Abstract: The spool impeller is a fully automatic cutting head for whirling filament vegetation trimmers, simpler, less expensive, and more reliable than the predecessors. Unlike the predecessors, the spool impeller does not waste filament. It consists of a single part, a small diameter spool attached to the drive shaft. The free end of filament coiled on the spool extends tangentially so that the tip traces a circle about the axis of rotation. In use, the coiled filament gradually unwinds to compensate for filament wear, maintaining a cutting swath of precisely constant size. There is no need for the operator to monitor the filament. Feeding new filament is controlled by the aerodynamic drag and centrifugal force acting directly on the extended filament. If the length of the extended filament is correct, drag and centrifugal force balance, and no unwinding or rewinding occurs. Too long, drag dominates over centrifugal force, rewinding the extended filament onto the spool just enough to restore the proper length.

Abstract: A rotary device for automatically dispensing and retracting a line, such as cutting filament for a vegetation trimmer, has a spool around which is wound a small coil of the line. The line has a cutting segment that extends radially from the spool. The cutting segment has a precise length that is automatically maintained by a balance of centrifugal force and aerodynamic drag. The rotary device also has additional storage capacity for the line. An additional supply of line for the rotary device beyond the small coil may be stored in many different forms while remaining ready for immediate deployment and use. Examples include extended storage loops of the line protruding from the spool, a second coil or reservoir of line located remotely from the spool, or a magazine of the line mounted to the spool.