42 The Forest Pkoducts Labokatorv 



piece. The result was the issuance of specifications wliich described 

 the kind, size and location of defects permissible. This specification 

 immediately made available many beams which had already been re- 

 jected, and increased greatly the yield of acceptable beams. 



Active investigation into the relative merits of various types of 

 built-up airplane wing beams was undertaken early in the spring of 

 1918 at the urgent request of the Bureau of Aircraft Production. The 

 need for such investigations had been apparent for a long time, and 

 fairly thorough knowledge of the history of the use of the various 

 types had been secured; but lack of ability to organize for this work 

 in addition to that already under way had prevented progress in the 

 study. Clearing of the way for this M'ork resulted in the evolution 

 of a satisfactory beam as the result of an intensive test and study of 

 300 beams comprising that number of individual variations of ten 

 main types of construction. Subsequent tests developed the best 

 types of splices for flanges and webs, and detailed data was secured 

 concerning the behavior of individual woods with different types of 

 glue used in making built-up beams. 



The "possibility of improvements in design, especially in the larger 

 beams, became evident; further, the matter of "form factors" to be 

 applied to beams of various forms in making strength calculations 

 assumed importance because cross section has an important bearing 

 on specific strength. Consequently, tests on built-up beams have been 

 continued since the armistice and several noteworthy improvements 

 brought out. 



As the engineers in charge became more familiar with aircraft 

 design and construction, they saw more and more details which needed 

 improvement. Among those aircraft parts which seemed to suffer 

 most from poor design were the wing ribs, not only of the training 

 planes, but also of the fighters. Almost the first test made showed 

 that improvements were possible, and a group of men was given the 

 task of designing, building and testing wing ribs. A standard type 

 for small and medium ribs was evolved and ribs of this type were 

 developed for a number of Army and Xavy planes. So far as known, 

 the new type was an improvement over all existing types. Later 

 several very efficient truss types were developed for larger planes. 



Interplane struts, both solid and hollow, though designed on the 

 basis of formulae which had been checked experimentally, were in- 



