Elements of descriptive geometry, with applications to isometric projection and othe forms of one-plane projection; a text-book for colleges and ingineering schools by O. E. Randall.

GENEIATION AND CLASSIFICATION OF LINES 83
projection of F is at f', on G-L, and f/-e' is the vertical projection
of the required tangent.
By this process the position of the vertical projection of the tangent to the helix is determined by two points, e' and f', and the
unsatisfactory task of drawing a rectilinear tangent to an irregular
curve is avoided.
217. Problem 144. Represent a left-handed helix whose radius is
4 and whose pitch is 8.
218. Problem 145. Find the point in which the right-handed helix
whose radius is 4 and pitch 10 intersects a horizontal plane 4 above H.
219. Problem 146. Find the point in which the right-handed
helix whose radius is 4 and pitch 9 intersects a plane containing the
axis and making an angle of 45 degrees with V.