Quite early it was apparent to us that we had on our hands a problem in spruce production which the Government itself must solve, if the airplane undertaking were not to fail at the outset. When we entered the war linen was exclusively used for the covering of wings; and it developed almost immediately that the United Kingdom was practically the sole source of linen. But the Irish looms could not begin to furnish us with our needs for this commodity. Later on came up the question of supplying dope and castor oil. Finally, during the last months of the war, it became necessary for us to follow up the production of all classes of our raw material, particularly in working out a suitable supply of steel tubing. But our great creative efforts in raw materials were confined to spruce, fabric, and dope.
The lumber problem involved vast questions of an industrial and technical character. We had to conduct a campaign of education in the knowledge of aircraft requirements that reached from the loggers themselves in the woods to the sawmill men, to the cut-up plants, and then followed through the processes of drying and sawing to the proper utilization of the lumber in the aircraft factories.
In working out these problems, while we drew heavily upon the experience in Europe, yet we ourselves added our own technical skill to the solution. The Signal Corps was assisted by the forest products laboratory at Madison, Wis., and by the wood section of the inspection department of the Bureau of Aircraft Production. The United States Forest Service contributed its share of technical knowledge. At the end of the war we considered that our practice in the handling of aircraft lumber was superior to that of either France or England.
THE SPRUCE PROBLEM.
Each airplane uses two distinct sorts of wood—first, the spruce or similar lumber for the wing beams or other plane parts; and second, mahogany, walnut, or other hardwoods for propellers. In each case the Army production authorities were involved both in securing the lumber and in educating manufacturers to handle it properly.
In an ordinary biplane there are two beams for each lateral wing, eight beams to the plane. These form the basis of strength for the wings. Because of the heavy stresses put upon the airplanes by battle conditions, only the most perfect and straight-grained wood is suitable for these beams. All cross-grained or spiral-grained material, or material too coarse in its structure, is useless.
Spruce is the best of all woods for wing beams. Our problem was to supply lumber enough for the wing beams, disregarding the other parts, as all other wood used in the manufacture of planes could be secured from cuttings from the wing-beam stock. At the beginning we built each beam out of one piece of wood; and this meant that the lumber must be extra long, thick, and perfect. Until we learned how to cut the spruce economically we found that only a small portion of the lumber actually logged was satisfactory for airplanes. An average sized biplane uses less than 500 feet of lumber. In the hands of skilled cutters this quantity can be worked out of 1,000 feet of rough lumber. But in the earlier days of the undertaking as high as 5,000 feet of spruce per plane were actually used because of imperfections in the lumber, lack of proper inspection at the mills, and faulty handling in transit and in the factories.
We also used certain species of fir in building training planes. This wood is, like spruce, light, tough, and strong. The only great source of supply of these woods was in the Pacific Northwest, although there was a modest quantity of suitable timber in West Virginia, North Carolina, and New England.