Extension length

Extract diagram of a recurve bow in archery (qualitative). Force-displacement curve with clarification of extension length, draw weight and throwing energy as well as stacking and breaking limit.

The extension length , English length draw is the archery a standardized parameter of the arc and a personal characteristic of the archers . In general, it is the measure of how far the bowstring has just moved out of a bow and especially as a fixed quantity and term, the maximum dimension of this range at full extension (English: full draw ). The extension length is specified according to the AMO standard in the unit international customs .

The graphical representation of the course of the tensile weight over the extension length in a coordinate system is the extension diagram of the arch.

Measurement of the extension length

The extension length as a parameter is standardized today .

AMO extension length: According to the AMO standard, the measure in inches from the nocking point of the tendon to the lowest point in the bow grip, the pivot point , plus 1¾ inches.

The nock point is the point on the string to which the end of the arrow - the Nock or cam - nocked is. It is the point of power transmission from the tendon to the arrow and the furthest from the bow when it is pulled out (tendon kink). The addition of the 1 3/4 inches is a historical artefact and takes into account older practice in which the extension length from the nocking point to the leading edge of the sheet was specified. Both figures are therefore roughly comparable.

A so-called inch or dimension arrow can be used to measure the outward length . It is an excessively long arrow without a point and fletching, with a nock at the end of the arrow and a recorded inch scale , the zero point of which is the lowest point in the nock. The arrow is placed, nocked and extended like a normal arrow. A second person reads the measure at the height of the pivot point by observing it from the side. Some dimension arrows have an attached caliper in the form of a ring or clip. This means that a shooter does not need a second person to read. After placing the arrow, the slider is pushed from the front of the bow to the arrow rest , which is usually vertically above the pivot point , or to the front edge of the bow. When pulling out, the arrow rest or the edge of the bow as a stop keeps the slider in the same position as the bow and the slider moves on the arrow as you pull out. The shooter slowly releases the string and can read the pull at the slider position on the arrow. Depending on the selected stop edge, a correction dimension for the pivot point must be included.

Draw length of an archer

The extension length as a regular maximum extension of the archer, called full extension , is a personal parameter of the archer . It is dependent on his body structure, for example his arm length or shoulder width and on the posture and the anchor technique used and thus the position of the anchor point of the shooter. The anchor point refers to the contact point between the drawing hand and the face, which is always the same as possible with each full extension, usually in the jaw or corner of the mouth. The head can be tilted more or less and the tendon can be drawn more or less far or high or in the middle of or into the face.

For the shooter, a constant exit length with every shot is a central element of his sporting technique. The contact with the anchor point is a sensory control of the reaching of the extension length and the always the same position of the anchor point also ensures a constant release process and therefore the same energy transfer to the arrow every time. The extension length in conjunction with the anchor point determine the constancy of the shooting speed of the arrow and thus its ballistic curve . An archer does not shoot at different target distances by means of different draw lengths and thus different arrow speeds, but solely by tilting the upper body and thus the bow, i.e. with an adapted shooting angle. The bow to the upper body remains in the same position in order to ensure a constant force geometry with every shooting process .

Some archers use a clicker for acoustic control of their draw length , it also serves to automate the shot process through conditioning .

When a shooter says she has "forty pounds on her fingers", she means the draw weight of her bow at her personal draw length.

The measurement is carried out according to the AMO standard.

Extension length of a bow

The extension length of the bow indicates the technically optimal full extension of the bow, the bow was built for this extension length. The draw length of the bow together with its draw weight is the most important characteristic of the bow. The specification of the draw weight of a bow always refers to its extension length.

Both are usually indicated together on the belly of the bow (side facing the archer) on the lower limb near the middle section, with longbows often on the side of the middle section.

The representation is draw weight @ draw length . A typical specification would be: 46 # @ 28 ″ . Say, "Forty-six pounds by twenty-eight inches."

Because the average archer has a personal draw length of 28 ″, most standard bows are optimized for a draw length of 28 ″. The extension length of the bow corresponds to the extension length of the shooter. Built optimized says here that those last area of combined extract curve is in the vicinity of the extension length of a flat yet possible slope has and still sufficiently far from the area of the stacking distance is ( excerpt chart , lying on the fingers force versus extension length ). In flat areas of the force-pull-out curve, deviations in the pull-out length cause less force changes than in areas with a steep gradient. In a flat area, the bow is therefore more forgiving of deviations when the shooter is fully extended, for example with improper anchoring.

About a bow that has a relatively flat force-extension curve in the vicinity of its extension length, a shooter says "the bow is soft", in the opposite case he says it is a "hard bow".

With a custom bow, the archer can have his bow built by a bow maker with little technical tolerance to his personal draw length and preferred draw weight. A shooter with a draw length of 26 ″, who can handle a draw weight of 35 pounds, then has the inscription 35 # @ 26 ″ on her bow , mostly handwritten and with the signature of the bow maker.

