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In flight dynamics, longitudinal stability is the stability of an aircraft in the longitudinal, or pitching, plane.This characteristic is important in determining whether an aircraft pilot will be able to control the aircraft in the pitching plane without requiring excessive attention or excessive strength.
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 Dutch roll stability is improved.
Stability is the ability of the aircraft to counteract disturbances to its flight path. According to David P. Davies, there are six types of aircraft stability: speed stability, stick free static longitudinal stability, static lateral stability, directional stability, oscillatory stability, and spiral stability. [5]: 164
X stability axis is aligned into the direction of the oncoming air in steady flight. (It is projected into the plane made by the X and Z body axes if there is sideslip). Y stability axis is the same as the Y body-fixed axis. Z stability axis is perpendicular to the plane made by the X stability axis and the Y body axis.
Longitudinal stability and control may be obtained with other wing configurations, including canard, tandem wing and tailless aircraft. Some types of aircraft are stabilized with electronic flight control; in this case, fixed and movable surfaces located anywhere along the aircraft may serve as active motion dampers or stabilizers.
Center of gravity (CG) limits are specified longitudinal (forward and aft) and/or lateral (left and right) limits within which the aircraft's center of gravity must be located during flight. The CG limits are indicated in the airplane flight manual. The area between the limits is called the CG range of the aircraft. Weight and Balance
Dihedral effect is a critical factor in the stability of an aircraft about the roll axis (the spiral mode). It is also pertinent to the nature of an aircraft's Dutch roll oscillation and to maneuverability about the roll axis. Longitudinal dihedral is a comparatively obscure term related to the pitch axis of an airplane.
Stability can be defined only when the vehicle is in trim; that is, there are no unbalanced forces or moments acting on the vehicle to cause it to deviate from steady flight. If this condition exists, and if the vehicle is disturbed, stability refers to the tendency of the vehicle to return to the trimmed condition.