Arrow velocity. (Modern Bowhunting).
Speculation and opinion have been offered on these questions for many years. Fortunately, in an effort to provide definitive answers, I have had the privilege of conducting scientific tests to collect empirical data on these subjects. In this, and my next column, I will address the results of these test projects.
The challenge, when addressing the downrange decay of arrow velocity, is to design tests that separate and study each individual arrow component. Only by changing one variable at a time is it possible to determine what effect each variable has on the final result. Conducting this type of research in a fair and accurate manner is a monumental task. Above all, the person performing the tests must be willing to let the chips fall where they may.
The tests referred to in this column were conducted with two chronographs and a shooting machine. Prior to testing, the two chronographs were placed as closely in tandem as possible and several arrows were shot through both machines at the same time. The order of the chronographs was then reversed and the procedure was performed again. This allowed correction for a minimal foot-per-second (fps) discrepancy between the chronographs. For verification, this same comparison between the two machines was conducted at the conclusion of the test.
Chronograph number one was set 1 yard from the shooting machine, number two 61 yards from the shooting machine (on some tests a chronograph was also placed at 31 yards). This arrangement permitted the accurate recording of each arrow's speed in at least two locations as it proceeded downrange.
The same test arrow was fired a minimum of three times during each test. Each series generated a high level of consistency in arrow speed, indicating the chronographs were functioning properly and that the data collected were accurate. All tests were repeated several months later.
Here are the results of the most interesting arrow velocity tests:
TEST #1 The Loss of Arrow Velocity as a Function of Fletching
Data from Test #1 indicate that the manner in which fletching is attached (i.e., right-wing, left-wing, straight, or straight offset) has only a minor effect on downrange velocity. Likewise, any speed differences between 4-inch, 41/2-inch, and 5-inch feathers were imperceptible by the chronographs.
When a three-fletch arrow was compared with a four-fletch arrow (three 4-inch vs. four 4-inch, left-wing, helical feathers), the average difference in speed at 61 yards was still a minimal 3 fps slower for the four-fletched arrow. As noted above, changes in fletching styles (not the number of fletchings) caused even less change in velocity at 61 yards.
I was surprised to observe that the size, configuration, and number of fletching used had such a small effect on downrange velocity. In addition, the evidence is overwhelming that helical fletching does not cause the excessive loss of velocity that some people had speculated it does, at least not within normal bowbunting ranges and with normal hunting weight arrows. From this I conclude that helical fletching may be best for broadhead-equipped arrows. It should be noted, however, that arrows used in the tests had only medium or average twist.
TEST #2 The Loss of Arrow Velocity as a Function of Point Type
It was interesting and surprising to observe the considerable effect that point design had on downrange velocity, particularly after noting the minimal effect of fletching styles. The launch speed for the arrows listed below was 210 fps. The listed arrival speed was recorded at 61 yards and is the average of three shots. The bullet-shaped (ogive) point proved to be the most efficient, with an arrival speed of 187 fps. The arrival speed for the field point was 185 fps, and for the Judo point 175 fps. The HTM rubber blunt proved to be the least efficient, with an arrival speed of 173 fps.
Possibly the most interesting observation of all is that a steel blunt and the eight broadhead designs tested had approximately the same speeds at 61 yards: 181 fps. Terminal velocities this similar might be somewhat unexpected considering such diverse point designs. Apparently, while the initial airflow and disturbances over the steel blunt and the broadheads may be quite different, the overall drag coefficients of the complete arrow assemblies must be similar.
As for point of impact, I feel it would be unwarranted to assume automatically that these two point types (steel blunts and broadheads) will have the same point of impact just because they have the same arrival speed. Conversely, it may not be correct to assume that an ogive point and a broadhead will exhibit different points of impact just because they have different arrival speeds. Too many other factors may influence arrow flight. At the same time, it is unlikely that all the heads tested would have the same point of impact at 61 yards, considering the diversity in speeds at that distance.
TEST #3 The Loss of Arrow Velocity as a Function of Fletching Material--Feathers versus Vanes
Most 5-inch vanes weigh substantially more than feathers of the same size (weight varies among various brands of vanes as well). For this test, 5-inch True Flight feathers were used to fletch arrow #1, 5-inch Bohning vanes arrow #2. The same jig and glue were used to fletch both arrows. When the arrows were completed, arrow #1 weighed 35 grains less than arrow #2. The additional weight at the rear of the vane-fletched arrow shifted balance point aft by 3.3 percent.
