Podcast
Questions and Answers
How is the underbalance of a control surface determined?
How is the underbalance of a control surface determined?
What is the correct overbalance moment equation?
What is the correct overbalance moment equation?
What is the correct balance condition for an aileron?
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?
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?
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.
