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CG location and stability is what it's all about.
The CG is a physical space within which the designer wants you to stay. But
little if anything is divulged about where that space's definition came
from.
Saying the CG is 15% to 30% of the MAC is interesting but
not conclusive without some assumptions of what the C in MAC stands
for.
If a reference is given to a percent of MAC where C
= Chord, then all is well and easily determined. However if C is intended to be
Center then all bets are off without being given the location of that point by
the aircraft designer.
The Mean Aerodynamic Chord is a
geometric calculation and is not influenced by flight forces.
The Mean
Aerodynamic Center of a wing is a point on the wing chord
which results in a constant moment when the wing angle of attack is changed. If
the cg is at the ac, the forces on the tail will be minimized.
Now keep
in mind that MAC (chord) will give, well gee, the chord of the wing and then
saying the CG is a % of MAC actually means something but using MAC (center)
fails to give a usable reference for the purposes of CG
determination.
So . . . I think we have to assume we're talking about MAC
where C = chord
Wolfgang
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There appear to be different definitions
for MAC out there. I am more familiar with MAC being used
for "mean aerodynamic center". I suppose MAC could
also refer to "mean aerodynamic chord", as you point out.
My text on stability and control (Etkin) uses ¯c (with the
bar over the c) for "mean aerodynamic chord". It is easy to tell
which definition is meant in diagrams or equations. It is
definitely not as clear in textual form. I suppose it is best to
spell out the intended definition.
Chris Zavatson
N91CZ
360std
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