Chrono scores

Timid Toad

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If you want to do that you'd have to use an extreme overweight arrow for all limbs to avoid screwing up the high energy limbs versus the inefficient ones. Then calculate back. You'll also have to work out how to avoid arrow contact with the riser through over stiffness as well as weakness. That'll give false readings.
Lots of people have tried to use a standard arrow and string and ended up with spurious results through it being the wrong spine for a fast limb or having fletching contact with the riser despite being machine-shot.
Some manufacturers do publish their draw force curves and they make interesting reading. Worth hunting them out if you can.
 

4d4m

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There's no point in fletching the shafts as the velocity would be measured at a very small distance beyond release from string. There would be no time for the arrow to stabilise, which leads on to my point below.

Arrow contact with the riser will certainly mess up tuning results and potentially accuracy but will it have a great effect on the velocity recorded?

I'm dubious it would actually scrub off more than a couple of fps at most. However what always I suspect when spurious results from chronos are mentioned is bad readings. Chronos are pernickety instruments and a large source of error with them is "the wrong thing" tripping the sensors. Obviously to accurately measure a projectile's velocity you need to clock its tip passing both sensors. With an arrow there's quite a high likelihood of the shaft rather than the point tripping one or both sensors, especially if the arrow comes off the string at an angle, or the chrono sensors are lined up with the arrow on the rest, but it comes off the rest during its power stroke. Which most of them do by my understanding.
 

4d4m

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I think the key criteria are efficiency and potential input energy. If you're comparing 2 limb sets which have the same draw weight and similar draw force curves, all things being equal, the winner will be the one with highest efficiency. If comparing 2 with the same efficiency then the winner will be the one with the better draw force curve (ie holds the most energy at full draw)
 

Timid Toad

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There's no point in fletching the shafts as the velocity would be measured at a very small distance beyond release from string. There would be no time for the arrow to stabilise, which leads on to my point below.

Arrow contact with the riser will certainly mess up tuning results and potentially accuracy but will it have a great effect on the velocity recorded?

I'm dubious it would actually scrub off more than a couple of fps at most. However what always I suspect when spurious results from chronos are mentioned is bad readings. Chronos are pernickety instruments and a large source of error with them is "the wrong thing" tripping the sensors. Obviously to accurately measure a projectile's velocity you need to clock its tip passing both sensors. With an arrow there's quite a high likelihood of the shaft rather than the point tripping one or both sensors, especially if the arrow comes off the string at an angle, or the chrono sensors are lined up with the arrow on the rest, but it comes off the rest during its power stroke. Which most of them do by my understanding.

From my own personal testing I can prove contact costs speed, yes.
 

KidCurry

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As an engineer I would not use a riser but build a frame/jig to hold the limbs ILF and Formula. As there is no reason the frame needs a central riser, just a support for the arrow, there would never be any contact, just a precise jig for testing each set of limbs then arrow spine becomes redundant, and a mechanical release to remove release variation.
 

Timid Toad

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How much, and was that shaft contact or fletch, with riser or rest?
Depends on shafts/limb mismatch but between 2fps and 20fps. I suspect it could well be worse than that. Level/position of contact also depends on mismatch.
 

Rik

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If you want to do that you'd have to use an extreme overweight arrow for all limbs to avoid screwing up the high energy limbs versus the inefficient ones. Then calculate back. You'll also have to work out how to avoid arrow contact with the riser through over stiffness as well as weakness. That'll give false readings.
Lots of people have tried to use a standard arrow and string and ended up with spurious results through it being the wrong spine for a fast limb or having fletching contact with the riser despite being machine-shot.
Some manufacturers do publish their draw force curves and they make interesting reading. Worth hunting them out if you can.
Don't use an arrow. Just a reference weight. Basically make the bow into a catapult. Couple that with a shoot through riser, maybe.
 

Timid Toad

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As an engineer I would not use a riser but build a frame/jig to hold the limbs ILF and Formula. As there is no reason the frame needs a central riser, just a support for the arrow, there would never be any contact, just a precise jig for testing each set of limbs then arrow spine becomes redundant, and a mechanical release to remove release variation.
Assuming you know which limbs have built in or neutral tiller, and can adjust accordingly?
 

Timid Toad

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Don't use an arrow. Just a reference weight. Basically make the bow into a catapult. Couple that with a shoot through riser, maybe.
Trouble with that is is still doesn't tell the OP which limbs reach 80yds etc.

And don't forget to take into account eye-chin distance for sights.

And then I would work out a factor to compensate against the shooting machine and a bit of well-worn cordovan.
 

