How is the shape of the blades of an air fan determined? Trial and error, or is there a theory behind it? What are they trying to maximize, volume of air dislocated per rotation?

  • $\begingroup$ I guess a follow up question is how do you measure the amount of air that is dislocated. $\endgroup$
    – archgoon
    May 9, 2011 at 19:24
  • $\begingroup$ More on fans: physics.stackexchange.com/q/9030/2451 $\endgroup$
    – Qmechanic
    May 9, 2011 at 19:35
  • $\begingroup$ +1 for using the Engineering tag. Got to support my kind :-) $\endgroup$ May 10, 2011 at 2:16
  • $\begingroup$ 'Dyson' make a blade-less fan. No idea how it works though :P $\endgroup$
    – qftme
    May 10, 2011 at 8:03
  • $\begingroup$ @qftme - there is a fan in base and then a series of angled holes in the ring shaped part that blow the air toward you. The clever part is that this high speed air drags more room air through the loop in the middle so gives you much more flow than the small hidden fan alone $\endgroup$ May 10, 2011 at 15:34

2 Answers 2


Mostly trial and error - but in a computer.

A combination of Computational Fluid Dynamics (modelling how the air flows over the blade) and Finite Element Modelling (how the stresses in the metal behave)

Both of these are complex areas - and when they come to together you need a lot of expensive computers and some even more expensive engineers.


I would guess the Lift/Drag ratio of the blades is important. Lift = wind thrust (and speed), and Drag = friction and power loss.

Since the part of the blade moves slower the closer to the center, the angle of attack needs to increase to provide the same wind speed. Keeping an even velocity profile is probably important in order to minimize losses due to turbulence.

There is probably a lot to be done with the wing-tips that is not done due to aesthetic reasons. pffft.


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