Appendix K to Part 36 - Noise Requirements for Tiltrotors Under Subpart K
14:1.0.1.3.20.14.283.1.44 : Appendix K
Appendix K to Part 36 - Noise Requirements for Tiltrotors Under
Subpart K K1
General K2
Noise Evaluation Measure K3
Noise Measurement Reference Points K4
Noise Limits K5
Trade-offs K6
Noise Certification Reference
Procedures K7
Test Procedures Section K1 General
This appendix prescribes noise limits and procedures for
measuring noise and adjusting the data to standard conditions for
tiltrotors as specified in § 36.1 of this part.
Section K2 Noise Evaluation Measure
The noise evaluation measure is the effective perceived noise
level in EPNdB, to be calculated in accordance with section A36.4
of Appendix A to this part, except corrections for spectral
irregularities must be determined using the 50 Hz sound pressure
level found in section H36.201 of Appendix H to this part.
Section K3 Noise Measurement Reference Points
The following noise reference points must be used when
demonstrating tiltrotor compliance with section K6 (Noise
Certification Reference Procedures) and section K7 (Test
Procedures) of this appendix:
(a) Takeoff reference noise measurement points -
As shown in Figure K1 below:
(1) The centerline noise measurement flight path reference
point, designated A, is located on the ground vertically below the
reference takeoff flight path. The measurement point is located
1,640 feet (500 m) in the horizontal direction of flight from the
point Cr where transition to climbing flight is initiated, as
described in section K6.2 of this appendix;
(2) Two sideline noise measurement points, designated as
S(starboard) and S(port), are located on the ground perpendicular
to and symmetrically stationed at 492 feet (150 m) on each side of
the takeoff reference flight path. The measurement points bisect
the centerline flight path reference point A.
(b) Flyover reference noise measurement points -
As shown in Figure K2 below:
(1) The centerline noise measurement flight path reference
point, designated A, is located on the ground 492 feet (150 m)
vertically below the reference flyover flight path. The measurement
point is defined by the flyover reference procedure in section K6.3
of this appendix;
(2) Two sideline noise measurement points, designated as
S(sideline), are located on the ground perpendicular to and
symmetrically stationed at 492 feet (150 m) on each side of the
flyover reference flight path. The measurement points bisect the
centerline flight path reference point A.
(c) Approach reference noise measurement points -
As shown in Figure K3 below:
(1) The centerline noise measurement flight path reference
point, designated A, is located on the ground 394 feet (120 m)
vertically below the reference approach flight path. The
measurement point is defined by the approach reference procedure in
section K6.4 of this appendix. On level ground, the measurement
point corresponds to a position 3,740 feet (1,140 m) from the
intersection of the 6.0 degree approach path with the ground
plane;
(2) Two sideline noise measurement points, designated as
S(starboard) and S(port), are located on the ground perpendicular
to and symmetrically stationed at 492 feet (150 m) on each side of
the approach reference flight path. The measurement points bisect
the centerline flight path reference point A.
Section
K4 Noise Limits
For a tiltrotor, the maximum noise levels, as determined in
accordance with the noise evaluation in EPNdB and calculation
method described in section H36.201 of Appendix H of this part,
must not exceed the noise limits as follows:
(a) At the takeoff flight path reference point: For a
tiltrotor having a maximum certificated takeoff weight (mass) of
176,370 pounds (80,000 kg) or more, in VTOL/Conversion mode, 109
EPNdB, decreasing linearly with the logarithm of the tiltrotor
weight (mass) at a rate of 3.0 EPNdB per halving of weight (mass)
down to 89 EPNdB, after which the limit is constant. Figure K4
illustrates the takeoff noise limit as a solid line.
(b) At the Flyover path reference point: For a tiltrotor
having a maximum certificated takeoff weight (mass) of 176,370
pounds (80,000 kg) or more, in VTOL/Conversion mode, 108 EPNdB,
decreasing linearly with the logarithm of the tiltrotor weight
(mass) at a rate of 3.0 EPNdB per halving of weight (mass) down to
88 EPNdB, after which the limit is constant. Figure K4 illustrates
the flyover noise limit as a dashed line.
(c) At the approach flight path reference point: For a
tiltrotor having a maximum certificated takeoff weight (mass) of
176,370 pounds (80,000 kg) or more, in VTOL/Conversion mode, 110
EPNdB, decreasing linearly with the logarithm of the tiltrotors
weight (mass) at a rate of 3.0 EPNdB per halving of weight (mass)
down to 90 EPNdB, after which the limit is constant. Figure K4
illustrates the approach noise limit as a dash-dot line.
Section
K5 Trade-Offs
If the noise evaluation measurement exceeds the noise limits
described in K4 of this appendix at one or two measurement
points:
(a) The sum of excesses must not be greater than 4 EPNdB;
(b) The excess at any single point must not be greater than 3
EPNdB; and
(c) Any excess must be offset by the remaining noise margin at
the other point or points.
Section K6 Noise Certification Reference Procedures
K6.1 General Conditions
(a)-(b) [Reserved]
(c) The takeoff, flyover and approach reference procedures must
be established in accordance with sections K6.2, K6.3 and K6.4 of
this appendix, except as specified in section K6.1(d) of this
appendix.
(d) If the design characteristics of the tiltrotor prevent test
flights from being conducted in accordance with section K6.2, K6.3
or K6.4 of this appendix, the applicant must revise the test
procedures and resubmit the procedures for approval.
(e) The following reference atmospheric conditions must be used
to establish the reference procedures:
(1) Sea level atmospheric pressure of 2,116 pounds per square
foot (1,013.25 hPa);
(2) Ambient air temperature of 77 °Fahrenheit (25 °Celsius, i.e.
