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To:  lml@lancaironline.net
Date: Mon, 26 Jan 2009 07:42:30 -0500
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From: "Robert Pastusek" <rpastusek@htii.com>
References: <list-3451696@logan.com>
In-Reply-To: <list-3451696@logan.com>
Subject: RE: [LML] air intake
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Ralf B wrote: 

 

I assume that the air intake in the tail is originally designed to be used
for the ac unit and that the previous owner cut a hole in the bottom of the
fuselage to force more air through the heat exchanger of ac unit. I want to
close the hole in my tail now since I am not using this air intake.

 

Would you recommend my plan or does the air intake in the tail serve another
purpose? 

 

 

Ralf,

The "original" Lancair IV did not have air conditioning, and was not
pressurized. The air intake in the tail was used to collect high pressure
air in this area and duct it forward for cabin ventilation/cooling. It
worked extremely well. When later models of the IV were pressurized, a
flapper valve was added where this ventilation air passed into the cockpit
at the rear pressure bulkhead so ventilation air could move forward into the
cockpit, but cockpit pressurization air could not "leak" backward through
the ventilation ducting. This system also works well, but you can either
have a "ventilated" or a pressurized cockpit; but not both at the same time.
As a result, some builders, especially those who installed air conditioners,
just eliminated the cockpit ventilation feature completely and used the A/C
for cooling. From your description, that's the configuration you have.the
air intake in the tail has not been connected to the cockpit through
ducting-typically along the fuselage top.

 

Before closing off the tail inlet, I'd check carefully on the air flow
through the A/C heat exchanger. It's possible the heat exchanger uses air
from both sources, although either should be adequate in most conditions.
You didn't say where the air exited the fuselage after it passed across the
heat exchanger.this is a consideration as well, as the total A/C
effectiveness/efficiency depends on the condenser working properly. If
you're satisfied with the outflow, I'd suggest plugging the tail opening
with Styrofoam to test the effect, and if the A/C and aircraft ventilation
systems still work to your satisfaction, glass over the plug and paint.

 

Hope this helps; glad to exchange information with you off-line if desired.

 

Bob Pastusek


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<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Ralf B wrote: </span><span =
style=3D'font-size:10.0pt;font-family:
"Arial","sans-serif"'><o:p></o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p>&nbsp;</=
o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'>I
assume that the air intake in the tail is originally designed to be used =
for
the ac unit and that the previous owner cut a hole in the bottom of the
fuselage to force more air through the heat exchanger of ac unit. I want =
to
close the hole in my tail now since I am not using this air =
intake.<o:p></o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p>&nbsp;</=
o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'>Would
you recommend my plan or does the air intake in the tail serve another =
purpose?
<o:p></o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p>&nbsp;</=
o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:10.0pt;font-family:"Arial","sans-serif";
color:#1F497D'><o:p>&nbsp;</o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Ralf,<o:p></o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>The &#8220;original&#8221; Lancair IV did not have air =
conditioning,
and was not pressurized. The air intake in the tail was used to collect =
high
pressure air in this area and duct it forward for cabin =
ventilation/cooling. It
worked extremely well. When later models of the IV were pressurized, a =
flapper
valve was added where this ventilation air passed into the cockpit at =
the rear
pressure bulkhead so ventilation air could move forward into the =
cockpit, but cockpit
pressurization air could not &#8220;leak&#8221; backward through the
ventilation ducting. This system also works well, but you can either =
have a &#8220;ventilated&#8221;
or a pressurized cockpit; but not both at the same time. As a result, =
some
builders, especially those who installed air conditioners, just =
eliminated the
cockpit ventilation feature completely and used the A/C for cooling. =
From your
description, that&#8217;s the configuration you have&#8230;the air =
intake in the
tail has not been connected to the cockpit through =
ducting&#8212;typically along
the fuselage top.<o:p></o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p>&nbsp;</o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Before closing off the tail inlet, I&#8217;d check =
carefully on
the air flow through the A/C heat exchanger. It&#8217;s possible the =
heat exchanger
uses air from both sources, although either should be adequate in most
conditions. You didn&#8217;t say where the air exited the fuselage after =
it
passed across the heat exchanger&#8230;this is a consideration as well, =
as the
total A/C effectiveness/efficiency depends on the condenser working =
properly. If
you&#8217;re satisfied with the outflow, I&#8217;d suggest plugging the =
tail
opening with Styrofoam to test the effect, and if the A/C and aircraft
ventilation systems still work to your satisfaction, glass over the plug =
and
paint&#8230;<o:p></o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p>&nbsp;</o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Hope this helps; glad to exchange information with you =
off-line
if desired.<o:p></o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p>&nbsp;</o:p></span></p>

<p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Bob Pastusek<o:p></o:p></span></p>

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