Rik

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Trouble with that is is still doesn't tell the OP which limbs reach 80yds etc.
Yes... But nothing will do that, except shooting a pair of limbs. Too many variables...

It's kind of like the "what arrows do I need for whitetail?" question you used to see all the time on usenet.
 

Whitehart

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Trouble with that is is still doesn't tell the OP which limbs reach 80yds etc.

And don't forget to take into account eye-chin distance for sights.

And then I would work out a factor to compensate against the shooting machine and a bit of well-worn cordovan.
All very valid points.

The issue is not will a limb reach 80 yards, but can I get a sight mark on the gold with my ability and technique.

The trend (driven by lower profit margins) for dealers to forego proper shooting facilities and stock levels in favour of internet turnover, resulting in archers being short changed by reducing the number of shops with facilities for archers to try equipment under the guidance of experienced shop staff. Furthering the trend for misinformation with archers to have to seek self help from anonymous reviews and assumptions is detrimental to archers getting the most out of their equipment. But that is what we have, when price and colour seems to be the major driving factors in equipment selection.

Many archers struggle to shoot the longer distances accurately because of form issues (the most common not tilting at the waist) and a poor set up. If Denise Parker can win Bronze at the Olympics with a reported 28lb on her fingers then people should be thinking in different directions.

It is very hard and time consuming to evaluate equipment and do real comparisons to validate manufactures claims (none of this "out of the box" rubbish we get today) - so far I have spent 2 weeks evaluating why there is no loss of arrow speed/kinetic energy, stored energy and even sight marks arrow spine and button spring tension are the same shooting an uukha 72" bow compared to my uukha 70" bow using the same limbs - where the only variable being the longer riser - results that go against all current thinking. But my real interest at the end of the day and the time consuming bit are not the numbers, but are my groups smaller and scores higher, that involves a lot of shooting even on less than perfect days like yesterday all the numbers are just that numbers.
 

Rik

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Looking at things from a slightly different angle...
Basic trajectory calculations suggest that it takes a velocity change of about 9 or 10 fps to drop a projectile off the bottom of the boss at 70m. That's not outside the range of possibility for two pairs of limbs of the same measured weight, but it sounds quite extreme... Call it a 5% difference in performance.
 

geoffretired

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Rik, I think that is a good place to start, as regards solving an archer's inability to reach a distance.( assuming it isn't simple bad form)
The next stage would be to know the speed of current arrows and choose limbs that are 10fps faster. Perhaps Bolerus had something like that in mind when he started this thread.
Without the data Bolerus is wanting to collect and sort out, is there a quicker way that might be accurate enough? Is there a rough guide, related to draw weight, that could be used to calculate the increase in poundage needed? Or something along the lines of.... if you can just reach 80y you need an extra XX pounds to reach 100y.
 

Whitehart

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Rik, I think that is a good place to start, as regards solving an archer's inability to reach a distance.( assuming it isn't simple bad form)
The next stage would be to know the speed of current arrows and choose limbs that are 10fps faster. Perhaps Bolerus had something like that in mind when he started this thread.
Without the data Bolerus is wanting to collect and sort out, is there a quicker way that might be accurate enough? Is there a rough guide, related to draw weight, that could be used to calculate the increase in poundage needed? Or something along the lines of.... if you can just reach 80y you need an extra XX pounds to reach 100y.
The difference between 80yards and 100yards could just be FOC of arrows along with type of arrow, weight of arrow and correct spine. Don't forget draw length and with some limb designs and construction bow length really is important.

There was a video where some guy was comparing top of the range Win Win with WNS all he did was plonk the limbs in the bow shoot both and then claim the WNS were 10fps slower without us ever seeing that he had a chrono. The cynic in me suggests he wanted to sell the more expensive limbs.
 

geoffretired

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Hi Andrew, thanks for that.
So, adding what you say to the mix.
The archer reached 80 but not 100y so the experienced archer suggests. Lighter arrows( unless the ones in use already are as light as possible) and that should include well matched lighter arrows.
Don't forget draw length and with some limb designs and construction bow length really is important.
I was thinking of the same archer using the same draw length with faster limbs. Faster limbs could include shorter or heavier,yes?
I was also thinking as a rough guide 2lbs extra or even 4lb.
I feel it needs to be a simple piece of advice; or simple options.
 

Whitehart

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Hi Andrew, thanks for that.
So, adding what you say to the mix.
The archer reached 80 but not 100y so the experienced archer suggests. Lighter arrows( unless the ones in use already are as light as possible) and that should include well matched lighter arrows.

