xmin := 0
xmax := Pi
ymin := 0
ymax := 6*Pi
xxx[x_, y_] := y/18*Sin[x]*Cos[y]
yyy[x_, y_] := y/18*Sin[x]*Sin[y]
zzz[x_, y_] := y/18*Cos[x] + y/6
ParametricPlot3D[{yyy[x, y], -xxx[x, y], zzz[x, y]}, {x, xmin, 
        xmax}, {y, ymin, ymax}, PlotPoints -> {15, 51}]