518 

14 CFR Ch. I (1–1–24 Edition) 

§ 27.727 

at ground contact in normal power-off 
landings. 

(b) If considered, the rotor lift speci-

fied in § 27.473(a) must be introduced 
into the drop test by appropriate en-
ergy absorbing devices or by the use of 
an effective mass. 

(c) Each landing gear unit must be 

tested in the attitude simulating the 
landing condition that is most critical 
from the standpoint of the energy to be 
absorbed by it. 

(d) When an effective mass is used in 

showing compliance with paragraph (b) 
of this section, the following formula 
may be used instead of more rational 
computations: 

W

W

h

d

h

d

n

n

W

W

L

e

j

e

=

×

+ −

(

)

+

=

+

1 L

and

;

where: 

W

e

= the effective weight to be used in the 

drop test (lbs.); 

W  =  W

M

for main gear units (lbs.), equal to 

the static reaction on the particular unit 
with the rotorcraft in the most critical 
attitude. A rational method may be used 
in computing a main gear static reac-
tion, taking into consideration the mo-
ment arm between the main wheel reac-
tion and the rotorcraft center of gravity. 

W  =  W

N

for nose gear units (lbs.), equal to 

the vertical component of the static re-
action that would exist at the nose 
wheel, assuming that the mass of the 
rotorcraft acts at the center of gravity 
and exerts a force of 1.0

g  downward and 

0.25

g forward. 

W  =  W

T

for tailwheel units (lbs.), equal to 

whichever of the following is critical: 

(1) The static weight on the tailwheel with 

the rotorcraft resting on all wheels; or 

(2) The vertical component of the ground 

reaction that would occur at the tailwheel, 
assuming that the mass of the rotorcraft 
acts at the center of gravity and exerts a 
force of l

g  downward with the rotorcraft in 

the maximum nose-up attitude considered in 
the nose-up landing conditions. 

h = specified free drop height (inches). 
L = ration of assumed rotor lift to the rotor-

craft weight. 

d  = deflection under impact of the tire (at 

the proper inflation pressure) plus the 
vertical component of the axle travels 
(inches) relative to the drop mass. 

n = limit inertia load factor. 
n

j

= the load factor developed, during impact, 

on the mass used in the drop test (i.e., 

the acceleration 

dv/dt  in  g’s recorded in 

the drop test plus 1.0). 

§ 27.727

Reserve energy absorption 

drop test. 

The reserve energy absorption drop 

test must be conducted as follows: 

(a) The drop height must be 1.5 times 

that specified in § 27.725(a). 

(b) Rotor lift, where considered in a 

manner similar to that prescribed in 
§ 27.725(b), may not exceed 1.5 times the 
lift allowed under that paragraph. 

(c) The landing gear must withstand 

this test without collapsing. Collapse 
of the landing gear occurs when a 
member of the nose, tail, or main gear 
will not support the rotorcraft in the 
proper attitude or allows the rotorcraft 
structure, other than the landing gear 
and external accessories, to impact the 
landing surface. 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–26, 55 FR 8001, Mar. 6, 
1990] 

§ 27.729

Retracting mechanism. 

For rotorcraft with retractable land-

ing gear, the following apply: 

(a) 

Loads.  The landing gear, retract-

ing mechansim, wheel-well doors, and 
supporting structure must be designed 
for— 

(1) The loads occurring in any ma-

neuvering condition with the gear re-
tracted; 

(2) The combined friction, inertia, 

and air loads occurring during retrac-
tion and extension at any airspeed up 
to the design maximum landing gear 
operating speed; and 

(3) The flight loads, including those 

in yawed flight, occurring with the 
gear extended at any airspeed up to the 
design maximum landing gear extended 
speed. 

(b) 

Landing gear lock. A positive 

means must be provided to keep the 
gear extended. 

(c) 

Emergency operation. When other 

than manual power is used to operate 
the gear, emergency means must be 
provided for extending the gear in the 
event of— 

(1) Any reasonably probable failure in 

the normal retraction system; or 

(2) The failure of any single source of 

hydraulic, electric, or equivalent en-
ergy. 

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