Neutral Point
A mathematical analysis of the longitudinal static stability of a complete aircraft (including horizontal stabilizer) yields the position of center of gravity at which stability is neutral. This position is called the neutral point. (The larger the area of the horizontal stabilizer, and the greater the moment arm of the horizontal stabilizer about the aerodynamic center, the further aft is the neutral point.)
The static center of gravity margin (c.g. margin) or static margin is the distance between the center of gravity (or mass) and the neutral point. It is usually quoted as a percentage of the Mean Aerodynamic Chord. The center of gravity must lie ahead of the neutral point for positive stability (positive static margin). If the center of gravity is behind the neutral point, the aircraft is longitudinally unstable (the static margin is negative), and active inputs to the control surfaces are required to maintain stable flight. Some combat aircraft that are controlled by fly-by-wire systems are designed to be longitudinally unstable so they will be highly maneuverable. Ultimately, the position of the center of gravity relative to the neutral point determines the stability, control forces, and controllability of the vehicle.
For a tailless aircraft, the neutral point coincides with the aerodynamic center, and so for longitudinal static stability the center of gravity must lie ahead of the aerodynamic center.
Read more about this topic: Longitudinal Static Stability
Famous quotes containing the words neutral and/or point:
“The lonely Earth amid the balls
That hurry through the eternal halls,
A makeweight flying to the void,
Supplemental asteroid,
Or compensatory spark,
Shoots across the neutral Dark.”
—Ralph Waldo Emerson (1803–1882)
“The great passion in a man’s life may not be for women or men or wealth or toys or fame, or even for his children, but for his masculinity, and at any point in his life he may be tempted to throw over the things for which he regularly lays down his life for the sake of that masculinity. He may keep this passion secret from women, and he may even deny it to himself, but the other boys know it about themselves and the wiser ones know it about the rest of us as well.”
—Frank Pittman (20th century)