A duct for a ducted-rotor aircraft may include internal structural components such as a spindle that is supported by a fuselage of the aircraft, first and second annular spars that are attached to an end of the spindle, a central hub that supports a motor of the aircraft, a plurality of stators that extend from the central hub to the second spar, and a plurality of ribs that are attached to the first spar and the second spar at respective opposed ends. The spindle may include an attachment interface to which the first and second spars are attached. The attachment interface may be disposed at the second end of the spindle. The attachment interface may define first and second arc-shaped planar surfaces to which the first and second spars, respectively, are attached.