title-14-part-27-sec27-501

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.

VerDate Sep<11>2014

09:06 Jun 28, 2024

Jkt 262046

PO 00000

Frm 00514

Fmt 8010

Sfmt 8010

Y:\SGML\262046.XXX

262046

jspears on DSK121TN23PROD with CFR

505

Federal Aviation Administration, DOT

§ 27.521

(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.

(2) With the rotorcraft in the level

landing attitude, a vertical ground re-
action load equal to one-half of the
vertical load determined under para-
graph (b) of this section. This load
must be—

(i) Applied only to the skid tube and

its attachment to the rotorcraft; and

(ii) Distributed equally over 33.3 per-

cent of the length between the skid
tube attachments and centrally located
midway between the skid tube attach-
ments.

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–2, 33 FR 963, Jan. 26,
1968; Amdt. 27–26, 55 FR 8000, Mar. 6, 1990]

§ 27.505

Ski landing conditions.

If certification for ski operation is

requested, the rotorcraft, with skis,
must be designed to withstand the fol-
lowing loading conditions (where

P is

the maximum static weight on each ski
with the rotorcraft at design maximum
weight, and

n is the limit load factor

determined under § 27.473(b).

(a) Up-load conditions in which—
(1) A vertical load of

Pn and a hori-

zontal load of

Pn/4 are simultaneously

applied at the pedestal bearings; and

(2) A vertical load of 1.33

P is applied

at the pedestal bearings.

(b) A side-load condition in which a

side load of 0.35

Pn is applied at the

pedestal bearings in a horizontal plane
perpendicular to the centerline of the
rotorcraft.

a torque load of 1.33

P (in foot pounds)

is applied to the ski about the vertical
axis through the centerline of the ped-
estal bearings.

ATER

OADS

§ 27.521

Float landing conditions.

If certification for float operation is

requested, the rotorcraft, with floats,
must be designed to withstand the fol-
lowing loading conditions (where the
limit load factor is determined under
§ 27.473(b) or assumed to be equal to
that determined for wheel landing
gear):

(a) Up-load conditions in which—
(1) A load is applied so that, with the

rotorcraft in the static level attitude,
the resultant water reaction passes