![Compound Bow full](https://upload.wikimedia.org/wikipedia/commons/5/59/Compound_Bow_full.jpg)
In modern
archery
Archery is the sport, practice, or skill of using a bow to shoot arrows.Paterson ''Encyclopaedia of Archery'' p. 17 The word comes from the Latin ''arcus'', meaning bow. Historically, archery has been used for hunting and combat. In m ...
, a compound bow is a
bow that uses a levering system, usually of cables and
pulley
A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that ...
s, to bend the limbs.
In general, compound bows are widely used in target practice and hunting.
The pulley/cam system grants the user a
mechanical advantage
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. The device trades off input forces against movement to obtain a desired amplification in the output force. The model for t ...
, and so the limbs of a compound bow are much stiffer than those of a
recurve bow
In archery, a recurve bow is one of the main shapes a bow can take, with limbs that curve away from the archer when unstrung. A recurve bow stores more energy and delivers energy more efficiently than the equivalent straight-limbed bow, giving a ...
or
longbow
A longbow (known as warbow in its time, in contrast to a hunting bow) is a type of tall bow that makes a fairly long draw possible. A longbow is not significantly recurved. Its limbs are relatively narrow and are circular or D-shaped in cross ...
. This rigidity makes the compound bow more energy-efficient than other bows, as less energy is dissipated in limb movement. The higher-rigidity, higher-technology construction also improves accuracy by reducing the bow's sensitivity to changes in temperature and humidity.
The pulley/cam system also confers a benefit called "let-off." As the string is drawn back, the cams rotate. The cams are
eccentric
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-center, in geometry
* Eccentricity (graph theory) of a v ...
rather than round, and so their effective radius changes as they rotate. Each of a compound bow's two cams features two tracks: an inner track which connects to the opposite limb or opposite cam through cables, and an outer track through which the bowstring runs. As the bow is drawn, the ratio of bowstring pay-out and cable take-up relative to limb-weight and leverage of the cams changes. By manipulation of the shapes of these cam tracks, different draw-stroke profiles can be created. A compound bow can be soft-drawing with a slow build-up to peak weight and a gradual let-off with a long "valley" at the end. It can also be hard-drawing with a very fast build-up to peak draw-weight, a long plateau where weight is maintained, and a quick let-off with a short valley. The let-off itself is the result of the cam profiles having passed center and approaching a condition very similar to a cam-lock. In some compound bows, if the draw-stops or draw-length modules are removed, they will self-lock at full draw and require professional equipment to unlock safely. Many compound bows offer 70–85% let off once they are pulled to full draw. This allows the shooter to relax and concentrate on the intended target at which they are shooting.
The compound bow was first developed in 1966 by
Holless Wilbur Allen Holless Wilbur Allen (July 12, 1909 Stilwell, Kansas – June 28, 1979 Billings, Missouri) was the inventor of the compound bow.
Allen revolutionized the archery industry worldwide with the invention and patent of the compound bow in the 1960s.
In ...
in
North Kansas City, Missouri
North Kansas City is a city in Clay County, Missouri, United States. It is also enclaved in Kansas City. Even though the name is similar to its larger counterpart, Kansas City, it is an independent municipality part of the Kansas City metropolit ...
, and a US patent was granted in 1969. The compound bow has become increasingly popular. In the United States, the compound is the dominant form of bow.
In literature of the early 20th century, before the invention of compound bows,
composite bow
A composite bow is a traditional bow made from horn, wood, and sinew laminated together, a form of laminated bow. The horn is on the belly, facing the archer, and sinew on the outer side of a wooden core. When the bow is drawn, the sinew (stret ...
s were described as "compound". This usage is now outdated.
Construction
A bow's central mount for other components such as the limbs, sights, stabilizers and quivers is called the riser. Risers are designed to be as rigid as possible. The central riser of a compound bow is usually made of
aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
,
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
alloy, or
carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
and many are made of
7075 aluminum alloy
7075 aluminium alloy (AA7075) is an aluminium alloy with zinc as the primary alloying element. It has excellent mechanical properties and exhibits good ductility, high strength, toughness, and good resistance to fatigue. It is more susceptible to ...
.
Limbs are made of fiberglass-based
composite material
A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...
s and are capable of taking high tensile and compressive forces. The limbs store all the energy of the bow – no energy is stored in the pulleys and cables. Draw weights of adult compound bows generally fall between , enabling arrow speeds of .
