How much does adding four fletchings instead of three change arrow speed?

The Committee, when it stripped the fourth fletching from the standard pattern, cited speed. It was not wrong on this narrow point, and the Codex does not lie to its petitioners. An additional vane adds aerodynamic drag, and drag costs velocity. The honest number, drawn from ballistic testing rather than catalog sentiment, is modest: adding a fourth vane of comparable size to the other three will cost you somewhere in the range of one to three feet per second at the muzzle, depending on vane surface area, vane height, and total arrow weight. A low-profile fourth vane — say, a 1.75-inch or 2-inch vane rather than a tall 4-inch helical — sits at the lower end of that penalty. A tall, steeply heliced fourth vane climbs toward the higher end.

To put that in proportion: a 1 fps loss on a 280 fps arrow is beneath the noise of a five-degree temperature change or a slight anchor variation. At hunting or target distances inside 60 yards, the trajectory difference is not measurable by the archer. The drag also bleeds a small amount of retained velocity downrange, so at 60-plus yards the gap between three and four vanes widens very slightly — still not a figure that decides a round, but honest arithmetic demands you know it.

What the fourth vane provides in return is a marginally faster restoring moment after paradox — the arrow recovers its line of flight slightly sooner because there is more steering surface acting on the boundary layer of the shaft. For a heavy hunting arrow, a long-helical three-fletch already does this well. For a lightweight, stiff-spined target shaft where recovery distance matters, the fourth vane earns its keep. The exchange — a feather of speed for a feather of stability — is the entire argument the Committee buried. The Codex records it here, as it has for six hundred years.