dihedral

Dihedral is the angle between the left and right wings (or tail surfaces) of an aircraft, measured from the horizontal plane. When viewed from behind the aircraft, a positive dihedral means both wings slope upward from the fuselage toward their tips. This is the most common configuration on fixed-wing aircraft, from small Cessnas to large transport planes.

Dihedral angle is typically measured in degrees, ranging from about 5 to 15 degrees on most general aviation aircraft. The angle is built into the wing structure during manufacture; it is not a result of deflection or wear. On some military jets and high-speed aircraft, dihedral may be minimal or even negative (anhedral), where the wings slope downward. Conversely, some unconventional designs use extreme dihedral angles of 25 degrees or more for specific aerodynamic purposes.

Why dihedral matters in maintenance

Dihedral provides inherent lateral stability. When an aircraft rolls slightly to one side, the lower wing presents more lift to the horizontal airflow, which naturally returns the aircraft to level flight. This passive stability reduces pilot workload and helps the aircraft recover from disturbances without active control input. During maintenance, any damage that alters wing geometry, such as wrinkled skin, bent spars, or improper wing attachment, can change the effective dihedral and compromise this stability.

Technicians must verify dihedral geometry after major wing work, structural repair, or any accident involving wing damage. Some aircraft require formal wing level checks using optical or laser measurement tools. If an inspection reveals that dihedral has shifted by more than the service limits specified in the maintenance manual, typically around 1 degree depending on the aircraft type, the wing structure must be corrected or replaced before the aircraft returns to service.

The term dihedral comes from Greek and literally means two planes. In aviation, it distinguishes this lateral wing arrangement from polyhedral wings, which have multiple angle changes along the span, or from anhedral and gull-wing configurations. Understanding dihedral is essential for anyone involved in aircraft assembly, alignment, inspection, or accident investigation.