How do ducted fans work?(how do you calculate thrust?)

[Arugela]

I'm trying to follow the calcualtions given in this thread on stack exchange I can't figure out how he got his answer.

https://aviation.stackexchange.com/a/16550

He says it's 4kg of thrust but I can't figure out the other stuff.

Ct*p*area*tip^2

0.03*1.225*?*0.6=4kg?!

 

Edited April 25 by Arugela

[magnemoe]

Area is the area of the ducted fan in m^2. who is pi*r^2 =0,0177 m^2 with an 15 cm fan 
but plugging that into the formula gives 0,000389  tip speed should be 0.6^2 who give an even lower value 0,000234 so something is wrong here

[Shpaget]

0,6M I presume is 0,6 Mach, but I'd expect m/s to be the expected unit, which gives us 24,75, so we're at least in the ballpark.

Also, he just might have borked the math.

Edited April 25 by Shpaget

[Nuke]

ducted fans are well tuned systems which can be well optimized. but that optimization usually comes at the cost of a vary narrow operational envelope. laminar flow wings have a similar problem. fan design in general is a deceptively complex problem.

Edited April 25 by Nuke