Dynamic spine
This is probably the most critical part to arrow construction as well as proper arrow flight. Having the correct spine goes a long way to superior arrow flight as well as eliminating tuning issues with one’s bow. Although spine can be manipulated, this can only be done to a certain degree before it affects the tuning of one’s setup. Spine charts are available for each arrow manufacturer providing the correct spine for any given setup; these have been tested to provide optimum performance and are the best starting point. Once the correct spine is selected most arrows have a range of components which can be used to fine tune the arrow further.
Hint: Fletching the cock vane on or opposite the spine can add to the consistency of the setup. Other factors regarding arrows that may influence speed, penetration, FOC and wind drift are.
Arrow weight (GPi)
This is the actual weight of the shafts construction material per inch of shaft length whether it is aluminum, all carbon or a combination of both. These vary per manufacturer or per process and raw material used.
FOC (forward of center)
FOC is a percentage given to the ratio of the distance of the balance point to the center of the arrow. FOC is considered to influence the arrows flight path with the higher FOC offering the truer path to the target. A higher FOC arrow therefore has a lighter tail end which allows the fletching’s to give a greater “steering” capability. Although the lighter tail is more susceptible to the wind, the heavier point keeps the arrow on target even though there may be tail drift.
The belief that a higher FOC arrow has greater penetration is a controversial subject as the weight of an arrow stays the same irrelevant of the FOC. From an engineering point, FOC position percentage has little to do with the actual penetration achieved. Both Kinetic Energy E=1/2mv² and Momentum P=mv both rely on the velocity and mass of the arrow. It is not specified where the mass is positioned but only the complete mass of the arrow. From a logic standpoint more weight forward will argue less shaft flex and therefore less energy loss and point of impact. Several tests have been done to affirm both sides of the subject.
Fletching)
There is a vast array of different size and shapes of fletches available. The length, height, direction and angle will determine how the arrow will react in flight. How arrows are fletched are personal preference regarding shape and size, higher profile and longer fletches are typically used by hunters as well as Indoor archers because of their ability to correct and “steer” the arrow quickly in a very short distance. Shorter and lower profile is used for longer distances having a longer time to react e.g. Field or 720. The size of the fletch also has an effect on the arrow when it comes to wind, especially in crosswinds, the larger the vane the more the wind will drift it.
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Hint: Fletching in the same direction the arrow turns when shot bare shaft i.e. bare shaft turns anti-clockwise, fletch left helical. Fletch with less angle for arrows used for longer range shooting, this helps maintain speed as the arrow turns slower and therefore has less rotational drag.
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