Small wind turbine mast design tips

[FEMdude]

I have to do a simple stress analysis for mast of a small wind turbine (3 blades, rotor diameter 4m).
For normal cases, almost anything would go, but in this case, the mast has to be longer (20m) to get the machine well above forest line.
Any recommendatios for the allowable deformation due to aerodynamic load, or for minimum eigenmodes in bending/torsion, please?

 

[csd72]

I would contact the manufacturer for the wind turbine and see if they have any operational limits for their equipment.