ORIGINAL: Joe Westrich
With a DF you escentally have a prop turning in a housing. It pulls itself on the air deflection from the blades spinning. It does not move forward from the thrust of the air comming out of the tail.
Hi Joe, Some food for thought here about props and airfoils. A propeller/airfoil never 'pulls' itself forward, it's a low pressure event that lifts or 'pulls' the top of an airfoil. A higher pressure result happens under it which lifts or 'pushes'.
In terms of props, it's ALWAYS called thrust.
http://www.grc.nasa.gov/WWW/K-12/airplane/propth.html