Bowmen of Skelmersdale

Timing - When is movement important?

Having looked at which movements are possible, we need to see when they most need to be under control to identify what needs to be done to help the archer. To take a simple example, residual limb vibration is not important before the bow has been shot! To help in thinking about bow behaviour and stabilisation, I find it useful to break up the shot into three main time periods:

Before the shot

The archer is close to or at full draw, intending to achieve a steady aim. Motion of any kind is undesirable; lateral and vertical movement are particularly to be avoided. The main forces on the bow are the (approximately equal and opposite) forces exerted by the archer on string and bow hand respectively, and gravity. This period lasts a few seconds (though it may seem like hours if the clicker is mis-set!).

During the shot

The bow limbs move sharply forward, propelling the arrow out of the bow. The arrow slides past the pressure button and rest for a few inches, then moves away from the bow as the shaft flexes. As the string passes its rest position, the arrow leaves the string, and in a properly tuned bow, is unaffected by further bow movement as it’s not in contact with the bow at all. (It’s worth remembering that the only part of the bow in contact with the arrow for most of this period is the string.) The main force on the bow is the pressure of the bow hand on the grip, which starts of almost exactly equal to the draw weight of the bow. The whole movement takes about 15 milliseconds.

After the shot

The limbs stop and rebound under tension from the string, and the string and limbs continue to vibrate, along with the riser, until all the ‘loose’ energy is dispersed by assorted friction, air damping, as sound, and by transmission to parts of the archer.

Asymmetric limb vibrations may continue for some time. The archer ‘follows through’. The bow, if left free, travels forward under the continuing pressure from the bow hand. Gravity takes over and the bow falls, pivoting round the bow sling or hand to bring the bow’s centre of gravity directly below the pivot point (exactly as a dropped plumb line comes to rest below its suspension point). The bow comes to rest and stops vibrating in a second or so.

What bow behaviour needs controlling?

Bow  movement

Timing - When is movement important?

Time and Motion

Controlling bow displacement

Weight, Mass and Inertia

Static and Dynamic properties

The misnamed TFC

Controlling bow balance

Centre of Gravity

Finding the centre of gravity

Changing the balance using weight

Weights and Distances

Rods, weights and risers

Controlling bow vibration

Causes of Bow Vibration

Reducing Vibration - Damping

Bow Resonance

Tuned damping - more on TFC’s