APPLYING THE DOPE TO AIRPLANE WINGS.
Yet when we had resolved the difficulties in the forests only part of the problem had been met. Next came the intricate industrial question of how to prepare this lumber for aircraft use. We possessed little knowledge as to the proper methods of seasoning this timber. The vast majority of woodworking plants in this country, such as furniture and piano makers, had always dried lumber to the end that it might keep its shape. We now were faced with the technical question of drying lumber so as to preserve its strength. The forest products laboratory worked out a scientific method for this sort of seasoning. Incidentally they discovered that ordinary commercial drying had seldom been carried on scientifically. The country will receive a lasting benefit from this instruction carried broadcast over the industry.
In the progress of our wood studies we discovered a method of splicing short lengths of spruce to make wing beams and in the later months of the production used these spliced beams exclusively at a great saving in raw materials. The use of laminated beams would probably have become universal in another year of warfare.
COTTON FABRIC AND DOPE.
The flying surfaces of an airplane are made by stretching cloth over the frames. When we came into war it was supposed that linen was the only common fabric with sufficient strength for this use, and linen was almost exclusively used by the airplane builders, although Italian manufacturers were trying to develop a cotton fabric. Of the three principal sources of flax, Belgium had been cut off from the allies, Russia was isolated entirely after the revolution there, and Ireland was left as the sole available land from which flax for airplane linen could be obtained.
As late as August, 1917, England assured us that she could supply all of the linen that would be needed. It rapidly became evident that England had underestimated our requirements. An average airplane requires 250 yards of fabric, while some of the large machines need more than 500 yards. And these requirements do not take into consideration the spare wings which must be supplied with each airplane. This meant a demand for millions of yards put upon the Irish supply, which had no such surplus above allied needs.
For some time prior to April 6, 1917, the Bureau of Standards at Washington had been experimenting with cotton airplane cloths. Out of the large variety of fabrics tested several promising experimental cloths were produced. The chief objection to cotton was that the dope which gave satisfactory results on linen failed to work with uniformity on cotton. Therefore, it became apparent that if we were to use cotton fabric, we should have to invent a new dope.
Two grades of cotton airplane cloth were finally evolved—A, which had a minimum strength of 80 pounds per inch, and B, with a minimum strength of 75 pounds per inch. Grade A was later universally adopted. This cloth weighed four and one-half ounces per square yard.