Piper Aircraft Corporation Cherokee 140 PA-28-140, Service Manual

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IV - STRUCTURES 01/31/08
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PIPER CHEROKEE SERVICE MANUAL
4-72. BALANCING EQUIPMENT (Refer to Figure 4-19).
The balancing must be done using a suitable tool capable of measuring unbalance in inch-pounds from
the centerline of the control surface hinge pin. See the tool configuration in Figure 4-19. Other tool
configurations may be used if accuracy is maintained and recalibration capability is provided.
To use this tool:
a. Ensure that the control surface is in its final Flight configuration, static wicks, trim tabs, trim tab
push pull rod and control surface tip (as applicable) should be installed. The surface should be
painted and trim/servo tabs should be in the neutral position.
NOTE: Because paint is a considerable balance factor, it is recommended that existing paint be
removed prior to repainting a control surface.
b. Place hinge bolts through control surfaces and place control surface on a holding fixture.
c. Calibrate the tool.
1. Avoiding rivets, place the balancing tool on the control surface with the tool’s hinge centerline
directly over the hinge line of the control surface.
2. Adjust the movable trailing edge support to fit the width of the control surface. Tighten the set
screw on the trailing edge support.
3. Adjust the trailing edge support vertically until the beam is parallel with the control surface
chord line.
4. Remove the tool from the control surface and balance the tool itself by adding or removing
nuts or washers from the beam balancing bolt. When balancing the tool, the movable weight
must be at the bar’s hinge centerline.
d. After balancing the tool, reattach it to the control surface per Figures 4-20 and 4-21. Keep the beam
positioned 90° from the control surface hinge line.
e. Determine balance of control surface by sliding movable weight along the balance beam.
f. Read the scale when the bubble level has been centered. Multiply by three to determine inch-lbs.
(I.E. - Since the movable weight weighs three pounds, every inch it is moved from the center of the
beam equals three inch-lbs of force.)
4-73. BALANCING AILERONS. (Refer to Figure 4-20.)
Position the aileron on the balancing fixture in a draft free area and in a manner which allows
unrestricted movement of the aileron. Place the tool on the aileron, avoid rivets and keep the beam
perpendicular to the hinge centerline. Calibrate the tool as described in Paragraph 4-72. Read the scale
when the bubble level has been centered by adjustment of the movable weight and determine the static
balance. If the static balance is not within the limits specified in Table IV-II, proceed as follows:
a. Leading Edge Heavy: This condition is highly improbable; recheck measurements and calculations.
b. Training Edge Heavy: There are no provisions for adding weight to balance weight to counteract a
trailing edge heavy condition; therefore, it will be necessary to determine the exact cause of the
unbalance. If the aileron is too heavy because of painting over old paint, it will be necessary to strip
all paint from the aileron and repaint. If the aileron is too heavy resulting from repair to the skin or
ribs, it will be necessary to replace all damaged parts and recheck the balance.