documentclass{article}
RequirePackage{pgfplots}
begin{document}
begin{tikzpicture}
begin{axis}[view={rad(60)}{rad(30)}, trig format=rad, title=all in radians,]
    addplot3+ [domain=0:4*pi,samples=19,samples y=0]
    ({sin(x)},
    {cos(x)},
    {2*x/(4*pi)});
    node [fill=white,draw=black,anchor=center] at
    ({sin(pi/2)},{cos(pi/2)},1) {X};
    end{axis}
end{tikzpicture}

end{document}