Contributions of Botany to Military Efficiency. 5d 
which is administered by the Forest Service of the Department of Agri- 
culture in co-operation with the University of Wisconsin. How extensive 
was this work may be judged by the fact that on September 1, 1918, all 
or part of ten buildings were being utilized by the Forest Products 
Laboratory and approximately 400 persons were engaged in its work. 
At that time 75 per cent of the work of the laboratory was concerned 
directly with the airplane problems.’ 
The great demand for airplane woods rendered it impossible to depend 
upon the slow method of air drying and necessitated tests of different 
types of kilns, various kilning procedures, their suitability for different 
species, and the effect of kilning on strength. Satisfactory kiln drying 
methods were determined, and these were introduced into commercial 
kiln drying establishments engaged in the curing of airplane stock. 
Research was also undertaken upon the factors which determine the 
suitability of certain species for steaming and bending into the various 
bent wood parts employed in airplane construction, as well as upon the 
best conditions for bending and the effects of bending on the strength 
of the wood. 
A particularly interesting feature of the work was that relating to 
the utilization of thin plywood for fuselage walls, the pontoons of flying 
boats, and eventually for the covering of the wings themselves. Since 
these were entirely new uses for laminated wood, tests were necessary 
for the best species and for the best combinations. It was also necessary 
to test the efficiency of various joints and splices, and the effect of vibra- 
tion on plywood strength, and to determine the best methods for stamp- 
ing and molding the new construction material. By September, 1918, 
tests on the strength of plywoods had been carried out with 56 series of 
panels, each series consisting of 40 panels and requiring 240 tests. 
Twenty-five species of wood were represented in these 56 series. Ply- 
wood was also found to be an excellent material for different parts of 
the airplane framework. For such uses a core of yellow poplar with 
thin layers of birch, mahogany or black walnut was shown to be sat- 
isfactory. 
Laminated construction is also used in the airplane propeller, al- 
though here the laminations are of much greater thickness than in ply- 
wood. Six to ten layers of something less than one inch thickness each 
are used in building up the propellers. At the Forest Products Labora- 
tory extended studies were made to determine what wood species are 
most suitable for this very exacting use, what types of construction are 
best, and what conditions of manufacture and what finish are most effec- 
3 For these and other statements relative to the aircraft work of the Forest Products 
Laboratory the writer is indebted to the “Aircraft Research Program” and other reports 
of the laboratory furnished through the kindness of the Acting Director. 
