There is no handy library or compilation of sound data for RC aircra;, but the author compiled a
chart that shows that the typical sound levels for various types of RC aircra;, at a reference distance
of 100 feet.
Noise is one of the major issues threatening RC airfields and many other recreational activities.
What you consider to be a pleasant
sound from a glow engine at 17,000
rpm can be an unbearable racket for the
neighbors who do not share your passion
for RC flight. Part of the definition of
noise is, “sound that is unwanted or
The sound factor draws many into RC
aircraft flying—a big part of the fun is
the engine noise. Some hobbyists avoid
electric-powered airplanes because of
the lack of engine sounds.
I choose to ride a large Honda touring
motorcycle which is no louder than
a typical car. My neighbor down the
street loves his Harley, complete with
loud aftermarket exhaust pipes. For
him, the noise is an integral part of the
experience. The neighborhood is not as
enamored, especially at 7 a.m.
The Basics of Noise
Our eardrums sense tiny fluctuations
in air pressure, which we interpret as
sound. The decibel scale is used for
expressing sound levels because we do
not perceive loudness in a linear fashion.
We detect loudness in a logarithmic
way, similar to the Richter scale for
Although an increase of 3 decibels
(dB) doubles the sound energy or
amplitude, it takes a change of 10 dB to
be judged as twice as loud. Each similar
decrease of 10 dB is considered to be
half as loud as the original sound.
Changes of 1 dB are not perceptible.
A 3 dB change can be heard by a critical
listener under ideal conditions. A 5 dB
change is normally the threshold where
a difference is readily noticeable, either
up or down.
A-weighted decibels (dBA) are
commonly used to measure sound levels.
The A-weighted scale deemphasizes low
frequencies to directly compare loudness
from different sounds. Theoretically, a
diesel locomotive measuring 80 dBA
has the same loudness as a cymbal at 80
dBA, although the frequency content is
Our ears and hearing system are
constructed to put more emphasis on
high-frequency sound than low tones.
It is important to hear a twig snap
(high-frequency) from behind as the
grizzly bear stalks you. Low-frequency
rumble from distant thunder miles
away is less critical. Most of the
information content from speech is in
the middle and higher frequencies, 500
Hz to 2000 Hz.
The time of day, duration, and
variability of sound affects the
annoyance factor. Steady sounds are less
annoying and more easily accepted than
a varying sound. Sounds with pure tones
or major fluctuations in level are more
noticeable, which is why those sounds
are used for alarms and sirens.
In the case of RC airplanes, the sound
levels change throughout the flight.
The variability makes the noise more
noticeable and annoying to the public.
Two common ways to express sound
levels are the equivalent continuous
noise level (Leq) and the momentary
maximum level (Lmax). The Leq
is the summed total of the sound
energy occurring throughout the
event or a time period. Although not
mathematically precise, Leq can be
thought of as the average sound level.
The Lmax is the loudest noise that
occurs, if only for a second or two.
It takes a more sophisticated sound
meter to measure Leq and calculate the
running average. A decent sound meter
of reasonable accuracy will cost at least
$300. An integrating sound meter that
can directly measure Leq typically costs
$1,500 or more.
There is no magic number to make
everyone happy and avoid annoying
or offending others. There also is not
a definite dB value where everyone
agrees that noise becomes a problem.
30 Model Aviation MARCH 2013 www.ModelAviation.com