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 | | From: | Lynn Coffelt | | Subject: | Center of pressure vs. aerodynamic center | | Date: | Tue, 11 Jan 2005 11:29:29 -0800 |
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Weight and Balance computations using moments (added, subtracted or
changed) in USAF aircraft (T.O. 1-1B-40) use a fixed starting point called
the reference datum. This fixed point, as pointed out, is normally near the
nose of the aircraft. It seems that the original drafted reference datum may
have been the nose, but as aircraft designs develop, the actual nose may
move forward or back on the drawings, but the reference datum stays in the
same place. It is most common for the reference datum to be several inches
ahead or behind the actual nose. Leading of course to the possibility of a
negative moment when something is added to a station forward of the
reference datum.
Of course this method is pretty simplistic, and I wonder if in some
critical applications, weights raised or lowered on a vertical axis might be
important considerations? The military (T.O. 1-1B-40) system only considers
weight adjustment along a longitudinal axis.
The almighty knows lateral balancing can be important too. I.e. one tip
tank empty and one full!!
Old Chief Lynn
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