with(plots):
a:=19/3;
z:=cos(a*t);
x:=(4-sin(2*a*t)/3)*cos(t);
y:=(4-sin(2*a*t)/3)*sin(t);
tubeplot([x,y,z],t=0..6*Pi,radius=0.2,numpoints=500,color=cyan,scaling=constrained,style=patch);