FOREST RESEARCH— IN THE WAR AND AFTER 



949 



wheels were dried with a loss of .37 of i per cent, spokes 

 for 60" wheels with a loss of .29 of i per cent, rims for 

 56" wheels with a loss of 2 per cent, and rims for 60" 

 wheels with a loss of i per cent. But even more im- 

 portant than losses is time, and time has been reduced 

 to one-twelfth. The type of kiln at the Rock Island 

 Arsenal was developed at the Forest Products Labora- 

 tory, as were also the methods followed ; and the man 

 who assisted in the initial operation was a Service expert. 



The drying of black walnut presented similar prob- 

 lems. Air-drying was the rule before the war. The 

 demand for rifles required the use of kilns, and with 

 the kilns came excessive losses. It is reported that one 

 plant adhering to an imperfect schedule lost 60,000 gun- 

 stock blanks, valued at $1.20 each when green, in a 

 single kiln run. Concerns following closely methods 

 developed by the Forest Service have been turning out 

 gunstocks with losses not uncommonly less than i per cent. 



If the war had continued the supply of naturally- 

 seasoned willow for artificial limbs would soon have been 

 exhausted. For 

 air seasoning a 

 period of three 

 to five years is 

 necessary. 

 Work under 

 way at the For- 

 e s t Products 

 L a b o r a t ory 

 promises to re- 

 duce this per- 

 iod to 60 or 70 

 days without 

 increase in 

 losses. 



A great vol- 

 ume of data on 

 the strength of 

 wood for prac- 

 t i c a 1 1 y all 

 American spe- 

 cies has been 

 built up in the 

 Forest Service during the past two decades. The num- 

 ber of individual tests amounted at the end of the war to 

 no less than 300,000 and covered 130 American species. 

 These tests were of constant and wide application during 

 the war in airplane construction and for practically every 

 other use where a knowledge of the strength of wood 

 was required. For example, they permitted the prepara- 

 tion of tables showing strength values at 15 per cent 

 moisture content which were adopted by both the Army 

 and the Navy as a basis for the design of all wooden 

 parts of aircraft. These data made it possible to select 

 the species most suitable for airplanes and to be sure of 

 the selection, and made it equally possible to reject 

 unsuitable species. They showed that the variation in 

 strength was so great as to render a considerable per- 

 centage of even the best woods unsuitable. By a density 



Photogaph by H. D. Tiemann 



DRY KILNS OF THE TIEMANN TYPE 



Built in the Pacific Northwest for seasoning airplane stock by the Bureau of Aircraft Production these 

 kilns have a daily capacity of 35,000 to 40,000 board feet of wing beam stock. From some of the charges 

 there was no degrade due to drying. Each of the 24 kilns holds 6 loads similar to those shown. 



requirement it became possible to insure the selection of 

 the strongest stock. By the admission of specified defects 

 in lightly stressed parts it was possible practically to 

 double the quantity of acceptable stock without sacri- 

 ficing anything in safety. The latter problem involved 

 little more than the application of data already available 

 and the assignment of one man for a period of about 

 three months. Many thousand men in the woods and 

 at the mills would have been needed to produce the same 

 quantity of spruce. 



One country lost many planes in flight because spiral- 

 grained spruce was used in construction. Forest Service 

 tests prevented similar losses on our part by showing 

 where the line between straight and spiral-grained ma- 

 terial could be drawn safely. Little was known at the 

 beginning of the war on the strength of plywood as a 

 material. The need for this information was supplied 

 very rapidly by an extensive series of tests which be- 

 came the basis of all of the present plywood specifications 

 and of plywood strength factors used in airplane design 



by both the 

 Army and the 

 Navy. In ad- 

 dition, the tests 

 made it possi- 

 ble to adopt 

 with safety the 

 u t i 1 ization of 

 more species 

 than had origi- 

 n a 1 1 y been 

 thought s u i t - 

 able and thus 

 prevented the 

 supply of ply- 

 wood from be- 

 coming, as it 

 might easily 

 have become, a 

 factor control- 

 ling a i r p lane 

 production. 

 Further ap- 

 plications of strength data were found in the design of 

 wing beams and wing ribs. Laminated wing beams, for 

 example, oflfer the opportunity to utilize a much larger 

 per cent of the spruce cut, a percentage far too low at 

 the best. Special supplemental tests developed types of 

 laminated and spliced wing beams as strong as the solid 

 wing beam of our first planes, and the types developed 

 have been adopted by the Army and Navy. As an ex- 

 ample of the special supplemental tests on wing ribs may 

 be cited those for an American combat plane produced in 

 large numbers. The weight of the standard rib was 

 reduced by one-third and the strength per unit of weight 

 was increased three times. The wing so developed was 

 adopted and similar designs were developed for six other 

 Army and Navy planes. Strength tests had a further 

 application in ship timber, and this and other information 



