Tractor screw \Tractor screw\ or Tractor propeller \Tractor propeller\ (Aviation) A propeller screw placed in front of the supporting planes of an airplane instead of behind them, so that it exerts a pull instead of a push. Hence, {Tractor monoplane}, {Tractor biplane}, etc. This is the most common arrangement for propellers on modern airplanes. [Webster 1913 Suppl.]