neutral static stability have neither the tendency to return  to equilibrium nor the tendency to continue displacement.  central point in the glider called the CG. This point is the  center of the glider’s total weight and varies with the loading  of the glider. Yaw is movement around the vertical axis, which can be  represented by an imaginary straight line drawn vertically  through the CG. Moving the rudder left or right causes the  glider to yaw the nose to the left or right. Moving the ailerons  left or right to bank moves the glider around the longitudinal  axis. This axis would appear if a line were drawn through the  center of the fuselage from nose to tail. Pulling the stick back  or pushing it forward, raising or lowering the nose, controls  the pitch of the glider or its movement around the lateral axis.  The lateral axis could be seen if a line were drawn from one  side of the fuselage to the other through the CG.  [Figure 3-20] Dynamic stability describes a glider’s motion and time  required for a response to static stability. In other words,  dynamic stability describes the manner in which a glider  oscillates when responding to static stability. A glider that  displays positive dynamic and static stability reduces its  oscillations with time. A glider demonstrating negative  dynamic stability is the opposite situation; its oscillations  increase in amplitude with time following a displacement.  A glider displaying neutral dynamic stability experiences  oscillations, which remain at the same amplitude without  increasing or decreasing over time.  Figure 3-21  illustrates  the various types of dynamic stability. A glider is in equilibrium when all of its forces are in balance.  Stability is defined as the glider’s ability to maintain a  uniform flight condition and return to that condition after  being disturbed. Often during flight, gliders encounter  equilibrium-changing pitch disturbances. These can occur in  the form of vertical gusts, a sudden shift in CG, or deflection  of the controls by the pilot. For example, a stable glider would  display a tendency to return to equilibrium after encountering  a force that causes the nose to pitch up. Both static and dynamic stability are particularly important for  pitch control about the lateral axis. Measurement of stability  about this axis is known as longitudinal stability. Gliders are  designed to be slightly nose heavy in order to improve their  longitudinal stability. This causes the glider to tend to nose  down during normal flight. The horizontal stabilizer on the tail  is mounted at a slightly negative AOA to offset this tendency.  When a dynamically stable glider oscillates, the amplitude  of the oscillations should reduce through each cycle and  eventually settle down to a speed at which the downward force  on the tail exactly offsets the tendency to dive.  [Figure 3-22] Static stability and dynamic stability are two types of  stability a glider displays in flight. Static stability is the initial  tendency to return to a state of equilibrium when disturbed  from that state. The three types of static stability are positive,  negative, and neutral. When a glider demonstrates positive  static stability, it tends to return to equilibrium. A glider  demonstrating negative static stability displays a tendency  to increase its displacement. Gliders that demonstrate  Adjusting the trim assists in maintaining a desired  pitch attitude. A glider with positive static and dynamic  longitudinal stability tends to return to the trimmed pitch  attitude when the force that displaced it is removed. If a glider  displays negative stability, oscillations increase over time. If  uncorrected, negative stability can induce loads exceeding  the design limitations of the glider. Vertical axis Longitudinal axis Lateral axis Y A W P I T C H R OL L  CG Figure 3-20.  Three axes of rotation. 3-10 Stability