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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

R

Ω

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

NE

— 

(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. 

(c) To produce the load required in 

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

NE

up to V

NE

or 

V

H

, 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

NE

or V

H

(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] 

C

ONTROL

S

URFACE AND

S

YSTEM

L

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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