196 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



being made. Tests also are being carried on to aid in the perfecting 

 of designs for propellers. A waterproof coating has been found 

 which i^ractically eliminates absorption of moisture in the com- 

 pleted propeller, and hence shrinking and swelling, which are the 

 cause of much propeller trouble. 



Extensive experiments are being made in connection with the use 

 of laminated construction in parts of airplanes. The production 

 of material would be enormously facilitated if it were not necessary 

 to rely on single pieces in constructing the wing beams of the planes, 

 for these beams can be secured only from the most perfect wood. 

 Various built-up beams and struts have been tested at the Madison 

 laboratory, and a number of designs "have been found satisfactory 

 and used in airplanes. Methods are also being perfected for the most 

 effective designs for various splices and joints, permitting the use 

 of small-sized material, which can be produced in large quantities. 



The use of laminated structures and veneers in airplanes requires 

 waterproof glue, an expert treatment of the wood, and a very care- 

 ful application of the glue in manufacturing the material. Water- 

 proof glues have been developed and demonstrated to manufacturers, 

 and the experiments have resulted in the drawing of specifications 

 for the whole process of manufacturing laminated structures and 

 veneers. Standard methods of tests have also been developed and a 

 system of inspection and certification perfected to insure the accept- 

 ance of satisfactory glues only. 



Plywood formed by gluing together several sheets of veneer will 

 be increasingly used for various parts of airplanes. It can be formed 

 or molded to the proper contour of the body or wing, and its pos- 

 sibilities as a substitute for linen, which has been generally used 

 for body and wing covering, are striking. Little information 

 has existed as to the properties of veneer and plywood as a struc- 

 tural material. Its greatest uses have been for industrial purposes, 

 where an exact Iviiowledge of its strength and stiffness was less 

 necessary. A plywood w^ing rib, w^hich supports the wing cover, has 

 been developed for one type of plane as a result of the veneer investi- 

 gations and has been adopted for standard production. The weight 

 of this rib is nearly one-third less than that of the standard de- 

 sign, but its strength is 200 per cent greater. The significance of 

 this may be realized when the importance of weight and strength 

 in airplane design is considered. The results of these tests are indi- 

 cative of what may be done for other similar airplane parts. 



The military branches have encountered a problem of great magni- 

 tude in connection with containers and crates for over-seas shipments. 

 There has been involved in the first place the question of suitable 

 species of wood for containers and crates, and, second, of the designs 

 which have the required strength and at the same time occupy a 

 minimum shipping space. The necessary investigations have been 

 conducted in cooperation with the Division of Purchase and Sup- 

 plies of the General Staff and the Ordnance Department. The result 

 has been the improvement of specifications for containers and crates, 

 and the use of many more species with a consequent very large saving 

 of cost to the Government and of shipping space, and with a great 

 reduction in loss by breakage. The results of former work on ship- 

 ping containers, conducted in cooperation with the Bureau of Ex- 

 plosives and the Association of Box Manufacturers, have been of di- 



