Aerodynamics of Flight

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