Doubt about windmill cleaning with helicopter

[Galtor]

Hello all,

I am an engineer currently involved in wind energy sector, and I found that windmill cleaning can be made with helicopters. Actually, I found more than 10 companies doing it now.

I found that the maximum wind speed at which the helicopter can clean is at 20 knots, and I do not understand if this is the helicopter limit or whether the water jet does not spot on the blade. Does anybody know?

Thanks a lot,