Page 171 - Aeronautical Engineer Data Book

142 Aeronautical Engineer’s Data Book
Jet efflux
Compressor

Inlet

Turbine
Compressor

The general aircraft noise 'footprint'

Runway Departure point 'D'

Approach point 'A'
Side point 'S'
Noise footprint shape for four-engine passenger jet
Fig. 9.7 Aircraft noise characteristics

Figure 9.7 shows the general shape of an
aircraft noise footprint and the resulting distri­
bution of noise in relation to the runway and
standardized noise measurement points.
Supersonic aircraft such as Concorde using
pure turbojet engines require specific noise
reduction measures designed to minimize the
noise level produced by the jet efflux. Even
using ‘thrust cutback’ and all possible technical
developments, supersonic aircraft are still
subject to severe restrictions in and around
most civil aviation airports.
Sonic booms caused by low supersonic
Mach numbers (< MA 1.15) are often not
heard at ground level, as they tend to be
refracted upwards. In some cases a portion of