HELICAL FLETCHING
Adrian Tippins explains all
When we start out in archery arrows are just seen as necessary components, and they all just have fletchings on. Even beginners with limited technical knowledge understand the function of fletchings, but don't really pay much more attention to them beyond selecting the size, shape and colour. As time goes by archers start to see subtle differences on colleague's and competitor's arrows, and eyes get opened to the fact that there's multiple types and ways of applying fletchings to a shaft. In this article, we're going to be taking a look at the very popular option of helical fletching.
Helical fletching settles an arrow faster by offering an increased amount of gyroscopic stabilisation via a higher drag factor. The word helical is derived from the word “helix” and means to have a helix or spiral twist. In terms of fletching, the feather or vane is literally spiralled around the diameter of the arrow shaft. This format of fletching is nothing new has in fact been around longer than you might think. No one really knows how helical format was discovered or who was the first to employ it. Some people apply the reasoning that the ancient practice of spiral binding of feathers to to wooden shafts naturally pulled the feathers around into a helix. The word “Helical” actually has it's first recorded use in the English language in 1605. Arrows, however, have been around for at least ten thousand years.
The normal way of fletching places the vane in a straight line down the shaft. A straight fletch maximises kinetic energy, momentum and shooting distance. To achieve this, the vane is placed in the clamp dead straight. Some jigs allow you to offset a straight vane. In this process the straight vane is placed on the arrow crooked over to the left or right. Helical fletching sees the vane twist around the diameter of the shaft creating an “S” curve in the vane when viewed from above. This profile is very similar to that found on aviation propellers. From behind the vane takes on the look of a fan blade. To achieve this specific curvature the jig clamps are manufactured with a pre-twisted curvature and are available in both left and right handed versions. I often get asked “what's the difference between offset and helical?” I normally give a simplified answer by stating that they do the same job, but helical is more
aggressive option.
To really understand the advantages of helical fletching it's important to understand what fletchings actually do for an arrow. Fletchings steer, stabilise and spin the arrow giving tidy and stable flight characteristics. If an arrow shaft is shot without any fletchings it will fly erratically and unstabilised in the direction decided by the bow's tuning. On a fletched shaft, the vanes steer the arrow thus straightening up the flight course. Vanes also impart certain amounts of drag, this in turn starts to rotate the arrow. A rotating projectile is much more stable and has a lot more long range accuracy. This rotational property is often referred to as “rifled or rifling”. To make a ballistic rifle more effective and accurate over a longer distance the inside of the guns barrel often has helical rifling grooves. These get the bullet spinning before it actually exits the barrel. It is said that the accuracy of a smooth bore (without grooves) rifle is reducing at only seventy five yards.
We can now start to understand that we need to have our arrows spinning and settled down very quickly to achieve accuracy and tight grouping at the longer distances. It's because of all these factors that spin vanes are the vane of choice for virtually all longdistance tournament recurve archers. Spin vanes are normally manufactured with a pretwisted helix for either hand orientation. This means they don't require a specially shaped clamp and can be applied straight down the arrow shaft. A good way to think of helical fletching with a regular plastic vane is the process of creating a twisted spin vane, but out of a heavier and more robust material. This practice is ideal for compound arrows.
A helical vane has more of its surface placed side on to the flight direction. The force of the air hitting the surface creates the necessary drag to start the arrow spinning and the “S” curve continues to channel the air
"A ROTATING PROJECTILE IS MUCH MORE STABLE AND HAS A LOT MORE LONG-RANGE ACCURACY."
stream. As the curvature of the vane is very important to the aerodynamics we have to be careful to select a vane with an appropriate length that allows us to get the full “S” shape, especially on a thin shaft. In my experience I have found the minimum length to be two inches. A helical vane can also be placed with an added offset if required. I wouldn't recommend going more than two degrees for a straight offset, and more than 1 degree for helical for arrows intended for long distance shooting. This is down to the fact that you can easily run into application issues and find it difficult to seat the front and rear of the vane properly on a tight diameter. The wider the shaft, the more aggressive one can be with the offset as the wider shaft offers a broader working platform. Do bear in mind that creating an arrow format with too much drag can have a negative effect on long range grouping as it can increase the parachuting effect. The term “parachuting” refers to the rear or the arrow going into a lateral spiralling motion due to the rear of the arrow decelerating faster than the point end of the arrow. Overly aggressive amounts of offset can also lead to clearance problems on rests and launchers too.
There aren't that many negatives surrounding helical fletching, apart from needing a little bit of specialist equipment to build. However, it's important to understand to that there is some loss of arrow speed. Many people including myself have gone to great lengths to test and understand the pros & cons of different arrow configurations. In summary, I have found a very small drop in arrow exit speed of around 1 fps. This is understandable due to the increased drag factor. The downrange speed difference then increases exponentially with an increase in distance. For example, in my latest test the
speed difference at 20 yards was 2 fps less which then increased to 3 fps at 30 yards. As a helical arrow will be spinning at a much higher RPM than a straight-fletched arrow the laws of physics dictate that the drag will also cause a faster rate of deceleration. There's no hard and fast formula for calculating such differences as it will vary person to person and bow to bow. Testing also revealed that there's no discernible difference in grouping performance between a straight offset vane and that of a helical. The only small difference is that the helical offers quicker stabilisation which can be an advantage over a shorter distance. If you're an archer who is only just making a given distance with the sight block bottoming out on the track, helical might not be for you. The increased drag and loss of arrow speed might just be enough of a factor to make your arrows fall short. However, if you're an archer who is shooting a decent poundage and effortlessly making the longest of distances with sight marks to spare then helical is definitely worth a try.
With so many options open to us for the creation of personally optimised arrows, it's really important to carry out some real-world testing to make sure we end up with kit that's going to enhance our performance instead of hindering it. Just because a fellow archer is using something to good effect it doesn't mean that it's going to work well for everyone. Thankfully fletchings are inexpensive, which allows us to try out various configurations without breaking the bank. It's worth asking your fellow archers if they have a few spare vanes that you could try. Often archers do have spares as supplies like spin vanes always come in packs of at least fifty. If supplies aren't available via charitable donations, don't be afraid to spend a little cash. Spending a small amount upfront for testing purposes will undoubtedly save you far more in the long run. It's always worth gluing plastic vanes onto some vinyl wraps. That way if you don't want to stick with a certain format you can easily strip it off without the possibility of compromising the integrity and finish of the shaft. You'll be able to run as much testing as you like and still keep the shafts in pristine condition. Good luck and good shooting.