UNITED STATES DEPARTMENT OF AGRICULTURE 
Washington, D. C. PROFESSIONAL PAPER February 20, 1923 ~ 
DECAYS AND DISCOLORATIONS IN 
AIRPLANE WOODS. 
By J. S. Boycr, Pathologist, Ofice of Investigations in Forest Pathology, 
Bureau of Plant Industry. 
CONTENTS. 
Page. Page. 
MALPTLOOUCTION — = a ose te eS 1 | Discolorations caused by fungi —----~ 24 
General considerations _____-__---_- 2 Sap stares Je Ob i ake ee ees 25 
Woods used for airplane construction_ 3 Brown-oak discolorations ___~_~ 29 
General defects of airplane woods__-_ 5 Decay. discolorations=——)—— =—-= 30 
<oler comparisons==. ———— —— 5 oo 14 | Decay in finished airplanes _______~_ 40 
Discolorations caused by wounds_--_ Deal OMIM IM Ayes ee See ee ee ee 42 
igehinins wounds'2222222 5-222 ee lalolteratures cited mse 3. = a Skee 45 
Sapsucker wounds] 3-2 =2- 20 | Defects of wood referred to in this 
EARN Ta Va HeCKS ona Se 20 bulletin, arranged by species____ 50 
meaemical \discolorations == 2-— 22 23 
INTRODUCTION. 
The purpose of this bulletin is to enumerate and describe the more 
important decays and discolorations to which woods used in air- 
crait construction are subject and the conditions under which they 
occur. It is well known that the initial or incipient stages of decay— 
_ that is, the first steps in weakening wood—are indicated by discolora- 
tions, but wood is subject to many color variations from the normal 
not caused by wood-destroying fungi. 
The value of recognizing the true nature of any given discolora- 
- tion or other abnormality is immediately apparent, sincé such knowl- 
_ edge will permit the free use of wood which, though seriously reduced 
in value from an esthetic standpoint by a disagreeable discoloration, 
is not mechanically weakened, while at the same time dangerous color 
variations can be detected. In the airplane industry, where the very 
finest quality of high-grade wood is demanded, and in which there is 
a maximum of unavoidable waste in the remanufacture of the lum- 
" ber, it is imperative that no suitable material be wasted or diverted 
_to another purpose, while at the same time it is equally important 
_ that all weakened material be excluded. 
This bulletin first considers certain defects in airplane woods not 
due to decay, but which must be readily recognized in order to avoid 
9997—23——_1 1 
