Published by admin on 03 Feb 2010 at 05:24 pm
To achieve accuracy with broadheads, straight arrow flight must follow,
and nothing decides this more than the fletching on the arrow.
By Joe Bell
Ask any qualified engineer and they’ll tell you that aerodynamics is a complicated subject. Variables are far and wide when dealing with air resistance and the shape of things. This is why designing aircraft is such a high-paying profession – it’s not easy.
This is also why tuning arrows for straight flight ca n sometimes wear out even the most experienced archers. We’ve learned over the years that to obtain precisely straight arrow flight, we must first choose the correctly spined arrow shaft for our bow. To find this out, we shoot this “bare” shaft through taut paper to see if it punches a neat bullet hole (or slight horizontal tear with a finger release). If it does, then it’s the correct shaft for our setup.
Once this is done, we’re left with choosing the proper amount of fletching for our arrows. The fletching on an arrow are responsible for one thing: to cause drag – or friction – that will help stabilize the arrow in flight, therefore allowing it to fly straight through the air and to its intended target. Of course, when you add a fixed-blade broadhead to the picture, this steering effect becomes much more complicated – similar to the aerodynamics behind building airplanes – because now the front end of the shaft wants to “steer” as well.
So in a sense, with fixed-blade broadheads – and even with mechanical broadheads – fletching size, configuration and the orientation in which they are attached is the only element that can control whether or not your arrows fly straight. This is why the subject of arrow fletching is so important.
According to Bob Mizek, one of New Archery Products’ top engineers, the most critical time the flight of a broadhead-tipped arrow is affected is when the arrow first comes out of the bow and before the arrow starts to rotate. “Aerodynamically speaking, the blades of a broadhead act like canards on an airplane,” Mizek said. “Anyway, unless the arrow comes off the string perfectly with perfect center-shot, perfect vertical orientation, perfect nock travel, and with no torque on the grip, the air stream will push against the side of one or more blades, forcing the arrow away from its desired path. Aerodynamically, this is called yaw if it’s left to right and pitch if it’s up and down.
“When the arrow rotates, centrifugal force pushes the arrow back towards its true center and reduces pitch and yaw (this would be a bad thing in an airplane for obvious reasons but is a good thing in an arrow since an arrow does not have a pilot to do course corrections),” Mizek added. “The sooner you can get the arrow rotating, the sooner yaw and pitch can be reduced or eliminated, resulting in tighter groups. Arrows that are tipped with field points or mechanical broadheads still benefit from the arrow rotating because one side of an arrow experiencing yaw or pitch feels air pressure more than the other, causing the arrow to fly inconsistently.”
As you may know, New Archer Products invented the new QuikSpin plastic vanes that were designed to maximize arrow spin, and therefore maximize arrow control and accuracy. The vanes are said to begin spinning an arrow almost immediately out of the bow. This in turn allows the arrow to experience air drag sooner in flight, which theoretically should make the arrow more stable and less susceptible to the forces of side air resistance that could push it off course.
“For reference, a typical arrow fletched offset with 4-inch QuikSpin vanes start rotating in only 18 inches. It reaches full rotation in two to three yards,” Mizek said. “The same arrow set up with conventional vanes typically requires 12 yards. The effect on accuracy by getting the arrow spinning sooner and then faster is incredible.
Are the Rules Changing?
Over the years, we’ve been told that the amount of air drag cased by fletching is dependent on its size and shape. For more air drag, you use longer fletching. For less, you use shorter fletching. For the ultimate in air drag, use the same size feathers. Right? Well, in the pat couple of years I’ve learned the rules may be changing.
While on a hunting trip with my good friend Bruce Barrie, I noticed his arrows were dressed with target-size vanes (they were Duravane’s 3-D vanes). I asked him how he could be shooting such a small vane, but he swore by what great arrow flight he was achieving with small fixed bladed heads, even at sever high speeds.
Later, a rep from Norway (the company that makes the Duravanes) told me that the secret behind these 2.3-inch vanes was its design. The vanes may be short, but the design is very rigid to deduce blade “flap” through the air, which increases its ability to create air drag. Plus, the vane’s compact size optimizes clearance with arrow rests.
