Question id 358 - Principles of Flight - ATPL - Airline Transport Pilot license

The 'effective dihedral' of an aeroplane component means the contribution of that component to the static lateral stability.
Dihedral is necessary for the execution of slip-free turns.
Dihedral contributes to dynamic but not to static lateral stability.
Effective dihedral is the angle between the 1/4-chord line and the lateral axis of the aeroplane.