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.

Figure 13-69.-Spar repair by insertion.

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.

holes. The beads stiffen the web portion of the rib. Rib repair by patching is shown in figure 13-71.

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