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Thread: Chrono scores

  1. #37
    It's an X Whitehart's Avatar
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    Quote Originally Posted by geoffretired View Post
    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.

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  3. #38
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    Quote Originally Posted by Timid Toad View Post
    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:

    Quote Originally Posted by Timid Toad View Post
    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.

    Quote Originally Posted by Timid Toad View Post
    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.

  4. #39
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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.

  5. #40
    It's an X I've taken part in an AIUK Ironman Shoot.The Fonz Award.AIUK subscriber. Timid Toad's Avatar
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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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  7. #41
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    Hi Andrew, I have not explained myself very well, I feel.
    I am not saying that the archer isn't part of the equation.
    All I am saying is that if an archer cannot reach 100y but can reach 80y, then a bit of extra speed is needed, if the archer's form is ignored, or considered sound enough.
    I understand that faster limbs may need stiffer arrows and that they may be heavier. But the experienced archer who helps the one with the issue, will take that into account.
    I also understand that the mouth open/closed has an effect, BUT one archer with a problem can be helped with that and then the advice can be given about reaching 100y.
    There are different reasons why some archers cannot reach 100y but if the reason is just that the arrows are travelling too slowly, and nothing else, then faster limbs, with arrows to match, is one solution.

  8. #42
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    Quote Originally Posted by Timid Toad View Post
    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.
    That's interesting, I've never experienced arrow contact that hard. Using my imagined test riser, if one experienced something as extreme as broken nocks then yes one would have to disregard those measurements.

    A test rig as proposed by Rik would eliminate the possibility of contact. In fact thinking about it more, the test rig could use a regular riser, but a compound style release with a D loop and perhaps a compound drop away rest. This would minimise flex. Note this is not trying to simulate an archer shooting a recurve bow, it's trying to measure the input and output energy of the limbs.

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