Home Technology Dihedral and Washout For Flight Stability

Dihedral and Washout For Flight Stability


This article will examine the basic concepts of dihedral and washout and explain why they are incorporated in the design of aircraft wings. A fixed wing aircraft’s dihedral is the angle that the wings or tailplanes are inclined upward from horizontal. The difference in the angle of attack experienced by the right and left wings during a sidelip causes dihedral to generate a stabilizing torque. When the aircraft does not move in the same direction as it moves through the air, this is called a sideslip. The wings of many sailplanes – especially the entry level models – are polyhedral. Andy Lennon describes what happens when a polyhedral sailplane is side-slipping.

“Thermal gliders have polyhedral—typically 5 degrees from root to 3/5 of the semi-span, with an increase of 3 degrees from the polyhedral joint to the wingtip. This type yaws when the rudder is applied. The air strikes the wing on a slight diagonal. The wind blowing on the outside edge of the turn exits the trailing edge slightly closer to fuselage. Due to the dihedral there is…

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