HOT AIR EXPAND SO MORE VELOCITY, MORE THRUST. 707 IS A TURBOJET SO IT USES MORE FUEL AT SHORTER DISTANCE . THE TURBO FAN PRODUCE ALMOST THE SAME POWER WITH LOWER FUEL USE AND LONGER DISTANCES.

FOR EXAMPLE A DYNMAX DUCTED FAN PRODUCE 12 TO 13 STATIC THRUST AT 20K RPM. A MODEL 12 # TURBINE AT IDLE PRODUCE 2 # OF THRUST AT 33.000 OR 50.000 RPM. IF YOU COULD INSTALL THE DYMINMAX FAN UNIT ONTO A MODEL JET ENGINE YOU COULD GET MORE ALMOST TO SAME POWER AT A LOWER RPM AND USE LESS FUEL.