The concept of compound bow

1. The source of compound bow energy: First of all, we should understand that the bow itself cannot create energy. The bow only plays a role in transferring energy. When we pull a compound bow, the limbs will bend inwards. This is the force of your bow pulling that is transferred to the limbs, and the deformation of the limbs converts the kinetic energy of your bow pulling into the potential energy of the limb deformation. When we release the bowstring, the potential energy stored in the limbs is transferred to the arrow through the displacement of the bowstring and converted into the kinetic energy of the arrow flying. This is how the energy transfer is completed. An important factor in choosing a bow is to see if the bow has "strength". In fact, it is the ability of the bow to store and release energy. There are two main meanings, one is how much energy the bow can store, and the other is how much energy can be effectively transferred to the arrow. There are three specific values ​​that can most affect the energy of the bow, namely draw weight, draw length and let-off.

2. What is IBO speed and AMO speed: This value is the first thing you see in many bow product introductions, such as IBO=305fps, etc. IBO is an industry standard for measuring the speed of arrows shot from a bow. This standard was developed by the International Bowhunting Organization, so it is called IBO speed. The IBO calculation method is the speed of a 70-pound bow with a 30-inch draw length and a 350-grain arrow. The proportional relationship of this calculation method is that each pound of draw weight pushes 5 grains of arrow weight (under the premise of not exceeding 80 pounds). In fact, the effect of draw length on speed can also have an impact. Generally, the speed will increase by 5fps for every inch of draw length. AMO speed is also an industry standard for calculating the speed of bows and arrows. This standard was developed by the Archery Manufacturers Organization, so it is called AMO speed. This calculation method was very popular in the past. The calculation method of AMO speed is: the speed of a 60-pound bow with a 30-inch draw length and a 540-grain (equal to 35.1 grams) arrow. The proportional relationship of this calculation method is that each pound of pulling force pushes 9 grains of arrow weight. This calculation method was popular in the past, but it is no longer used in current advertising.

3. Axle-to-axle: The upper and lower parts of a compound bow are made of two pulley mechanisms. The distance between the centers of these two pulleys is the axle-to-axle of the bow. The axle-to-axle reflects the size of a bow. With the continuous improvement of bow making technology, the size of bows is becoming more and more compact. Now most compound bows are basically under 36 inches in size. They are easy to carry, light and beautiful. Now bows look like they want to buy. However, too small a size will also have a certain impact on the performance of the bow. A. Bows with a wheelbase less than 32” are very compact and are the favorite of those who like to hunt in trees. They are very maneuverable and easy to carry. However, this bow also has some shortcomings, especially the short wheelbase, which makes it difficult to master the accuracy at long distances. It requires more practice and is best to use a mechanical release device. B. Bows with a wheelbase of 33”-38” have both accuracy and maneuverability. This size is the most popular and the best choice for many safari hunters. C. Bows with a wheelbase of more than 38” can bring the best accuracy and are very suitable for use in archery competitions and other occasions. The longer draw length can bring more stability and accuracy. People who use this bow can use a release device or fingers to release the arrow.

4. Brace height: Brace height refers to the distance between the main string and the lowest point of the handle support. This indicator affects both the speed and maneuverability of the bow. The average string length of a compound bow is currently 7.5". A shorter string length can increase the speed of the bow, and a longer string length can make the bow easier to control. A bow with a short string length (5"-6.5") has a larger range of pulling force, which means that the distance from the beginning of the bow to the full pull of the bow is longer, so the bow will store more energy and the arrow will be more stressed. However, such excessive energy output will make your bow more difficult to control. A bow with a longer string length (7.5"-9") is easier to control, but its shooting power will be slightly smaller. In order to have a good combination between speed and maneuverability, you should try to choose a bow with a string length between 6.5-8, so that you can basically have a better balance between speed and maneuverability.

5. Let-off ratio %): When shooting a traditional bow, the pulling force is always the same or increasing. However, due to the pulley mechanism used in modern compound bows, the pulling force will fluctuate. After the force is applied to the peak, the force will be reduced until the bow is fully drawn. Generally, modern compound bows have 1 high and 1 low effort ratio options. When you choose a high ratio, it means that you can use less force to maintain the full bow state after the bow is fully drawn. Generally, bows are defaulted to the high ratio state when they leave the factory. For example, a 70-pound bow with an 80% effort ratio, when you fully draw the bow, you only need 14 pounds of pulling force to keep the bow in the full bow state (70×(1-80%)=14). Both states have their own advantages. In the case of a high effort ratio, the user can divert his energy from drawing the bow and focus more on aiming and adjusting his posture. In the case of a low effort ratio, the bow will store more energy, and the arrow will often be shot faster.

6. Limb projection distance (limb tiller): This parameter is very important. It is an indicator to measure whether the bow is installed properly and whether the bow is normal. By measuring the projection distance of the upper and lower bows, we can understand whether the upper and lower bows are installed consistently.

7. Kinetic energy of arrow: We all know from high school physics that the kinetic energy of a moving object is determined by its mass and speed. The standard formula is: E=1/2 mv2, where E means kinetic energy, m is the mass of the object, in kilograms. V is the speed of the object, in meters per second. We can also calculate the kinetic energy of an arrow shot by a certain bow through the above formula, but considering that the imperial system is used in compound bow applications, we need to reconvert the units of the above formula. We calculate the kinetic energy of the arrow using the fps speed and the weight of the arrow using the unit of gram. After a series of conversions (I will not describe the process, if you are interested and patient, you can try to calculate this process yourself), the formula for calculating the kinetic energy of the arrow is: E= mv2/450240 where m is the weight of the arrow, in grains, and 1 grain is equal to 0.065 grams. V is the speed of the arrow, in fps, feet per second. Through an example, we can calculate the kinetic energy of an arrow shot by a bow. Let's take the Tribute from bowtech, which has the highest technical indicators, as an example to calculate how much kinetic energy the arrow shot by this bow has. Tribute is the bow with the highest pulling force at present. It can use a 100# bow piece (about 45.4 kg, which can only be pulled by a superman). At this pulling force, a 500-milligram arrow (32.5-gram arrow) is shot, and the IBO speed is 328fps (100 meters per second). How much kinetic energy can the arrow shot by Tribute have? The calculation result is as follows: E=500×3282/450240=119.5 joules. This is basically the highest kinetic energy that a bow can achieve in archery. Although it is amazing! But this cannot be compared with a gun.