Curved plane derived parts
 

Hello,
I would like to create a derived part that is a curved plane around (externally) the entire three-bladed turbine (I attach figures).
I would like this plane to remain constantly away from the center of the profile (a sort of external offset).
How can I do it?

easy to do using an arbitrary section with a surface drawn in 3d cad or imported - read Post-Processing > Accessing Solution Data through Derived Parts > Defining Implicit Sections > Defining an Arbitrary Section