John, et al
<<I
am suspicious of those cute little NACA vents you guys use for tank vents. I am
thinking they may not be as effective as they need to be at higher altitudes
(lower indicated airspeeds). I think maybe NACA vents work better when there is
airflow through them, rather than being used to generate a static
pressure.>>
I have three reports on NACA (submerged) inlets posted
here:
http://www.n91cz.com/Interesting_Technical_Reports/Technical_Papers.htm
NACA ACR 5120 – A experimental Investigation of
NACA Submerged-Duct Entrances (3.3 Mb)
NACA RM A7130 – An Experimental Investigation of
the Design Variables for NACA Submerged Duct Entrances (2.5 Mb)
NACA RM A50E02 – Pressure Distribution and Ram
Recovery Characteristics of NACA Submerged Inlets at High Subsonic Speeds (1.7
Mb)
Static pressure is
certainly less than maximum at zero inlet velocity ratio, but can still be
respectable. At least one of the reports tests down to zero flow.
These
are interesting reading, in particular if you are trying to use a NACA scoop to
cool something.
<<My RV8 has streamlined tank vents that
stick out about 1 1/2 inches into the air stream to get out of the boundary
layer and generate a positive pressure inside the tank. >>
I did something similar sticking out
about .75 inches. There was so much pressure in the tank you could see the
ribs. I later used a spare air speed indicator to trim down the
tube and knock the pressure down to 0.2 psi.
Chris Zavatson
N91CZ
360std
www.N91CZ.com
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