The measurement is carried out according to the AMO standard.

Extension diagram - extension length and throw energy

The extension diagram of a bow shows its technical spring characteristic - the course of the respective holding force of the pulling hand at the respective extension length. To determine it, a measuring arrow is placed on it and the string is pulled out piece by piece with a bow balance instead of the pulling hand and the extension length is read off at a sufficient number of support points on the measuring arrow and the associated holding force on the bow balance and entered in a coordinate system. At the end the points are graphically connected to form the force-pull-out curve.

Physically, the pull-out diagram is a force-displacement diagram and thus the area under the curve is the pull-out work used by the shooter ( work = force × distance ). It corresponds to the deformation energy already stored in the bow up to the associated extension length , which it transmits to the arrow via the bowstring when loosening with a loss of efficiency. With an efficiency of 100%, the extraction work is the maximum possible kinetic energy that can be transferred to the arrow and, depending on the weight of the arrow (mass ), determines its maximum possible launch speed . ${\ displaystyle \ textstyle W_ {A}}$ ${\ displaystyle \ textstyle S}$ ${\ displaystyle \ textstyle W _ {\ text {pot}}}$ ${\ displaystyle \ textstyle \ eta}$ ${\ displaystyle \ textstyle W _ {\ text {kin}}}$ ${\ displaystyle m}$ ${\ displaystyle \ textstyle v}$

{\ displaystyle {\ text {Extract}} \ \ int _ {S_ {0}} ^ {S} F (s) \, ds \ = \ W _ {\ text {Extract}} ^ {\ text {Sagittarius}} \ = \ W _ {\ text {potential}} ^ {\ text {arch}} \ = \ {\ tfrac {1} {\ eta}} \ W _ {\ text {kinetic}} ^ {\ text {arrow}} \ = \ {\ tfrac {1} {\ eta}} \ cdot {\ frac {1} {2}} \ mv ^ {2} \ quad {\ text {Kinetic energy of the arrow}}}

{\ displaystyle {\ text {Arrow speed}} \ quad v = {\ sqrt {{\ frac {2 \ eta} {m}} \ cdot \ int _ {S_ {0}} ^ {S} F (s) \ , ds}}}

A bow is an energy converter and a power converter and therefore technically a machine. It converts the pulling work carried out relatively slowly by the shooter when pulling out via intermediate storage as deformation energy in the bow into the fast throwing energy of the limbs when firing, and the throwing energy in turn via the tendon into the kinetic energy of the even faster arrow. This conversion is all the more effective the greater the extension length, the stacking limits it.

In order to compare and assess the force curve and thus the energy storage behavior of the bow, a straight spring characteristic is often drawn in its extension diagram in such a way that it intersects the force-extension curve of the bow at the zero point and at its specified extension length.

Stacking and draw length of the archer

If the archer pulls the bow beyond its extension length, the bow will reach the stacking area . It feels increasingly "harder" - the gradient of the force-pull-out curve is increasing and the effort required for each additional pull-out unit increases rapidly. Sagittarius says, "The bow closes". A controlled power dosage, pull-out and shot are no longer possible. There is a risk of material damage or breakage. At the same time, the efficiency of the bow decreases - despite the bow's increasing energy input per pull-out unit, the arrow speed hardly changes or can even decrease. How far behind the draw length of the bow the stacking starts and how much is bow-specific and depends on the bow type and production. How good-natured the bow is when it is fired, even in the stacking area that begins, and how resistant it is there against material damage or breakage, is determined by the quality of the tillering . Long bows with a length of 70 ″, for example, tend to be softer in the area of their extension length and with more play behind them up to stacking than short bows of e.g. B. 64 ″.

Stacking is a problem for archers with above average draw length when shooting a standard bow. They shoot long bows more often. Experienced archers with a high level of consistency in their sporting technique can better master a bow in the stacking area. Less problematic is a shorter extension length of the archer than that of the bow, however the archer does not use the energetic possibilities of the bow and in the limbs less energy is stored in relation to their inert mass, the efficiency is lower. The archer can compensate for this within limits by choosing a bow with a higher draw weight.

standardization

The guideline for archery is the standardization introduced into archery for the first time in the 1950s by the Archery Manufacturers Organization , now known as the AMO standard . The organization changed its name to the Archery Trade Association in 2002 , so that the AMO standard is now also known as the ATA standard .

Individual evidence

↑ AMO Standards Committee: AMO Standards Layout ( Memento from September 6, 2015 in the Internet Archive ), p. 9, Field Publication FP-3, 2000. In: texasarchery.org . (PDF), accessed on August 28, 2016.

[1] AMO Standards Committee: AMO Standards Layout ( Memento from September 6, 2015 in the Internet Archive ), p. 9, Field Publication FP-3, 2000. In: texasarchery.org . (PDF), accessed on August 28, 2016.