Right helical for RW feathes, left helical for LW feathers. Right will rotate the arrow clockwise, left counterclockwise. It dosn't matter, just don't mix up RW and LW on th same arrow.
When you say "straight fletch" do you mean off set? You should offset your feathers... at least 2 degrees, to get the arrow spinning a bit and stabilized. Same rule: RW feathers, right off set, and vice versa. The ony time I don't off set feathers, is when I'm making replica war arrows.