In the most common configuration, there is a
cam
Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bind ...
or
wheel
A wheel is a circular component that is intended to rotate on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machines. Wheels, in conjunction wi ...
at the end of each limb. The shape of the cam may vary somewhat between different bow designs. There are several different concepts of using the cams to store energy in the limbs, and these all fall under a category called bow eccentrics. The four most common types of bow eccentrics are Single Cam, Hybrid Cam, Dual Cam and
Binary Cam The binary cam is a design for the pulley system of a compound bow. Craig Yehle, director of research and development at Bowtech Archery, received a patent for the design on December 11, 2007. Bowtech started equipping its bows with the new cam de ...
. However, there are also other less common designs, like the Quad Cam and Hinged. Cams are often described using their "let-off" rating. As a cam is rotated, the force required to hold the bow in position reaches a peak and then decreases as the bow approaches maximum extension (a position known as "the wall"). The percent-difference between the maximum force encountered during the draw and the force required to hold the bow in full extension is the "let-off". This value is commonly between 65% and 80% of the peak weight for recently designed compound bows, although some older compound bows provided a let-off of only 50% and some recent designs achieve let-offs in excess of 90%.
The photo on the right shows the axle attaching the limb to cam is mounted at the edge of the cam as opposed to the center. As the string is drawn the cam turns and imparts force to compress the limb. Initially, the archer has the 'short' side of the cam, with the leverage being a mechanical disadvantage. High energy input is therefore required. When near full draw is reached, the cam has turned to its full extent, the archer has gained mechanical advantage, and the least amount of force needs to be applied to the string to keep the limbs bent. This is known as "let off". The lower holding weight enables the archer to maintain the bow fully drawn and take more time to aim. This let-off enables the archer to accurately shoot a compound bow with a much higher peak draw weight than other bows (see below).
However, there are some youth-oriented compound bows with low draw weights that have no let-off and have a maximum draw length deliberately set farther than the majority of young shooters would reach. This effectively makes the bow function very similar to a recurve, with the draw length determined by the shooter's preferred anchor point. This removes the necessity to adjust the bow draw length or use a different bow for different shooters (or to change bows as the shooter gets older). An example of this type of bow is the Genesis, which is standard equipment in the U.S.
National Archery in the Schools Program.
Compound
bow string
A bowstring joins the two ends of the bow stave and launches the arrow. Desirable properties include light weight, strength, resistance to abrasion, and resistance to water. Mass has most effect at the center of the string; of extra mass in th ...
s and cables are normally made of
high-modulus polyethylene and are designed to have great tensile strength and minimal stretchability, so that the bow transfers its energy to the arrow as efficiently and durably as possible. In earlier models of compound bows, the cables were often made of plastic-coated steel.
Comparison to other bow types
Technical advantages
* The function of the cam systems (known as the 'eccentrics') is to maximize the energy storage throughout the draw cycle and provide let-off at the end of the cycle (less holding weight at full draw). A traditional recurve bow has a very linear draw weight curve - meaning that as the bow is drawn back, the draw force becomes heavier with each inch of draw (and most difficult at full draw). Therefore, little energy is stored in the first half of the draw, and much more energy at the end where the draw weight is heaviest. The compound bow operates with a different weight profile, reaching its peak weight within the first few inches of the draw, and remaining more flat and constant until the end of the cycle where the cams "let-off" and allow a reduced holding weight. This manipulation of the peak weight throughout the draw (accomplished by the elliptical shape of the cams that change leverage and mechanical advantage) is why compound bows store more energy and shoot faster than an equivalent peak weight
recurve bow
In archery, a recurve bow is one of the main shapes a bow can take, with limbs that curve away from the archer when unstrung. A recurve bow stores more energy and delivers energy more efficiently than the equivalent straight-limbed bow, giving a ...
or
longbow
A longbow (known as warbow in its time, in contrast to a hunting bow) is a type of tall bow that makes a fairly long draw possible. A longbow is not significantly recurved. Its limbs are relatively narrow and are circular or D-shaped in cross ...
.
*The design of the cams directly controls the acceleration of the arrow. What is termed a "soft cam" will accelerate the arrow more gently than a "harder" cam. Novice archers will typically shoot a soft cam whereas a more advanced archer may choose to use a harder cam to gain speed. Bows can be had with a variety of cams, in a full spectrum from soft to hard.
*Some pulley systems use a single cam at the bottom of the bow and a round idler wheel at the top of the bow instead of two identical cams. This design eliminates the need for a separate control cable and instead uses a single long string that begins at the cam on the bottom of the bow, travels over the wheel on top, and back to the bottom cam. A separate buss cable then connects the bottom cam to the top limb.
