JAR 27.923 Rotor drive system and
control mechanism tests
(a) Each part tested as prescribed in this
paragraph must be in a serviceable condition at
the end of the tests. No intervening disassembly
which might affect test results may be
conducted.
(b) Each rotor drive system and control
mechanism must be tested for not less than
100 hours. The test must be conducted on the
rotorcraft, and the torque must be absorbed by
the rotors to be installed, except that other
ground or flight test facilities with other
appropriate methods of torque absorption may
be used if the conditions of support and
vibration closely simulate the conditions that
would exist during a test on the rotorcraft.
(c) A 60-hour part of the test prescribed in
sub-paragraph (b) of this paragraph must be run
at not less than maximum continuous torque and
the maximum speed for use with maximum
continuous torque. In this test, the main rotor
controls must be set in the position that will give
maximum longitudinal cyclic pitch change to
simulate forward flight. The auxiliary rotor
controls must be in the position for normal
operation under the conditions of the test.
(d) A 30-hour or, for rotorcraft for which
the use of either 30-minute OEI power or
continuous OEI power is requested, a 25-hour
part of the test prescribed in sub-paragraph (b)
of this paragraph must be run at not less than
75% of maximum continuous torque and the
minimum speed for use with 75% of maximum
continuous torque. The main and auxiliary rotor
controls must be in the position for normal
operation under the conditions of the test.
(e) A 10-hour part of the test prescribed in
sub-paragraph (b) of this paragraph must be run
at not less than take-off torque and the maximum
speed for use with take-off torque. The main
and auxiliary rotor controls must be in the
normal position for vertical ascent.
(1) For multi-engine rotorcraft for
which the use of 2½ minute OEI power is
requested, 12 runs during the 10-hour test
must be conducted as follows:
(i) Each run must consist of at
least one period of 2½ minutes with
take-off torque and the maximum speed
for use with take-off torque on all
engines.
(ii) Each run must consist of at
least one period for each engine in
sequence, during which that engine
simulates a power failure and the
remaining engines are run at 2½-minute
OEI torque and the maximum speed for
use with 2½-minute OEI torque for
2½ minutes.
(2) For multi-engine turbine-powered
rotorcraft for which the use of 30-second and
2-minute OEI power is requested, 10 runs
must be conducted as follows:
(i) Immediately following a
take-off run of at least 5 minutes, each
power source must simulate a failure, in
turn, and apply the maximum torque and
the maximum speed for use with
30-second OEI power to the remaining
affected drive system power inputs for
not less than 30 seconds, followed by
application of the maximum torque and
the maximum speed for use with
2-minute OEI power for not less than
2 minutes. At least one run sequence
must be conducted from a simulated
1[‘flight idle’ condition. When
conducted on a bench test, the test
sequence must be conducted following
stabilisation at take-off power.]
(ii) For the purpose of this
paragraph, an affected power input
includes all parts of the rotor drive
system which can be adversely affected
by the application of higher or
asymmetric torque and speed
prescribed by the test.
(iii) This test may be conducted
on a representative bench test facility
when engine limitations either preclude
repeated use of this power or would
result in premature engine removal
during the test. The loads, the vibration
frequency, and the methods of
application to the affected rotor drive
system components must be
representative of rotorcraft conditions.
Test components must be those used
1[to show compliance with the]
remainder of this paragraph.
(f) The parts of the test prescribed in subparagraphs
(c) and (d) of this paragraph must be
conducted in intervals of not less than
30 minutes and may be accomplished either on
the ground or in flight. The part of the test
prescribed in sub-paragraph (e) of this paragraph
must be conducted in intervals of not less than
5 minutes.
(g) At intervals of not more than five hours
during the tests prescribed in sub-paragraphs (c),
(d), and (e) of this paragraph, the engine must be
stopped rapidly enough to allow the engine and
rotor drive to be automatically disengaged from
the rotors.
(h) Under the operating conditions
specified in sub-paragraph (c) of this paragraph,
500 complete cycles of lateral control, 500
complete cycles of longitudinal control of the
main rotors, and 500 complete cycles of control
of each auxiliary rotor must be accomplished. A
‘complete cycle’ involves movement of the
controls from the neutral position, through both
extreme positions, and back to the neutral
position, except that control movements need not
produce loads or flapping motions exceeding the
maximum loads or motions encountered in
flight. The cycling may be accomplished during
the testing prescribed in sub-paragraph (c) of
this paragraph.
(i) At least 200 start-up clutch engagements
must be accomplished –
(1) So that the shaft on the driven side
of the clutch is accelerated; and
(2) Using a speed and method
selected by the applicant.
(j) For multi-engine rotorcraft for which
the use of 30-minute OEI power is requested,
five runs must be made at 30-minute OEI torque
and the maximum speed for use with 30-minute
OEI torque, in which each engine, in sequence,
is made inoperative and the remaining engine(s)
is run for a 30-minute period.
(k) For multi-engine rotorcraft for which
the use of continuous OEI power is requested,
five runs must be made at continuous OEI torque
and the maximum speed for use with continuous
OEI torque, in which each engine, in sequence,
is made inoperative and the remaining engine(s)
is run for a 1-hour period.
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