Traditionally, there were 2, 3 or 4 fletches (fins of feathers) attached to the back of an arrow, though some African tribes are known to have used up to 8 feathers to increase stability even further.
Evenly shaped and sized feathers would be attached to the back of an arrow with some type of adhesive glue, or even sewn onto the shaft using silk thread. The fletches would be evenly spaced around the outside of the shaft. Placement of the fletching and precision were critical, as all feathers have a natural curve, based on which wing of a bird they are taken from.
Also, feathers have one smooth and one rough side, which creates a slight aerodynamic differential; this is what gives a fletched arrow its natural spin as it moves through the air. This spinning typically begins well after the arrow has cleared the shelf of the bow, in mid-flight. Each fletch can also vary in shape (triangular, parabolic) and size (3-10 inches in length; 1-4 inches in height). For thousands of years, this type of aerodynamic add-on helped archers improve their arrows’ flight distance, accuracy and lethality.
Feathers are also able to compress and bounce back to their original shape, which is important for archers shooting off the shelf of their bow. As the arrow passes over the shelf, the feathers are pressed down, so the arrow is smoothly released, without any erratic movement during the release. Vanes, however, will not compress down, so if shot from the shelf of the bow, the flight of the arrow will immediately have some wobble due to the vane striking the shelf when it is released.