Ducted Fan Design

This is a Mathcad document converted into HTML. I hope the formatting works in your browser, as it is rather a bear to convert. I probably won't be updating this page very often. I will instead try to keep the source MathCad file up to date. There are some obvious shortcomings to some of these calculations. The thrust required is based on what I could find on the web, and is only based on parasitic drag. Clearly this should have both parasitic and induced drag, but that would require lift/drag information that I don't have. If anyone has information that could help me fine tune these numbers, I would appreciate it.

Values in blue are inputs, values in yellow are interesting outputs.




Establish the atmospheric conditions:









Fan parameters:




<-- Fan and disk combined efficiency estimate


Targeted performance:





Value typically listed for Cozy MkIV, which includes induced drag


Estimated engine parameters:







Calculate the available torque



Estimate cruise power needed assuming infinite mass flow



Calculate mass flow given additional power available





Calculate the "capture area" given relative airspeed and mass flow






Calculate the air pressure at the front face of the fan










Estimate the amount of swirl power:





Determine the required exit velocity the attain the desired thrust








Calculate the air pressure on the aft fan face



"Stinger" radius at exit








Alternate ways to estimate pressure at aft face of fan.





Calculate the power required at the fan to pump the pressure up from p2 to p3



If necessary, try fine tuning mass flow to reduce the power requirements



Recalculate capture area:



Determine the pressure at the front face of the fan:







Calculate the swirl power





Determine the exit velocity to create the required thrust:






Calculate the pressure at the aft face of the fan:












Calculate the power required at the fan to pump the pressure up from p2 to p3



Check the fan blade tip speeds to ensure the airfoil critical Mach is not exceeded







Find the effective blade pitch



Estimate the fuel efficiency:









Evaluate the performance envelope of a particular fan geometry