I was thinking of the same archer using the same draw length with faster limbs. Faster limbs could include shorter or heavier,yes?
I was also thinking as a rough guide 2lbs extra or even 4lb.
I feel it needs to be a simple piece of advice; or simple options.
That's the issue it is not simple and just down to equipment - an extra 2lb could mean new arrows which will be heavier you could end up with more weight and worse sight marks and if you can't handle the extra weight you just miss faster.

Everyone is different and should be treated as such.

Shoot 80 yards with your mouth closed and then shoot 80 yards with your mouth open - mouth open and your arrows will go high, like wise elbow low and high. It could be that you are just not putting your draw hand under the jaw bone but half way up the face. Those that actually have an extreme side anchor think they are pulling the bow back further but in terms of eye to hand distance it is reduced resulting in a worse sight mark.

All these things and more are why some have no problems with sight marks at longer distances compared to others despite all the numbers Draw weight arrow length etc being the same.

This is why IMO a database of speeds requires all these caveats or overtime it will become part of the folklore of archery short cuts.

Archer and equipment form the solution not one or the other in isolation.
 

4d4m

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Depends on shafts/limb mismatch but between 2fps and 20fps. I suspect it could well be worse than that. Level/position of contact also depends on mismatch.
But you said:

From my own personal testing I can prove contact costs speed, yes.
Which suggests you have empirical data. So was it 2fps or 20fps?

20 fps is a pretty big loss of energy. It is approx 6 ft.lbs which is the muzzle energy of air rifles used for 10M olympic target shooting and the legal limit for air pistols in the UK. Based on arrow velocity of 200 fps and mass of 350 grains (31 ft.lbs) dropping to 180 fps with same arrow (25 ft.lbs). That is quite a whack which could chip paint and possibly crack or even snap the shaft.

Assuming you know which limbs have built in or neutral tiller, and can adjust accordingly?
Probably irrelevant for this sort of testing. Built in tiller is where one limb has slightly less resistance than the other, to compensate for the draw force acting asymmetrically on the limbs. I can never remember whether it's the top or bottom but it doesn't matter for these purposes. In this case the limbs are tested as a pair so the force is distributed over both. Evenly or unevenly, it's the same total. It would be quite possible to allow the test rig to pivot so the force was evenly distributed.

One point from earlier is it shouldn't be an extreme overweight arrow, as that would flatter less efficient limbs and not allow more efficient ones to shine. Heavier limbs and tips reach a lower max speed and soak up more of the available kinetic energy. The arrow weights used should be within the range of real world arrows as this is what the limbs are designed to propel. This is why I proposed a light, medium and heavy reference arrow.
 

4d4m

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The point is the experimental test rig doesn't answer whether X limbs will allow an archer to reach 80 yards with a sightmark. It just gives a comparison figure of velocity with reference equipment. I'm proposing that energy storage capacity and energy efficiency are the key criteria that it boils down to when removing as many variables as possible. These are empirically measurable and should be a good comparator.

If I have some limbs that can store 50 joules (36 ft.lbs) of energy at my draw length and are say 80% efficient, I have a theoretical maximum energy of 40 joules (29.5 ft.lbs) which would be 194 fps with my 350 grain arrows. Real world will be different, almost certainly lower due to other inefficiencies. So maybe I get 180 fps with these limbs and can't quite get a sightmark at 80yds.

If I'm considering some limbs with a similar DFC, that also store 50 joules at my draw length, but give an efficiency rating of 85% on the test rig, that's a theoretical max of 42.5 joules (31.3 ft.lbs) which would be a theoretical arrow speed of 201 fps. So I might reasonably expect faster real world arrow speed from the new limbs, and perhaps the same losses apply proportionally to the energy and lead me to expect an arrow speed on the new limbs of 184 fps. So those limbs would be good candidates to try in a shop with access to a chrono.

This model could of course be refined by feeding real world results back. It would be interesting to see if a predictable relationship between the real world and theoretical results might be derived. A percentage factor an archer could apply to theoretical figures to get an estimate.
 

Timid Toad

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Both, depending how badly the mismatch between limbs and shafts, as I stated. The shafts giving the hardest hits - enough to break nocks - lose the most speed. You'll really hear that. Shredded plastifletch lose less, shredded spinwings and no other signs (like nothing to be seen in a powder test) lose 2fps. I've done a lot of testing. There is no one answer. And as I've always shot off my fingers, there is individual variation shot to shot too. Minor, but it's there.
 
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