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501 

Federal Aviation Administration, DOT 

§ 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. 

(c) For empennage arrangements 

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 

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502 

14 CFR Ch. I (1–1–24 Edition) 

§ 27.471 

separately. The flight conditions must 
be selected so the maximum design 
loads are obtained on each surface. In 
the absence of more rational data, the 
unsymmetrical horizontal tail surface 
loading distributions described in this 
section must be assumed. 

[Amdt. 27–26, 55 FR 7999, Mar. 6, 1990, as 
amended by Amdt. 27–27, 55 FR 38966, Sept. 
21, 1990] 

G

ROUND

L

OADS

 

§ 27.471

General. 

(a) 

Loads and equilibrium. For limit 

ground loads— 

(1) The limit ground loads obtained 

in the landing conditions in this part 
must be considered to be external loads 
that would occur in the rotorcraft 
structure if it were acting as a rigid 
body; and 

(2) In each specified landing condi-

tion, the external loads must be placed 
in equilibrium with linear and angular 
inertia loads in a rational or conserv-
ative manner. 

(b) 

Critical centers of gravity. The crit-

ical centers of gravity within the range 
for which certification is requested 
must be selected so that the maximum 
design loads are obtained in each land-
ing gear element. 

§ 27.473

Ground loading conditions 

and assumptions. 

(a) For specified landing conditions, 

a design maximum weight must be 
used that is not less than the max-
imum weight. A rotor lift may be as-
sumed to act through the center of 
gravity throughout the landing impact. 
This lift may not exceed two-thirds of 
the design maximum weight. 

(b) Unless otherwise prescribed, for 

each specified landing condition, the 
rotorcraft must be designed for a limit 
load factor of not less than the limit 
inertia load factor substantiated under 
§ 27.725. 

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

§ 27.475

Tires and shock absorbers. 

Unless otherwise prescribed, for each 

specified landing condition, the tires 
must be assumed to be in their static 
position and the shock absorbers to be 
in their most critical position. 

§ 27.477

Landing gear arrangement. 

Sections 27.235, 27.479 through 27.485, 

and 27.493 apply to landing gear with 
two wheels aft, and one or more wheels 
forward, of the center of gravity. 

§ 27.479

Level landing conditions. 

(a) 

Attitudes.  Under each of the load-

ing conditions prescribed in paragraph 
(b) of this section, the rotorcraft is as-
sumed to be in each of the following 
level landing attitudes: 

(1) An attitude in which all wheels 

contact the ground simultaneously. 

(2) An attitude in which the aft 

wheels contact the ground with the for-
ward wheels just clear of the ground. 

(b) 

Loading conditions. The rotorcraft 

must be designed for the following 
landing loading conditions: 

(1) Vertical loads applied under 

§ 27.471. 

(2) The loads resulting from a com-

bination of the loads applied under 
paragraph (b)(1) of this section with 
drag loads at each wheel of not less 
than 25 percent of the vertical load at 
that wheel. 

(3) If there are two wheels forward, a 

distribution of the loads applied to 
those wheels under paragraphs (b)(1) 
and (2) of this section in a ratio of 
40:60. 

(c) 

Pitching moments. Pitching mo-

ments are assumed to be resisted by— 

(1) In the case of the attitude in para-

graph (a)(1) of this section, the forward 
landing gear; and 

(2) In the case of the attitude in para-

graph (a)(2) of this section, the angular 
inertia forces. 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964; 29 
FR 17885, Dec. 17, 1964] 

§ 27.481

Tail-down landing conditions. 

(a) The rotorcraft is assumed to be in 

the maximum nose-up attitude allow-
ing ground clearance by each part of 
the rotorcraft. 

(b) In this attitude, ground loads are 

assumed to act perpendicular to the 
ground. 

§ 27.483

One-wheel landing conditions. 

For the one-wheel landing condition, 

the rotorcraft is assumed to be in the 
level attitude and to contact the 

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