title-14-part-25-sec25-177

225

Federal Aviation Administration, DOT

§ 25.177

(i) The wing flaps retracted;
(ii) The center of gravity in the most

adverse position (see § 25.27);

(iii) The most critical weight be-

tween the maximum takeoff and max-
imum landing weights;

(iv) 75 percent of maximum contin-

uous power for reciprocating engines or
for turbine engines, the maximum
cruising power selected by the appli-
cant as an operating limitation (see
§ 25.1521), except that the power need
not exceed that required at

;

and

(v) The airplane trimmed for level

flight with the power required in para-
graph (b)(1)(iv) of this section.

(2) With the landing gear retracted at

low speed, the stick force curve must
have a stable slope at all speeds within
a range which is the greater of 15 per-
cent of the trim speed plus the result-
ing free return speed range, or 50 knots
plus the resulting free return speed
range, above and below the trim speed
(except that the speed range need not
include speeds less than 1.3

SR1

, nor

speeds greater than the minimum
speed of the applicable speed range pre-
scribed in paragraph (b)(1), nor speeds
that require a stick force of more than
50 pounds), with—

(i) Wing flaps, center of gravity posi-

tion, and weight as specified in para-
graph (b)(1) of this section;

(ii) Power required for level flight at

a speed equal to (

+ 1.3

SR1

)/2; and

(iii) The airplane trimmed for level

flight with the power required in para-
graph (b)(2)(ii) of this section.

(3) With the landing gear extended,

the stick force curve must have a sta-
ble slope at all speeds within a range
which is the greater of 15 percent of the
trim speed plus the resulting free re-
turn speed range, or 50 knots plus the
resulting free return speed range,
above and below the trim speed (except
that the speed range need not include
speeds less than 1.3

SR1

, nor speeds

greater than

LE,

nor speeds that re-

quire a stick force of more than 50
pounds), with—

(i) Wing flap, center of gravity posi-

tion, and weight as specified in para-
graph (b)(1) of this section;

(ii) 75 percent of maximum contin-

uous power for reciprocating engines
or, for turbine engines, the maximum

cruising power selected by the appli-
cant as an operating limitation, except
that the power need not exceed that re-
quired for level flight at

; and

(iii) The aircraft trimmed for level

flight with the power required in para-
graph (b)(3)(ii) of this section.

(c)

Approach. The stick force curve

must have a stable slope at speeds be-
tween

and 1.7

SR1

, with—

(1) Wing flaps in the approach posi-

tion;

(2) Landing gear retracted;
(3) Maximum landing weight; and
(4) The airplane trimmed at 1.3

SR1

with enough power to maintain level
flight at this speed.

(d)

Landing. The stick force curve

must have a stable slope, and the stick
force may not exceed 80 pounds, at
speeds between

and 1.7

SR0

with—

(1) Wing flaps in the landing position;
(2) Landing gear extended;
(3) Maximum landing weight;
(4) The airplane trimmed at 1.3 V

SR0

with—

(i) Power or thrust off, and
(ii) Power or thrust for level flight.
(5) The airplane trimmed at 1.3

SR0

with power or thrust off.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–7, 30 FR 13117, Oct. 15,
1965; Amdt. 25–108, 67 FR 70827, Nov. 26, 2002;
Amdt. 25–115, 69 FR 40527, July 2, 2004]

§ 25.177

Static lateral-directional sta-

bility.

(a) The static directional stability

(as shown by the tendency to recover
from a skid with the rudder free) must
be positive for any landing gear and
flap position and symmetric power con-
dition, at speeds from 1.13 V

SR1

, up to

, V

, or V

(as appropriate for

the airplane configuration).

