How to Noise Test a Model Aircraft
(The BMFA way)
How to noise test a fixed wing model aircraft
- Measurements should be taken in the open air and away from noise reflecting
surfaces such as buildings, cars, and hedges.
- The wind speed should not be over 3 metres per second (force 2)
- Measure a distance of 7 meters and place marks on the ground. If there
are existing marks, double check to make sure they have not been moved.
- Make sure that the foam wind muffler is fitted to the sound meter, this
is VERY IMPORTANT.
- Set the sound meter switches as follows.
- Set the "function" switch to "A weighting"(this is
the closest representation to what a human can hear).
- ii. Set the "response" switch to "S" (Slow).
- iii. Turn on the meter and select the "range" to "Lo".
- For safety, a third party who should stand on the opposite side of the
tester to the noise meter should hold the transmitter. Failing this the person
holding the noise meter should have control of the transmitter.
- The engine in the model should be tuned to obtain maximum RPM at full throttle.
- The model should be upwind of the noise meter.
- The model should be held between 1 and 2 meters off the ground and as far
from the person holding it as possible, this is due to reflected noise.
- The sound metre should be 1.2 meters off the ground (approx shoulder height)
and out to one side at arms length this is to reduce the amount of reflected
- Holding the engine over the marker at all times, the testing of the model
can now commence as follows
- model pointing directly at the meter
- model pointing 90° to left of meter
- model pointing directly away from the meter
- model pointing 90° to right of meter
- The highest reading should be used.
BMFA ADVICE ON THE NOISE
The noise testing procedure noted in the DoE (Department of the Environment)
noise code above should be followed carefully but to get the best results it
is strongly recommended that you should take special note of the following:
Make sure that no noise reflecting surfaces are near the test site. This means
not just buildings but cars, concrete, models, model boxes and even hard packed
earth. Do the test over grass.
Do not take measurements when there is any appreciable background noise. Traffic
on a nearby road, other models flying or being readied for flight and even people
talking near the meter can affect the readings.
Wind blowing across the microphone has a big effect on readings. Do not test
on breezy days and when you do test, use a microphone windshield.
Make sure that the actual microphone is over the end of the seven metre tape,
not your hand or the centre of the meter.
Think carefully about the four test positions of the model at the other end
of the tape. As a suggestion, for the sideways-on readings put the fuselage
on the seven metre mark, for the nose-on reading put the propeller over the
mark and for the tail-on reading line the trailing edge of the wing up with