Aircraft Maintenance: Flight Controls Balancing

Determining Underbalance or Overbalance of Control Surfaces

• Underbalance (tail heavy) or overbalance (nose heavy) of a control surface can be determined in several ways
• Methods include suspending weights from a balance weight attachment screw (Figure 7-1, Detail A) and placing a metal bar of known weight parallel to the control surface hinge line (Figure 7-1, Detail B)

Balancing Instructions

Aileron

• Place aileron in balance fixture upside down
• Aileron is 100-percent balanced when the flat surface (underside) is 3 degrees down from the horizontal, measured near the center hinge
• Specification for the aileron is nominally 100-percent static balanced
• Unbalance should still be measured and compared with the specification, even if it swings near the 30 position

Calculating Unbalance Moment

• Unbalance moment (Mu) is calculated by multiplying the total weight suspended by its distance from the hinge line (Mu = W x D)
• Example: Mu = 0.750 x 3 = 2.25 inch-pounds (aileron)
• Example: Mu = 1.50 x 3 = 4.50 inch-pounds (aileron)
• Example: Mu = 8.50 x 5 = 42.5 inch-pounds (rudder)
• Example: Mu = 0.250 x 10 = 2.50 inch-pounds (elevator)

Elevator and Rudder

• Place control surface in balancing fixture, ensuring free rotation at hinge points
• Rudder and elevator are 100 percent balanced when the trailing edge is level with the hinge line
• Verify that the proper amount of weight was added or removed after rebalancing
• Check each surface for unbalance (Mu) using the General Balancing Procedure until the surface is balanced according to specifications

Learn about the methods to determine underbalance or overbalance of a control surface in aircraft maintenance, including suspending weights and calculating unbalance moment.