centre of lift
That point on an aircraft where all the various lifting forces act. If the centre or lift is not coincident with the centre of gravity on the fore/aft axis, the plane will pitch, if not coincident on the lateral axis, it will roll.
centre of lift: where all wing force acts as one point
The centre of lift is the single point through which the total aerodynamic lifting force of an aircraft can be assumed to act. In practice, lift is distributed across the entire wing surface, fuselage, and tail; the centre of lift is a convenient fiction that lets engineers treat this distributed load as a concentrated force for purposes of calculating pitch and roll moments. Its location depends on airspeed, angle of attack, and control surface deflection, meaning it is not fixed but shifts in flight.
The position of the centre of lift relative to the centre of gravity (CG) determines the aircraft's pitching tendency. If the centre of lift lies behind the CG, the aircraft will pitch nose-down; if ahead, it will pitch nose-up. Similarly, lateral imbalance between centre of lift and CG causes roll. Designers position the wing and tail to keep the centre of lift close to the CG across the aircraft's normal operating envelope, using horizontal stabilisers and elevator deflection to manage pitch when they diverge.
Critical shifts in normal flight
The centre of lift moves forward as airspeed increases and as the angle of attack decreases. Conversely, slow flight or high angles of attack shift it rearward. Control surface deflection, especially flap extension, also alters the pressure distribution and thus the centre of lift position. An aircraft loaded with fuel and cargo experiences a rearward shift in CG, which may push the centre of gravity outside the acceptable range relative to the centre of lift, requiring ballast or fuel transfer to restore balance.
In maintenance, understanding centre of lift is essential when interpreting loading charts, weight-and-balance calculations, and pitch trim requirements. Damage to the wing leading edge, misrigged control surfaces, or asymmetric ice accumulation can shift the effective centre of lift and produce unexpected trim demands or handling faults. Excessive trim wheel input, nose-heavy or tail-heavy tendencies reported by pilots, and uncommanded pitch oscillations all point to potential centre-of-lift anomalies that warrant inspection of wing geometry and control rigging.