﻿UNITED STATES DEPARTMENT OF AGRICULTURE 



4W9"^-ft. 



f BULLETIN No. 1128 »# 



Washington, D. C. 



PROFESSIONAL PAPER 



February 20, 1923 



DECAYS AND DISCOLORATIONS IN 

 AIRPLANE WOODS. 



By J. S. Boyce, Pathologist, Office of Investigations in Forest Pathology, 

 Bureau of Plant Industry. 



CONTENTS. 



Page. 



Introduction 1 



General considerations 2 



Woods used for airplane construction. 3 



General defects of airplane woods 5 



Color comparisons 14 



Discolorations caused by wounds 17 



Lightning wounds 17 



Sapsucker wounds . 20 



Pith-ray flecks 20 



Chemical discolorations 23 



Page. 



Discolorations caused by fungi 24 



Sap-stain 25 



Brown-oak discolorations 29 



Decay discolorations 30 



Decay in finished airplanes 40 



Summary 42 



Literature cited 1 45 



Defects of wood referred to in this 



bulletin, arranged by species 50 



INTRODUCTION. 



The purpose of this bulletin is to enumerate and describe the more 

 important decays and discolorations to which woods used in air- 

 craft 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, since such knowl- 

 edge will permit the free use of wood which, though seriously reduced 

 in value from an aesthetic 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 



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