. Department bulletin. Agriculture; Agriculture. 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
. Department bulletin. Agriculture; Agriculture. 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 we
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