Evening star. [volume] (Washington, D.C.) 1854-1972, 1931-01-25
$50 wly Winning
the Battle against
AUiatim s Greatest
Hazard, Science
Noov Goes One Step
Further in Giving
Pilot Eyes to Pierce
Dangerous Mists.
BY JOHN L. COONTZ.

n SOUND WAVE shot down to the
4 m earth and its echo reflected back to
- the pilot in q plane in sciences
final answer to fog;s challenge that
it can't be conquered by aviation
As a result of the reflected echo IL mas been
conquered. according to officials of the United
States Army Air Corps and Of the General Elec-
trio Co. who. co-jointely. have perfected
Bound-wave sending and understanding device
for plane use, called sonic altimeter
The sonic altimeteT, recently tested success
fully at Boiling Field, Washington. D. c.. is
startling in its simplicity. 1t consists OF nothing
more than two horns, one OF which, motor
driven sends to the earth sound wave ana
the other Of which, few seconds later, receives
it back again. It is located In the cockpit OF
nlane. the sending horn in front Of the pilot,
between him and the engine, the receiving horn
In his rear receiving stethoscope, adJustabfe
to the ears of the pilot, is attached 70 TINS norm.
The time that it takes q sound wave TO go
from q plane to the cath and come back again
Is measured. AS it travels at certain speed
always the elapsed time in each instance ndi-
Gates to the pilot his altitude. A dial records
all heights more than SO feet above the ground.
In the tests recently conducted at Boiling
Field the sonic altimeter worked perfectly. In
many of them the pilot was enShrouded in
covered cockpit. In each instance he was able
70 read his position above the earth correctly.
At about i've feet above the ground the whistle
and echo of the sonic altimeter blend into one
perfect. ms Is the SigndA 1OE SAAS pAot W
pub back the stick of his plane and settle down
safely or pancake" to the ground.
Lieut.. Roland Birnns of the Air Corps, who
made q test fight equipped with the altimeter,
describes It's use and value.
SGT ENTERED the cockpit Of plane operated
by Lieut. Hegenberger and equipped with .
sonic altimeter. In the rear cockpit was pair
OF stethoscopes, to al appearances the same as
A. 49, m
plugged In on the main line. Before taking
on Lieut.. Hegenberger got the apparatus to
working In order that I might familiarise my
self with the sound Of the whistle. Then he
shut on the apparatus and took on to an aiti-
tude Of several hundred feet. Then he set the
device IN operation again.
you could hear the emitted whistle sharply.
nc 500 feet altitude the echo sounded about one
second after the emitted sound. The sound
wave travels at speed Of leo feet per second.
Our exact altitude was indicated by the gauge
I'm Lieut. Hegenberger's cockpit.
at was interesting in flying over nat coun-
try and then suddenly over the hills by st.
Elizabeth's Hospital back Of Boiling Field to
note the quickening response and the short time
It took for the answering echo as we few over
the hills. Over woods and broken country the
echo was not as sharp as over the open, nat
fields.
"Lieut. Hegenberger banked around the north
angle of Boiling Field, headed his plane for
Paying attention only to the altitude and to
the longitudinal motion of the plane, de-
creased my speed by pulling back the throttle
and gliding at about rs miles per hour for the
field with my head ducked down inside the
cowling. relying only on the sonic aitimeter to
indicate to me the distance I was from the
ground. Lieut. Hegenberger corrected any ten
dency on my part to veer of to one side or
the other Of the course or to drop a wing of
the plane, although this was hardly necessary
rs the plane. q Douglas basic training plane,
was very stable lateralIy and directionally. His
main function was to see that I avoided any
obstruction, such as towers at the Navy Yard
and other airplanes which might be flying in
the vicinity.
"Below so feet one does not rely on the gauge
30 indicate altitude, but on his aural or ear
senses alone. At so feet the echo comes back
yenth of second later; at five feet it comes
back hundredth Of q second later. BY that
time the average person cannot distinguish
between the emitted whistle and the echo They
blend as one sharp note A few feet above
that, Lieut. Hegenberger later told me Chat It
was about IL feet from the ground, pulled the
stick back slightly and the air speed meter went
down below SIS miles an hour, which is about
staIling speed OF the airplane
~T71e sorTud was Just beginning to blend as
one shasr 1ote in my ears when felt the
plane pancake" suddenly and bounce aIightly,
making what would be considered under normal
circumstances a fair three point landing.
Ideut Hegenberger told me later that had
spancaied'' the plane from about i've feeA But