266 JOURNAL OF FORESTRY 



The growing use of plywood in airplane construction carried with it 

 a growing demand for production of waterproof glues in quantity and 

 for the improvement of their quality. Our production facilities in the 

 United States at the beginning of the war were inadequate. We had 

 comparatively few glues, and the formulae of those which were being 

 produced were not generally available. The work of the Forest Service 

 developed several formulse w'hich were demonstrated to manufacturers 

 as needed. This work, together with other assistance to the military 

 departments and to the manufacturers, resulted not only in increasing 

 by two or three hundred per cent the quality of the plywood produced, 

 but also resulted in a direct saving to the Government of several million 

 dollars. 



For plywood as a material there was at the beginning of the war 

 no technical information on strength: This was secured rapidly until 

 several thousand tests gave the basis for fairly satisfactory plywood 

 design. These tests were the basis of all the present waterproof ply- 

 wood specifications and of plywood strength factors used in airplane 

 design by both the Army and the Navy. The tests have already re- 

 sulted in throwing open the field of use to a number of species formerly 

 considered unsuitable, and the supply of plywood was removed as a 

 factor controlling aircraft production, which it might easily have 

 become. 



Strength tests of wood as such and of plywood as a material led 

 logically into tests of airplane parts and were leading still further into 

 tests of assemblies of parts, such as wings, fuselages, etc. As an ex- 

 ample of what the specialist in the strength properties of wood can do 

 beyond the airplane designer may be cited tests on the wing ribs of the 

 De Haviland "4." Weight for these ribs was reduced by 30 per cent 

 and strength per unit of weight was increased 300 per cent. The wing 

 rib so developed was adopted. Similar designs w^ere developed for six 

 other Army and Navy planes. 



The work of the forester was not completed, however, by furnishing 

 material on the properties and conditioning and use of wood in air- 

 planes. To decide upon the best substitutes for spruce it was necessary, 

 in addition to knowing strength and other properties and methods of 

 conditioning, to know the total and available stand and what might be 

 expected in production. Then in a number of cases there was the 

 problem of stimulating production. Our program included, therefore, 

 field studies not only of the eastern spruces, comparable in everything 

 except size with the Sitka spruce of the Northwest, but also other pos- 



