anhedral

Anhedral is the geometric angle by which an aircraft's wings slope downward from their root at the fuselage to their tip. It is measured as a negative dihedral angle, typically expressed in degrees below the horizontal. Where a wing rises away from the fuselage (positive dihedral), an anhedral wing descends. Most high-wing aircraft and some fighter jets exhibit anhedral by design; the C-130 Hercules and F-16 are familiar examples.

The primary function of anhedral is to reduce roll stability and improve turning performance in combat or aerobatic flight. Because anhedral makes the aircraft naturally want to roll, pilots must apply corrective control input, which makes the plane respond faster to roll commands. This trades away the stability that dihedral provides, so anhedral is chosen only when the penalty is worth the benefit. In transport and commercial aviation, anhedral is avoided except where wing clearance dictates it, as when engines or cargo pods extend below the wing.

Measurement and Variants

Anhedral is measured from the root rib (where the wing meets the fuselage) to the tip rib, using a datum line perpendicular to the fuselage centerline. The angle is usually small, between 2 and 8 degrees on military aircraft that employ it. Some designs use partial anhedral on the outer wing panels only, while keeping the root nearly level. This blended approach preserves some lateral stability near the root while gaining the turn performance at the tip.

Maintenance technicians check anhedral during structural inspection and after repair to damaged wing roots or tips. Incorrect anhedral after wing work can degrade handling characteristics and, in extreme cases, create unexpected roll tendencies that affect safety. Measurement requires a level fuselage reference and dial indicators or optical instruments on the wing structure itself.

The term itself comes from the Greek prefix an- (without) and the word hedral (face or side), so anhedral literally means a configuration without the rising face of traditional dihedral wings. In the wider context of aircraft geometry, anhedral sits opposite dihedral and complements other stability features like sweep, taper, and center of gravity location.