775
Federal Aviation Administration, DOT
§ 29.923
(2) For single-engine rotorcraft, each
rotor drive system must be so arranged
that each rotor necessary for control in
autorotation will continue to be driven
by the main rotors after disengage-
ment of the engine from the main and
auxiliary rotors.
(3) Each rotor drive system must in-
corporate a unit for each engine to
automatically disengage that engine
from the main and auxiliary rotors if
that engine fails.
(4) If a torque limiting device is used
in the rotor drive system, it must be
located so as to allow continued con-
trol of the rotorcraft when the device
is operating.
(5) If the rotors must be phased for
intermeshing, each system must pro-
vide constant and positive phase rela-
tionship under any operating condi-
tion.
(6) If a rotor dephasing device is in-
corporated, there must be means to
keep the rotors locked in proper phase
before operation.
[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as
amended by Amdt. 29–12, 41 FR 55472, Dec. 20,
1976; Amdt. 29–40, 61 FR 21908, May 10, 1996]
§ 29.921
Rotor brake.
If there is a means to control the ro-
tation of the rotor drive system inde-
pendently of the engine, any limita-
tions on the use of that means must be
specified, and the control for that
means must be guarded to prevent in-
advertent operation.
§ 29.923
Rotor drive system and con-
trol mechanism tests.
(a)
Endurance tests, general. Each
rotor drive system and rotor control
mechanism must be tested, as pre-
scribed in paragraphs (b) through (n)
and (p) of this section, for at least 200
hours plus the time required to meet
the requirements of paragraphs (b)(2),
(b)(3), and (k) of this section. These
tests must be conducted as follows:
(1) Ten-hour test cycles must be used,
except that the test cycle must be ex-
tended to include the OEI test of para-
graphs (b)(2) and (k), of this section if
OEI ratings are requested.
(2) The tests must be conducted on
the rotorcraft.
(3) The test torque and rotational
speed must be—
(i) Determined by the powerplant
limitations; and
(ii) Absorbed by the rotors to be ap-
proved for the rotorcraft.
(b)
Endurance tests; takeoff run. The
takeoff run must be conducted as fol-
lows:
(1) Except as prescribed in para-
graphs (b)(2) and (b)(3) of this section,
the takeoff torque run must consist of
1 hour of alternate runs of 5 minutes at
takeoff torque and the maximum speed
for use with takeoff torque, and 5 min-
utes at as low an engine idle speed as
practicable. The engine must be de-
clutched from the rotor drive system,
and the rotor brake, if furnished and so
intended, must be applied during the
first minute of the idle run. During the
remaining 4 minutes of the idle run,
the clutch must be engaged so that the
engine drives the rotors at the min-
imum practical r.p.m. The engine and
the rotor drive system must be acceler-
ated at the maximum rate. When de-
clutching the engine, it must be decel-
erated rapidly enough to allow the op-
eration of the overrunning clutch.
(2) For helicopters for which the use
of a 2
1
⁄
2
-minute OEI rating is requested,
the takeoff run must be conducted as
prescribed in paragraph (b)(1) of this
section, except for the third and sixth
runs for which the takeoff torque and
the maximum speed for use with take-
off torque are prescribed in that para-
graph. For these runs, the following
apply:
(i) Each run must consist of at least
one period of 2
1
⁄
2
minutes with takeoff
torque and the maximum speed for use
with takeoff 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 en-
gines are run at the 2
1
⁄
2
-minute OEI
torque and the maximum speed for use
with 2
1
⁄
2
-minute OEI torque for 2
1
⁄
2
min-
utes.
(3) For multiengine, turbine-powered
rotorcraft for which the use of 30-sec-
ond/2-minute OEI power is requested,
the takeoff run must be conducted as
prescribed in paragraph (b)(1) of this
section except for the following:
(i) Immediately following any one 5-
minute power-on run required by para-
graph (b)(1) of this section, simulate a
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