There are three general types of rib construction, as
shown in figure 4-70. 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 holes. The beads
stiffen the web portion of the rib. Rib repair by patching
is shown in figure 4-71.
BULKHEADS.--Any major vertical structural
member of a semimonocoque fuselage, hull, or float
may be considered a bulkhead. Bulkheads serve to
maintain the required external contour at the station
Figure 4-71.--Rib repair by patching.
where they are located. They also give rigidity and
strength to the structure.
Bulkhead construction is similar to that used for
wing ribs. It consists of a web reinforced by angle
stiffeners. The web is attached to the skin by formed
flanges or extruded angles, which serve as capstrips.
Non-watertight bulkheads may have lightening holes,
and most bulkheads are cut out to give clearance for
stringers. The stringers are usually attached to the
bulkhead by angle clips.
The repair of the web and formed flange of a
bulkhead is similar to that used for the rib web and
flange repair; however, the structural repair manual
must be consulted for specific information on the repair
of a particular bulkhead.
Figure 4-70.--Types of ribs.