Refer to figures.
Static Longitudinal stability is the aircraft's natural tendency when disturbed in pitch, to return to its former trimmed angle of attack without pilot input, and is desirable throughout the aircraft's complete speed range.
The position of the CG directly affects the magnitude of the longitudinal static stability, the tailplane downforce and the stalling speed because its position determines the length of the arm of any restoring moment.
A forward movement of the CG increases the positive longitudinal static stability of an aircraft but decreases the manoeuvrability and control response because the moment arm is increased in length and increases the nose-down pitching moment. Thus, the elevators have less nose-up authority.
The most direct appreciation of the manoeuvring stability of an aeroplane is obtained from a plot of stick force versus load factor.
The aeroplane with positive manoeuvring stability should demonstrate a steady increase in stick force with increase in load factor or “g”.
When the aeroplane has high static stability, the manoeuvring stability will be high and a high stick force gradient will result. As the CG moves aft, the stick force gradient decreases with decreasing manoeuvring stability.
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