Expert: Paul Soderman - 4/29/2004

Question
I'm working on designing a ducted fan for large scale model use and I wanted to know what airfoils would be the best candidates for that application.

also I want to try different blade designs but I was wondering if there were any web based references that might have blade pictures on them, maybe something with a front view so I can duplicate the different blade styles.

Thanks,
Chris


Answer
Hi Chris

You asked a tough question.  I understand that modern fans now have three-dimensional blade design.  That is, the airfoil section, chord, and sweep vary along the radius in order to maximize efficiency.  But the commercial designs are proprietary.  When I did a Google search on ducted fans I got a hit on a book:  Ducted Fan Design by Piolenc and Wright, but you have to buy it.  I can't see from their book photo if the inlet lip is sharp or not.  Sharp lips have flow separation that can feed into the fan.  A thicker, rounded inlet lip is much better.  There is also a need to keep the rotor and stators sufficiently separated to minimize flow interference.  There was a lot of work done by NASA some years ago on fan and inlet and duct design - see NASA reports by Ken Mort or by others at Glenn Research Center.  When I need an airfoil shape I turn to the classic book:  Theory of Wing Sections by Abbott and Doenhoff (Dover).  Beyond that, I don't know much about ducted fans.

Paul