Targetware: Flight Model Development

Targetware ACM File Guide

REFERENCE: Center of Gravity (cg)

The center of gravity is critical to aircraft stability.  Depending on the surface areas of the wing and stabilizer, the distance between each and the maximum lift coefficient of each, there is a range, usually measured as a percentage of the mean aerodynamic chord (that which divides the wing into 2 equal areas), that the cg can be within for the plane to be positively stable.  Fuel tanks and ammunition must be placed on the aircraft so that as they are consumed, the center of gravity doesn't move very much and stays within the design limits.  The cg should be placed at the center of lift, so the tail surfaces can be of a smaller area, for control purposes only.  In this configuration, the plane exhibits positive stability, that is to initiate a pitching motion, the pilot displaces the control.  To maintain the motion, the controls are held displaced and to stop the motion, the controls are neutralized.  A plane that is neutrally stable is much more difficult to fly, requiring an input to initiate the motion, centering the controls to maintain the motion and an opposite input to stop the motion.