I felt compelled to compose this missive this after receiving a weekly “tech tip” from an archery only web-site containing the prominent statement:
“Shooting a heavier arrow (shaft + tip) will not necessarily give you more penetration (kinetic energy) over a lighter arrow. Check it for yourself ... take your bow and shoot a heavy arrow and a light arrow through a chronograph, then calculate the kinetic energy. I bet the values aren't much different.”
In deference to those espousing (and being led to believe) such an all encompassing statement related to a complex sub-set (archery) in the science of ballistics, I would submit that so much sales hype circulates in the archery market touting arrow speed and really very little discussion time is spent on what I have come to believe is the more critical topic of reliably, humanly dispatching game. After all, the vast majority of shekels spent in the archery industry today are dedicated to deer hunting. Shouldn’t that really be the central issue and not just lauding the ability to launch arrows to 60 yards and beyond? Being able to hit a target at range accurately is important; however, if the pursuit revolves around the ethical killing of game, hitting accurately and killing reliably are not necessarily one and the same topic.
Please bear with me if you’ve heard all this before.
An arrow’s penetration (or lack thereof) is based on a number of variables.
The current rage in archery advertisement centers on velocity. From a simple calculation using an arrow’s weight and it’s velocity at impact, a number, kinetic energy (k.e.) as commonly measured in foot pounds, can be obtained. Basing conclusions about an arrow’s ability to penetrate solely upon velocity, k.e. or a combination of both can be misleading and even cruel. If one were to base their decision on using a particular arrow set up based solely upon k.e., he is missing large parts of the arrow penetration equation.
Killing with an arrow has little to do with actual energy transferred to the target (as is commonly found in the firearms industry). If one stops to think about it, were the arrow to actually drop all of its retained energy into the target at point of impact, the arrow would not penetrate at all (as in the case of a small game “blunt” type arrow). An arrow actually performs better when less of its retained energy is shed in the target and penetration is affected by the slicing action provided by a well designed broadhead that maintains its shape and sharpness while performing its duties of destroying the vital circulatory and/or respiratory systems.
Two of the most overlooked factors in arrow choice for maximizing penetration are inertia and friction imparted to the arrow combination as it passes through a given target.. Inertia is a body’s propensity to maintain speed and direction based primarily upon its mass. Yes, it takes more energy to start a massive projectile moving but it also requires more effort to change its direction or to stop that travel. In other words: We absolutely want that broadhead to penetrate as far as possible into and beyond (if possible) the target. The arrow’s “impact” has little or nothing to do with its intended purpose.
More massive projectiles may or may not strike with more kinetic energy but they tend to retain more of their initial velocity while in flight and during encounters with the target.
Friction related penetration is also affected by:
1. Diameter of the shaft (smaller shaft diameter equals less surface area drag and resistance while inside the target thus greater penetration)
2. Number and angle of cutting edges of broadhead (i.e. a more gradual angle to the cutting edge provides less resistance and better penetration, two cutting edges require less energy to penetrate than three edges, three edges require less than four edges)
3. Smooth transition from broadhead ferrule to arrow shaft promotes penetration (a larger ferrule with smaller O. D. shaft penetrates better than same sized shaft and ferrule while a larger shaft than ferrule penetrates more poorly than either of the above)
4. Stiffer shaft penetrates better than a more flexible shaft (less energy is consumed in shaft flexing and increased lateral friction after impact and more energy is retained for forward movement)
Of course, taking any one of the above factors outlined above to an extreme (i.e. very heavy shaft but too slow to even find the target) does our goal of successfully harvesting game no good.
My admonition to everyone is to be aware of the decisions you are making when choosing an arrow/bow combination. Be careful to filter the advertising propaganda possibly spread by the counter salesperson and television/magazine/catalog ads from the physics of what you actually need to do. There is no free lunch and the current focus on speed and kinetic energy as the end-all be-all to our archery problems is short sighted. While desirable for the 3-D course, that intense commercial focus on speed alone has actually produced a dramatically increased level of struck and wounded game escaping because of inadequate penetration. Merely being able to hit our target is insufficient if we can not reliably bring our intended quarry to ground in an ethical and humanely quick fashion.
Not to put too fine a point on it (all puns aside) but the broadhead needs to make it all the way through those vitals and hopefully out the other side producing a wound channel that allows maximum loss of vital fluids and/or gasses. On deer that can be reliably done at 200 feet per second at 20 yards with a sharp broadhead and a reasonably stiff, heavy arrow every time the mark is hit.
Hitting a foam target is not the same as hitting one of God’s creatures.
I hope this gives some food for thought.
Topic: Arrow Pentration Factors (Read 619 times)
