CS 25.175 Demonstration of static longitudinal stability

ED Decision 2003/2/RM

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% 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 V_SR1.

(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 93 km/h (50 kt) 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 V_SR1 nor speeds greater than V_FC/M_FC, nor speeds that require a stick force of more than 222 N (50 lbf)), with –

(i)      The wing-flaps retracted;

(ii)     The centre of gravity in the most adverse position (see CS 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 CS 25.1521), except that the power need not exceed that required at V_MO/M_MO; 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 93 km/h (50 kt) 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 V_SR1 nor speeds greater than the minimum speed of the applicable speed range prescribed in subparagraph (b)(1) of this paragraph, nor speeds that require a stick force of more than 222 N (50 lbf)), 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 ; 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 93 km/h (50 kt) 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 V_SR1, nor speeds greater than V_LE, nor speeds that require a stick force of more than 222 N (50 lbf)), 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 V_LE; 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 V_SW, and 1·7 V_SR1 with –

(1)     Wing-flaps in the approach position;

(2)     Landing gear retracted;

(3)     Maximum landing weight; and

(4)     The aeroplane trimmed at 1·3 V_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 356 N (80 lbf) at speeds between V_SW, and 1·7 V_SR0 with –

(1)     Wing-flaps in the landing position;

(2)     Landing gear extended;

(3)     Maximum landing weight;

(4)     The aeroplane trimmed at 1·3 V_SR0 with –

(i)      Power or thrust off, and

(ii)     Power or thrust for level flight.