Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-06-09


absolutely impossible to calculate strains O.
stresses, resistances or shock This information
was obtained only after the cut-and-try method
One of the first big problems in parachute
construction was to make it strong enough to
Withstand the great shock and strain imposed
upon 1t when used from an airplane. Previously
the parachute had been used only in jumps
from balloons, which did not impose any great
amount of strain on them.
When Maj. Hoffman took charge Of the para
chute branch; he discovered that up to that
time, parachutes had been tested from airplanes
with no more than q 50-pound weight. He i'm
mediately discontinued this practice, realizing
that the parachute must not only be made
strong enough to hold together and carry one
man under any conditions but that it should
possess reserve strengthen other words, q
factor of safety.
Through a process of calculation 1t was de-
termined that the terminal velocity of a man
falling freely would be at the rate of about $50
miles an hour. The problem, then, was TO de.
sign a parachute which would function upon
being opened, when carrying 200 pounds travels
ing at that velocity.
In conducting the tests, the time-fuse mecha-
nism taken from the nose of artillery shell
was utilized. The parachute with weight at
tached was dropped from airplane and,
after falling for a predetermined number Of
seconds, the fuse operated a release mechanisna
which in turn caused the parachute to open.
These tests were continued and notifications
made from time to time, until parachute body
and rigging we're devised which held together
under load of 200 pounds when opened after
a free fall Of 16 seconds:
THE utilization of the artillery shell time.
fuse mechanism in all of the parachute
drop tests proved rather cumbersome propo-
sition, and caused Mai Hoffman to seek the
solution of another puzzle-determine what
load released from an airplane flying at MAKE
mum speed would produce q strain on q para
chute similar to that imposed by a 16-second
fall Drop tests followed, wherein the load ON
the parachute was gradually increased until ft
was found that a weight of 400 pounds, released
from an observation afrplane flying at a speed
of 100 miles an hour. would cause as great,
not a somewhat greater strain on the parachute,
than that produced by a weight of 200 pounds
after falling free for is seconds.
BY a slow process of development, fabric
was developed capable of withstanding the
necessary amount of strain. This fabric, an
Oriental silk, was chosen because of its great
strength, elasticity. light weight. small bulk
when compressed and long life Unlike cotton,
it is not as much affected by the ravages Of
mildew, and If ignited by a match, the burn
ing part in the silk will bubble and 60 out, and
If blast of air is blown on the burning silk
the fire will 60 out Immediately
Its strength Is about SO pounds to the inch
An important factor in parachute design Is
the amount of air which can leak through the
fabric Even though silk would be tremen-
dously strong if woven tightly. the great air
pressure would cause 1t to burst. If the ma
terial is too porous, the parachute would not
open readily; hence the porosity of the silk
presented difficult nut to crack. Parachutes
measuring 80, SO and 40 feet in diameter were
constructed for experimental purposes. These
we're later cut down to smaller sizes.
In the course of the experimental work It
found that, at times certain of the rig
gng lii ss of the parachute would break during :
drop tets, Maj. Hoffman attacked this prob
lem by devising a mechanism for measuring
and recording the shock on each individual
cord during test. The suspension cords or
shroud lines were at first made Of braided linen
cord, but by gaining the co-oeration of a promi-
nent manufacturer of fishing line, braided
silk cord wss developed which was found to be
highly satisfactory.
In keeping with its policy of encouraging
private enterprise, the Army Air Corps was I'm
constant touch with parachute manufacturers.
informing hem Of all developments as they