Longitudinal Dihedral
Angle between the angles of incidence of the wing and tailplane. Positive if the wing incidence is greater.All-moving tails or tails with trim systems that move the stabilizer have variable angles of incidence. Therefore the longitudinal dihedral is variable in flight.
Vertical Stabilizer
A vertical stabilizer provides directional (or yaw) stability and usually comprises a fixed fin and movable control rudder hinged to its rear edge. Less commonly, there is no hinge and the whole fin surface is pivoted for both stability and control. When an aircraft encounters a horizontal gust of wind, yaw stability causes the aircraft to turn into the wind, rather than turn in the same direction. Fuselage geometry, engine nacelles and rotating propellers all influence lateral static stability and affect the required size of the stabilizer.
