does not seal well, you will never pressurize. It only takes a tiny leak to bleed off several psi.
Tom O
N241DM
On Apr 11, 2008, at 6:44 PM, Bill Wade wrote:
I looked at the IV/IV-P Handbook but still have some questions-
Does the NACA vent/blower provide good ventilation or would it be wise to build in another source as well?
Does the flapper valve do a good job of sealing the duct in pressurized mode- especially if you change over in flight- or would it be helpful to install a positive valve of some sort?
Thanks very much- Bill Wade IV-P
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