499 

Federal Aviation Administration, DOT 

§ 27.339 

§ 27.307

Proof of structure. 

(a) Compliance with the strength and 

deformation requirements of this sub-
part must be shown for each critical 
loading condition accounting for the 
environment to which the structure 
will be exposed in operation. Struc-
tural analysis (static or fatigue) may 
be used only if the structure conforms 
to those structures for which experi-
ence has shown this method to be reli-
able. In other cases, substantiating 
load tests must be made. 

(b) Proof of compliance with the 

strength requirements of this subpart 
must include— 

(1) Dynamic and endurance tests of 

rotors, rotor drives, and rotor controls; 

(2) Limit load tests of the control 

system, including control surfaces; 

(3) Operation tests of the control sys-

tem; 

(4) Flight stress measurement tests; 
(5) Landing gear drop tests; and 
(6) Any additional test required for 

new or unusual design features. 

(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; Amdt. 27–26, 55 FR 7999, Mar. 6, 1990] 

§ 27.309

Design limitations. 

The following values and limitations 

must be established to show compli-
ance with the structural requirements 
of this subpart: 

(a) The design maximum weight. 
(b) The main rotor r.p.m. ranges 

power on and power off. 

(c) The maximum forward speeds for 

each main rotor r.p.m. within the 
ranges determined under paragraph (b) 
of this section. 

(d) The maximum rearward and side-

ward flight speeds. 

(e) The center of gravity limits cor-

responding to the limitations deter-
mined under paragraphs (b), (c), and (d) 
of this section. 

(f) The rotational speed ratios be-

tween each powerplant and each con-
nected rotating component. 

(g) The positive and negative limit 

maneuvering load factors. 

F

LIGHT

L

OADS

 

§ 27.321

General. 

(a) The flight load factor must be as-

sumed to act normal to the longitu-
dinal axis of the rotorcraft, and to be 
equal in magnitude and opposite in di-
rection to the rotorcraft inertia load 
factor at the center of gravity. 

(b) Compliance with the flight load 

requirements of this subpart must be 
shown— 

(1) At each weight from the design 

minimum weight to the design max-
imum weight; and 

(2) With any practical distribution of 

disposable load within the operating 
limitations in the Rotorcraft Flight 
Manual. 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–11, 41 FR 55468, Dec. 20, 
1976] 

§ 27.337

Limit maneuvering load fac-

tor. 

The rotorcraft must be designed for— 
(a) A limit maneuvering load factor 

ranging from a positive limit of 3.5 to 
a negative limit of 

¥

1.0; or 

(b) Any positive limit maneuvering 

load factor not less than 2.0 and any 
negative limit maneuvering load factor 
of not less than 

¥

0.5 for which— 

(1) The probability of being exceeded 

is shown by analysis and flight tests to 
be extremely remote; and 

(2) The selected values are appro-

priate to each weight condition be-
tween the design maximum and design 
minimum weights. 

[Amdt. 27–26, 55 FR 7999, Mar. 6, 1990] 

§ 27.339

Resultant limit maneuvering 

loads. 

The loads resulting from the applica-

tion of limit maneuvering load factors 
are assumed to act at the center of 
each rotor hub and at each auxiliary 
lifting surface, and to act in directions, 
and with distributions of load among 
the rotors and auxiliary lifting sur-
faces, so as to represent each critical 
maneuvering condition, including 
power-on and power-off flight with the 
maximum design rotor tip speed ratio. 
The rotor tip speed ratio is the ratio of 
the rotorcraft flight velocity compo-
nent in the plane of the rotor disc to 

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