9. Aircraft Balancing and Center of Gravity Control

Paper

Abstract

Proper airplane balancing and center of gravity location is one of the basic factors which insure successful design. Due to external and internal forces, and moments acting upon the airplane in flight, its motion is performed about its center of gravity. The equations of motion and of static and dynamic stability of the aircraft take into consideration its weight and center of gravity location, as well as mass moment of inertia. All factors combined affect the aerodynamic performance and the load carrying capacity of the aircraft.
Both the weight and the center of gravity, if roughly estimated, are subject to considerable variation. As the design progresses, the weight, in the great majority of cases, increases at a certain rate, while the center of gravity has a considerable tendency to shift toward the tail.
Inasmuch as the proper longitudinal, or fore and aft, center of gravity location plays the most important part in the aircraft design and operation, the vertical center of gravity location, even though significant, is far less important.
The center of gravity of an airplane may travel within short limits (several inches) determined by the actual flight testing. In the design stage, it is possible to set a conservative limit as to the range of CG travel on the basis of wind-tunne1 test data.
This paper offers a list of practical suggestions that may be used by the airplane designer or aircraft weight control engineer as well as by the operator, whether military or commercial. Some of the listed means of aircraft balancing and center of gravity control are applicable strictly to aircraft that are in the process of design, while others can be app1ied to the airplanes in actual service, as well as to the ones still on the drafting board. At times it is necessary to combine several of these means in order to avoid weight penalty and to correct the unbalanced condition of the aircraft.