page-84

568

14 CFR Ch. I (1–1–19 Edition)

Pt. 27, App. B

longitudinal control force stability at crit-
ical combinations of weight and center of
gravity at the conditions specified in para-
graph IV (b) or (c) of this appendix, as appro-
priate. The stick force must vary with speed
so that any substantial speed change results
in a stick force clearly perceptible to the
pilot. For single-pilot approval, the airspeed
must return to within 10 percent of the trim
speed when the control force is slowly re-
leased for each trim condition specified in
paragraph IV(b) of the this appendix.

(b)

For single-pilot approval:

(1)

Climb.

Stability must be shown in climb

throughout the speed range 20 knots either
side of trim with—

(i) The helicopter trimmed at V

;

(ii) Landing gear retracted (if retractable);

and

(iii) Power required for limit climb rate (at

least 1,000 fpm) at V

or maximum contin-

uous power, whichever is less.

(2)

Cruise.

Stability must be shown

throughout the speed range from 0.7 to 1.1 V

or V

NEI

, whichever is lower, not to exceed

knots from trim with—

(i) The helicopter trimmed and power ad-

justed for level flight at 0.9 V

or 0.9 V

NEI

whichever is lower; and

(ii) Landing gear retracted (if retractable).
(3)

Slow cruise.

Stability must be shown

throughout the speed range from 0.9 V

MINI

1.3 V

MINI

or 20 knots above trim speed, which-

ever is greater, with—

(i) the helicopter trimmed and power ad-

justed for level flight at 1.1 V

MINI

; and

(ii) Landing gear retracted (if retractable).
(4)

Descent.

Stability must be shown

throughout the speed range 20 knots either
side of trim with—

(i) The helicopter trimmed at 0.8 V

or 0.8

NEI

(or 0.8 V

for the landing gear extended

case), whichever is lower;

(ii) Power required for 1,000 fpm descent at

trim speed; and

(iii) Landing gear extended and retracted,

if applicable.

(5)

Approach.

Stability must be shown

throughout the speed range from 0.7 times
the minimum recommended approach speed
to 20 knots above the maximum rec-
ommended approach speed with—

(i) The helicopter trimmed at the rec-

ommended approach speed or speeds;

(ii) Landing gear extended and retracted, if

applicable; and

(iii) Power required to maintain a 3

glide

path and power required to maintain the
steepest approach gradient for which ap-
proval is requested.

crew of two pilots must comply with the pro-
visions of paragraphs IV(b)(2) and IV(b)(5) of
this appendix.

Static Lateral Directional Stability.

(a)

Static directional stability must be positive
throughout the approved ranges of airspeed,

power, and vertical speed. In straight and
steady sideslips up to

from trim, direc-

tional control position must increase with-
out discontinuity with the angle of sideslip,
except for a small range of sideslip angles
around trim. At greater angles up to the
maximum sideslip angle appropriate to the
type, increased directional control position
must produce an increased angle of sideslip.
It must be possible to maintain balanced
flight without exceptional pilot skill or
alertness.

(b) During sideslips up to

from trim

throughout the approved ranges of airspeed,
power, and vertical speed, there must be no
negative dihedral stability perceptible to the
pilot through lateral control motion or
force. Longitudinal cyclic movement with
sideslip must not be excessive.

VI.

Dynamic stability.

(a) For single-pilot

approval—

(1) Any oscillation having a period of less

than 5 seconds must damp to

⁄

amplitude in

not more than one cycle.

(2) Any oscillation having a period of 5 sec-

onds or more but less than 10 seconds must
damp to

⁄

amplitude in not more than two

cycles.

(3) Any oscillation having a period of 10

seconds or more but less than 20 seconds
must be damped.

(4) Any oscillation having a period of 20

seconds or more may not achieve double am-
plitude in less than 20 seconds.

(5) Any aperiodic response may not achieve

double amplitude in less than 6 seconds.

(b) For helicopters approved with a min-

imum crew of two pilots—

(1) Any oscillation having a period of less

than 5 seconds must damp to

⁄

amplitude in

not more than two cycles.

(2) Any oscillation having a period of 5 sec-

onds or more but less than 10 seconds must
be damped.

(3) Any oscillation having a period of 10

seconds or more may not achieve double am-
plitude in less than 10 seconds.

VII.

Stability Augmentation System (SAS).

(a) If a SAS is used, the reliability of the

SAS must be related to the effects of its fail-
ure. Any SAS failure condition that would
prevent continued safe flight and landing
must be extremely improbable. It must be
shown that, for any failure condition of the
SAS that is not shown to be extremely im-
probable—

(1) The helicopter is safely controllable

when the failure or malfunction occurs at
any speed or altitude within the approved
IFR operating limitations; and

(2) The overall flight characteristics of the

helicopter allow for prolonged instrument
flight without undue pilot effort. Additional
unrelated probable failures affecting the con-
trol system must be considered. In addi-
tion—

VerDate Sep<11>2014

12:50 Apr 30, 2019

Jkt 247046

PO 00000

Frm 00578

Fmt 8010

Sfmt 8002

Y:\SGML\247046.XXX

247046

spaschal on DSK3GDR082PROD with CFR