Section 27.659

14 CFR Ch. I (1-1-19 Edition)

(1) There must be means for venting
the internal pressure of the blade;
(2) Drainage holes must be provided
for the blade; and
(3) The blade must be designed to prevent water from becoming trapped in
it.
(b) Paragraphs (a)(1) and (2) of this
section does not apply to sealed rotor
blades capable of withstanding the
maximum pressure differentials expected in service.
[Amdt. 27-2, 33 FR 963, Jan. 26, 1968]

Section 27.659

Mass balance.

(a) The rotors and blades must be
mass balanced as necessary to - 
(1) Prevent excessive vibration; and
(2) Prevent flutter at any speed up to
the maximum forward speed.
(b) The structural integrity of the
mass balance installation must be substantiated.
[Amdt. 27-2, 33 FR 963, Jan. 26, 1968]

Section 27.661

Rotor blade clearance.

There must be enough clearance between the rotor blades and other parts
of the structure to prevent the blades
from striking any part of the structure
during any operating condition.
[Amdt. 27-2, 33 FR 963, Jan. 26, 1968]

Section 27.663 Ground resonance prevention
means.
(a) The reliability of the means for
preventing ground resonance must be
shown either by analysis and tests, or
reliable service experience, or by showing through analysis or tests that malfunction or failure of a single means
will not cause ground resonance.
(b) The probable range of variations,
during service, of the damping action
of the ground resonance prevention
means must be established and must be
investigated during the test required
by Section 27.241.
[Amdt. 27-2, 33 FR 963, Jan. 26, 1968, as
amended by Amdt. 27-26, 55 FR 8000, Mar. 6,
1990]

spaschal on DSK3GDR082PROD with CFR

CONTROL SYSTEMS
Section 27.671

General.

(a) Each control and control system
must operate with the ease, smooth-

ness, and positiveness appropriate to
its function.
(b) Each element of each flight control system must be designed, or distinctively and permanently marked, to
minimize the probability of any incorrect assembly that could result in the
malfunction of the system.
Section 27.672 Stability augmentation, automatic, and power-operated systems.
If the functioning of stability augmentation or other automatic or
power-operated systems is necessary to
show compliance with the flight characteristics requirements of this part,
such systems must comply with Section 27.671
of this part and the following:
(a) A warning which is clearly distinguishable to the pilot under expected
flight conditions without requiring the
pilot-s attention must be provided for
any failure in the stability augmentation system or in any other automatic
or power-operated system which could
result in an unsafe condition if the
pilot is unaware of the failure. Warning
systems must not activate the control
systems.
(b) The design of the stability augmentation system or of any other automatic or power-operated system must
allow initial counteraction of failures
without requiring exceptional pilot
skill or strength by overriding the failure by movement of the flight controls
in the normal sense and deactivating
the failed system.
(c) It must be shown that after any
single failure of the stability augmentation system or any other automatic or power-operated system - 
(1) The rotorcraft is safely controllable when the failure or malfunction
occurs at any speed or altitude within
the approved operating limitations;
(2) The controllability and maneuverability requirements of this part are
met within a practical operational
flight envelope (for example, speed, altitude, normal acceleration, and rotorcraft configurations) which is described
in the Rotorcraft Flight Manual; and
(3) The trim and stability characteristics are not impaired below a level
needed to permit continued safe flight
and landing.
[Amdt. 27-21, 49 FR 44433, Nov. 6, 1984; 49 FR
47594, Dec. 6, 1984]

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