Federal Aviation Administration, DOT

Section 27.395

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

Section=

V cos a
R

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 (radians 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]

Section 27.351 Yawing conditions.
(a) Each rotorcraft must be designed
for the loads resulting from the maneuvers specified in paragraphs (b) and (c)
of this section with - 
(1) Unbalanced aerodynamic moments about the center of gravity
which the aircraft reacts to in a rational or conservative manner considering
the principal masses furnishing the reacting inertia forces; and
(2) Maximum main rotor speed.
(b) To produce the load required in
paragraph (a) of this section, in unaccelerated flight with zero yaw, at forward speeds from zero up to 0.6 VNE - 
(1) Displace the cockpit directional
control suddenly to the maximum deflection limited by the control stops or
by the maximum pilot force specified
in Section 27.397(a);
(2) Attain a resulting sideslip angle
or 90Section, 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 unaccelerated flight with zero yaw, at forward speeds from 0.6 VNE up to VNE or
VH, whichever is less - 
(1) Displace the cockpit directional
control suddenly to the maximum deflection limited by the control stops or

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

Section 27.361 Engine torque.
(a) For turbine engines, the limit
torque may not be less than the highest of - 
(1) The mean torque for maximum
continuous power multiplied by 1.25;
(2) The torque required by Section 27.923;
(3) The torque required by Section 27.927; or
(4) The torque imposed by sudden engine 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, respectively.
[Amdt. 27-23, 53 FR 34210, Sept. 2, 1988]

CONTROL SURFACE AND SYSTEM LOADS
Section 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
SectionSection 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]

Section 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 Section 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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Section 27.341 Gust loads.
The rotorcraft must be designed to
withstand, at each critical airspeed including hovering, the loads resulting
from a vertical gust of 30 feet per second.

by the maximum pilot force specified
in Section 27.397(a);
(2) Attain a resulting sideslip angle
or 15Section, whichever is less, at the lesser
speed of VNE or VH;
(3) Vary the sideslip angles of paragraphs (b)(2) and (c)(2) of this section
directly with speed; and
(4) Return the directional control
suddenly to neutral.