title-14-part-27-sec27-483

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]

ROUND

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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§ 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—