Generally, longerons are comparatively heavy members that do
approximately the same work as stringers.
longerons are somewhat similar; however, because of their weight,
heavier rivets must be used in repairing longerons. Sometimes bolts
are used in place of rivets; but it takes more time to install bolts,
and greater accuracy in fit is required.
For example, if bolts are
used, the bolt holes must be drilled for a light drive fit. That is,
the bolt must fit the hole tightly enough to require light hammering
to be seated in the hole.
For these reasons, bolts are not as
suitable as rivets. If the longeron consists of a formed section and
an extruded angle section, regard each section as separate. Make the
repair using the same procedures as for stringers; however, keep the
rivet spacing (pitch) between four and six rivet diameters.
The main spanwise members of the wings, stabilizers, and other
airfoils are spars, sometimes called beams.
They can extend the
airfoil's entire length or only a portion of the length.
designed primarily to take the bending loads on wings or other
Figure 2-14 shows spar repair by insertion.
The spar consists of
extruded capstrips, a sheet metal web or plate, and vertical angle
stiffeners or reinforcements. Repairs on spars may not be permitted
because they are such highly stressed members. The repair, if it is
permitted, must be of the highest quality workmanship and in strict
conformity with the instructions in the applicable technical manual.