Fletches, Fletches, … and Fletches

While we have been on the topic of arrows, I had another question emailed in (ruis.steve@gmail.com) on this very topic.

“I have another boring question, what is the difference between shield vanes, parabolic, Spin Wings. Not physically of course. 🙂
Best regards,
<name withheld>”

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The shapes of vanes make very little difference, except aesthetically (which I do not discount, I enjoy shooting a lovely bow more than shooting an ugly one). The factors that affect vane’s performance are: surface area, roughness of that surface, and angle the vane makes with the shaft. In addition, the possibly largest factor is mass. Of fletches having the same size and shape, plastic vanes are the heaviest, then feathers, then Mylar vanes (Spin Wings, etc.). Mylar vanes also operate differently from the others but their main advantage is having so little mass.

Since vanes function by exerting drag on the back part of the arrow (the front half was made deliberately heavier with the addition of the arrow point, so it has more inertia, aka resistance to changes in its motion). So the drag created by the vanes is actually slowing the arrow down, but the front has a higher resistance to that change in speed, so the vanes serve to bring the rear of the arrow into the flight path of the front by basically tugging backward on the shaft.

Larger fletches of any kind will always produce “more correction” and slower arrow speeds. You will note that people shooting indoors use much large vanes (favoring steerage over speed) while those shooting outdoors use the smallest possible vanes (favoring speed over steerage). Faster arrows are affected less by wind and gravity, for example, for the simple reason that the arrows are exposed to the forces involved for less time.

And, obviously, the shape matters if you are having a fletching “clearance problem,” that is the fletches (or usually a fletch), is clipping the rest or the riser on its way out. Some people opt for low profile vanes rather than high profile ones for this reason, but this is not the only way to address this issue.

The behavior of vanes in flight is complicated. If you have seen any high speed video, you will see that feathers tend to “lay down” reducing their surface area dramatically, and all fletches flutter in flight, changing their angle of attack, as it were.