226
14 CFR Ch. I (1–1–24 Edition)
§ 25.181
(2) From V
MO
/M
MO
to V
FC
/M
FC
, 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
SR
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
SR
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]
S
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).
(c) The following procedures must be
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
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