Federal Aviation Administration, DOT

Section 27.483

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.

Section 27.477

[Amdt. 27-26, 55 FR 7999, Mar. 6, 1990, as
amended by Amdt. 27-27, 55 FR 38966, Sept.
21, 1990]

(a) Attitudes. Under each of the loading conditions prescribed in paragraph
(b) of this section, the rotorcraft is assumed 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 forward 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
Section 27.471.
(2) The loads resulting from a combination 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 moments are assumed to be resisted by - 
(1) In the case of the attitude in paragraph (a)(1) of this section, the forward
landing gear; and
(2) In the case of the attitude in paragraph (a)(2) of this section, the angular
inertia forces.

GROUND LOADS
Section 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 condition, the external loads must be placed
in equilibrium with linear and angular
inertia loads in a rational or conservative manner.
(b) Critical centers of gravity. The critical centers of gravity within the range
for which certification is requested
must be selected so that the maximum
design loads are obtained in each landing gear element.
Section 27.473 Ground loading
and assumptions.

conditions

(a) For specified landing conditions,
a design maximum weight must be
used that is not less than the maximum weight. A rotor lift may be assumed 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
Section 27.725.
[Amdt. 27-2, 33 FR 963, Jan. 26, 1968]

spaschal on DSK3GDR082PROD with CFR

Section 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.

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.
Section 27.479

Level landing conditions.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964; 29
FR 17885, Dec. 17, 1964]

Section 27.481

Tail-down landing conditions.

(a) The rotorcraft is assumed to be in
the maximum nose-up attitude allowing ground clearance by each part of
the rotorcraft.
(b) In this attitude, ground loads are
assumed to act perpendicular to the
ground.
Section 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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