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National Advisory Committee for Aeronautics, Technical Notes - A Survey of the Aircraft Noise Problem with Special Reference to its Physical Aspects

This brief survey is aimed at providing a background for various
general phases of the aircraft-noise problem. Material has been drawn
from National Advisory Committee for Aeronautics noise—research programs
at the Langley Laboratory, from visits to various organizations which
are concerned in some way with the aircraft—noise problem, and from a
review of the literature. The effects of noise are discussed briefly as
a background for the reader and brief discussions of the physical chars
acteristics of aircraft noise and some ways of protection from noise are
also included along with a limited bibliography of research work
applying to the aircraft-noise problem.

These and other related studies indicate that no easy and inexpenr
sive solution to the aircraft-noise problem is available at present.
Reductions of noise at the source are possible in some cases, as for the
propeller and the reciprocating engine, but only if a possible performs
ance penalty is acceptable. The problem of providing adequate protec-
tion is in many cases expensive and is complicated by the intense low;
frequency content of the noise from most aircraft—noise sources.

The problem of aircraft noise and its reduction has been of interest
for many years but is becoming of greater concern because of the higher
noise levels being generated and the ever increasing number of people
being affected. Developments of more powerful propulsion systems for
military and commercial use have inherently resulted in higher noise
levels. Thus not only are passengers, crews, and service personnel of
airplanes affected to a greater degree, but so are larger groups of
people working and living near airports and test facilities. Because of
the widespread interest in this subject and because of its importance,
the National Advisory Committee for Aeronautics, other governmental
agencies, and aircraft companies are continuing their basic research
relative to aircraft-noise problems in general, in an attempt to define
the present and future scope of the problem and to explore the possi—
bilities of their solution.