tail. As forces such as turbulence and gusts act to displace  the aircraft, the pilot reacts by providing opposing control  forces to counteract this displacement.  Some aircraft are subject to changes in the location of the CG  with variations of load. Trimming devices, such as elevator  trim tabs and adjustable horizontal stabilizers, are used to  counteract the moments set up by fuel burnoff and loading  or off-loading of passengers or cargo.  maneuverability of the aircraft. If the aircraft is to provide  maximum utility, it must be safely controllable to the full  extent of these limits without exceeding the pilot’s strength  or requiring exceptional flying ability. If an aircraft is to fly  straight and steady along any arbitrary flight path, the forces  acting on it must be in static equilibrium. The reaction of  any body when its equilibrium is disturbed is referred to as  stability. The two types of stability are static and dynamic.  Each aircraft handles somewhat differently because each  resists or responds to control pressures in its own way. For  example, a training aircraft is quick to respond to control  applications, while a transport aircraft feels heavy on the  controls and responds to control pressures more slowly.  These features can be designed into an aircraft to facilitate  the particular purpose of the aircraft by considering certain  stability and maneuvering requirements. The following  discussion summarizes the more important aspects of an  aircraft’s stability, maneuverability, and controllability  qualities; how they are analyzed; and their relationship to  various flight conditions.  Stability is the inherent quality of an aircraft to correct for  conditions that may disturb its equilibrium and to return to  or to continue on the original flight path. It is primarily an  aircraft design characteristic. The flight paths and attitudes an  aircraft flies are limited by the aerodynamic characteristics of  the aircraft, its propulsion system, and its structural strength.  These limitations indicate the maximum performance and  Static stability has been defined as the initial tendency to  return to equilibrium that the aircraft displays after being  disturbed from its trimmed condition. Occasionally, the  initial tendency is different or opposite from the overall  tendency, so a distinction must be made between the two.  Dynamic stability refers to the aircraft response over time  Static stability refers to the initial tendency, or direction of  movement, back to equilibrium. In aviation, it refers to the  aircraft’s initial response when disturbed from a given pitch,  yaw, or bank.  Static Stability  Aircraft Design Characteristics  Stability  Dynamic Stability  Figure 5-21.  Types of static stability.  5-14  • Positive static stability—the initial tendency of the  aircraft to return to the original state of equilibrium  after being disturbed.  [Figure 5-21]  • Neutral static stability—the initial tendency of  the aircraft to remain in a new condition after its  equilibrium has been disturbed.  [Figure 5-21]  • Negative static stability—the initial tendency of the  aircraft to continue away from the original state of  equilibrium after being disturbed.  [Figure 5-21]  Positive Static Stability  Neutral Static Stability  Negative Static Stability  CG CG CG CG Applied  force  Applied force  Applied force 