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Questions and Answers
How is the underbalance of a control surface determined?
What is the correct overbalance moment equation?
What is the correct balance condition for an aileron?
What is the maximum allowable underbalance for a rudder if $W = 8$ pounds and $D = 5$ inches?
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What action is required if an aileron is underbalanced by $4.50$ inch-pounds, which exceeds the allowable underbalance?
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Study Notes
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
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Description
Learn about the methods to determine underbalance or overbalance of a control surface in aircraft maintenance, including suspending weights and calculating unbalance moment.
