Page 170 - Aeronautical Engineer Data Book

Aircraft performance 141

Thrust reduction point

D

450 m
Aircraft approach path
S
6500 m

A
A : Arrival measuring location
2000 m
D : Departure measuring location
S : Side measuring location
Variation of noise limits
with aircraft weight
Limits on:
Departure: 93 dB
Side: 102 dB 108 dB: all measurements
Approach: 102 dB

34 000 kg 272 000 kg
Aircraft take-off weight (max.)

Fig. 9.6 Airport noise measurement locations
9.4.1 Aircraft noise spectrum
The nature of an aircraft’s noise spectrum and
footprint depends heavily on the type of engine
used. Some rules of thumb are:
• The predominant noise at take-off comes
from the aircraft engines.
• During landing, ‘aerodynamic noise’ (from
pressure changes around the airframe and
control surfaces) becomes more significant,
as the engines are operating on reduced
throttle settings.
• Low bypass ratio turbofan engines are
generally noisier than those with high
bypass ratios.
• Engine noise energy is approximately
7
proportional to (exhaust velocity) .