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503 

Federal Aviation Administration, DOT 

§ 27.497 

ground on one aft wheel. In this atti-
tude— 

(a) The vertical load must be the 

same as that obtained on that side 
under § 27.479(b)(1); and 

(b) The unbalanced external loads 

must be reacted by rotorcraft inertia. 

§ 27.485

Lateral drift landing condi-

tions. 

(a) The rotorcraft is assumed to be in 

the level landing attitude, with— 

(1) Side loads combined with one-half 

of the maximum ground reactions ob-
tained in the level landing conditions 
of § 27.479 (b)(1); and 

(2) The loads obtained under para-

graph (a)(1) of this section applied— 

(i) At the ground contact point; or 
(ii) For full-swiveling gear, at the 

center of the axle. 

(b) The rotorcraft must be designed 

to withstand, at ground contact— 

(1) When only the aft wheels contact 

the ground, side loads of 0.8 times the 
vertical reaction acting inward on one 
side, and 0.6 times the vertical reaction 
acting outward on the other side, all 
combined with the vertical loads speci-
fied in paragraph (a) of this section; 
and 

(2) When all wheels contact the 

ground simultaneously— 

(i) For the aft wheels, the side loads 

specified in paragraph (b)(1) of this sec-
tion; and 

(ii) For the forward wheels, a side 

load of 0.8 times the vertical reaction 
combined with the vertical load speci-
fied in paragraph (a) of this section. 

§ 27.493

Braked roll conditions. 

Under braked roll conditions with 

the shock absorbers in their static po-
sitions— 

(a) The limit vertical load must be 

based on a load factor of at least— 

(1) 1.33, for the attitude specified in 

§ 27.479(a)(1); and 

(2) 1.0 for the attitude specified in 

§ 27.479(a)(2); and 

(b) The structure must be designed to 

withstand at the ground contact point 
of each wheel with brakes, a drag load 
at least the lesser of— 

(1) The vertical load multiplied by a 

coefficient of friction of 0.8; and 

(2) The maximum value based on lim-

iting brake torque. 

§ 27.497

Ground loading conditions: 

landing gear with tail wheels. 

(a) 

General.  Rotorcraft with landing 

gear with two wheels forward, and one 
wheel aft, of the center of gravity must 
be designed for loading conditions as 
prescribed in this section. 

(b) 

Level landing attitude with only the 

forward wheels contacting the ground. In 
this attitude— 

(1) The vertical loads must be applied 

under §§ 27.471 through 27.475; 

(2) The vertical load at each axle 

must be combined with a drag load at 
that axle of not less than 25 percent of 
that vertical load; and 

(3) Unbalanced pitching moments are 

assumed to be resisted by angular iner-
tia forces. 

(c) 

Level landing attitude with all 

wheels contacting the ground simulta-
neously. 
In this attitude, the rotorcraft 
must be designed for landing loading 
conditions as prescribed in paragraph 
(b) of this section. 

(d) 

Maximum nose-up attitude with 

only the rear wheel contacting the 
ground.  
The attitude for this condition 
must be the maximum nose-up attitude 
expected in normal operation, includ-
ing autorotative landings. In this atti-
tude— 

(1) The appropriate ground loads 

specified in paragraphs (b)(1) and (2) of 
this section must be determined and 
applied, using a rational method to ac-
count for the moment arm between the 
rear wheel ground reaction and the 
rotorcraft center of gravity; or 

(2) The probability of landing with 

initial contact on the rear wheel must 
be shown to be extremely remote. 

(e) 

Level landing attitude with only one 

forward wheel contacting the ground. In 
this attitude, the rotorcraft must be 
designed for ground loads as specified 
in paragraphs (b)(1) and (3) of this sec-
tion. 

(f) 

Side loads in the level landing atti-

tude. In the attitudes specified in para-
graphs (b) and (c) of this section, the 
following apply: 

(1) The side loads must be combined 

at each wheel with one-half of the max-
imum vertical ground reactions ob-
tained for that wheel under paragraphs 
(b) and (c) of this section. In this condi-
tion, the side loads must be— 

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