To answer this question, you need to state how many blades in the fan. This will make a triangle on the same side. If there is 3 blade, that means the blade angle would be 360/3=120.
If you divide the triangle into 2 identical triangles with 60 degrees each, you can find the halfway of the blade distance by using this:
1/2 blade distance= blade length * sin 60=
1/2 blade distance= 20*0.866= 17.32m
Then the full distance would be:
17.32m*2= 34.64m
