Physics:Static margin
In aircraft analysis, static margin is defined as the distance between the center of gravity and the neutral point of the aircraft, expressed as a percentage of the mean aerodynamic chord of the wing.[1][2] A greater static margin makes the aircraft more longitudinally stable.[1]
Conventional aircraft have the center of lift behind the center of gravity, so the wings generate a pitching down moment. For a trimmed aircraft, as the airspeed varies from the trimmed airspeed, a force will be required on the control column to prevent the aircraft climbing or descending. As the center of gravity moves aft, this control force will be reduced.[why?] The "neutral point" is defined as the location for the center of gravity where the control force is zero. If the center of gravity is forward of the neutral point, the aircraft has positive static margin and will be longitudinally stable. If the center of gravity is aft of the neutral point, the aircraft has negative static margin, and will be longitudinally unstable and hard to control.[1][why?]
Some aircraft such as fighter aircraft may have negative static margin. This makes them unstable but more manoeuvrable. Computer control will be required to assist the pilot.[1]
Excessive positive static margin leads to too great longitudinal stability, which makes the aircraft "stiff" in pitch and hard to flare.
Missiles
For missiles with symmetric airfoils, the neutral point and the center of pressure are coincident and the term neutral point is not used.[citation needed]
An unguided rocket must have a large positive static margin so the rocket shows minimum tendency to diverge from the direction of flight given to it at launch. In contrast, guided missiles usually have a negative static margin for increased maneuverability.[citation needed]
See also
References
- ↑ 1.0 1.1 1.2 1.3 "The Effect of High Altitude and Center of Gravity on The Handling Characteristics of Swept-wing Commercial Airplanes". Aero Magazine (Boeing) 1 (2). http://www.boeing.com/commercial/aeromagazine/aero_02/textonly/fo01txt.html. Retrieved 29 June 2022.
- ↑ Caughey, David A. (2011). "3. Static Longitudinal Stability and Control". Introduction to Aircraft Stability and Control Course Notes for M&AE 5070. Sibley School of Mechanical & Aerospace Engineering, Cornell University. p. 28. https://courses.cit.cornell.edu/mae5070/Caughey_2011_04.pdf. Retrieved 29 June 2022.
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