ABSTRACT
When an aircraft is in a disturbance in flight, the aircraft will be in unexpected rotating motions. The aircraft is stable if it is able to produce a correct amount of moment in a correct direction to overcome the disturbance to restore the equilibrium. Aircraft can rotate about three axes: pitching – rotating about lateral axis; rolling – rotating about longitudinal axis; and yawing – rotating about directional axis. Where the aerodynamic center (AC) exactly lies on an aerofoil is dependent on the design of the aerofoil. There are a number of ways to calculate the location of AC on the chord. In this chapter, the method to find the AC is to use superposition concept with the information of lift and drag coefficients of the aerofoil. When an aircraft is in an equilibrium position, it can encounter an unexpected force. The unexpected force exerts on the aircraft, and can produce a pitch moment.
