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Subject: [LML] Re: Horizontal Induction
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From: Thomas N Thibault <tnthibault@raytheon.com>
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Scott,

A while back you said:


Grayhawk is piping up even when Tom is right.
 
 Generally,
KIAS Hg."
150   1.1
175   1.5
200   2.0
225   2.5
250   3.1

These numbers are not theoretical since this is how the pitot/static 
system converts ram pressure differential into indicated airspeed



Your comments were in response to my saying "theoretically possible RAM 
air pressure recovery."  What I meant by "theoretical" was that some of 
the air coming in the inlet feeds the engine itself, so all pressure can 
not be recovered the way a pitot tube does.

I think, at 2700 RPM a 360 cu in engine consumes 486,000 = 2700/2 * 360 cu 
in of air per minute.  I also think that the servo inlet is about 3" in 
diameter.  If true, then the incoming air is moving at about 57 Kts.  I 
got this by the following:

V = air volume per minute / area of inlet = 486,000 / 7.069 = 68,750 in 
per minute = 56.58 nm per hour.

If true, then with an inlet velocity of 200 Kts. and perfect recovery of 
pressure by an airbox, some of the theoretical pressure is still lost 
because the engine is sucking out a cylinder of air moving at about 57 
Kts., so the resulting pressure has to be less than 2" Hg. 

Yes/No/maybe??  If yes, then isn't the max pressure obtainable at 200 
Kts., just under 1.1" Hg.

Tom Thibault
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<br><font size=3 face="Times New Roman">Scott,</font>
<br>
<br><font size=3 face="Times New Roman">A while back you said:</font>
<form action=http://mail.lancaironline.net:81/lists/lml/Message/46964.html method=post>
<table width=100%>
<tr>
<td width=100%>
<table width=100%>
<tr>
<td colspan=3>
<table width=100%>
<tr>
<td width=100%><font size=2 face="Arial">Grayhawk is piping up even when
Tom is right.</font>
<br><font size=2 face="Arial">&nbsp;</font>
<br><font size=2 face="Arial">&nbsp;Generally,</font>
<br><font size=2 face="Arial">KIAS Hg.&quot;</font>
<br><font size=2 face="Arial">150&nbsp;&nbsp; 1.1</font>
<br><font size=2 face="Arial">175&nbsp;&nbsp; 1.5</font>
<br><font size=2 face="Arial">200&nbsp;&nbsp; 2.0</font>
<br><font size=2 face="Arial">225&nbsp;&nbsp; 2.5</font>
<br><font size=2 face="Arial">250&nbsp;&nbsp; 3.1</font>
<br>
<br><font size=2 face="Arial">These numbers are not theoretical since&nbsp;this
is how the pitot/static system converts ram pressure differential&nbsp;into
indicated airspeed</font></table>
<br></table>
<br></table>
<br>
<br><font size=3 face="Times New Roman">Your comments were in response
to my saying &quot;theoretically possible RAM air pressure recovery.&quot;
&nbsp;What I meant by &quot;theoretical&quot; was that some of the air
coming in the inlet feeds the engine itself, so all pressure can not be
recovered the way a pitot tube does.</font>
<br>
<br><font size=3 face="Times New Roman">I think, at 2700 RPM a 360 cu in
engine consumes 486,000 = 2700/2 * 360 cu in of air per minute. &nbsp;I
also think that the servo inlet is about 3&quot; in diameter. &nbsp;If
true, then the incoming air is moving at about 57 Kts. &nbsp;I got this
by the following:</font>
<br>
<br><font size=3 face="Times New Roman">V = air volume per minute / area
of inlet = 486,000 / 7.069 = 68,750 in per minute = 56.58 nm per hour.</font>
<br>
<br><font size=3 face="Times New Roman">If true, then with an inlet velocity
of 200 Kts. and perfect recovery of pressure by an airbox, some of the
theoretical pressure is still lost because the engine is sucking out a
cylinder of air moving at about 57 Kts., so the resulting pressure has
to be less than 2&quot; Hg. &nbsp;</font>
<br>
<br><font size=3 face="Times New Roman">Yes/No/maybe?? &nbsp;If yes, then
isn't the max pressure obtainable at 200 Kts., just under 1.1&quot; Hg.</font>
<br>
<br><font size=3 face="Times New Roman">Tom Thibault</font></form>
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