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Old 12-09-2001, 02:36 PM
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Ollie
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Join Date: Dec 2001
Location: Punta Gorda, FL
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Default CG Location

The location of the CG relative to the neutral point(NP) determines the static stability. When the CG is at the NP the plane is neutrally stable and the plane goes where it is pointed without diverging or correcting itself. When the CG is aft of the NP the plane diverges and tucks under. When the CG is ahead of the NP, the plane returns to a trimmed flight speed and attitude after a disturbance. How strongly the plane returns to its trimmed flight condition depends on how far the CG is ahead of the NP. The desired stability and CG varies from pilot to pilot depending on reflexes and flying skill. It also varies with the type of flight characteristics the pilot expects.

The NP and CG can be calculated to arrive at a safe starting CG which should then be refined by adjustments between test flights.There is a small uncertainty in the aerodynamic center (AC) of the wing because it varies a little with airfoil. Some airfoils at low reynolds numbers have AC locations that shift a little with angle of attack. These variations and uncertanties make the final adjustments by flight testing necessary.
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