Figure 4-68.--Stringer repair by insertion.
NOTE: The above repair is permissible when the
damage does not exceed two-thirds of the width of one
leg of the stringer and is not over 12 inches in length.
When the damage is of such length that a single
reinforcement splice would involve an excessive
amount of material and work, a repair by insertion
should be made. See figure 4-68.
SPARS.--Spars (also called beams) are the main
spanwise members of the wing, stabilizers, and other
airfoils. They may run the entire length of the airfoil.
Spars are designed primarily to take bending loads
imposed on the wing or other airfoil.
The most common type of spar construction
consists of extruded capstrips, a sheet metal web or
plate, and a vertical angle stiffener. Since spars are very
highly stressed members, their repair may not be
permitted; and if permitted, must be made in strict
accordance with instructions given in the structural
repair manual, using the best possible workmanship.
Figure 4-69 shows a spar web repair by insertion.
RIBS.--Ribs are the principal chordwise structural
members in the wings, stabilizers, and other airfoils.
Ribs serve as formers for the airfoil. They give it shape
and rigidity and also serve to transmit stresses from the
skin to the spars. They are designed to resist both
compression and shear loads.
Figure 4-69.--Spar repair by insertion.