Coupling Effects

There are several interactions or couplings involving lateral-directional controls and motions that are important considerations in providing satis­factory handling or riding qualities for an airplane. We have already seen one of these, a coupling between yaw and aileron displacement. Similarly, the rudder deflection can produce a rolling moment, since the center of pressure

generally lies above the center of denoted in coefficient form by:

Си,

Other couplings include:

c, r

cNp

Си

These represent, respectively, a rolling moment due to yawing, a yawing moment due to rolling, and a rolling moment resulting from sideslip! This last coupling is an important and well-known one that is called “dihedral effect.”