A Dkcknxiai. Kfa'oki) 43 



spected and selected in a manner wliieli did not seem to insnre accept- 

 ance of all suitable struts and the rejection of all unsuitable ones. 

 Further, there arose numerous questions concerning the actual 

 strength of certain struts and fittings. A rather extensive series of 

 strut tests was therefore undertaken to answer these ([uestions and 

 various others which arose from time to time concerning special types 

 of struts. These tests showed definitely that methods of inspection 

 could be improved materially and that certain special ty])es of strut 

 were not satisfactory. A non-injurious method of test or inspection 

 was devised, and later adopted by the Army, whereby the actual maxi- 

 mum load which each strut can bear is determined. Several note- 

 worthy types of large built-up struts were developed for the l)ig 

 flying boats being designed by the Xavy. 



The improvements in design resulting from the exi)erimental 

 development of beams, ribs and struts made evident the desirability 

 of similar work on other air craft parts. Tests were undertaken as 

 o])})ortunity offered, on various special details which were giving 

 trouble, and in several cases the development of new principles of 

 construction was carried out. In most instances these centered about 

 the use of plywood. Shortly after our entrance into the war. a very 

 elaborate investigation into the mechanical properties of plywood had 

 been initiated, since there was no information available upon this 

 subject and its importance in connection with aircraft design was 

 evident. As this investigation proceeded, the possibilities in the 

 structural use of this material became greater and greater, and the 

 new knowledge was applied as quickly as possible. Mention has 

 already been made of the new type of wing rib, a large part of the 

 success of which depends upon the efficient use of plywood webs. 

 Much of the progress made in wing beam design likewise was due to 

 the application of the new data to the design of these important parts. 



Several large elevator spars were designed for Xavy flying boats, 

 and in the progress of the test an entirely new type of construction 

 was perfected. The use of spirally or diagonally wound veneer over 

 the core provided very high resistance to torsional stresses with ex- 

 tremely low weight. The net result was a very strong and stiff spar 

 with the minimum weight. 



A new engine bearer was designed for the De Haviland plane. 

 This bearer is of plywood about an inch thick, cut out of the solid sheet 



