Tractor screw(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 monoplaneTractor biplane, etc. This is the most common arrangement for propellers on modern airplanes.
Do not construct models (intended for actual flight) with a tractor screw-main plane in front and tail (behind).
"The Theory and Practice of Model Aeroplaning" by V. E. Johnson