spaschal on DSK3GDR082PROD with CFR

Section 25.177

14 CFR Ch. I (1-1-19 Edition)

(v) The airplane trimmed for level
flight with the power required in paragraph (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 percent of the trim speed plus the resulting 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 VSR1, nor
speeds greater than the minimum
speed of the applicable speed range prescribed in paragraph (b)(1), nor speeds
that require a stick force of more than
50 pounds), with - 
(i) Wing flaps, center of gravity position, and weight as specified in paragraph (b)(1) of this section;
(ii) Power required for level flight at
a speed equal to (VMO + 1.3 VSR1)/2; and
(iii) The airplane trimmed for level
flight with the power required in paragraph (b)(2)(ii) of this section.
(3) With the landing gear extended,
the stick force curve must have a stable slope at all speeds within a range
which is the greater of 15 percent of the
trim speed plus the resulting 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 VSR1, nor speeds
greater than VLE, nor speeds that require a stick force of more than 50
pounds), with - 
(i) Wing flap, center of gravity position, and weight as specified in paragraph (b)(1) of this section;
(ii) 75 percent of maximum continuous power for reciprocating engines
or, for turbine engines, the maximum
cruising power selected by the applicant as an operating limitation, except
that the power need not exceed that required for level flight at VLE; and
(iii) The aircraft trimmed for level
flight with the power required in paragraph (b)(3)(ii) of this section.
(c) Approach. The stick force curve
must have a stable slope at speeds between VSW and 1.7 VSR1, with - 
(1) Wing flaps in the approach position;
(2) Landing gear retracted;
(3) Maximum landing weight; and

(4) The airplane trimmed at 1.3 VSR1
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 VSW and 1.7 VSR0 with - 
(1) Wing flaps in the landing position;
(2) Landing gear extended;
(3) Maximum landing weight;
(4) The airplane trimmed at 1.3 VSR0
with - 
(i) Power or thrust off, and
(ii) Power or thrust for level flight.
(5) The airplane trimmed at 1.3 VSR0
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]

Section 25.177 Static lateral-directional stability.
(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 condition, at speeds from 1.13 VSR1, up to
VFE, VLE, or VFC/MFC (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 controls free) for any landing gear and flap
position and symmetric power condition, may not be negative at any airspeed (except that speeds higher than
VFE need not be considered for flaps extended configurations nor speeds higher than VLE for landing gear extended
configurations) in the following airspeed ranges:
(1) From 1.13 VSR1 to VMO/MMO.
(2) From VMO/MMO to VFC/MFC, 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 section. In straight, steady sideslips over
the range of sideslip angles appropriate
to the operation of the airplane, the aileron and rudder control movements
and forces must be substantially proportional to the angle of sideslip in a

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