653
Federal Aviation Administration, DOT
§ 27.501
(ii) At the ground contact point, if
there is a lock, steering device or shim-
my damper (the rear wheel being as-
sumed to be in the trailing position).
(i)
Taxiing condition. The rotorcraft
and its landing gear must be designed
for loads that would occur when the
rotorcraft is taxied over the roughest
ground that may reasonably be ex-
pected in normal operation.
§ 27.501
Ground loading conditions:
landing gear with skids.
(a)
General. Rotorcraft with landing
gear with skids must be designed for
the loading conditions specified in this
section. In showing compliance with
this section, the following apply:
(1) The design maximum weight, cen-
ter of gravity, and load factor must be
determined under §§ 27.471 through
27.475.
(2) Structural yielding of elastic
spring members under limit loads is ac-
ceptable.
(3) Design ultimate loads for elastic
spring members need not exceed those
obtained in a drop test of the gear
with—
(i) A drop height of 1.5 times that
specified in § 27.725; and
(ii) An assumed rotor lift of not more
than 1.5 times that used in the limit
drop tests prescribed in § 27.725.
(4) Compliance with paragraphs (b)
through (e) of this section must be
shown with—
(i) The gear in its most critically de-
flected position for the landing condi-
tion being considered; and
(ii) The ground reactions rationally
distributed along the bottom of the
skid tube.
(b)
Vertical reactions in the level land-
ing attitude. In the level attitude, and
with the rotorcraft contacting the
ground along the bottom of both skids,
the vertical reactions must be applied
as prescribed in paragraph (a) of this
section.
(c)
Drag reactions in the level landing
attitude. In the level attitude, and with
the rotorcraft contacting the ground
along the bottom of both skids, the fol-
lowing apply:
(1) The vertical reactions must be
combined with horizontal drag reac-
tions of 50 percent of the vertical reac-
tion applied at the ground.
(2) The resultant ground loads must
equal the vertical load specified in
paragraph (b) of this section.
(d)
Sideloads in the level landing atti-
tude. In the level attitude,and with the
rotorcraft contacting the ground along
the bottom of both skids, the following
apply:
(1) The vertical ground reaction must
be—
(i) Equal to the vertical loads ob-
tained in the condition specified in
paragraph (b) of this section; and
(ii) Divided equally among the skids.
(2) The vertical ground reactions
must be combined with a horizontal
sideload of 25 percent of their value.
(3) The total sideload must be applied
equally between the skids and along
the length of the skids.
(4) The unbalanced moments are as-
sumed to be resisted by angular iner-
tia.
(5) The skid gear must be inves-
tigated for—
(i) Inward acting sideloads; and
(ii) Outward acting sideloads.
(e)
One-skid landing loads in the level
attitude. In the level attitude, and with
the rotorcraft contacting the ground
along the bottom of one skid only, the
following apply:
(1) The vertical load on the ground
contact side must be the same as that
obtained on that side in the condition
specified in paragraph (b) of this sec-
tion.
(2) The unbalanced moments are as-
sumed to be resisted by angular iner-
tia.
(f)
Special conditions. In addition to
the conditions specified in paragraphs
(b) and (c) of this section, the rotor-
craft must be designed for the fol-
lowing ground reactions:
(1) A ground reaction load acting up
and aft at an angle of 45 degrees to the
longitudinal axis of the rotorcraft.
This load must be—
(i) Equal to 1.33 times the maximum
weight;
(ii) Distributed symmetrically among
the skids;
(iii) Concentrated at the forward end
of the straight part of the skid tube;
and
(iv) Applied only to the forward end
of the skid tube and its attachment to
the rotorcraft.
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