Do turnbuckles twist the flight control wires?
Yes the cables can be twisted if proper care is not administered during tightening. There are tools that allow for tightening the buckle while keeping both ends untwisted. From this article:


  Cable tensions are adjusted by twisting the turnbuckles that connect different sections of cable together. It’s a simple system, but you need to hold each cable end stable while turning the turnbuckle in order to avoid putting twisting stress on the cable itself. If you work alone, you may want to invest in a cable turnbuckle tool that holds both cable ends stable while you twist the turnbuckle barrel.