Here's a little more information that might help clarify. The stability of the plane in flight is determined by the relationship between the center of Gravity and the Aerodynamic Center (Center of Lift). The lift component will always act perpendicular to the wings at the aerodynamic center and gravity will always act perpendicular to the ground at the center of gravity. Typically, the aerodyamic center is between 25-33 percent of the average chord of the wing. The plane will always tend to turn up or down around the center of Gravity. If the Center of Lift is coincident with the center of Gravity, no matter what direction the plane is flying in, there will be no differential moment developed between the two, and the plane will simply continue in whatever direction it is pointed (theoretically optimum for pattern flying). If the Center of gravity is directly below the aerodynamic center (as in a properly balanced high wing trainer), when the plane is flying straight and level, there is no angular moment developed between the two. If the plane points up,or down the relationship between the aerodynamic center and the center of gravity will develop a righting moment between the two, causing the plane to want to return to straight and level flight. For low wing planes, exactly the opposite is true, which makes them a little less stable, unless there is some dihedral put into the wing to raise the aerodynamic center closer to or above the center of gravity.

When it gets interesting is when the center of gravity is either in front of (nose heavy) or behind (tail heavy) the aerodynamic center. In the nose heavy condition, during straight and level flight there is a moment developed causing the nose to drop, and this is offset by elevator. If the direction of airflow over the wing is changed (up or down turbulence), the relationship between the CG and AC tends to cause a righting moment pointing the nose of the aircraft into the air flow, making the plane stable in the air flow again. In the tail heavy condition, a change in the airflow due to turbulence causes the moment arm to push the plane perpendicular to the air flow, making the plane VERY unstable in turbulence. Hence the expression "Nose heavy planes fly poorly, tail heavy planes fly once".

Do a google search on "Aerodymanic Center" and you'll get some very interesting graphics explaining the effects.

Brad