Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Mon, 11 Aug 2003 08:53:57 -0400
Message-ID: <redirect-2517213@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: fuel tank pressure
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<<After my wings were painted at the auto body shop, the painter needed
space and moved the wings out into the sun.  Later, that evening, it was
time to move the wings back to the hangar and one (still warm from the sun)
was loaded into a long van.>>

A way to figure out the pressure change:  Pressure in a constant volume
vessel will change proportionally to the absolute temperature.  At normal
room temp the absolute temp is about 550 deg R.  So for every 55 degrees
change the pressure will change 10%, or about 1.5 psi.  Going from inside to
direct sun probably didn't change the temperature that much, although it
could have.  Also, the weight of the fuel in the tanks is substantial.  The
wing is probably at least a foot deep (from the vent to the lowest point in
the tank) making for about 0.4 psi just sitting there per foot of depth.  At
4 G's the pressure would be about 1.4 psi, maybe as high as 2 psi (only on
the bottom skin).  Of course, there are also aerodynamic loads.  I'm not
even close to an expert, but with an average wing loading of 20 psf the peak
pressure difference as a gross approximation must be more than twice that,
or about 0.25 psi.  Then go to the 4G design load factor and you have 1 psi.
Regardless of how you think of it the wing will experience relative
pressures in the range of 1 psi in service so that is probably a reasonable
pressure at which to test.  5 psi may not be reasonable.

Gary Casey
ES #157