Where is the center of gravity for most airplanes located in relation to the center of lift?

• A. Behind the center of lift.
• B. Ahead of the center of lift.
• C. Coinciding with the center of lift.
• D. Far above the center of lift.

Answer: (B)

Longitudinal stability is achieved when the center of gravity is ahead of the center of lift. The weight acts through the CG, while lift effectively acts at the center of lift. If the aircraft pitches up, the lift increases and acts behind the CG, creating a nose-down moment that tends to restore the level attitude. This restoring torque is what keeps the airplane stable. If the CG were behind the center of lift, a pitch disturbance would produce a nose-up moment and the airplane could become unstable, tending to rotate further away from level flight. For most airplanes, placing the CG forward of the center of lift provides that positive static stability, with the aerodynamic center of the wing near the 25% chord region serving as a reference.