Code of Federal Regulations - Title 14

202

14 CFR Ch. I (1–1–14 Edition)

§ 23.171

(3) Landing gear retracted;
(4) Wing flaps in the takeoff posi-

tion(s); and

(5) An angle of bank not exceeding 5

degrees.

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as
amended by Amdt. 23–21, 43 FR 2318, Jan. 16,
1978; Amdt. 23–34, 52 FR 1828, Jan. 15, 1987;
Amdt. 23–42, 56 FR 351, Jan. 3, 1991; 56 FR
5455, Feb. 11, 1991; Amdt. 23–50, 61 FR 5189,
Feb. 9, 1996]

TABILITY

§ 23.171

General.

The airplane must be longitudinally,

directionally, and laterally stable
under §§ 23.173 through 23.181. In addi-
tion, the airplane must show suitable
stability and control ‘‘feel’’ (static sta-
bility) in any condition normally en-
countered in service, if flight tests
show it is necessary for safe operation.

§ 23.173

Static longitudinal stability.

Under the conditions specified in

§ 23.175 and with the airplane trimmed
as indicated, the characteristics of the
elevator control forces and the friction
within the control system must be as
follows:

(a) A pull must be required to obtain

and maintain speeds below the speci-
fied trim speed and a push required to
obtain and maintain speeds above the
specified trim speed. This must be
shown at any speed that can be ob-
tained, except that speeds requiring a
control force in excess of 40 pounds or
speeds above the maximum allowable
speed or below the minimum speed for
steady unstalled flight, need not be
considered.

(b) The airspeed must return to with-

in the tolerances specified for applica-
ble categories of airplanes when the
control force is slowly released at any
speed within the speed range specified
in paragraph (a) of this section. The ap-
plicable tolerances are—

(1) The airspeed must return to with-

in plus or minus 10 percent of the origi-
nal trim airspeed; and

(2) For commuter category airplanes,

the airspeed must return to within plus
or minus 7.5 percent of the original
trim airspeed for the cruising condition
specified in § 23.175(b).

speed so that any substantial speed
change results in a stick force clearly
perceptible to the pilot.

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as
amended by Amdt. 23–14, 38 FR 31820 Nov. 19,
1973; Amdt. 23–34, 52 FR 1828, Jan. 15, 1987]

§ 23.175

Demonstration of static longi-

tudinal stability.

Static longitudinal stability must be

shown as follows:

(a)

Climb. The stick force curve must

have a stable slope at speeds between
85 and 115 percent of the trim speed,
with—

(1) Flaps retracted;
(2) Landing gear retracted;
(3) Maximum continuous power; and
(4) The airplane trimmed at the speed

used in determining the climb perform-
ance required by § 23.69(a).

(b)

Cruise. With flaps and landing

gear retracted and the airplane in trim
with power for level flight at represent-
ative cruising speeds at high and low
altitudes, including speeds up to V

, as appropriate, except that

the speed need not exceed V

—

(1) For normal, utility, and acrobatic

category airplanes, the stick force
curve must have a stable slope at all
speeds within a range that is the great-
er of 15 percent of the trim speed plus
the resulting free return speed range,
or 40 knots plus the resulting free re-
turn speed range, above and below the
trim speed, except that the slope need
not be stable—

(i) At speeds less than 1.3 V

; or

(ii) For airplanes with V

estab-

lished under § 23.1505(a), at speeds
greater than V

; or

(iii) For airplanes with V

es-

tablished under § 23.1505(c), at speeds
greater than V

(2) For commuter category airplanes,

the stick force curve must have a sta-
ble slope at all speeds within a range of
50 knots plus the resulting free return
speed range, above and below the trim
speed, except that the slope need not be
stable—

(i) At speeds less than 1.4 V

; or

(ii) At speeds greater than V

;

(iii) At speeds that require a stick

force greater than 50 pounds.

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