*When a compound bow is drawn, the limbs are pulled in toward each other by the cables, unlike a longbow or recurve where the limbs flex in the direction of the bow string. This difference allows modern compounds to have limbs that are closer to horizontal instead of angled. The horizontal, or "parallel" limb configuration minimizes the recoil and vibration felt by the shooter when the arrow is released, as the forces going upward at the top limb and downward at the bottom limb cancel each other out.
*The pulley system will usually include some rubber-covered blocks that act as draw-stops. These provide a solid "wall" that the archer can draw against. These draw stops can be adjusted to suit the archer's optimum draw-length, which helps the archer achieve a consistent anchor point and a consistent amount of force imparted to the arrow on every shot, further increasing accuracy.
Technical disadvantages
* A relatively larger number of moving parts requires additional maintenance and creates more points of failure.
*
Dry firing
Dry firing is the practice of simulating the discharge of a firearm without any live ammunition, or practicing with an inert laser/infrared training platform and may also include the use of a target/feedback system. The terms also commonly re ...
is more likely to damage or destroy a compound bow due to the greater amount of energy stored and released.
* Unlike traditional bows, replacing the string or cables or making adjustments to let-off or draw length often require a bow press, a specialized tool used for compressing the limbs, taking tension off the cables and string.
*Drawing a compound bow with the fingers increases the likelihood of torquing the bowstring, and thus derailing the string from the cams. Thus often requiring the use of a mechanical release-aid.
*Usually heavier than recurves and longbows.
Circumstantial advantages
* Compound archers often use a mechanical release aid to hold and release the string. This attaches to the bowstring near the point where the arrow attaches, the nocking point, and permits the archer to release the string with a squeeze of a trigger or a slight increase of tension. The use of a release aid gives a more consistent release than the use of fingers on the string as it minimises the arrow oscillation which is inevitable when the bowstring is released directly from the fingers.
* In tournaments, competition rules for compound archers allow bows with a sighting system, consisting of a "
peep sight
Iron sights are a system of physical alignment markers (usually made of metallic material) used as a sighting device to assist the accurate aiming of ranged weapons (such as a firearm, airgun, crossbow or even compound bow), or less commonly ...
" held within the bowstring that acts as a back sight, however front sights attached to the riser are allowable in other classes. Some front sights are magnifying and/or adjustable for targets at different distances. Some sights have multiple "pins" set up for targets at different distances.
Circumstantial disadvantages
*The relatively low holding weight of a compound bow compared to a recurve bow makes the compound more sensitive to certain shooting form faults when the archer is at full draw. In particular, it's easier for the archer to torque (twist) the bow around the vertical axis, leading to left-right errors, and also a plucked or snatched release can have more effect.
Specifications
AMO (Archery Manufacturers and merchants Organization) standard draw length is the distance from the string at full draw to the lowest point on the grip plus . Because the draw force may increase more or less rapidly, and again drop off more or less rapidly when approaching peak draw, bows of the same peak draw force can store different amounts of energy. Norbert Mullaney has defined the ratio of stored energy to peak draw force (S.E./P.D.F.). This is usually around but can reach .
The efficiency of bows also varies. Normally between 70–85% of the stored energy is transferred to the arrow. This stored energy is referred to as
potential energy
In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors.
Common types of potential energy include the gravitational potentia ...
. When transferred to the arrow it is referred to as
kinetic energy
In physics, the kinetic energy of an object is the energy that it possesses due to its motion.
It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its accele ...
. The product of S.E./P.D.F. and efficiency can be called th
power factor There are two measurement standards of this quantity – AMO and IBO speed. AMO is defined as the initial velocity of a arrow when shot from a bow with a peak draw weight of and draw length . IBO speed is defined as the initial velocity of an arrow with a weight of per pound of draw weight. Most manufacturers measure IBO speeds using a draw weight of and draw length of .
Brace height is the distance from the pivot point of the grip to the string at rest. Typically a shorter brace height will result in an increased power stroke, but comes at the price of a bow that's less forgiving to shooter error and having harsher string slap.
