Arrow Shaft Design and Performance
by George Tekmitchov, Easton Sr Engineer/International Technical Advisor
Easton offers three major arrow shaft design technologies-Parallel shafts, tapered shafts, and barrelled shafts. Each of these technologies offer performance advantages for specific purposes. Let’s discuss these and get a better understanding of the place each of these has in Easton’s designs.
Parallel-design shafts are easily the most common, most available, and least costly type of arrow shaft design today. Well suited for all-around use, parallel designs in either aluminum or carbon have the advantage of easily available, standardized components, and little guesswork when it comes to setup and tuning. Because there are fewer manufacturing steps needed, parallel shafts can be made much more inexpensively than non-parallel shafts. However, the main reason parallel shafts ARE parallel has as much to do with the expediency of manufacturing and production as with the ultimate performance of the arrow shaft.
For ultimate performance, especially in an outdoor environment, we must turn our attention to two alternatives- barreled, and tapered shafts.
The tapered shaft concept is thousands of years old. Ancient archers knew that by tapering the rear of the shaft and maintaining a bigger diameter in the front of the shaft, the arrow had better performance. For one thing the tapered shape slightly reduces drag. It also promotes a higher front-of-center balance with equivalent point weight. And, for a finger shooter, a correctly designed rear taper can provide a more forgiving behavior in the event of small release variations. This might be why ancient examples or evidence of tapered shafts can be found in nearly all cultures, even though they likely did not fully understand the physics behind these advantages.
Today, specialty designs such as the Easton X10 ProTour have been introduced with a reverse taper- with a more aerodynamic front and stiffer rear half for better compound bow launch. This design was proven by being used to set nearly every existing compound bow world record standing today.
There are many advantages to the tapered shaft, but some trade offs. The main trade off of tapered shafts is the increased cost of production. The technology needed to taper an arrow shaft isn’t particularly complex, but maintaining excellent spine and straightness standards for a tapered shaft is technically challenging and quite expensive. In fact, this is where most of the added cost comes from.
The tapered shaft is the ultimate in performance for compunds shot with a release device.
As good as tapered shafts can be, in some particular uses- specifically, finger release- a barreled shaft offers even more advantage. Like tapered shafts, barreled shafts are a concept dating to antiquity. The legendary flight archery accomplishments of the Ottoman sultans were all accomplished with barreled shafts, for some very good reasons.
A well-designed barreled shaft has improved aerodynamics, over even a tapered shaft. A properly designed barreled shaft also has an ideal, custom-per-spine flex pattern to allow a more forgiving finger release and ideal clearance. The well-designed barreled shaft has optimized mass distribution and more flexible tuning options.
By making the rear half of the barreled shaft less stiff than the front, clearance for finger shooters is improved from recurve bows. This characteristic also makes small variations in finger release much less of a problem.
By shifting mass weight forward and distributing it over the center of the shaft, front of center balance is improved, which allows for an ideal ballistic behavior from the arrow shaft.
Of course, this ultimate performance also comes at a price. It is much more difficult to build a barreled shaft with excellent tolerances than either a parallel or a tapered shaft. A tremendous investment in technology and considerable experience is needed to successfully build such arrow shafts.
Tolerances must be held to a much higher standard, material selection and specifications must be made much more tightly, and the fundamental behavior of a barreled shaft means that each and every spine size needs a custom designed materials callout, shape and flex pattern.
On the other hand, the extra effort and cost are clearly worthwhile, as no arrow shaft made today can outperform the accuracy and aerodynamic performance of fully barreled designs such as Easton’s X10. This is demonstrated by the fact that the X10 holds every single recurve bow world record, Olympic record, and has won every Olympic title since its introduction in 1996.
Proper tuning of barreled shafts does require a somewhat better than basic understanding of tuning and the ability to take accurate measurements of draw weight, draw length, and other parameters. In addition, special care must be taken to ensure the correct centershot is set on the bow. However, once properly set up (perhaps with the assistance of an experienced tuner or coach) the barreled shaft is the ultimate for accuracy and performance for recurve finger shooters.