Aircraft Flight Controls Balancing

Study Notes

Determining underbalance or overbalance of a control surface can be done in several ways, as illustrated in Figure 7-1.

To determine the balance of an aileron, place it in a balance fixture upside down.
The aileron is 100% balanced when the flat surface is 3 degrees down from horizontal, measured near the center hinge.
The specification for the aileron is nominally 100-percent static balanced.
If an aileron is underbalanced, the unbalance moment can be calculated by multiplying the weight by the distance D.
The allowable underbalance (tail heavy) is 4 inch-pounds.

To determine the balance of an elevator or rudder, place the control surface in a balancing fixture, ensuring free rotation at hinge points.
The elevator and rudder are 100% balanced when the trailing edge is level with the hinge line.
The final step in rebalancing is verification that the proper amount of weight was added or removed.

To adjust the balance, follow the procedure until the surface is balanced according to the specifications.
If a surface is underbalanced, additional weight must be added forward of the hinge line.
The required amount of weight can be estimated by dividing the number of inch-pounds out of tolerance by the distance from the hinge line at which the weight will be added.
If a surface is overbalanced, weight must be removed from the balance weights in the nose of the surface.
The total adjustment to be made is the unbalance moment plus the minimum amount of underbalance specified.