506 

14 CFR Ch. I (1–1–24 Edition) 

§ 27.547 

vertically through the center of grav-
ity; and 

(2) The vertical load prescribed in 

paragraph (a)(1) of this section is ap-
plied simultaneously with an aft com-
ponent of 0.25 times the vertical com-
ponent. 

(b) A side-load condition in which— 
(1) A vertical load of 0.75 times the 

total vertical load specified in para-
graph (a)(1) of this section is divided 
equally among the floats; and 

(2) For each float, the load share de-

termined under paragraph (b)(1) of this 
section, combined with a total side 
load of 0.25 times the total vertical 
load specified in paragraph (b)(1) of 
this section, is applied to that float 
only. 

M

AIN

C

OMPONENT

R

EQUIREMENTS

 

§ 27.547

Main rotor structure. 

(a) Each main rotor assembly (in-

cluding rotor hubs and blades) must be 
designed as prescribed in this section. 

(b) [Reserved] 
(c) The main rotor structure must be 

designed to withstand the following 
loads prescribed in §§ 27.337 through 
27.341: 

(1) Critical flight loads. 
(2) Limit loads occurring under nor-

mal conditions of autorotation. For 
this condition, the rotor r.p.m. must be 
selected to include the effects of alti-
tude. 

(d) The main rotor structure must be 

designed to withstand loads simu-
lating— 

(1) For the rotor blades, hubs, and 

flapping hinges, the impact force of 
each blade against its stop during 
ground operation; and 

(2) Any other critical condition ex-

pected in normal operation. 

(e) The main rotor structure must be 

designed to withstand the limit torque 
at any rotational speed, including zero. 
In addition: 

(1) The limit torque need not be 

greater than the torque defined by a 
torque limiting device (where pro-
vided), and may not be less than the 
greater of— 

(i) The maximum torque likely to be 

transmitted to the rotor structure in 
either direction; and 

(ii) The limit engine torque specified 

in § 27.361. 

(2) The limit torque must be distrib-

uted to the rotor blades in a rational 
manner. 

(Secs. 604, 605, 72 Stat. 778, 49 U.S.C. 1424, 
1425) 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–3, 33 FR 14105, Sept. 18, 
1968] 

§ 27.549

Fuselage, landing gear, and 

rotor pylon structures. 

(a) Each fuselage, landing gear, and 

rotor pylon structure must be designed 
as prescribed in this section. Resultant 
rotor forces may be represented as a 
single force applied at the rotor hub at-
tachment point. 

(b) Each structure must be designed 

to withstand— 

(1) The critical loads prescribed in 

§§ 27.337 through 27.341; 

(2) The applicable ground loads pre-

scribed in §§ 27.235, 27.471 through 27.485, 
27.493, 27.497, 27.501, 27.505, and 27.521; 
and 

(3) The loads prescribed in § 27.547 

(d)(2) and (e). 

(c) Auxiliary rotor thrust, and the 

balancing air and inertia loads occur-
ring under accelerated flight condi-
tions, must be considered. 

(d) Each engine mount and adjacent 

fuselage structure must be designed to 
withstand the loads occurring under 
accelerated flight and landing condi-
tions, including engine torque. 

(Secs. 604, 605, 72 Stat. 778, 49 U.S.C. 1424, 
1425) 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–3, 33 FR 14105, Sept. 18, 
1968] 

E

MERGENCY

L

ANDING

C

ONDITIONS

 

§ 27.561

General. 

(a) The rotorcraft, although it may 

be damaged in emergency landing con-
ditions on land or water, must be de-
signed as prescribed in this section to 
protect the occupants under those con-
ditions. 

(b) The structure must be designed to 

give each occupant every reasonable 
chance of escaping serious injury in a 
crash landing when— 

(1) Proper use is made of seats, belts, 

and other safety design provisions; 

VerDate Sep<11>2014 

09:06 Jun 28, 2024

Jkt 262046

PO 00000

Frm 00516

Fmt 8010

Sfmt 8010

Y:\SGML\262046.XXX

262046

jspears on DSK121TN23PROD with CFR