%Developable on a helix
[t,v] = meshgrid(0:pi/10:4*pi,0:.1:4);
a = 2;
x = cos(t)-v.*sin(t);
y = sin(t)+v.*cos(t);
z = a*(t+v);
surfl(x,y,z);
T = ['Developable surface on the helix (cos t, sin t, at), for a = ', num2str(a)]
title(T);
xlabel('x');ylabel('y');zlabel('z');