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noise measurement, sound propagation is affected not
only by "inverse square" and atmospheric attenuation,
but also by ground absorption and reflection effects
which depend mainly on the angle y.
Nute 1.- Chapter 8, 8.7.5, in Part II places limits un the
maximum adjustments that may be made between test and reference
flight procedures and conditions.
7.3 The equations given in 7.2 are convenient for Note 2 .Ad justments of noise levels for test to reference
calculation by means of a computer. conditions may be made, subject to agreement by the certificating
authnriq, by the merhnds nf this sectinn The mrrections
are derivedfrom sets of curves linking the instant at
which the PNLTM is emitted,for each reference procedure with
8. ADJUSTMENT OF appropriate parameters. The sensitivity curves provide noise
HELICOPTER FLIGHT level variations as a fitnction of the parameter for which a
TEST RESULTS correction is necessary.
8.1 General
8.1.1 Adjustments shall be made to the measured noise
data by the methods of this section. Compliance with the test
conditions of Chapter 8, 8.7.5, is necessary for the test to be
acceptable. Adjustments shall be made for differences between
test and reference flight procedures and shall account for
differences in the following:
a) helicopter flight path and velocity relative to the flight
path reference point;
b) sound attenuation in air;
c) in the overflight case, parameters affecting the noise
generating mechanisms such as those described in 8.5.
8.1.2 Adjustments to the measured noise data shall be
made using the methods prescribed in 8.3 and 8.4, for differences
in the following:
8.2 Flight profiles
Note.- Flight profles for the test conditions are described
by their geometq relatiw to the ground, together with the
associated helicopter speed.
8.2.1 Take-off profile
Note 1.- Figure A2-4 illustrates typical test and reference
profles.
a) During actual testing the helicopter is initially stabilized
in level flight at the best rate of climb speed, Vy, at a
point A and corttinues to a point B where take-offpower
is applied and a steady climb is initiated. A steady climb
shall be maintained throughout the 10 dB-down period
and beyond to the end of the certijication flight path
(point F).
APP 2-19 2411 1105
Annex 16 - Environmental Protection Volume I
Table A2-4. Values of q(6)
A term of quadratic interpolation shall be used where necessary.
Table A2-5. Value off,
Centrefreguency Centre frequency
of the IN of the IN
octave band fo octave band A,
(Hz) (Hz) (Hz) (Hz)
APP 2-20
Appendix 2 Annex 16 - Environmental Protection
b) Position K1 is the take-offflight path refrence point and illustrated in Figure A2- 7 for take-08 overflight and approach
NKI is the distancefrom the initiation of the steady climb measurements.
to the take-offflight path reference point. Positions K,'
and K1" are associated noise measurement points located a) XY represents the useful portion of the measured flight
on a line at right angles to and at the specified distance path and XrYr that of the corresponding rderence flight
JLom the take-offflight track TM. path.
c) The distance TM is the distance over which the heli- b) Q represents the helicopter position on the measured
copter position is measured and synchronized with the flight path at which the noise was emitted and observed
noise measurements (see 2.3.2 of this appendix). as PNLTM at the noise measuring point K. Q, is the
corresponding position on the reference flight path and
Note 2.- The position ofpoint B moy vary within the limits K, the reference noise measuring point. QK and Q,.Kr
allowed by the certificating authority. are resuectivel~ the measured and reference noise
8.2.2 Overflight profile
propagation paths, Q, being located on the assumption
that QK and Q,.K,. form the same angle 8 with their
respective flight paths.
Note.- Figure A2-5 illustrates a typical overjlight proJile. 8.3.1 The one-third octave band levels SPL(i) comprising
a) The helicopter is stabilized in level flight at point D and PNL (the PNL at the moment of PNLTM observed at K) shall
flies through point W, overhead theflight path reference be adjusted to reference levels SPL(i), as follows:
point, to point E, the end of the noise certification
overjlight flight path.
b) Position K2 is the overflight flight path reference point + 20 log (QKIQA)
and K2W is the height of the helicopter overhead the
overjlight flight path reference point. Positions K i and In this expression:
K2" are associated noise measurement points located on -the term 0.01 [a(i) - a(i),] QK accounts for the effect
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