Evening star. [volume] (Washington, D.C.) 1854-1972, 1930-10-26
REDUCING AIRPLANE NOISES
BY FREDERIC J. HASKIN.

Realizing that the American people
are particularly insistent upon comfort
| in travel, manufacturers and operators
| OF commercial aircraft are devoting
serious attention to the reduction Of
| noise produced by aircraft. In this
work assistance is being given by such
| technical organizations of the Govern
ment as the National Bureau Of
Standards.
Noise Is considered by many to be
the greatest drawback to airplane travel.
While there has been steady growth in
the use Of planes by travellers in the
United States, 1t is believed by the
owners of commercial lines that there
would be more If the noise could be
| modified
Plane pilots and wartime aviators In
| some cases suffered impairment of hear
ing as result Of the incessant roar Of
the propeller and the exhaust In the
| early days OF flying. planes did not have
cabins. Pilot and passengers sat in
open cockpits. The passenger planes
now in use commercially are all cabin
planes and this lessons the noise some
what, but 1t still Is sufficiently deafening
| to preclude ordinary conversation.
Inasmuch as very considerable per-
centage Of Americas conversation Is
| carried on by travellers who usually are
| not occupied with anything else en-
route. a system Of travel which rules
| out this pastime is not especially at
tractive. The commercial line opera
tors realize that while many people
VIII travel by plane once or twice for
the novelty Of the experience, or, in
emergencies. to reach destination with
all possible speed, they will not make
regular practice of using planes If
they cannot talk. The idea Of q travel
ing man absolutely unable to tell O
story while en- route to the next town
Is too fantastic to grasp.
Engineers who have been working on
the problem are attacking 1t from two
angles. First, they are seeking to re-
duce the volume of noise at the source.
That IS, they are experimenting with
methods OF so lubricating and tuning
the engine and the propeller that less
| noise will be generated. Second, they
are seeking means Of insulating the
cabin so that a minimum of sound will
enter. AS planes now are designed,
practically all of the noise Is generated
from outside the cabin. To be sure,
the source Is Immediately adjacent, and
vibration as well as sound Is trans
mitted through the structure itself 10
the interior Of the plane. But the
sounds released into the air can be
excluded to some extent.
Insulating the CabinA
Experiments made by the Bureau of
Standards with methods for Insulating
against noise promise that plane cabins
can be so constructed that noise will
be reduced to q volume at which the
interior disturbance will be no greater
than that experienced In o Pullman
car or motor bus. Conversation be-
tween persons sitting next to each
other will be DOSgible
The technicians have concluded that
propeller noise can be reduced by de-
creasing the tip speed Of the revolving
blades. New designs arrange the gear
ing In such a manner as to accom-
plish this. Mufders are being provided
for engines. 1t Is known that the
hotter the exhaust gases the louder the
sound of their explosion. Therefore,
cooling devices have been designed to
cool the gases as they pass through
the mufaer.
Principal attention has been given
to the insulation of the cabin itself.
The Bureau Of Standards has expert
mented with materials and with the
fundamental principles Of acoustics