The aerodynamic load on aircraft wings will vary due to such factors as increased lift with changes in airspeed, cargo loading in the aircraft, and flap setting. Aircraft wings, particularly aircraft with high aspect ratios, are subjected to bending deformation and twist deformation of the wings as the aerodynamic load on the wings vary.
The twist deformation can cause serious degradation in aerodynamic performance. Since the center of lift of the wing is located behind the center of torsion, as lift on the wing increases, the leading edge of the wing will twist down. This decreases the angle of attack of the wing and reduces its efficiency. As the angle of attack is decreased the outer edge of the wing twists downward due to aerodynamic forces and causes the wing to flex downward.