“The stiffness of the limbs makes the compound bow more energy efficient than other designs”
TECHNOLOGY
The compound bow
Discover how new-and-improved technology has transformed the traditional bow and arrow into a whole new beast… The power of the compound bow comes from its construction, comprising three components: a riser and two limbs. The riser is the central part of the bow that is held and is made of aluminium alloy, or carbon fibre, for maximum strength. The limbs are bolted to the riser and are made of a more flexible composite, allowing them to bend to store energy as the bow is drawn. The stiffness of the limbs makes the compound bow much more energy efficient than other designs, with hardly any vibration. The composite construction also provides an advantage over wooden alternatives because it is much less affected by temperature and
humidity, enabling the archer to shoot accurately in varying weather conditions. However, the rigidity of the compound bow would make it incredibly hard to draw if the strings were attached directly to the limbs, so a pulley-driven levering system is used. As the string is drawn, the pulleys take in the cables, which draws the limbs of the bow together, storing energy. The system uses asymmetrical cams, so that as the string goes beyond 50-80 per cent of the draw length – towards the point at which the arrow is ready to fire – the amount of force needed to pull the string is reduced. This allows the archer to hold the bow at full draw for longer, granting steadier shooting.
Anatomy of a modern bow
Idler wheel
Some clever tweaks and additions give the compound bow a great advantage over the recurve bow or longbow
Some bows have just one cam wheel; the idler wheel ensures even draw on the string, keeping the arrow straight.
Beyond the bow… To line up distant shots, archers often use sights with fibre-optic pins – different-coloured pins are set for varying distances, allowing the archer to adjust the shot. Scopes can also be added to magnify the target and increase aiming accuracy. Instead of using their fingers to draw the string, compound bow archers often use a mechanical release. Shaped like a small pincer, the release fits into the hand and pinches the string, enabling the bow to be fired more smoothly; using a release like this makes each shot much more consistent and predictable. Reducing vibration is also important in archery, as any unwanted movement will disturb the path of the arrow. Competitive archers and hunters often attach dampeners to the bow to nullify vibrating.
Limb The limbs store the potential energy used to fire the arrow and are made of composite materials capable of withstanding great force.
Sight window Cut-out areas above the grip enable the archer to line up their shot.
Arrow rest Bow string
Cable rod
Constructed from high-modulus polyethylene, the string and cables resist stretching and possess high tensile strength.
This ensures that the vanes of the arrow do not get tangled in the cables, disrupting the flight path.
Supports and guides the arrow, absorbing any unwanted movement and granting a straight shot.
Grip A sturdy handle allows the archer to hold the bow steady even at full draw.
These magnify the force applied to the string and thus reduce the effort required to hold the bow when at full draw.
062 | How It Works
Riser The central mount for the bow’s components is made from a rigid material like aluminium alloy or carbon fibre. © Corbis
Cam wheel
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