CS-VLA 177  Static directional and lateral

ED Decision 2003/18/RM

(a)                            Three-control aeroplanes. The stability requirements for three-control aeroplanes are as follows:

(1)                            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 appropriate to the take-off, climb, cruise, and approach configurations. This must be shown with power up to maximum continuous power, and at speeds from 1.2 V_S1 up to maximum allowable speed for the condition being investigated. The angle of skid for these tests must be appropriate to the type of aeroplane. At larger angles of skid up to that at which full rudder is used or a control force limit in CS-VLA 143 is reached, whichever occurs first, and at speeds from 1.2 V_S1 to V_A, the rudder pedal force must not reverse.

(2)                            The static lateral stability, as shown by the tendency to raise the low wing in a slip, must be positive for any landing gear and flap positions. This must be shown with power up to 75% of maximum continuous power at speeds above 1.2 V_S1, up to the maximum allowable speed for the configuration being investigated. The static lateral stability may not be negative at 1.2 V_S1. The angle of slip for these tests must be appropriate to the type of aeroplane, but in no case may the slip angle be less than that obtainable with 10° of bank.

(3)                            In straight, steady slips at 1.2 V_S1 for any landing gear and flap positions, and for power conditions up to 50% of maximum continuous power, the aileron and rudder control movements and forces must increase steadily (but not necessarily in constant proportion) as the angle of slip is increased up to the maximum appropriate to the type of aeroplane. At larger slip angles up to the angle at which full rudder or aileron control is used or a control force limit contained in CS-VLA 143 is obtained, the rudder pedal force may not reverse. Enough bank must accompany slipping to hold a constant heading. Rapid entry into, or recovery from, a maximum slip may not result in uncontrollable flight characteristics.

(b)                            Two-control (or simplified control) aeroplanes. The stability requirements for twocontrol aeroplanes are as follows:

(1)                            The directional stability of the aeroplane must be shown by showing that, in each configuration, it can be rapidly rolled from a 45° bank in one direction to a 45° bank in the opposite direction without showing dangerous skid characteristics.

(2)                            The lateral stability of the aeroplane must be shown by showing that it will not assume a dangerous attitude or speed when the controls are abandoned for two minutes. This must be done in moderately smooth air with the aeroplane trimmed for straight level flight at 0-9 V_H or V_C, whichever is lower, with flaps and landing gear retracted, and with a rearward centre of gravity.