The Salkowski Curves were studied in 1909, and have constant curvature, and non-constant torsion.
They are a subset of the slant helix curves. There are also "anti-Salkowski curves.
A third particular slant helix is included in the script.
The paper of Ahmad T. Ali is here:
http://www.sciencedirect.com/science/article/pii/S1110256X11000289
For the slant helix example, curves with rational n can be closed, with the right PI length.




- Brian