651
Federal Aviation Administration, DOT
§ 27.493
§ 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
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.
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