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Monday, January 12, 2015

The Bow Manufacturer's Quest for 400 FPS

From "The Hobbit" movies to "The Hunger Games" series, films featuring archers are driving bow sales up. Sports manufacturer Escalade is projecting that increased archery interest will contribute a 9 percent sales growth over the coming year. Meanwhile the National Archery in the Schools Program (NASP) has spread from Kentucky throughout the country since 2002. With this growth comes greater demand for faster bows. To meet this need for speed, manufacturers are pushing technology's limits to tackle a physical barrier that has defied engineers for the last decade: creating a compound bow that can realistically exceed 400 FPS.

The Formula



Just as auto engine power is measured in horsepower, a compound bow's FPS rating (foot-pound-seconds) measures how powerfully it can fire. As horseback archer Dan Sawyer explains, the way a bow stores power is similar to a spring. Just as a spring builds potential energy when compressed, the work done by drawing a bow stores energy in the string. When the archer releases the string, the stored energy is released at a rate proportionate to the bow's FPS rating, along with other variables such as the peak draw weight of the bow, the length of the draw and the mass of the arrow. Archery Calculator provides an online tool for crunching these numbers to see how fast your bow can fire. The speed of your arrow, along with its momentum, helps determine how much penetration your shot can achieve.

The Barrier



When building faster bows, manufacturers face a barrier posed by archery physics and industry standards. As Hunter's Friend webmaster Michael Blanton explains, the International Bowhunting Organization (IBO) currently standardizes FPS measurements by using a 70-pound draw weight, a 30-inch draw, and an arrow weight of five grains per pound of draw. These numbers determine how much energy must be stored to shoot an arrow at a given FPS rate. To achieve 400 FPS, 124.378 foot-pounds are required.

Theoretically, this can be achieved by adjusting certain variables. For instance, shortening the distance between the string and the pivot point of the bow's grip known as the brace height, changes how far you're actually pulling the string, affecting how much energy the bow stores.

However, in practice, other variables complicate the picture. These include efficiency lost due to friction and vibration, along with the need to gradually ramp up to and down from maximum draw weight for a smooth pull. With today's technology and standards, a 400 FPS compound bow would be uncontrollable.

The State of the Art



These realities determine the limits of today's technology. Since IBO standards were adopted in 2005, maximum speeds under ideal test conditions have climbed from 315 to over 350 FPS, reports Outdoor Life. In 2014 Bowtech released the RPM 360, which achieves 360 FPS, while PSE achieved 370 FPS with the Full Throttle. Bows from these and other top manufacturers are available from leading suppliers such as Cabela's and other select outlets.

The Next Stage



To achieve faster bows without a major technological breakthrough, manufacturers are currently confined to making minor improvements to efficiency, such as reduced friction and slicker cable slides. However, Blanton suggests that today's bows may be tough enough to justify modifying IBO ratings standards to allow lighter arrows that fly faster. This could be the easiest way to achieve 400 FPS.

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