title-14-part-27-sec27-395

500

14 CFR Ch. I (1–1–24 Edition)

§ 27.341

the rotational tip speed of the rotor
blades, and is expressed as follows:

μ =

V cos a

where—

V = The airspeed along flight path (f.p.s.);
a = The angle between the projection, in the

plane of symmetry, of the axis of no
feathering and a line perpendicular to
the flight path (radians, positive when
axis is pointing aft);

omega = The angular velocity of rotor (radi-

ans per second); and

R = The rotor radius (ft).

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–11, 41 FR 55469, Dec. 20,
1976]

§ 27.341

Gust loads.

The rotorcraft must be designed to

withstand, at each critical airspeed in-
cluding hovering, the loads resulting
from a vertical gust of 30 feet per sec-
ond.

§ 27.351

Yawing conditions.

(a) Each rotorcraft must be designed

for the loads resulting from the maneu-
vers specified in paragraphs (b) and (c)
of this section with—

(1) Unbalanced aerodynamic mo-

ments about the center of gravity
which the aircraft reacts to in a ration-
al or conservative manner considering
the principal masses furnishing the re-
acting inertia forces; and

(2) Maximum main rotor speed.
(b) To produce the load required in

paragraph (a) of this section, in unac-
celerated flight with zero yaw, at for-
ward speeds from zero up to 0.6 V

—

(1) Displace the cockpit directional

control suddenly to the maximum de-
flection limited by the control stops or
by the maximum pilot force specified
in § 27.397(a);

(2) Attain a resulting sideslip angle

or 90

, whichever is less; and

(3) Return the directional control

suddenly to neutral.

paragraph (a) of this section, in unac-
celerated flight with zero yaw, at for-
ward speeds from 0.6 V

up to V

, whichever is less—

(1) Displace the cockpit directional

control suddenly to the maximum de-
flection limited by the control stops or

by the maximum pilot force specified
in § 27.397(a);

(2) Attain a resulting sideslip angle

or 15

, whichever is less, at the lesser

speed of V

or V

;

(3) Vary the sideslip angles of para-

graphs (b)(2) and (c)(2) of this section
directly with speed; and

(4) Return the directional control

suddenly to neutral.

[Amdt. 27–26, 55 FR 7999, Mar. 6, 1990, as
amended by Amdt. 27–34, 62 FR 46173, Aug. 29,
1997]

§ 27.361

Engine torque.

(a) For turbine engines, the limit

torque may not be less than the high-
est of—

(1) The mean torque for maximum

continuous power multiplied by 1.25;

(2) The torque required by § 27.923;
(3) The torque required by § 27.927; or
(4) The torque imposed by sudden en-

gine stoppage due to malfunction or
structural failure (such as compressor
jamming).

(b) For reciprocating engines, the

limit torque may not be less than the
mean torque for maximum continuous
power multiplied by—

(1) 1.33, for engines with five or more

cylinders; and

(2) Two, three, and four, for engines

with four, three, and two cylinders, re-
spectively.

[Amdt. 27–23, 53 FR 34210, Sept. 2, 1988]

ONTROL

URFACE AND

YSTEM

OADS

§ 27.391

General.

Each auxiliary rotor, each fixed or

movable stabilizing or control surface,
and each system operating any flight
control must meet the requirements of
§§ 27.395, 27.397, 27.399, 27.411, and 27.427.

[Amdt. 27–26, 55 FR 7999, Mar. 6, 1990, as
amended by Amdt. 27–34, 62 FR 46173, Aug. 29,
1997]

§ 27.395

Control system.

(a) The part of each control system

from the pilot’s controls to the control
stops must be designed to withstand
pilot forces of not less than—

(1) The forces specified in § 27.397; or
(2) If the system prevents the pilot

from applying the limit pilot forces to
the system, the maximum forces that

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§ 27.427

the system allows the pilot to apply,
but not less than 0.60 times the forces
specified in § 27.397.

(b) Each primary control system, in-

cluding its supporting structure, must
be designed as follows:

(1) The system must withstand loads

resulting from the limit pilot forces
prescribed in § 27.397.

(2) Notwithstanding paragraph (b)(3)

of this section, when power-operated
actuator controls or power boost con-
trols are used, the system must also
withstand the loads resulting from the
force output of each normally ener-
gized power device, including any sin-
gle power boost or actuator system
failure.

(3) If the system design or the normal

operating loads are such that a part of
the system cannot react to the limit
pilot forces prescribed in § 27.397, that
part of the system must be designed to
withstand the maximum loads that can
be obtained in normal operation. The
minimum design loads must, in any
case, provide a rugged system for serv-
ice use, including consideration of fa-
tigue, jamming, ground gusts, control
inertia, and friction loads. In the ab-
sence of rational analysis, the design
loads resulting from 0.60 of the speci-
fied limit pilot forces are acceptable
minimum design loads.

(4) If operational loads may be ex-

ceeded through jamming, ground gusts,
control inertia, or friction, the system
must withstand the limit pilot forces
specified in § 27.397, without yielding.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–26, 55 FR 7999, Mar. 6,
1990]

§ 27.397

Limit pilot forces and torques.

(a) Except as provided in paragraph

(b) of this section, the limit pilot
forces are as follows:

(1) For foot controls, 130 pounds.
(2) For stick controls, 100 pounds fore

and aft, and 67 pounds laterally.

(b) For flap, tab, stabilizer, rotor

brake, and landing gear operating con-
trols, the follows apply (R = radius in
inches):

(1) Crank, wheel, and lever controls,

[1 + R]/3

50 pounds, but not less than

50 pounds nor more than 100 pounds for
hand operated controls or 130 pounds
for foot operated controls, applied at

any angle within 20 degrees of the
plane of motion of the control.

(2) Twist controls, 80R inch-pounds.

[Amdt. 27–11, 41 FR 55469, Dec. 20, 1976, as
amended by Amdt. 27–40, 66 FR 23538, May 9,
2001]

§ 27.399

Dual control system.

Each dual primary flight control sys-

tem must be designed to withstand the
loads that result when pilot forces of
0.75 times those obtained under § 27.395
are applied—

(a) In opposition; and
(b) In the same direction.

§ 27.411

Ground clearance: tail rotor

guard.

(a) It must be impossible for the tail

rotor to contact the landing surface
during a normal landing.

(b) If a tail rotor guard is required to

show compliance with paragraph (a) of
this section—

(1) Suitable design loads must be es-

tablished for the guard; and

(2) The guard and its supporting

structure must be designed to with-
stand those loads.

§ 27.427

Unsymmetrical loads.

(a) Horizontal tail surfaces and their

supporting structure must be designed
for unsymmetrical loads arising from
yawing and rotor wake effects in com-
bination with the prescribed flight con-
ditions.

(b) To meet the design criteria of

paragraph (a) of this section, in the ab-
sence of more rational data, both of the
following must be met:

(1) One hundred percent of the max-

imum loading from the symmetrical
flight conditions acts on the surface on
one side of the plane of symmetry, and
no loading acts on the other side.

(2) Fifty percent of the maximum

loading from the symmetrical flight
conditions acts on the surface on each
side of the plane of symmetry but in
opposite directions.

where the horizontal tail surfaces are
supported by the vertical tail surfaces,
the vertical tail surfaces and sup-
porting structure must be designed for
the combined vertical and horizontal
surface loads resulting from each pre-
scribed flight condition, considered