Oldaro
04-22-2005, 03:15 AM
Understanding Arrow Energy And Efficiency
Kinetic energy is currently recognized as the standard measure of the amount of penetration ability your arrow possesses. I'm sure you've read about minimum recommended energy levels for hunting different types of game, or for using mechanical broadheads. In this column I'll show you how to determine your kinetic energy with or without traditional measuring instruments.
Your arrow's kinetic energy can also help you determine your bow's efficiency. Efficiency is defined as kinetic energy of the arrow just after it leaves the bow divided by the potential energy that went into drawing it, multiplied by 100. In other words, it is the ratio of energy out vs. energy in. As you can see, efficiency relates to arrow speed directly. Since speed is a primary goal of most of the bows on the market today, it pays to understand the role of efficiency in bow performance. But first, kinetic energy.
As the arrow leaves the string there is still plenty of energy contained in the limbs and the string. This energy creates vibration and noise. A bow with a high efficiency has less energy in the bow after the arrow is gone.
DETERMINING KINETIC ENERGY
To determine your arrow's kinetic energy you need to know two things: the arrow's weight and the arrow's speed. Weight is most accurately attained with a grain scale, while a chronograph is used to accurately measure speed. Unfortunately, not every bowhunter has access to these instruments. Here are some tips for calculating weight and speed without expensive equipment.
Arrow weight without a grain scale: You can get very close to your finished arrow weight using the following estimates for each component and referring to your arrow company's literature to get the shaft weight:
Five inch vanes: 30 grains
Four inch vanes: 25 grains
Five inch feathers: 20 grains
Four inch feathers: 15 grains
Indexing nock systems: 20 to 30 grains*
Standard nocks: 15 grains
Aluminum inserts: 30 to 50 grains*
Composite inserts: 10 to 20 grains*
Point outsert for carbon: 15 grains
Nock outsert for carbon: 15 grains
* Weight depends on shaft size. In general, larger shaft size corresponds with a component weight on the higher end of the scale.
Arrow speed without a chronograph: You can approximate your arrow speed using the following simple table. First, shoot your bow at a target from 20 yards using your 20 yard pin. Mark the center of your group. Next, shoot from 40 yards, still using your 20 yard pin and aiming at the same point on the target as before. Mark the center of this group, and measure the distance between the two marks. Refer to the table for your arrow speed.
Approximate Arrow Speed (fps) / Spread between 20 & 40 yard groups ('')
220 28.7
240 24.2
260 20.6
280 17.7
300 15.5
320 13.6
330 12.8
Doing the calculations:
The following formula should be used to calculate your arrow's kinetic energy. Use finished arrow weight expressed in grains and arrow speed in feet per second.
KE = (arrow weight) ./. 450,800 X (arrow speed)2
Recommended standards: It has been offered by some experts that 45 ft-lb of arrow energy is a good minimum for whitetail deer, while 55 ft-lb is a proper minimum for elk and caribou. It has been further suggested by several in the broadhead business that an extra 10 ft-lb should be added to each of these minimums when mechanical broadheads are used. These, of course, are only rough guidelines. Many animals have been taken through the years, and will continue to be, with well-placed arrows carrying much less energy.
Arrows come in many sizes and weights. A heavy arrow will soak up more of the bow's potential energy on release and will thus increase the bow's efficiency rating. It will also make the bow quieter. This is why heavy arrows carry more penetration energy than lighter arrows - they soak up more energy from the bow.
_________________________________________________
To add a very helpfull link to this post would be appropriate I think.
This is Bow Jackson's page. One of THE BEST personal pages around with more links than you can shake a bent stick at!
It also has THE BEST Arrow Calculators around. Plug in your info and get all the info you'll ever need!
To view links or images in this forum your post count must be 1 or greater. You currently have 0 posts.
Enjoy! "Tejas Raz"
Kinetic energy is currently recognized as the standard measure of the amount of penetration ability your arrow possesses. I'm sure you've read about minimum recommended energy levels for hunting different types of game, or for using mechanical broadheads. In this column I'll show you how to determine your kinetic energy with or without traditional measuring instruments.
Your arrow's kinetic energy can also help you determine your bow's efficiency. Efficiency is defined as kinetic energy of the arrow just after it leaves the bow divided by the potential energy that went into drawing it, multiplied by 100. In other words, it is the ratio of energy out vs. energy in. As you can see, efficiency relates to arrow speed directly. Since speed is a primary goal of most of the bows on the market today, it pays to understand the role of efficiency in bow performance. But first, kinetic energy.
As the arrow leaves the string there is still plenty of energy contained in the limbs and the string. This energy creates vibration and noise. A bow with a high efficiency has less energy in the bow after the arrow is gone.
DETERMINING KINETIC ENERGY
To determine your arrow's kinetic energy you need to know two things: the arrow's weight and the arrow's speed. Weight is most accurately attained with a grain scale, while a chronograph is used to accurately measure speed. Unfortunately, not every bowhunter has access to these instruments. Here are some tips for calculating weight and speed without expensive equipment.
Arrow weight without a grain scale: You can get very close to your finished arrow weight using the following estimates for each component and referring to your arrow company's literature to get the shaft weight:
Five inch vanes: 30 grains
Four inch vanes: 25 grains
Five inch feathers: 20 grains
Four inch feathers: 15 grains
Indexing nock systems: 20 to 30 grains*
Standard nocks: 15 grains
Aluminum inserts: 30 to 50 grains*
Composite inserts: 10 to 20 grains*
Point outsert for carbon: 15 grains
Nock outsert for carbon: 15 grains
* Weight depends on shaft size. In general, larger shaft size corresponds with a component weight on the higher end of the scale.
Arrow speed without a chronograph: You can approximate your arrow speed using the following simple table. First, shoot your bow at a target from 20 yards using your 20 yard pin. Mark the center of your group. Next, shoot from 40 yards, still using your 20 yard pin and aiming at the same point on the target as before. Mark the center of this group, and measure the distance between the two marks. Refer to the table for your arrow speed.
Approximate Arrow Speed (fps) / Spread between 20 & 40 yard groups ('')
220 28.7
240 24.2
260 20.6
280 17.7
300 15.5
320 13.6
330 12.8
Doing the calculations:
The following formula should be used to calculate your arrow's kinetic energy. Use finished arrow weight expressed in grains and arrow speed in feet per second.
KE = (arrow weight) ./. 450,800 X (arrow speed)2
Recommended standards: It has been offered by some experts that 45 ft-lb of arrow energy is a good minimum for whitetail deer, while 55 ft-lb is a proper minimum for elk and caribou. It has been further suggested by several in the broadhead business that an extra 10 ft-lb should be added to each of these minimums when mechanical broadheads are used. These, of course, are only rough guidelines. Many animals have been taken through the years, and will continue to be, with well-placed arrows carrying much less energy.
Arrows come in many sizes and weights. A heavy arrow will soak up more of the bow's potential energy on release and will thus increase the bow's efficiency rating. It will also make the bow quieter. This is why heavy arrows carry more penetration energy than lighter arrows - they soak up more energy from the bow.
_________________________________________________
To add a very helpfull link to this post would be appropriate I think.
This is Bow Jackson's page. One of THE BEST personal pages around with more links than you can shake a bent stick at!
It also has THE BEST Arrow Calculators around. Plug in your info and get all the info you'll ever need!
To view links or images in this forum your post count must be 1 or greater. You currently have 0 posts.
Enjoy! "Tejas Raz"