Assembly And Rigging Sectional And Final Practice Test

In an articulated rotor blade, there are three independent motions about the blade’s hinge axes: flap, lead/lag, and feather. Flap is the up-and-down motion about the flap hinge, letting the blade respond to cyclic lift. Lead/lag is movement along the plane of rotation about the lead/lag hinge, driven by centrifugal forces and drag to accommodate inertia and drag effects. Feather is rotation about the feather axis, changing the blade pitch to control lift. These three actions are the separate degrees of freedom the hub articulation provides for each blade, enabling the blade to adapt to changing air loads while staying attached to the rotor hub. Other terms describe airplane body attitudes or nonstandard blade motions, so they don’t capture the three independent hinge-driven motions that define articulated rotor blades.