Evening star., 1941-01-25
BY JOSEPH s. EDGERTON
Star Staff Corresnondent.

SLaE OLalI Correspondence.
INDIANAPOLIS, Jan. 25.-Work-
ing parts of the modern aircraft
engine are something like toy bal
loons-as long as the surface is in
tact they are good, but nick the sur
face and they are gone.
Because every part Of an aircraft
engine must be reduced in weight
to the ultimate ounce, every bit of
metal which does not perform useful
service or provide needed strength
must be cut away. A hollow tube
may be stronger than a solid shaft,
because the outer surface carries
most of the load.
On this theory, hollow crankshafts
and other parts make up the modern
airplane engine. The strength may
be in the surface, and any surface
weakness may be fatal-literally IA
tai, since the life of the airplane
pilot and his crew may depend upon
continuous perfect operation of the
engine.
AS result, there is not moving
piece of steel in the Allison engine,
built here for the Army and England
by General Motors Corp, or, for
that matter, in any other modern
airplane engine. Every steel surface
is polished as bright as any mirror.
That polish is safeguard against
the slightest scratch, which imme-
diately becomes visible. 1t also is a
safeguard against even the touch
of sweaty finger that might cause
corrosion and disaster.
o. T. Kreusser, director of Allison
production and training, explained
picturesquely:
"A toy balloon is strong as long
as its surface is intact. 1t will with
stand a great amount Of tension
and distortion of its own structure
and the air inside. But prick it with
pin, and, pouf! The whole
thing is gone. The parts Of an air.
craft engine, in similar manner, are
strong only so long as they are per-
feet: a scratch may spoil the whole
job"
Defy Teeth Of Finest File.
Many Of the mirror bright sur
faces OF the aircraft engine are fur
ther protected by heat-treating in
electric furnaces and oil baths or by
other methods which make them so
hard and tough they will turn the
teeth of the finest file without re-
celving a scratch.
Dry ice plays its part in assembly
OF the Allison engine. Steel engine
cylinders are deliberately machined
100 large to go into the bores pro-
Vloed Tor them in the crankcase,
which is Of aluminium alloy. The
aluminium goes into an electric
furnace which heats it from 470 to
500 degrees centigrade.
Beside the furnace is a biz wooden
oox OF dry ice in which the steel
cylinders are placed until they are
chilled to II degrees below zero.
The aluminium expands, the steel
contracts until the cylinders slide
smoothly into the bores which a
short while before were too big for
them. AS normal temperatures
return to the heated and chilled
metals they lock together in a grip
which outlastS the engine.
Reflections Reduced.
So precise must be the construc-
ton OF every part of the engine that
an error of as much as three one
thousands of an inch in the position
or size of the hole for the hold-down
bolt results in rejection of the part
During the early days of Allison
production reflections we're FREQUENT
and very costly. Today reflections
amount to only S per cent of the
1000 parts which go into each
engine
Another example of the care sur
rounding production of these engines
for American and British fighting
planes is the fact that final as
sembly takes place in locked cages.
After their first green run" on the
test stands each engine is completely
disaSsembled and every part in
spected. The 1000 parts then 20
into cages. where they are locked in
with the men who assemble them.
This is done to prevent any posi-
ollity OF sabotage during the critical
hnal assembly. 1t is merely an added
protection, since every Allison en-
ploye has been subjected to scrutiny
OF the Federal Bureau of Investipa-
tlon 10 make sure OF his loyalty, and
no employe is permitted near the