Expert: Paul Soderman - 12/24/2009

Question
I design axial fans using a method based on A J Stepanoff's work. While this has been successful, I think one aspect needs clarifying. He recommends solidity = 4.75 x head coefficient. I suspect a smaller constant than 4.75 is correct. If so, a slight improvement in efficiency could be realized by reducing skin drag.

Can you help?

Answer
Pat
I am not familiar with Stepanoff's work.  I would use the axial fan design methodology described by W. Rae and A. Pope:  Low-Speed Wind Tunnel Testing (2nd edition, John Wiley & Sons).  They include many parameters to arrive at solidity in the analysis and correlate efficiency with advance ratio and L/D. You could try your ideas in their procedure to see if you are moving in the right direction.
Paul