Arrow Speed and Kinetic EnergyBy Jon Henry
Speed ... Oh How We Love it!
Fast cars, fast computers, fast wide receivers, fast-drying paint, fast-acting weed-killer.....if it's fast, we love it. And when it comes to our archery equipment, it's no different. Show most guys a brand new bow, and their first question is likely to be "How fast does it shoot?" Right or wrong, speed is a major consideration for most archers. And it's great to see how advancements in materials and design technologies have made today's compound bows better, faster, and more fun to shoot than ever before.
Of course, there will always be a few dissenters in the crowd, those who'll loftily claim they don't care about speed. But the market trends don't lie. Archery consumers are taking advantage of these innovations, buying high-performance bows and speed-boosting gadgets by the trainload. And nothing yields such a predictable and significant increase in speed like a good set of lightweight carbon arrows. So let's examine the pro's and con's to shooting lightweight arrows. Let's find out where they help, where they hurt, and where they don't really make a difference.
Arrow Mass Affects Arrow Velocity
When all other variables are constant, arrow speed has an inverse relationship with arrow mass. Of course there is a point of diminishing returns, but as arrow mass increases, arrow speed decreases. As arrow mass decreases, arrow speed increases. Your bow will only generate a certain amount of energy (given its particular settings), and it uses that energy to get the arrow moving. The less the arrow weighs, the faster that energy can make the arrow accelerate. The heavier the arrow, the less acceleration is achieved. Interestingly, a bow transfers energy into a heavier arrow more efficiently than it does into a light arrow (more on this in a moment). Nonetheless. the rule still applies, lighter arrows go faster - heavier arrows go slower.
Arrow Mass vs. Velocity Chronograph Test
To illustrate this point, we prepared 9 arrows, ranging from 250 grains up to 650 grains in precisely 50 grain increments. Each arrow was fired from our test bow (60#/28" Bowtech Patriot) through the chronograph and the results were recorded (table below). Five trials were conducted for each arrow - to achieve a reliable speed measurement (average). Each arrow was fired from the same distance, from the same shooter, and without any modifications to the bow's settings during the test. The test was conducted at our indoor range, where lighting and environmental conditions could be held constant throughout our test.
Click here for larger image.
As you can see, as arrow mass increased - arrow velocity decreased. Mathematically, the inverse relationship isn't exactly linear, but close enough to illustrate the concept.
OK. But is Faster Necessarily Better?
Maybe. From a standpoint of accuracy, you may find that lightweight arrows will yield some surprising benefits. From the moment your arrow is released from the bow, it begins to lose trajectory. As it succumbs to the effects of gravity and air resistance, it's flight path (trajectory) changes and the arrow eventually begins to drop back to earth. Arrows which fly more quickly hold their trajectory better than slower arrows. So archers who shoot lighter-faster arrows will have less need to adjust for distance - since the faster arrows will hold a "flatter" trajectory within a given distance. In effect, the faster arrow allows you to make more mistakes in yardage estimation. If you mis-estimate a deer to be 25 yards away, and it is actually 30 yards away, the fast arrow still lands lower than expected, but it "misses" its mark by a smaller margin. Look at the trajectory chart on the right from our Bowtech Patriot experiment. The heavier arrows nosedive more quickly than the lighter faster arrows. So whether you're a hunter or competition 3D shooter, you may find that faster arrows actually add a little forgiveness into your shooting, allowing you to make an error in yardage estimation without paying such a heavy price.
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