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Three cases for static stability: following a pitch disturbance, aircraft can be unstable, neutral, or stable. If an aircraft is longitudinally statically stable, a small increase in angle of attack will create a nose-down pitching moment on the aircraft, so that the angle of attack decreases.
Some swept-wing aircraft have an unstable Dutch roll. If the Dutch roll is very lightly damped or unstable, the yaw damper becomes a safety requirement, rather than a pilot and passenger convenience. Dual yaw dampers are required and a failed yaw damper is cause for limiting flight to low altitudes, and possibly lower Mach numbers, where the ...
The vertical positioning of the wing changes the roll stability of an aircraft. An aircraft with a "high" wing position (i.e., set on top of the fuselage) has a higher roll stability. For example, the Cessna 152. An aircraft with a "low" wing (i.e., underneath the fuselage) has less roll stability. The Piper Pawnee uses a "low" wing.
Longitudinal stability refers to the stability of an aircraft in pitch. For a stable aircraft, if the aircraft pitches up, the wings and tail create a pitch-down moment which tends to restore the aircraft to its original attitude. For an unstable aircraft, a disturbance in pitch will lead to an increasing pitching moment.
If the spiral mode is stable, the aircraft will slowly return to wings-level, if it is unstable, the aircraft will slowly diverge from wings-level. Dihedral effect and yaw stability are the two primary factors that affect the stability of the spiral mode, although there are other factors that affect it less strongly.
This includes the human-machine interface. The way in which particular vehicle factors affect flying qualities has been studied in aircraft for decades, [3] and reference standards for the flying qualities of both fixed-wing aircraft [4] and rotary-wing aircraft [5] have been developed and are now in common use. These standards define a subset ...
A Boeing 737 uses an adjustable stabilizer, moved by a jackscrew, to provide the required pitch trim forces. Generic stabilizer illustrated. A horizontal stabilizer is used to maintain the aircraft in longitudinal balance, or trim: [3] it exerts a vertical force at a distance so the summation of pitch moments about the center of gravity is zero. [4]
Pilots of such aircraft are trained to avoid sudden and drastic increases in power at low altitude and low airspeed as it may be difficult to recover from an accelerated stall under these conditions. [37] A notable example of an air accident involving a low-altitude turning flight stall is the 1994 Fairchild Air Force Base B-52 crash.