Albuquerque morning journal. [volume] (Albuquerque, N.M.) 1903-1926, 1921-09-22

gratifying results by number Of
government departments, indus
trial associations and individuals
Thousands of tests have shown the
exact value of each kind Of wood
for box construction. Special
studies of nails and mailing have
shown just what size of nail to use
with each kind and thickness OF
wood and how far apart to space
the nails to secure the best results.
The actual design of various kinds
of boxes has been thoroughly
studied and the efficiency of vari-
GUS types of construction deter
mined. The merits of wires and
strapping and of various methods
of applying and fastening them
have been analysed. Studies have
also been made upon veneer boxes
and upon fiber containers of many
types.
Airplane Propcllers.
One of the greatest troubles ex-
perienced with airplane propellers
during the war was caused by the
warping and twisting of the blades
hodl LILO ups anu lctl 80 pSllCuI-
age of the propellers received at
the front were rejected on this ac-
count.
In order to determine the cause
and to develop methods of pre-
venting this trouble, a number of
experimental propellers were man
ufactured for the war and navy
departments by the forest products
laboratory.
The propellers were made Of
Central American and African ma
hogany, using carefully selected
stock, uniform in density and
moisture content, and were stored
under uniform atmospheric con-
ditions for 80 days between the
out and final carving OPP
erations. After the standard fin.
ish, consisting Of five coats of spar
varnish. had been applied. they
were again stored under the same
for observation as to
warping and twisting.
These propellers were made up
and handled much more carefully
than the commercial product, and
every possible effort made to pro-
duce perfect results. After ex-
posture to very damp or humid
atmosphere for three or four
months, it was found that every
propeller had warped or twisted
or otherwise changed shape to such
an extent that made them unac-
ceptable for use. They had all
absorbed about five per cent of
moisture through the five coats of
spar varnish. and thismoisture
caused all the trouble. The treat
ments to which these propellers
were exposed, namely, being manu-
featured in a relatively dry con-
dition and later exposed to moist
is very similar to that
which is normally received by pro-
pellers made in the United States
and shipped to France. Ere
quently propellers are made in a
moist climate and
to drier one. and trouble
from change Of shape due to dry
ng is almost sure to result.
There is only one way in which
.rouble from change of shape due
20 changes in moisture may be OBJ
Waited, and that is to prevent these
moisture changes. The expert
nents just outlined show that 1t
s impossible even under ideal man
lfacturing conditions to produce
which will not warp or
'wist with changes in moisture.
These changes may be prevented
,ither by applying moisture
proof coating or by keeping the
)ropellers under uniform atmos-
,heric conditions throughout their
life. At present. the aluminium
eaf covering developed by the For
st Products Laboratory is the only
moisture-proof coating
which has been successfully applied
o propellers. 1t is not possible
o keep propellers under absolute
Y uniform atmospheric conditions
Turing manufacture and service,
nut these conditions can be ap-
'roached by making up the pro- J