[ykoheel]

Dihedral



Is the upward angle from horizontal in a fixed-wing aircraft or bird wing from root to tip, as viewed from directly in front or behind the aircraft Dihedrals are also used in some types of kites such as box kites The aerodynamic stabilizing qualities of the dihedral were first described by Sir George Cayley in 1808/09 Downward angled wings have negative dihedral, or anhedral Wings with local dihedral angles that change along the span are polyhedral

The purpose of positive dihedral is to confer stability in the longitudinal (roll) axis Most aircraft in the civilian or transport sector use dihedral for roll stability The dihedral angle is usually greater on low-wing aircraft, compared to an otherwise similar high-wing aircraft

Anhedral

Military fighter aircraft often have near zero dihedral, or anhedral this reduces inherent stability, but increases maneuverability many modern military aircraft have relaxed stability, and require continuous small corrections made by on-board computers

Pronounced anhedral is also often seen on aircraft with a high mounted wing, such as the BAe 146, Lockheed Galaxy and others In such designs, the high mounted wing is above the center of mass which confers roll stability due to the pendulum effect also called the Keel effect, so additional dihedral is not required In fact, such designs can be excessively stable, so the anhedral is added to cancel out some of the roll stability to ensure that the aircraft can be easily maneuvered