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Date: Fri, 19 Aug 2011 12:23:06 -0400
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From: liegner@earthlink.net
Reply-To: liegner@earthlink.net
Subject: RE: What are your numbers?? LIVP and LOP
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We all have leaky cabins.  It is just a matter of degree. =20

My cabin maintains full cabin pressure at 16000' (simply for example) down =
to 24" MAP, but not in the flight levels.  At FL240, it is less compliant w=
ith a more rapid drop and slower recovery (degrading at 28" MAP). =20

My Duke's valve is set for a slow climb (regardless of actual altitude) to =
avoid ear pops.  A faster Duke's response rate/setting would prevent a rapi=
d decompression with big throttle pull (heading to lower MAP).

After a successful climb to flight levels, at FL240 level cruise, with cabi=
n differential 5.0 psi (and stable), 34" MAP (or 31" MAP) on the throttle: =
 if you pull back to 28" MAP, who among us will maintain a steady 5.0 psi d=
ifferential?  Or will your cabin climb (maybe above 12.5K') with the thrott=
le pull?  And at 28" MAP, how long will it take to restore a 5 psi differen=
tial at FL 240 after some additional Duke's Valve outflow restriction (base=
d on rate setting)?  Will your spouse's ears pop, and will she ask about th=
e pressurization concern?

A reduction from 36.5" MAP (full power ) to 28" MAP (a 8.5" or 3 psi drop i=
n siphoning of MAP for cabin), who does not experience a reduced cabin diff=
erential?

Likewise, if you set the cabin rate high (to avoid this rapid drop at Fligh=
t Level cruise), would you not also experience a rapid pressurization durin=
g your take off role, when the MAP rises from 10" to 38.5" inside of a few =
seconds, and the Duke's setting allows a rapid cabin change?  Perhaps the c=
abin altitude setting (airport elevation) prevents this.  Perhaps I need to=
 change from a slow climb to a rapid climb rate.

Jeff


you probably have a leaky cabin

>If I quickly reduced MAP to 31", and particularly to 28" MAP, the cabin al=
titude=20
>would quickly climb to >14,000' and the Duke's regulator would take severa=
l minutes=20
>to equilibrate.=C2=A0 And even then, it might not be able to restore 5.0 p=
si=20
>differential (at 28" MAP).=C2=A0 So, all this talk of lower MAP