652
14 CFR Ch. I (1–1–14 Edition)
§ 27.497
§ 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—
(i) For the forward wheels, 0.8 times
the vertical reaction (on one side) act-
ing inward, and 0.6 times the vertical
reaction (on the other side) acting out-
ward; and
(ii) For the rear wheel, 0.8 times the
vertical reaction.
(2) The loads specified in paragraph
(f)(1) of this section must be applied—
(i) At the ground contact point with
the wheel in the trailing position (for
non-full swiveling landing gear or for
full swiveling landing gear with a lock,
steering device, or shimmy damper to
keep the wheel in the trailing posi-
tion); or
(ii) At the center of the axle (for full
swiveling landing gear without a lock,
steering device, or shimmy damper).
(g)
Braked roll conditions in the level
landing attitude. In the attitudes speci-
fied in paragraphs (b) and (c) of this
section, and with the shock absorbers
in their static positions, the rotorcraft
must be designed for braked roll loads
as follows:
(1) The limit vertical load must be
based on a limit vertical load factor of
not less than—
(i) 1.0, for the attitude specified in
paragraph (b) of this section; and
(ii) 1.33, for the attitude specified in
paragraph (c) of this section.
(2) For each wheel with brakes, a
drag load must be applied, at the
ground contact point, of not less than
the lesser of—
(i) 0.8 times the vertical load; and
(ii) The maximum based on limiting
brake torque.
(h)
Rear wheel turning loads in the
static ground attitude. In the static
ground attitude, and with the shock
absorbers and tires in their static posi-
tions, the rotorcraft must be designed
for rear wheel turning loads as follows:
(1) A vertical ground reaction equal
to the static load on the rear wheel
must be combined with an equal
sideload.
(2) The load specified in paragraph
(h)(1) of this section must be applied to
the rear landing gear—
(i) Through the axle, if there is a
swivel (the rear wheel being assumed
to be swiveled 90 degrees to the longi-
tudinal axis of the rotorcraft); or
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