As would be expected, arrow #1 had a faster launch speed than arrow #2 (210 vs. 204 fps), and at 31 yards #1 was still moving an average of 4 fps faster than #2. However, at 61 yards, arrow #1 had an average arrival speed of 187.7 fps, compared to 188 fps for #2.
This test demonstrated what occurs when shafts of the same size are fletched with feathers vs. vanes. Although the feather-fletched arrow slows more quickly, it still has a shorter elapsed travel time out to 61 yards, and it may have a slightly flatter trajectory.
Even though this test showed that feathers generally have a slight speed advantage, the difference is not significant at bowhunting ranges. Both vanes and feathers have their strong points, and I suggest you choose the material that works best for you.
TEST #4 The Loss of Arrow Velocity as a Function of Arrow Weight
The challenge in Test #4 was construction of the test arrows. The arrows had to have the same length, the same outside diameter, and uniform foc (front of center) balance points. Finally, they had to have precise but wide-ranging weights--400, 500, and 600 grains. The required arrow weights were achieved by using shafts with different wall thicknesses. Balance points were kept similar by removing weight from the point and installing weight-compensating inserts in the rear of the shafts.
Because of the diversity in wall thick-nesses, an obvious concern was that a wide variance in spine (stiffness) might affect test results. The following observations led me to conclude that the changes in spine had no effect on the outcome of this test:
1. During the test, all of the arrow flights appeared to be similar.
2. Because the same launch speed had to be maintained for all arrows, the draw weight of the test bow was reduced considerably for the more lightly spined arrows.
3. During Test #5 (see below), a 2213 arrow very similar to the one used in Test #4 was launched at a substantially higher velocity with similar percentage results.
Velocity of the 600-grain arrow decreased by 5.55 percent over 31 yards and 10.32 percent over 61 yards. Velocity of the 500-grain arrow decreased by 5.71 percent over 31 yards and 11.59 percent over 61 yards. Velocity of the 400-grain arrow decreased by 8.73 percent over 31 yards and 16.35 percent over 61 yards.
This test demonstrated that lighter arrows lose velocity more quickly as they travel downrange. This loss seems to become much more significant with arrows weighing less than 450 grains.
Therefore, bowhunters who prefer to shoot such arrows should be aware that lightweight arrows have a much greater propensity to lose kinetic energy as they move downrange. Of course, if a bowhunter starts out with a higher than normal amount of kinetic energy, he may not be concerned with the additional loss. But, with this information, everyone can make a logical decision.
TEST #5 The Loss of Arrow Velocity as a Function of Launch Velocity
The purpose of Test #5 was to investigate the loss of velocity for arrows launched at different speeds. Draw weight was changed to achieve different launch speeds for the same arrow. A 404-grain 2213 launched at 200 fps slowed by 32 fps--16 percent of its initial velocity-while traveling 61 yards. When that same 2213 was launched at 240 fps, it slowed by 37 fps--15.4 percent of its initial velocity--over the same distance. IT is interesting to note that the fps loss was different, but the percentage of velocity lost remained similar for both speeds. It would be fascinating to see whether this trend would continue as arrow speeds are increased.
This test then was conducted with an A/C/C 3-71, which also weighed 404 grains. Its length and balance point were similar to the 2213, but it was dramatically stiffer. When launched at 200 and 240 fps, speeds at 61 yards for the A/C/C were remarkably similar to those of the 2213. This test led me to conclude that, given good arrow flight, spine variances have minimal effect on downrange velocity.
* Size, configuration, and number of fletching have minimal effect on arrow velocity at 61 yards. In addition, evidence is overwhelming that helical fletching does not cause significant loss of velocity, at least not within normal bowhunting ranges.
* Point style does have a significant bearing on arrow speed at 61 yards.
* Drag coefficient differs between feathers and vanes. As expected, vanes have less drag. Thus, they maintain a higher percentage of their initial speed over any given distance.
* Because a feather-fletched hunting arrow weighs less, it is slightly faster within normal bowhunting ranges than its vane-fletched counterpart.
* Lighter arrows lose velocity faster as they travel downrange. This loss seems to become much more significant with arrow weights below 450 grains.
* Arrows launched at higher speeds evidently lose velocity more quickly than do arrows launched at slower speeds. However, the limited test results reported here indicate that percentages of velocity lost at 61 yards remain similar for arrows with different launch speeds.
Data collected during these tests are believed to be extremely accurate. This is not meant to imply, however, that all downrange velocity questions have been answered. On the contrary, I look forward to future research efforts.
In my next column we'll take an in-depth look at broadhead penetration and kinetic energy. I'm sure you'll find the test results fascinating.
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|Date:||Aug 1, 2003|
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