ISA + 10 °C);
(3) Relative humidity of 70 percent; and
(4) Zero wind.
(f) For tests conducted in accordance with sections K6.2, K6.3,
and K6.4 of this appendix, use the maximum normal operating RPM
corresponding to the airworthiness limit imposed by the
manufacturer. For configurations for which the rotor speed
automatically links with the flight condition, use the maximum
normal operating rotor speed corresponding with the reference
flight condition. For configurations for which the rotor speed can
change by pilot action, use the highest normal rotor speed
specified in the flight manual limitation section for the reference
conditions.
K6.2 Takeoff Reference Procedure. The takeoff reference
flight procedure is as follows:
(a) A constant takeoff configuration must be maintained,
including the nacelle angle selected by the applicant;
(b) The tiltrotor power must be stabilized at the maximum
takeoff power corresponding to the minimum installed engine(s)
specification power available for the reference ambient conditions
or gearbox torque limit, whichever is lower. The tiltrotor power
must also be stabilized along a path starting from a point located
1,640 feet (500 m) before the flight path reference point, at 65 ft
(20 m) above ground level;
(c) The nacelle angle and the corresponding best rate of climb
speed, or the lowest approved speed for the climb after takeoff,
whichever is the greater, must be maintained throughout the takeoff
reference procedure;
(d) The rotor speed must be stabilized at the maximum normal
operating RPM certificated for takeoff;
(e) The weight (mass) of the tiltrotors must be the maximum
takeoff weight (mass) as requested for noise certification; and
(f) The reference takeoff flight profile is a straight line
segment inclined from the starting point 1,640 feet (500 m) before
to the center noise measurement point and 65 ft (20 m) above ground
level at an angle defined by best rate of climb and the speed
corresponding to the selected nacelle angle and for minimum
specification engine performance.
K6.3 Flyover Reference Procedure. The flyover reference
flight procedure is as follows:
(a) The tiltrotor must be stabilized for level flight along the
centerline flyover flight path and over the noise measurement
reference point at an altitude of 492 ft (150 m) above ground
level;
(b) A constant flyover configuration selected by the applicant
must be maintained;
(c) The weight (mass) of the tiltrotor must be the maximum
takeoff weight (mass) as requested for noise certification;
(d) In the VTOL/Conversion mode:
(1) The nacelle angle must be at the authorized fixed operation
point that is closest to the shallow nacelle angle certificated for
zero airspeed;
(2) The airspeed must be 0.9VCON and
(3) The rotor speed must be stabilized at the maximum normal
operating RPM certificated for level flight.
K6.4 Approach Reference Procedure. The approach reference
procedure is as follows:
(a) The tiltrotor must be stabilized to follow a 6.0 degree
approach path;
(b) An approved airworthiness configuration in which maximum
noise occurs must be maintained;
(1) An airspeed equal to the best rate of climb speed
corresponding to the nacelle angle, or the lowest approved airspeed
for the approach, whichever is greater, must be stabilized and
maintained; and
(2) The tiltrotor power during the approach must be stabilized
over the flight path reference point, and continue as if
landing;
(c) The rotor speed must be stabilized at the maximum normal
operating RPM certificated for approach;
(d) The constant approach configuration used in airworthiness
certification tests, with the landing gear extended, must be
maintained; and
(e) The weight (mass) of the tiltrotor at landing must be the
maximum landing weight (mass) as requested for noise
certification.
Section K7 Test Procedures
K7.1 [Reserved]
K7.2 The test procedures and noise measurements must be
conducted and processed to yield the noise evaluation measure
designated in section K2 of this appendix.
K7.3 If either the test conditions or test procedures do
not comply to the applicable noise certification reference
conditions or procedures prescribed by this part, the applicant
must apply the correction methods described in section H36.205 of
Appendix H of this part to the acoustic test data measured.
K7.4 Adjustments for differences between test and
reference flight procedures must not exceed:
(a) For takeoff: 4.0 EPNdB, of which the arithmetic sum of delta
1 and the term −7.5 log (QK/QrKr) from delta 2 must not in total
exceed 2.0 EPNdB;
(b) For flyover or approach: 2.0 EPNdB.
K7.5 The average rotor RPM must not vary from the normal
maximum operating RPM by more than ±1.0 percent throughout the 10
dB-down time interval.
K7.6 The tiltrotor airspeed must not vary from the
reference airspeed appropriate to the flight demonstration by more
than ±5 kts (±9 km/h) throughout the 10 dB-down time interval.
K7.7 The number of level flyovers made with a head wind
component must be equal to the number of level flyovers made with a
tail wind component.
K7.8 The tiltrotor must operate between ±10 degrees from
the vertical or between ±65 feet (±20 m) lateral deviation
tolerance, whichever is greater, above the reference track and
throughout the 10 dB-down time interval.
K7.9 The tiltrotor altitude must not vary during each
flyover by more than ±30 ft (±9 m) from the reference altitude
throughout the 10 dB-down time interval.
K7.10 During the approach procedure, the tiltrotor must
establish a stabilized constant speed approach and fly between
approach angles of 5.5 degrees and 6.5 degrees throughout the 10
dB-down time interval.
K7.11 During all test procedures, the tiltrotor weight
(mass) must not be less than 90 percent and not more than 105
percent of the maximum certificated weight (mass). For each of the
test procedures, complete at least one test at or above this
maximum certificated weight (mass).
K7.12 A tiltrotor capable of carrying external loads or
external equipment must be noise certificated without such loads or
equipment fitted
K7.13 The value of VCON used for noise certification must
be included in the approved Flight Manual.
[78 FR 1139, Jan. 8, 2013]