DIHEDRAL EFFECT
When an airplane is laterally sideslipping, dihedral wings cause an increase in angle of attack and lift on the down-going wing. The up-going wing has a reduced angle of attack and a decrease in lift (Figure 1-9-20). This difference in lift creates a rolling moment that rights the airplane and stops the sideslip. Wings that are straight have neutral lateral static stability. Dihedral wings are the greatest positive contributors to lateral static stability. Anhedral wings are the greatest negative contributors to lateral static stability.
The angle of incidence of a wing is the angle between the airplane’s longitudinal axis and the chordline of the wing.
Dihedral angle is the angle between the spanwise inclination of the wing and the lateral axis. More simply, it is the upward slope of the wing when viewed from the front. A negative dihedral angle is called an anhedral angle (sometimes cathedral). The T-34C has dihedral wings to improve lateral stability. (Resource T-34 Manual)
Dihedral Some aircraft are designed so that the outer tips of the wings are higher than the wing roots. The upward angle thus formed by the wings is called dihedral. [Figure 5-28] When a gust causes a roll, a sideslip will result. This sideslip causes the relative wind affecting the entire airplane to be from the direction of the slip. When the relative wind comes from the side, the wing slipping into the wind is subject to an increase in AOA and develops an increase in lift. The wing away from the wind is subject to a decrease in angle of attack, and develops a decrease in lift. The changes in lift effect a rolling moment tending to raise the windward wing, hence dihedral contributes to a stable roll due to sideslip. [Figure 5-29
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