Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-05-26
AVIATION
BY JOSEPH S. EDGERTON.

wood shelters the crew. Even WITH
this protection, the engineers are
not absolutely sure of their safety.
In their little armored cubicle
the research workers have control
of the engines operating the pro-
peller and have before them in
StrumentS showing the progress
of every phase of the experiment.
So they may watch the blade
without exposing themselves, a
transit has been arranged for
vision through a narrow slit in the
armor plate, the observers sight
ing through the transit by means
of a periscope-lik arrangement
of mirrors from deep under the
armored roof.
Provide Weak Link.
"The construction of the ar
mored roof has been carefully
planned to take up anticipated
Shocks" Mr.. Smith said. I'VE
realize that we must let the
energy of the blade destroy
something before its force is ex-
pended. That is the reason for
the steel and the more resilient
wood construction. We expect that
when a fragment of propeller
strikes the roof of the dugout the
top layer of two-inch steel will
crumble and curl like a hairpin.
We hope, of course, that the ar
NOR we have set up will be Suf-
ficient to absorb all the blow, but
we can't be certain that it will.
There is a possibility that steel
blade may get all the way
through"
AS a means of taking up the
unbalanced pull" resulting when
a test blade breaks off unevenly,
weak link" has been built into
the jack shaft, which is designed
to break under a stress of 10000
pounds. This weak link is formed
by a shaft coupling connected
with bolts, which shear off when
the danger point is reached.
Naturally if the blade should
break off in the upper part OF the
arc, it will fly eff into space rather
than crash into the bomb proof
room below. To care for this, a
movable bomb-proof pad" which
will check the fight of the blade
must be constructed completely
around it. This pad, which is de-
signed to give under the blow ana
thus deaden the shock, will be
constructed OF. layers of six inches
of oak, two inches of steel and
six inches more Of oak.
Without such an obstruction to
stop the fragments of the blade,
it is estimated that such frag-
ments would travel three to four
miles through the air.
Noise Is Terrific.
The noise of such a stand in
operation is almost incredible, Mr..
Smith said. It Is so fendiSh that
the nerves sometimes give way
and listeners suffer the most acute
physical pain. One big, stalwart
employee who was kept on duty in
the McCook Field bomb-proof
while an obstinate propeller was
being induced to give up" be-
came nauSeated purely from the
terrific noise. Mr.. Smith says that
the sound Of the big stand will be
clearly audible in Dayton, five
miles away, above the usual noises
of the city.
A special type of ear defense
equipment, composed Of a hard
rubber plug, with a gold screen
and special sound abSorbing fill
ing, has been devised to help
deaden some of the sound.
Use of the stands for testing
new types Of propellers, especially
the variable pitch type of blade,
about which comparatively little
is known, is expected to be a great
boon to every flyer, Army people
say. The shattering of a propeller
in the air usually is sufficient to
tear the engine away from It's
mounting and destroy the plane.
If the propeller happens to be be-
side the fuSelage and the blade
lets go on that side the ship may
very likely be cut in two, it was
pointed out.
Except on stands Of this char
acter there is no place where pro-
pellerS may be tested up to the
point of destruction so that the
weaknesses may be remedied In
subsequent models.