Dihedral is used to stabilize the airplane about which axis?

Dihedral primarily stabilizes an airplane about the longitudinal axis, which runs from the nose to the tail. The dihedral angle refers to the upward angle of the wings from horizontal. When an airplane with dihedral experiences a roll due to turbulence or a bank angle initiated by the pilot, the wing that is lower (the one that is closer to the horizontal) creates more lift compared to the higher wing. This differential lift causes the airplane to return to level flight, thereby increasing lateral stability.

The lateral axis is typically concerned with pitch and stability in that domain, while vertical stability relates to yaw. The transverse axis is unclear in conventional terms as it can sometimes refer to lateral stability as well, but in this context, the focus is primarily on how dihedral affects rolling motions related to the longitudinal axis. The corrective moment produced by dihedral increases overall stability during flight, effectively counteracting unwanted rolling motions and promoting a naturally stable flight attitude.