RIBS.—Ribs are the principal chordwise struc-
tural 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.
There are three general types of rib construction,
as shown in figure 13-70. The reinforced rib and the
truss rib are both relatively heavy as compared to the
former rib. They are located only at points where the
greatest stresses are imposed. Former ribs are located
at frequent intervals throughout the airfoil.
The reinforced rib is similar in construction to
that of spars. It consists of upper and lower capstrips
joined by a web plate. The web is reinforced between
the capstrips by vertical and diagonal angles. The
reinforced rib is more widely used than the truss rib.
The truss rib consists of capstrips reinforced
solely by vertical and diagonal crossmembers. It is
used in the wings of some of the Navy’s larger
aircraft.
Former ribs are made of formed sheet metal and
are very light in weight.
The bent-up portion of a
former rib is correctly referred to as the flange. The
vertical portion is called the web. The web is
generally constructed with lightening holes, with
beads formed between the holes.
The lightening
holes lessen the weight of the rib without decreasing
the strength. Rigidity of lightening hole areas is
accomplished by flanging the edges of the lightening
Figure 13-70.—Types of ribs.
Figure 13-69.—Spar repair by insertion.
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