This same concept is the premise behind Bohning’s excellent new Blazer vane. At only 2 inches long, this vane is said to offer all the stabilization required to properly steer fixed-blade broadheads. The Blazer vane is slightly more than 1/2-inch tall and the vane is very rigid so wind flap is nearly if not completely eliminated.
Personally, I believe some longer/larger fletching is more prone to “flapping” when they are subjected to high speeds. With slower arrow speeds, air resistance isn’t as violent, therefore arrows fletched with longer/larger fletching provide excellent air drag and arrow control. But with modern speed bows and carbon arrows, reducing arrow speed isn’t really an option, nor do most bowhunters want slow arrow speed.
NAP’s QuikSpin vanes, I’m told, were not only designed to spin the arrow faster but also to prevent from flapping wildly in the air stream. How is this done? The vane incorporates micro-grooves on one side that promote rigidity, even at that critical moment when the arrow immediately leaves the bow.
Arizona Archery Enterprises uses a “rough” finish on its Elite Plastifletch that promotes better steering in flight. The vanes are also made of special material that has better memory (ability to flap back to shape) to reduce the affects of vane flap.
Norway adds a unique, slightly tapered “blade” on their Duravanes from the base of the vane to the top to enhance steering power and to reduce vane weight. This same feature is said to eliminate blade flap and noise, too.
What about feathers? Feathers are said to offer about twice the amount of air drag as equal size vanes. The reason for this can be attributed to a feather’s surface, which is rough and full of natural “slits” that apparently cause for more air resistance or drag.
What about the orientation of fletching, the manner in which they are fletched on the shaft – either straight, offset or helical offset?
While designing the QuikSpin vane, New Archery Products has conducted many tests on the affects of air drag caused by various types of arrow fletching.
“We determined with a rather detailed and complex series of tests that to stabilize a broadhead at about 260 feet per second the arrow needs to turn about one rotation over 3 yards,” said Cary J. Pickands, technical support specialist for New Archery Products. “Our previously recorded data was then able to provide even more information, and in this case, very useable information. We looked at each data set and found the range at which each fletching type produced one full turn.”
During testing, Pickands and other members of NAP’s staff discovered that standard 4-inch vanes (AAE Plastifletch, Duravane, Bohning Killer Vanes, etc.) fletched with a 1/16-inch offset reaches one full rotation between 12 to 15 yards; 5-inch helical feathers fletched with a 3- to 4- degree wrap reaches one full rotation in between 4 and 7 yards; NAP QuickSpin 4-inch vanes fletched perfectly straight reaches one full rotation between 4 and 7 yards; and NAP QuikSpin 4-inch vanes fletched with a 1/16-inch offset reached one full rotation between 1 and 4 yards.
“As far as we can tell arrow speed has no effect on whether the vane will control the arrow,” Pickands said. “We’ve shot broadhead-tipped arrows in excess of 330 fps with phenomenal accuracy and precision.”
Testing Fletching: What Really Works?
Ultimately, only you can decide what fletching type and orientation provides adequate steering for your particular arrows and broadhead combination. Shooting different combinations of fletching with your chosen broadhead usually does this.
My good friend Ron Way, who is an engineer in the aerospace industry, told me that there are many variables that affect aerodynamics and stable flight, whether it is an aircraft or an arrow. “Very small variation can change the dynamics of flight such as the grip on the handle, a poor release, out-or-position anchor (from leaning/twisting), wind, or low or high altitudes (air density),” he said. “An arrow that is marginally stable can show decent flight when conditions are good but can be horrible if one or more of the variables change.”
Arrow Trajectory and Fletching
Ideally you should equip your arrow shafts with the smallest possible fletching that will stabilize your broadhead. This way, you can maximize your arrow’s downrange speed for flatter trajectory. Smaller fletching also means less side air resistance of the arrow that translates into less horizontal arrow drift. Also, consider the orientation of your fletching; the more offset and/or helical you apply to fletching, the slower the arrow will fly because more drag is occurring.
It Comes Down to Accuracy
The bottom line with fletching is what produces the best accuracy for you. While testing some of today’s modern fletching. I’ve noticed that in some cases the length of the fletching is not as important as the stiffness (or in other cases the memory) and the height of the fletching. The greater the stiffness (or memory) and the taller the fletch air drag becomes more pronounced for increased arrow stabilization. But then again, that’s just another impression in the world of aerodynamics.
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