On the Darboux ruled surface of a general helix in the Nil?

Nil geometry is one of the eight geometries of Thurston's conjecture. In this paper we study in Nil 3-space and the Nil metric with respect to the standard coordinates (x,y,z) is gNil3=(dx)2+(dy)2+(dz-xdy)2 in IR3. In [8] we have already and out the explicit parametric equation of a general helix and Frenet vector yields, with first and second curvatures k1 and k2; respectively, in Nil 3-Space. Here we and out the parametric equations of the Darboux ruled surface of the general helix in Nil Space Nil3: