title-14-part-27-sec27-521

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

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506

14 CFR Ch. I (1–1–24 Edition)

§ 27.547

vertically through the center of grav-
ity; and

(2) The vertical load prescribed in

paragraph (a)(1) of this section is ap-
plied simultaneously with an aft com-
ponent of 0.25 times the vertical com-
ponent.

(b) A side-load condition in which—
(1) A vertical load of 0.75 times the

total vertical load specified in para-
graph (a)(1) of this section is divided
equally among the floats; and

(2) For each float, the load share de-

termined under paragraph (b)(1) of this
section, combined with a total side
load of 0.25 times the total vertical
load specified in paragraph (b)(1) of
this section, is applied to that float
only.

AIN

OMPONENT

EQUIREMENTS

§ 27.547

Main rotor structure.

(a) Each main rotor assembly (in-

cluding rotor hubs and blades) must be
designed as prescribed in this section.

(b) [Reserved]
(c) The main rotor structure must be

designed to withstand the following
loads prescribed in §§ 27.337 through
27.341:

(1) Critical flight loads.
(2) Limit loads occurring under nor-

mal conditions of autorotation. For
this condition, the rotor r.p.m. must be
selected to include the effects of alti-
tude.

(d) The main rotor structure must be

designed to withstand loads simu-
lating—

(1) For the rotor blades, hubs, and

flapping hinges, the impact force of
each blade against its stop during
ground operation; and

(2) Any other critical condition ex-

pected in normal operation.

(e) The main rotor structure must be

designed to withstand the limit torque
at any rotational speed, including zero.
In addition:

(1) The limit torque need not be

greater than the torque defined by a
torque limiting device (where pro-
vided), and may not be less than the
greater of—

(i) The maximum torque likely to be

transmitted to the rotor structure in
either direction; and

(ii) The limit engine torque specified

in § 27.361.

(2) The limit torque must be distrib-

uted to the rotor blades in a rational
manner.

(Secs. 604, 605, 72 Stat. 778, 49 U.S.C. 1424,
1425)

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–3, 33 FR 14105, Sept. 18,
1968]

§ 27.549

Fuselage, landing gear, and

rotor pylon structures.

(a) Each fuselage, landing gear, and

rotor pylon structure must be designed
as prescribed in this section. Resultant
rotor forces may be represented as a
single force applied at the rotor hub at-
tachment point.

(b) Each structure must be designed

to withstand—

(1) The critical loads prescribed in

§§ 27.337 through 27.341;

(2) The applicable ground loads pre-

scribed in §§ 27.235, 27.471 through 27.485,
27.493, 27.497, 27.501, 27.505, and 27.521;
and

(3) The loads prescribed in § 27.547

(d)(2) and (e).

balancing air and inertia loads occur-
ring under accelerated flight condi-
tions, must be considered.

(d) Each engine mount and adjacent

fuselage structure must be designed to
withstand the loads occurring under
accelerated flight and landing condi-
tions, including engine torque.

(Secs. 604, 605, 72 Stat. 778, 49 U.S.C. 1424,
1425)

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–3, 33 FR 14105, Sept. 18,
1968]

MERGENCY

ANDING

ONDITIONS

§ 27.561

General.

(a) The rotorcraft, although it may

be damaged in emergency landing con-
ditions on land or water, must be de-
signed as prescribed in this section to
protect the occupants under those con-
ditions.

(b) The structure must be designed to

give each occupant every reasonable
chance of escaping serious injury in a
crash landing when—

(1) Proper use is made of seats, belts,

and other safety design provisions;