Airplane Stability
Dynamic stability describes the behavior of the aircraft after disturbance. When the aircraft is disturbed, the forces change an the dominate ones deteirmen the stability. An aircraft that is dynamicly stable will experience an oscillation that is quickly damped.
Lateral axis
Longitudinal axis
Vertical Axis
Static Stability is the airplain initial response after disturbence. An airplane with some positive stability is much easier to fly than an unstable airplane that shows a tendency to diverge from the trimmed flight attitude. A stable airplane can almost be flown with hands off and requier gudince rather than second to second control with unstable airplane
An Aircraft that is dynamicly stable will experience an oscillation that is quickly dampbed Positive – oscillations are
dampened 
An AIrcraft with neutrual dynamic stability will flolow a contiuing, undamped oscillation Neutral – oscillations remain
consistent
An aircraft that is dynamically unstable will have increasingly divergent oscillation imagesNegative – oscillations
become worse .
If an aircraft tends to return so its trimmed condition, it has a positive static stability.
If an aircraft has a negative static stability it is un stable and will diverge further when disturbed.
If an aircraft has neutrual static stability, it will tend tostay in it's new conditiion.
Longitudinal Stability
Pitch attitude
To be longitudinally stable, an airplane must have a neutral tendancy to return to the same attitude in pitch after any disturbance a longitudinally stable airplane tends to maintain the trimed condition of flight and is therfore easy to fly in Pitch
Stability around the lateral axis
The longitudinal stability of an airplane is determined by the size of the horizontial stabilizer and it's distance form Center of Gravity. The further the CG the greater of the horizontal satbilizer and ther for the greater the leverage effect of the horizontal stabilizer
For climb
For cruise level
For descent
You must always load your airplane so the actual CG position fall within the allowable range other wize the Pitch movment will not be as sufficient.
When the C.G in an airplane is located at the rear of the aft C.G limits, the airplane becomes less stable and may be unable to recover for a Stall
The horizontal stabilizer is designed
to provide a downward force to
balance the lift-weight couple
Lateral stability
Lateral stability is the natural ability of the airplane to recover from adisturbance in the lateral plane which is rolling about the longitudinal axis
The Axis from front to back.
The wings return to it's natural position
Design characteristics that provide lateral stability:
Dihedral
Sweep-Back
Aerodynamic characteristics for lateral stability
High Keel Effect
Pendulum Effect
Low wing results in side-slip which uses
Dihedral, Wing Sweep-Back and High Keel to achive lateral stability
High wing aircraft will generally require less dihedral than a low wing due to pendulum effec
Roll.
Yoke
yoke controls the roll movment of an airplane. Rotating the control wheel controls the ailerons and the roll axis.
Acheived by turning the wings
Directional Stability
Stability about the normal axis
yaw
If an aircraft has positive directional stability, the fuselage aligns
itself with the relative air flow.
Directional stability of an airplane is its natural tendency to recover from a disturbance after a disturbance in the yawing plane about the vertical axis
Designs to assure directional stabilitys Vertical stabilizer
Keel effect and Wing sweep-back
If the airplane is diturbed by the airfolow from its nose or tail it will recover.
Rudders
Yaw is followed by roll in the same direction
due to the difference in speed and lift on
different wings.