High Speed Movies - Archery

A typical sports archery arrow will reach 60-90m/s at the moment of being shot from the bow. The time of the take-off is therefore in the range of some 1/100s. A large amount of energy is re-distributed within the system archer/bow/arrow within this time, effecting high dynamic stresses and deformations. Especially the bending of the arrow - dubbed as the "archer's paradoxon", is important to be controlled by the archer by careful materials selection and tuning. High speed movies help us to gain more insight in the mechanics of archery.

Movie #1: Arrow shot, showing bending, 2008

Technical Data

Frame rate [fps]	600
Resolution [px x px]	432 x 192 (rotated)
Viewing duration [mm:ss]	00:05
Realtime duration [s]	0.25
Filesize [kB]	546

Download Quicktime Movie "CIMG5593_Abschuss_Pfeilflug_HS600.mov"
Please respect the copyright of the author!

Story/Action

Archer: Frederik Arbeiter
Camera: Annette Preuss

As soon as the archer releases the tension in his fingers, the force of the bow will start to release the string and accelerate the arrow. In our movie, this takes 6 frames equal to 0.01 seconds. The inertia of the fingers pushes the string and the tail of the arrow to the left (=away from the bow). At the same time, the string - no longer counteracted by the archer's hand, transmits the force of the bow limbs to the tail of the arrow. Due to the elasticity of the arrow shaft, and the weight concentration in the arrow head, the arrow is now bent (imagine the arrow being a spring with a force acting on it at one end in a skew angle - rule: the heavier the head, and the weaker the shaft, the higher is the bending), and at the same time accelerated forward.. It can be seen, that the bending of the arrow is inverted just in time to avoid collision with the riser. This is the secret of the so called archer's paradoxon - being not all too paradox at all! Once being free from the string, the arrow and vibrates with its natural frequency - similar to a tuning fork - using the elastic energy inserted into the system by the initial bending and the acceleration. It will continue to oscillate, until the internal friction in it's shaft material and the external aerodynamic friction forces have damped all the vibration energy out. Since the arrow moves quickly out of focus, this point can not be fixed in our movie. By the strong vibrations of the limbs after the shot, it can be seen that a lot of energy remained in the bow, instead of being transferred to the arrow.

The arrow shown is an Easton ACE 670, length ~70cm, point weight 100grs., being shot from a 68" limbs 38lbs. The frequency of oscillation determined by frame counting in this movie is approximately 86Hz .

Movie #2: Arrow in flight, 2008

Technical Data

Frame rate [fps]	1200
Resolution [px x px]	336 x 96
Viewing duration [mm:ss]	00:15
Realtime duration [s]	0.375
Filesize [kB]	815

Download Quicktime Movie "CIMG7093_Pfeilflug_Rotation_HS1200.mov"
Please respect the copyright of the author!

Story/Action

Archer: Frederik Arbeiter
Camera: Ulrich Kanstinger

This movie shows the shot and flight of an arrow - as the previous movie - but gives more attention to the phase after the arrow leaves the bow. Due to the high frame rate of this movie, additional to the oscillation, also the beginning of rotation of the arrow around it's own axis can be identified. While it is very difficult to actually give a number to the rotation speed (about 25 frames = 0.625 seconds are estimated to complete the first rotation), it can be seen clearly how the spinning accelerates very quickly. Additional to the action of the arrow, the torsional vibration of the aiming sight following the shot can be seen, giving an idea of the high stresses this component has to absorb - and explaining why sometimes archers have problems with breaking screws of their sights, especially if they employ a heavy sighting tunnel.

Movie #3: Vibrations of the bow and attached equipment, 2008

Technical Data

Frame rate [fps]	600
Resolution [px x px]	432 x 192
Viewing duration [mm:ss]	00:06
Realtime duration [s]	0.3
Filesize [kB]	770

Download Quicktime Movie "CIMG7116_Stabi_Vibrationen_HS600.mov"
Please respect the copyright of the author!

Story/Action

Archer: Frederik Arbeiter
Camera: Ulrich Kanstinger

An arrow is shot at short range on a target. The string, as well as the stabilization rod, both show beating consisting of low and high frequencies simultanously.

Movie #4: Arrow impact on the target, 2008

Technical Data

Frame rate [fps]	1200
Resolution [px x px]	336 x 96
Viewing duration [mm:ss]	00:16
Realtime duration [s]	0.4
Filesize [kB]	781

Download Quicktime Movie "CIMG1845_Pfeil_in_Scheibe_HS1200.mov"
Please respect the copyright of the author!

Story/Action

Archer: unknown
Camera: Frederik Arbeiter

An arrow, shot from 30m distance is approaching the target. This arrow's oscillations (see above movies) are already damped, but the arrow can be seen rotating along its long axis. On impact, seemingly the arrow shaft penetrating the straw is "gripped" by the straw and forced into another angle. Probably it aligns in the direction where it experiences the least resistance against penetrating the target, e.g. the direction of the compressed straw fibers, or the remaining impact channel of a previously shot arrow. This application of bending moment at the fromnt of the arrow induces an S-shaped bending mode. This mode is superimposed by the primary mode of oscillation, a pendulum- like movement of the tail. The magnitude of the arrow bending is unusually high in this movie. In typical impact situations, approximately a third of the amplitude was observed.

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