title-14-part-27-sec27-497

503

Federal Aviation Administration, DOT

§ 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—

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504

14 CFR Ch. I (1–1–24 Edition)

§ 27.501

(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

(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.