﻿DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. 6 



and, ultimately, decay. Then, too, it is almost impossible for the 

 stock in the center of the pile ever to become properly dry. 



At best, however, air drying is a matter of months, even with soft- 

 woods, while proper kiln drying can be accomplished within one to 

 three weeks or so, depending on the thickness of the stock. As a 

 rule, hardwoods both kiln-dry and air-dry more slowly. 



Air-dried stock should be shipped in the same manner as kiln- 

 dried and handled in the same way at the factory, except that it 

 must be kiln-dried to the proper moisture content before it is condi- 

 tioned in the shop. 



The principles given briefly in the foregoing paragraphs, together 

 with their application and underlying reasons, are brought out in 

 detail in the following pages. 



WOODS USED FOR AIRPLANE CONSTRUCTION. 



The most important wood for aircraft construction is spruce, 

 including red, white, and Sitka spruce (Picea rub ens Sarg., P. cana- 

 densis (Mill.) B. S. P., and P. sitchensis (Bong.) Trautv. and 

 Mayer), but of these Sitka spruce, on account of its much larger 

 size and the consequently greater quantity of clear lumber that can 

 be obtained, is paramount. By far the greatest proportion of the 

 lumber entering into the construction of most present-day airplanes 

 is spruce or one of its substitutes. The combination of strength 

 properties with light weight found in spruce is not duplicated in any 

 other wood. Most of the beams in the directing surfaces are prefer- 

 ably of spruce or a soft wood, as are many of the struts, and these 

 parts account for the bulk of the timber in an airplane. 



An excellent substitute for spruce is Port Orford cedar (Cham- 

 aecyparis lawsoniana (Murr.) Pari.), which is slightly heavier. 

 Unfortunately the supply of this splendid wood is decidedly lim- 

 ited. Douglas fir (Pseudotsuga taxifolia (Lam.) Br.), though much 

 heavier than spruce, is an extensively used substitute. Other woods 

 which can play some part in this way or may be used for special 

 purposes where a softwood is needed are western white pine (Pinus 

 monticola Dough), sugar pine (P. lambertiana Dough), western 

 hemlock (Tsuga heterophylla (Eaf.) Sarg.), white fir (Abies con- 

 color (Gord.) Parry), amabilis fir (A. amabilis (Loud.) Forbes), 

 noble fir (A. nobilis Lindl.), yellow or tulip' poplar (Liriodendron 

 tulipifera, Linn.), basswood (Tilia americana Linn.), incense cedar 

 (Libocedrus decurrens Torr.), and western red cedar (Thuja plicata 

 Don.). Certain parts of an airplane frame as a rule are made from 

 hardwoods. In such parts great strength and toughness are re- 

 quisite. Here, commercial white ash x stands supreme. For ex- 

 ample, it is unsurpassed for longerons -in those fuselages not con- 

 structed wholly or mostly of veneer. Black ash (Fraxinus nigra 

 Marsh), which does not possess sufficient stiffness for use in highly 

 stressed parts, can be distinguished from white ash (2; 30, p. 47 ; 68, 

 p. 62). 2 White oak, 3 hard maple (Acer saccharum Marsh), and 



1 Commercial white ash includes white ash (Fraxinus americana Linn.), green ash (F. 

 lanceolata Borkh.), blue ash (F. quadra ngulata Michx.), and Biltniore ash ( F. biltmoreana 

 Beadle). 



2 Serial numbers (italic) in parentheses refer to " Literature cited " at the end of this 

 bulletin. 



s White oak as used here includes white oak (Quercus alba Linn.), bur oak (Q. macro- 

 carpa Michx.), cow oak (Q. michauxii Xutt), and post oak (Q. minor (Marsh) Sarg.). 



