Measures for Progress: A History of the National Bureau of Standards

THE AIRPLANE IN THE LABORATORY 185
of petroleum. They yielded the first quantitative data reported anywhere
on the power-producing qualities of gasolines, and resulted in liberalizing
the excessively rigid specifications set by the French for the aviation gasoline
we were sending them, and incidentally were using ourselves.63
Designing an engine to lift the vast Government airplane program
off the ground was only half the task. New woods or wood substitutes had
to be found for airframes and materials for covering wings and fuselages.
Spruce, considered most airplane construction, became scarce
through oversea demands even before we entered the war. in exhaustive
tests of proposed substitutes, more than 20 other kinds of wood, shaped as
ribs, beams, and struts, went under the impact- and fatigue-testing machines
of the Bureau. Although a laminated spruce, made of the waste in solid-
beam construction, proved satisfactory, it was considered too costly, and only
beams of fir showed practical promise.
The spruce shortage and the desirability of building a nonflammable,
or at least fire-resistant, plane led to a great deal of work on metal airplane
parts. Several sheet metal companies even proposed an all-metal plane,
similar to the German Fokker introduced early in 1918. The companies
were far from encouraged when the wings on one all-metal mockup sent to
the Bureau for testing proved to have a low safety factor. The plane went
back for redesign.64
Metal wing and fuselage frames seemed more promising, and nu-
merous alloy steels were tested before attention finally centered on aluminum.
Weight for weight, some of the structural beams of aluminum ranked well
above Sitka spruce in strength tests, and in test flights an experimental plane
with wing beams and ribs of aluminum demonstrated "the possibility of the
successful manufacture of airplanes with metal-wing frames." 65 Only the
discovery of a satisfactory nonflammable or fire-resistant wing and fuselage
covering remained, and this problem had still not been solved when hostilities
ceased.
The development of an acceptable mercerized cotton fabric and even
a strong paper of jute and manila rope stock as substitutes for linen in air-
plane wing construction has already been mentioned. No form of glue or
adhesive, however, could be found that would fasten either cotton or paper
to the frame and at the same time render them waterproof and fireproof.
For this purpose, better airplane dopes had to be found.
A cellulose acetate made in Germany by Bayer was the dope usually
applied to the fabric on wing and fuselage, in order to shrink the material,
"War Work," pp. 16—24, 30—32; NBS Annual Report 1919, P. 26.
64 "War Work," p. 33. For another all-metal design turned down by the Bureau, see
letter, SWS to NACA, July 27, 1918 (NBS Box 13, INM).
"War Work," p. 34.