JAR 25.175 Demonstration of static longi-tudinal
stability
Static longitudinal stability must be shown as
follows:
(a) Climb. The stick curve must have a stable
slope at speeds between 85% and 115% of the
speed at which the aeroplane –
(1) Is trimmed with –
(i) Wing-flaps retracted;
(ii) Landing gear retracted;
(iii) Maximum take-off weight;
and
(iv) The maximum power or thrust
selected by the applicant as an operating
limitation for use during climb; and
(2) Is trimmed at the speed for best
rate-of-climb except that the speed need not be
[less than 1·3 VSR 1 .]
(b) Cruise. Static longitudinal stability must
be shown in the cruise condition as follows:
(1) With the landing gear retracted at
high speed, the stick force curve must have a
stable slope at all speeds within a range which
is the greater of 15% 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 VSR 1 nor speeds greater than]
VFC/MFC, nor speeds that require a stick force
of more than 50 pounds), with –
(i) The wing-flaps retracted;
(ii) The centre of gravity in the
most adverse position (see JAR 25.27);
(iii) The most critical weight
between the maximum take-off and
maximum landing weights;
(iv) The maximum cruising power
selected by the applicant as an operating
limitation (see JAR 25.1521), except that
the power need not exceed that required
at VMO/MMO; and
(v) The aeroplane trimmed for
level flight with the power required in
sub-paragraph (iv) above.
(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% 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 VSR 1 nor speeds greater than the]
minimum speed of the applicable speed range
prescribed in sub-paragraph (b)(1) of this
paragraph, nor speeds that require a stick force
of more than 50 pounds), with –
(i) Wing-flaps, centre of gravity
position, and weight as specified in sub-paragraph
(1) of this paragraph;
(ii) Power required for level flight
[at a speed equal to 2
SR1 1·3V V MO
; and]
(iii) The aeroplane trimmed for
level flight with the power required in
sub-paragraph (ii) above.
(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% 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 VSR 1 , nor speeds greater than VLE, nor]
speeds that require a stick force of more than
50 pounds), with –
(i) Wing-flap, centre of gravity
position, and weight as specified in sub-paragraph
(b)(1) of this paragraph;
(ii) 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 aeroplane trimmed for
level flight with the power required in
sub-paragraph (ii) above.
(c) Approach. The stick force curve must
[have a stable slope at speeds between VSW, and
1·7 VSR 1 with –]
(1) Wing-flaps in the approach
position;
(2) Landing gear retracted;
(3) Maximum landing weight; and
[(4) The aeroplane trimmed at 1·3 VSR 1 ,]
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 VSR 0]
with –
(1) Wing-flaps in the landing position;
(2) Landing gear extended;
(3) Maximum landing weight;
[(4) The aeroplane trimmed at 1·3 VSR 0]
with –
(i) Power or thrust off, and
(ii) Power or thrust for level
flight.
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