Which stability description applies when the airplane holds a new attitude after a control input?

Which stability description applies when the airplane holds a new attitude after a control input?

• A. Neutral longitudinal static stability
• B. Positive static stability
• C. Negative static stability
• D. Lateral stability

Answer: (A)

Static stability in the pitch axis describes how the airplane behaves after you disturb its attitude. If, after you move the control and release, the airplane tends to return to its original pitch, that’s positive static stability. If it tends to continue moving away from the original pitch, that’s negative static stability. If, however, it stays at the new attitude you set and doesn’t return or diverge, that’s neutral static stability. The scenario described—holding a new attitude after a control input—fits neutral longitudinal static stability, because there’s no restoring moment pulling it back nor a further moment pushing it away; the airplane simply remains at the new pitch. The term longitudinal specifies the pitch or nose-up/nose-down motion about the lateral axis, whereas lateral stability would concern roll about the longitudinal axis.

Static stability in the pitch axis describes how the airplane behaves after you disturb its attitude. If, after you move the control and release, the airplane tends to return to its original pitch, that’s positive static stability. If it tends to continue moving away from the original pitch, that’s negative static stability. If, however, it stays at the new attitude you set and doesn’t return or diverge, that’s neutral static stability. The scenario described—holding a new attitude after a control input—fits neutral longitudinal static stability, because there’s no restoring moment pulling it back nor a further moment pushing it away; the airplane simply remains at the new pitch. The term longitudinal specifies the pitch or nose-up/nose-down motion about the lateral axis, whereas lateral stability would concern roll about the longitudinal axis.