Code of Federal Regulations - Title 14

663

Federal Aviation Administration, DOT

§ 27.671

(b) No bearing factor need be used on

a part for which any larger special fac-
tor is prescribed.

§ 27.625

Fitting factors.

For each fitting (part or terminal

used to join one structural member to
another) the following apply:

(a) For each fitting whose strength is

not proven by limit and ultimate load
tests in which actual stress conditions
are simulated in the fitting and sur-
rounding structures, a fitting factor of
at least 1.15 must be applied to each
part of—

(1) The fitting;
(2) The means of attachment; and
(3) The bearing on the joined mem-

bers.

(b) No fitting factor need be used—
(1) For joints made under approved

practices and based on comprehensive
test data (such as continuous joints in
metal plating, welded joints, and scarf
joints in wood); and

(2) With respect to any bearing sur-

face for which a larger special factor is
used.

must be treated as a fitting up to the
point at which the section properties
become typical of the member.

(d) Each seat, berth, litter, safety

belt, and harness attachment to the
structure must be shown by analysis,
tests, or both, to be able to withstand
the inertia forces prescribed in
§ 27.561(b)(3) multiplied by a fitting fac-
tor of 1.33.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–35, 63 FR 43285, Aug. 12,
1998]

§ 27.629

Flutter.

Each aerodynamic surface of the

rotorcraft must be free from flutter
under each appropriate speed and
power condition.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–26, 55 FR 8000, Mar. 6,
1990]

OTORS

§ 27.653

Pressure venting and drain-

age of rotor blades.

(a) For each rotor blade—
(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 pre-

vent 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 ex-
pected in service.

[Amdt. 27–2, 33 FR 963, Jan. 26, 1968]

§ 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 sub-
stantiated.

[Amdt. 27–2, 33 FR 963, Jan. 26, 1968]

§ 27.661

Rotor blade clearance.

There must be enough clearance be-

tween 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]

§ 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 show-
ing through analysis or tests that mal-
function 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 § 27.241.

[Amdt. 27–2, 33 FR 963, Jan. 26, 1968, as
amended by Amdt. 27–26, 55 FR 8000, Mar. 6,
1990]

ONTROL

YSTEMS

§ 27.671

General.

(a) Each control and control system

must operate with the ease, smooth-
ness, and positiveness appropriate to
its function.

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