A DlA KXXIAL KkC'OKI) 41 



or kilns hased on laboratory ideas with modifications to suit particular 

 conditions in their product. 



The drying schedules embodied in this specification were consid- 

 ered perfectly practical and safe from the stand})()int of the strength 

 of the wood : however, it seemed desirable, especially in the case of 

 various woods which were being considered as substitutes for spruce 

 and for mahogany and walnut (for propellers), to secure additional 

 data on the effect of \ arious drying schedides. including those specified, 

 upon the mechanical properties of the wood. These data were in- 

 tended to determine the limits, as to drying schedules, which could 

 not be exceeded with safety, it being advantageous, of course, to dry 

 the stock as rapidly as permissible. Therefore, a comprehensive pro- 

 gram of drying and testing was initiated. Thousands of strength tests 

 were made upon carefully matched specimens, green, air-dried, and 

 kiln-dried, and the effect of the drying upon the strength determined 

 by analysis of the data. 



Work an Design of Aircraft Parts 



There Mas immediate demand for accin-ate strength figures for 

 woods used in aircraft design, and it was possible to supply much of 

 this information from data on hand. A study of the data availalile 

 on most American species resulted in the approval in specifications 

 of suitable substitute species for woods commonly used in airplane 

 manufacture. The list of approved substitute woods issued by the 

 Bureau of Aircraft Production was based ujjon the residts of these 

 studies. 



Designs and specifications for airplane wing beams presented 

 many perplexing problems: to secure reasonable ({uantities of per- 

 fect beams, each machined out of a single ])iece of wood, was quite 

 impossiljle. It became necessary, therefore, to devise ways and means 

 for the production of satisfactory beams from defective material. Two 

 general lines of attack were followed, namely, ( 1 ) a study of defects 

 and (2) the development of built-up beams. 



]Much attention had been mven to defects and their effect on 

 strength prior to the war. but further study of earlier results coupled 

 'vvith some additional tests gave complete data on the relation of pitch 

 pockets, knots, cross grain and spiral grain to the strength of a given 



