Hi Sandor,
The differential length function of the loop is
D[ loop[u,n] ],u]
The length differential is
( (#.#)^(1/2) &) [ D[ loop[u,n] ],u] ] == ( ( 209 + 8 Cos[ n u] + Cos[2 n u])/2) ^(1/2)
This function is periodic with jumps by the winding length for a single loop.
Regards Roland