i take sections of wing and draw a line with pencil from leading edge
to
tr=
ailing edge every 18 inches or so. then, with 800 (you can use 600)
you'll
=
sand two sections at a time using spanwise strokes, working from
leading
ed=
ge to trailing edge.

Did you really mean spanwise and not chordwise??? When I worked at
S-H, we NEVER sanded spanwise. It was either chordwise or
alternating 45 degrees off chordwise. FWIW......