USEFUL load-carrying capacity is a measure of the comparative value of two airplanes of the same size, having identical powerplants, speed, rate of climb and other flying characteristics. It seems to be feasible to combine in the same airplane both the greatest ability to carry useful load and the least cost of construction.
Blanked and pressed metal work offers substantial advantage to the extent that parts, particularly sub-assemblies, can be made directly by machine in complete units ready to set in the final assembly.
The author shows and describes the methods followed by his organization in forming the members, building the frames and assembling the units of metal aircraft. Trusses are blanked and the web members pressed to ¾-circle form. Dies for long members are variable in length by being made in pieces that can be removed or inserted as desired. Flanged-tube sections are employed for truss chords. Members are secured together by riveting, the rivets being accessible for machine setting and punching.
Flanged tubing for truss structures is made by drawing a strip of sheet metal through a die that forms it into a circular or an elliptical section and leaves a desired form of flange along the edges to which other parts can easily be fastened. Hollow-bulb angles also are made from drawn strips and have various uses. They form convenient conduits for electric wires.
By the construction described, a high ratio of strength to weight is obtained. With economical design in metal, the load-carrying structure need not exceed 10 per cent of the gross flying-weight, and 40 per cent of the gross weight can be pay-load. In reasonable quantities, the cost of production of such airplanes should be lower than is possible with wooden structures.
Use by the Navy of a number of flying-boats and pursuit airplanes of this type for 3 and 4 years, and inspection of similar wings built for the Navy in 1920 and 1921, show that corrosion does not offer a very difficult problem in construction.