134 Discussion of Industries 
tity would have been very much larger, and instead of five 
builders of airplanes and airplane parts dozens would have 
been listed. Although the airplane industry is still in the 
formative period, it is certain that it has come to stay. Some 
manufacturers believe that.metal will be substituted for wood 
to a very large extent, while others are uncertain whether, 
after a trial of substitutes, wood will not yet be the substance 
finally chosen as the best all-round material. 
The airplane industry is highly specialized, each firm getting 
many of its parts from numerous other makers. Not only 
must the workmanship of a plane be of the highest grade and 
very carefully inspected, but the- wood used must be of the 
very best quality possible to obtain, and selected with the 
utmost care. At the opening of the war the industry knew 
little about the proper kiln-drving of airplane wood, the proper 
construction of laminated or built-up parts, the proper use of 
glues, the detection of hidden defects, and the weakening effect 
of spiral grain. All of these poimts and many more were 
studied during the war, especially by the Forest Products 
Laboratory of the United States Forest Service, at Madison, 
Wisconsin, where a large force of men with good equipment 
was constantly at work to help perfect military planes. Con- 
siderable quantities of veneer are used in airplanes; but this 
material does not appear in the table, veneers being discussed 
in the appendix. 
Strength and lightness are two prime requisites of the air- 
plane, and the woods used are selected on that basis. The cost 
of the wood is a secondary consideration. In order to obtain 
certain qualities, laminated wood, always stronger than single 
grain, was resorted to and cut from clear stock of the species 
listed in the table. 
Sitka spruce, which is abundant in Washington and Oregon, 
contributed over two-thirds of the wood reported. This wood is 
favored because it is more uniform than many others. It 
contains few hidden defects and surface indications are gen- 
erally a good criterion of the quality of the piece. It is 
possible that some eastern red spruce from the Adirondacks 
