Wind Tunnel Creation +more then 3 speeds

[Airfoil_111]

I am making a wind tunnel to test the lift of an airfoil when chaning the variables of angle of attack and air velocity. For a good EEI I need more then 3 speeds. However, all the people I know only have 3 speed fans, I don't know how to get more speeds as the wind tunnel gets built around the fan. Any ideas??

 

[berkeman]

I am making a wind tunnel to test the lift of an airfoil when chaning the variables of angle of attack and air velocity. For a good EEI I need more then 3 speeds. However, all the people I know only have 3 speed fans, I don't know how to get more speeds as the wind tunnel gets built around the fan. Any ideas??

You should be able to make a continuously-variable speed fan by using PWM drive on a DC electric motor. What kind of fans do you have to choose from? Can you make your own?