Arrows used
Arrows used with compound bows do not differ significantly from those used with recurve bows, being typically either
aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
alloy,
carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
, or a composite of the two materials. Wooden arrows are not commonly used on compound bows because of their fragility. Most arrows in use today are of the carbon fiber variety. An important distinction arrow-wise between recurve bows and compound bows is that of arrow spine. Compound bows and target recurve bows with fully center-shot cutaway risers tend to be very forgiving in regard to spine selection. Modern compound bows are typically equipped with substantially stiffer arrows than an equivalent draw-length and draw-weight recurve bow would be. Another advantage of the center-shot riser is that the arrow need not bend around the riser (nearly as much or at all) during the shot. Fine-tuning may be accomplished by adjustment of the arrow rest, or nock point on the string, rather than by changing arrow-length and tip weight.
Manufacturers produce arrow shafts with different weights, different spines (stiffness), and different lengths in the same model of shaft to accommodate different draw weights and lengths, matched to archers' different styles, preferences and physical attributes.
Arrow stiffness (spine) is an important parameter in finding arrows that will shoot accurately from any particular bow (see
Archer's paradox
The archer's paradox is the phenomenon of an arrow traveling in the direction it is pointed at full Bow draw, draw, when it seems that the arrow would have to pass through the starting position it was in before being drawn, where it was pointe ...
), the spine varying with both the construction and length of the arrow.
Another important consideration is that the IBO (International Bowhunter Organization) recommends at least of draw weight as a safety buffer. This means a bow that draws would need at least a finished-with-tip arrow. Shooting arrows lighter than this guideline risks damage to the bow similar to that caused by dry-firing, which can in turn cause injury to the archer or anyone standing nearby. Shooting arrows that are too light also voids most manufacturer warranties.
See also
*
Bow shape
In archery, the shape of the bow is usually taken to be the view from the side. It is the product of the complex relationship of material stresses, designed by a bowyer. This shape, viewing the limbs, is designed to take into account the cons ...
*
Bow (weapon)
The bow and arrow is a ranged weapon system consisting of an elasticity (physics), elastic launching device (bow) and long-shafted projectiles (arrows). Humans used bows and arrows for hunting and aggression long before recorded history, and the ...
*
Binary cam The binary cam is a design for the pulley system of a compound bow. Craig Yehle, director of research and development at Bowtech Archery, received a patent for the design on December 11, 2007. Bowtech started equipping its bows with the new cam de ...
*
Crossbow
A crossbow is a ranged weapon using an elastic launching device consisting of a bow-like assembly called a ''prod'', mounted horizontally on a main frame called a ''tiller'', which is hand-held in a similar fashion to the stock of a long fi ...
*
English longbow
The English longbow was a powerful medieval type of bow, about long. While it is debated whether it originated in England or in Wales from the Welsh bow, by the 14th century the longbow was being used by both the English and the Welsh as a ...
*
Flatbow
A flatbow is a bow with non- recurved, flat, relatively wide limbs that are approximately rectangular in cross-section. Because the limbs are relatively wide, flatbows will usually narrow and become deeper at the handle, with a rounded, non-bend ...
*
Horse archer
A horse archer is a cavalryman armed with a bow and able to shoot while riding from horseback. Archery has occasionally been used from the backs of other riding animals. In large open areas, it was a highly successful technique for hunting, f ...
*
Yumi
is the Japanese term for a bow. As used in English, refers more specifically to traditional Japanese asymmetrical bows, and includes the longer and the shorter used in the practice of and , or Japanese archery.
The was an important weap ...
Construction techniques
*
Self bow
A self bow or simple bow is a bow made from a single piece of wood. Extra material such as horn nocks on the ends, or built-up handles, would normally be accepted as part of a self bow. Some modern authorities would also accept a bow spliced toge ...
*
Cable-backed bow
A cable-backed bow is a bow reinforced with a cable on the back. The cable is made from either animal, vegetable or synthetic fibers and is tightened to increase the strength of the bow. A cable will relieve tension stress from the back of the ...
*
Laminated bow
A laminated bow is an archery bow in which different materials are laminated together to form the bow stave itself. Traditional composite bows are normally not included, although their construction with horn, wood, and sinew might bring them withi ...
*
Composite bow
A composite bow is a traditional bow made from horn, wood, and sinew laminated together, a form of laminated bow. The horn is on the belly, facing the archer, and sinew on the outer side of a wooden core. When the bow is drawn, the sinew (stret ...
References
;General references
* (1992) ''The Traditional Bowyers Bible Volume 1''. The Lyons Press.
* (1992) ''The Traditional Bowyers Bible Volume 2''. The Lyons Press.
* (1994) ''The Traditional Bowyers Bible Volume 3''. The Lyons Press.
External links
Extensive article on the compound bow ''Twenty-five years after Allen's patent of December 1969.''
{{Authority control
Bows (archery)