title_body: EDF Simplified Thrust Calculation?
upvoted_answer: The problem you have found is that you are trying to calculate the efficiency and lift coefficient of your fan, which isn't possible. There's no simple calculation to convert power to thrust because it will depend on the angle of attack of the blades to the airstream.
  The mass flow rate is calculated on the velocity of air through the fan, not the motor speed.
  The 'Free Stream' velocity is the air speed of the aircraft, or zero for a static test rig. You could measure the exhaust velocity with a pitot tube - a simple length of clear tube with some water held in a U-bend would work to compare static and dynamic pressure. However if you're measuring things, you might as well measure the thrust directly.
  The alternative is to look up the thrust figures for commercially available EDFs, and scale them to allow for any difference in power (I'd guess that a 3D printed fan can't run as fast as a commercial unit)
  Having said that, it must be possible to take the normal lift equation (1/2 * lift coefficient * air density * area * air speed squared) and treat the fan blades as wings and integrate for the change of speed with radius. I guess the problem is that you could estimate the maximum lift-coefficient to 1 but it could be 30% higher or lower, and you probably want a more accurate answer.
  If you look on-line, you'll find a number of power-to-thrust calculators for RC propeller aircraft, but they all rely on measured values for specific propellers. I've not seen one that includes values for EDFs, presumably because EDF thrust is highly dependant on inlet and exhaust shape.