A Decennial Record 41 



or kilns based on laboratory ideas witb modifications to suit particular 

 conditions in their product. 



The drying schedules embodied in this sj^ecification were consid- 

 ered perfectly practical and safe from the standpoint of the strength 

 of the Mood; however, it seemed desirable, especially in the case of 

 various woods which were being considered as substitutes for spruce 

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

 data on the effect of various drying schedules, 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 on Design of Aircraft Parts 



There was immediate demand for accm-ate strength figiu-es 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 available 

 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 upon the results of these 

 studies. 



Designs and specifications for airplane wing beams presented 

 many perplexing pro})lems: to secure reasonable quantities of per- 

 fect beams, each machined out of a single piece of wood, was quite 

 impossible. 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. 



3Iuch attention had lieen given to defects and their eff'ect on 

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

 with some additional tests gave complete data on the relation of pitch 

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



