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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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