(b) The static lateral stability (as

shown by the tendency to raise the low
wing in a sideslip with the aileron con-
trols free) for any landing gear and flap
position and symmetric power condi-
tion, may not be negative at any air-
speed (except that speeds higher than
V

need not be considered for flaps ex-

tended configurations nor speeds high-
er than V

for landing gear extended

configurations) in the following air-
speed ranges:

(1) From 1.13 V

SR1

to V

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226

14 CFR Ch. I (1–1–24 Edition)

§ 25.181

(2) From V

to V

, unless

the divergence is—

(i) Gradual;
(ii) Easily recognizable by the pilot;

and

(iii) Easily controllable by the pilot.
(c) The following requirement must

be met for the configurations and speed
specified in paragraph (a) of this sec-
tion. In straight, steady sideslips over
the range of sideslip angles appropriate
to the operation of the airplane, the ai-
leron and rudder control movements
and forces must be substantially pro-
portional to the angle of sideslip in a
stable sense. This factor of proportion-
ality must lie between limits found
necessary for safe operation. The range
of sideslip angles evaluated must in-
clude those sideslip angles resulting
from the lesser of:

(1) One-half of the available rudder

control input; and

(2) A rudder control force of 180

pounds.

(d) For sideslip angles greater than

those prescribed by paragraph (c) of
this section, up to the angle at which
full rudder control is used or a rudder
control force of 180 pounds is obtained,
the rudder control forces may not re-
verse, and increased rudder deflection
must be needed for increased angles of
sideslip. Compliance with this require-
ment must be shown using straight,
steady sideslips, unless full lateral con-
trol input is achieved before reaching
either full rudder control input or a
rudder control force of 180 pounds; a
straight, steady sideslip need not be
maintained after achieving full lateral
control input. This requirement must
be met at all approved landing gear and
flap positions for the range of oper-
ating speeds and power conditions ap-
propriate to each landing gear and flap
position with all engines operating.

[Amdt. 25–135, 76 FR 74654, Dec. 1, 2011]

§ 25.181

Dynamic stability.

(a) Any short period oscillation, not

including combined lateral-directional
oscillations, occurring between 1.13 V

and maximum allowable speed appro-
priate to the configuration of the air-
plane must be heavily damped with the
primary controls—

(1) Free; and
(2) In a fixed position.

(b) Any combined lateral-directional

oscillations (‘‘Dutch roll’’) occurring
between 1.13 V

and maximum allow-

able speed appropriate to the configu-
ration of the airplane must be posi-
tively damped with controls free, and
must be controllable with normal use
of the primary controls without requir-
ing exceptional pilot skill.

[Amdt. 25–42, 43 FR 2322, Jan. 16, 1978, as
amended by Amdt. 25–72, 55 FR 29775, July 20,
1990; 55 FR 37607, Sept. 12, 1990; Amdt. 25–108,
67 FR 70827, Nov. 26, 2002]

TALLS

§ 25.201

Stall demonstration.

(a) Stalls must be shown in straight

flight and in 30 degree banked turns
with—

(1) Power off; and
(2) The power necessary to maintain

level flight at 1.5 V

SR1

(where V

SR1

cor-

responds to the reference stall speed at
maximum landing weight with flaps in
the approach position and the landing
gear retracted).

(b) In each condition required by

paragraph (a) of this section, it must
be possible to meet the applicable re-
quirements of § 25.203 with—

(1) Flaps, landing gear, and decelera-

tion devices in any likely combination
of positions approved for operation;

(2) Representative weights within the

range for which certification is re-
quested;

(3) The most adverse center of grav-

ity for recovery; and

(4) The airplane trimmed for straight

flight at the speed prescribed in
§ 25.103(b)(6).

used to show compliance with § 25.203;

(1) Starting at a speed sufficiently

above the stalling speed to ensure that
a steady rate of speed reduction can be
established, apply the longitudinal
control so that the speed reduction
does not exceed one knot per second
until the airplane is stalled.

(2) In addition, for turning flight

stalls, apply the longitudinal control
to achieve airspeed deceleration rates
up to 3 knots per second.

(3) As soon as the airplane is stalled,

recover by normal recovery techniques.

(d) The airplane is considered stalled

when the behavior of the airplane gives