The fletchings were all straight, not helical, Have just finished a fletching DVD with Mark Stretton and we have filmed these arrows from the MR and they show close ups of where the Fletching lay in the glue and they are straight.....all of the ones that have the glue still in place, there is not one arrow there which has any evidence of a helical fletch.....Sorry Bow-Toxo, I am sure you mis heard Alex's answer.
Also the lengths of the arrows does differ, there are arrows of 27" right through to 33" but the vast majority are 30.5", these are also covered in the DVD in some detail.