title-14-part-27-sec27-177

497

Federal Aviation Administration, DOT

§ 27.177

§ 27.171

Stability: general.

The rotorcraft must be able to be

flown, without undue pilot fatigue or
strain, in any normal maneuver for a
period of time as long as that expected
in normal operation. At least three
landings and takeoffs must be made
during this demonstration.

§ 27.173

Static longitudinal stability.

(a) The longitudinal control must be

designed so that a rearward movement
of the control is necessary to obtain an
airspeed less than the trim speed, and a
forward movement of the control is
necessary to obtain an airspeed more
than the trim speed.

(b) Throughout the full range of alti-

tude for which certification is re-
quested, with the throttle and collec-
tive pitch held constant during the ma-
neuvers specified in § 27.175(a) through
(d), the slope of the control position
versus airspeed curve must be positive.
However, in limited flight conditions
or modes of operation determined by
the Administrator to be acceptable, the
slope of the control position versus air-
speed curve may be neutral or negative
if the rotorcraft possesses flight char-
acteristics that allow the pilot to
maintain airspeed within

5 knots of

the desired trim airspeed without ex-
ceptional piloting skill or alertness.

[Amdt. 27–21, 49 FR 44433, Nov. 6, 1984, as
amended by Amdt. 27–44, 73 FR 10999, Feb. 29,
2008]

§ 27.175

Demonstration of static longi-

tudinal stability.

(a)

Climb. Static longitudinal sta-

bility must be shown in the climb con-
dition at speeds from Vy

10 kt to Vy

+ 10 kt with—

(1) Critical weight;
(2) Critical center of gravity;
(3) Maximum continuous power;
(4) The landing gear retracted; and
(5) The rotorcraft trimmed at

(b)

Cruise. Static longitudinal sta-

bility must be shown in the cruise con-
dition at speeds from 0.8 V

10 kt to

0.8 V

+ 10 kt or, if V

is less than 0.8

, from V

10 kt to V

+ 10 kt,

with—

(1) Critical weight;
(2) Critical center of gravity;
(3) Power for level flight at 0.8 V

, whichever is less;

(4) The landing gear retracted; and
(5) The rotorcraft trimmed at 0.8 V

or V

, whichever is less.

(c)

NE.

Static longitudinal stability

must be shown at speeds from V

kt to V

with—

(1) Critical weight;
(2) Critical center of gravity;
(3) Power required for level flight at

10 kt or maximum continuous

power, whichever is less;

(4) The landing gear retracted; and
(5) The rotorcraft trimmed at V

10 kt.

(d)

Autorotation. Static longitudinal

stability must be shown in autorota-
tion at—

(1) Airspeeds from the minimum rate

of descent airspeed

10 kt to the min-

imum rate of descent airspeed + 10 kt,
with—

(i) Critical weight;
(ii) Critical center of gravity;
(iii) The landing gear extended; and
(iv) The rotorcraft trimmed at the

minimum rate of descent airspeed.

(2) Airspeeds from best angle-of-glide

airspeed

10 kt to the best angle-of-

glide airspeed + 10 kt, with—

(i) Critical weight;
(ii) Critical center of gravity;
(iii) The landing gear retracted; and
(iv) The rotorcraft trimmed at the

best angle-of-glide airspeed.

(Secs. 313(a), 601, 603, 604, and 605 of the Fed-
eral Aviation Act of 1958 (49 U.S.C. 1354(a),
1421, 1423, 1424, and 1425); and sec. 6(c) of the
Dept. of Transportation Act (49 U.S.C.
1655(c)))

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–2, 33 FR 963, Jan. 26,
1968; Amdt. 27–11, 41 FR 55468, Dec. 20, 1976;
Amdt. 27–14, 43 FR 2325, Jan. 16, 1978; Amdt.
27–21, 49 FR 44433, Nov. 6, 1984; Amdt. 27–34, 62
FR 46173, Aug. 29, 1997; Amdt. 27–44, 73 FR
10999, Feb. 29, 2008]

§ 27.177

Static directional stability.

(a) The directional controls must op-

erate in such a manner that the sense
and direction of motion of the rotor-
craft following control displacement
are in the direction of the pedal motion
with the throttle and collective con-
trols held constant at the trim condi-
tions specified in § 27.175(a), (b), and (c).
Sideslip angles must increase with
steadily increasing directional control
deflection for sideslip angles up to the
lesser of—

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498

14 CFR Ch. I (1–1–24 Edition)

§ 27.231

(1)

25 degrees from trim at a speed of

15 knots less than the speed for min-
imum rate of descent varying linearly
to

10 degrees from trim at V

;

(2) The steady state sideslip angles

established by § 27.351;

(3) A sideslip angle selected by the

applicant, which corresponds to a
sideforce of at least 0.1g; or

(4) The sideslip angle attained by

maximum directional control input.

(b) Sufficient cues must accompany

the sideslip to alert the pilot when the
aircraft is approaching the sideslip
limits.

paragraph (a) of this section, the side-
slip angle versus directional control
position curve may have a negative
slope within a small range of angles
around trim, provided the desired head-
ing can be maintained without excep-
tional piloting skill or alertness.

[Amdt. 27–44, 73 FR 11000, Feb. 29, 2008]

ROUND AND

ATER

ANDLING

HARACTERISTICS

§ 27.231

General.

The rotorcraft must have satisfac-

tory ground and water handling char-
acteristics, including freedom from un-
controllable tendencies in any condi-
tion expected in operation.

§ 27.235

Taxiing condition.

The rotorcraft must be designed to

withstand the loads that would occur
when the rotorcraft is taxied over the
roughest ground that may reasonably
be expected in normal operation.

§ 27.239

Spray characteristics.

If certification for water operation is

requested, no spray characteristics
during taxiing, takeoff, or landing may
obscure the vision of the pilot or dam-
age the rotors, propellers, or other
parts of the rotorcraft.

§ 27.241

Ground resonance.

The rotorcraft may have no dan-

gerous tendency to oscillate on the
ground with the rotor turning.

ISCELLANEOUS

LIGHT

EQUIREMENTS

§ 27.251

Vibration.

Each part of the rotorcraft must be

free from excessive vibration under
each appropriate speed and power con-
dition.

Subpart C—Strength Requirements

ENERAL

§ 27.301

Loads.

(a) Strength requirements are speci-

fied in terms of limit loads (the max-
imum loads to be expected in service)
and ultimate loads (limit loads multi-
plied by prescribed factors of safety).
Unless otherwise provided, prescribed
loads are limit loads.

(b) Unless otherwise provided, the

specified air, ground, and water loads
must be placed in equilibrium with in-
ertia forces, considering each item of
mass in the rotorcraft. These loads
must be distributed to closely approxi-
mate or conservatively represent ac-
tual conditions.

significantly change the distribution of
external or internal loads, this redis-
tribution must be taken into account.

§ 27.303

Factor of safety.

Unless otherwise provided, a factor of

safety of 1.5 must be used. This factor
applies to external and inertia loads
unless its application to the resulting
internal stresses is more conservative.

§ 27.305

Strength and deformation.

(a) The structure must be able to

support limit loads without detri-
mental or permanent deformation. At
any load up to limit loads, the defor-
mation may not interfere with safe op-
eration.

(b) The structure must be able to

support ultimate loads without failure.
This must be shown by—

(1) Applying ultimate loads to the

structure in a static test for at least
three seconds; or

(2) Dynamic tests simulating actual

load application.