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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

=20

NACA ACR 5120
<http://www.n91cz.com/Interesting_Technical_Reports/NACA-ACR-5120.pdf>
- A experimental Investigation of NACA Submerged-Duct Entrances (3.3 Mb)

=20

NACA RM A7130
<http://www.n91cz.com/Interesting_Technical_Reports/NACA-RM-A7130.pdf>
- An Experimental Investigation of the Design Variables for NACA
Submerged Duct Entrances (2.5 Mb)

=20

NACA RM A50E02
<http://www.n91cz.com/Interesting_Technical_Reports/NACA_inlet_efficienc
y.pdf>  - 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.=20

<<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.

=20
Chris Zavatson
N91CZ
360std
www.N91CZ.com

=20


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<P dir=3Dltr style=3D"MARGIN-RIGHT: 0px"><FONT size=3D2>John, et =
al<BR><BR>&lt;&lt;I=20
am suspicious of those cute little NACA vents you guys use for tank =
vents. I am=20
thinking they may not be as effective as they need to be at higher =
altitudes=20
(lower indicated airspeeds). I think maybe NACA vents work better when =
there is=20
airflow through them, rather than being used to generate a static=20
pressure.&gt;&gt;<BR><BR>I have three reports on NACA (submerged) inlets =
posted=20
here:<BR><A=20
href=3D"http://www.n91cz.com/Interesting_Technical_Reports/Technical_Pape=
rs.htm">http://www.n91cz.com/Interesting_Technical_Reports/Technical_Pape=
rs.htm</A></FONT></P>
<DIV><FONT size=3D2><FONT face=3DArial =
color=3D#0000ff></FONT></FONT>&nbsp;</DIV>
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<P class=3DMsoNormal style=3D"MARGIN: 0in 281.25pt 0pt 1.5in"><A=20
href=3D"http://www.n91cz.com/Interesting_Technical_Reports/NACA-ACR-5120.=
pdf"><FONT=20
size=3D2>NACA ACR 5120</FONT></A><FONT size=3D2> &#8211; A experimental =
Investigation of=20
NACA Submerged-Duct Entrances (3.3 Mb)</FONT></P>
<P class=3DMsoNormal style=3D"MARGIN: 0in 281.25pt 0pt =
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href=3D"http://www.n91cz.com/Interesting_Technical_Reports/NACA-RM-A7130.=
pdf"><FONT=20
size=3D2>NACA RM A7130</FONT></A><FONT size=3D2> &#8211; An Experimental =
Investigation of=20
the Design Variables for NACA Submerged Duct Entrances (2.5 =
Mb)</FONT></P>
<P class=3DMsoNormal style=3D"MARGIN: 0in 281.25pt 0pt 1.5in"><o:p><FONT =

size=3D2>&nbsp;</FONT></o:p></P>
<P class=3DMsoNormal style=3D"MARGIN: 0in 281.25pt 0pt 1.5in"><A=20
href=3D"http://www.n91cz.com/Interesting_Technical_Reports/NACA_inlet_eff=
iciency.pdf"><FONT=20
size=3D2>NACA RM A50E02</FONT></A><FONT size=3D2> &#8211; Pressure =
Distribution and Ram=20
Recovery Characteristics of NACA Submerged Inlets at High Subsonic =
Speeds (1.7=20
Mb)</FONT></P></DIV>
<P dir=3Dltr style=3D"MARGIN-RIGHT: 0px"><BR><BR><FONT size=3D2>Static =
pressure is=20
certainly less than maximum at zero inlet velocity ratio, but can still =
be=20
respectable.&nbsp; At least one of the reports tests down to zero =
flow.<BR>These=20
are interesting reading, in particular if you are trying to use a NACA =
scoop to=20
cool something.&nbsp;<BR><BR>&lt;&lt;My RV8 has streamlined tank vents =
that=20
stick out about 1 1/2 inches into the air stream to get out of the =
boundary=20
layer and generate a positive pressure inside the tank. =
&gt;&gt;</FONT></P><FONT=20
size=3D2>
<P dir=3Dltr style=3D"MARGIN-RIGHT: 0px"><BR>I did something similar =
sticking out=20
about .75 inches.&nbsp; There was so much pressure in the tank you could =
see the=20
ribs.&nbsp; I later used a spare air speed indicator to trim down the=20
tube&nbsp;and knock the pressure down to 0.2 psi.</P>
<DIV><FONT face=3DArial color=3D#0000ff></FONT>&nbsp;</DIV>
<DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2>Chris =
Zavatson</FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2>N91CZ</FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial size=3D2>360std</FONT></DIV>
<DIV align=3Dleft><FONT face=3DArial =
size=3D2>www.N91CZ.com</FONT></DIV></DIV>
<P dir=3Dltr style=3D"MARGIN-RIGHT: 0px"><FONT face=3DArial=20
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