Author Topic: Pyramid vs everything else  (Read 1935 times)

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Offline Badger

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Re: Pyramid vs everything else
« Reply #90 on: November 08, 2017, 03:05:05 pm »
  Energy storage and efficiency are too different but important characteristics. Many of the things that increase energy storage will also reduce efficiency.
One area that Kooi and many others from that period got wrong was efficiency losses due to hysteresis. It doesn't have to be nearly as high as they indicated, almost all of it is induced by the bowyer during construction of the bow, proper techniques can greatly reduce it.

Offline willie

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Re: Pyramid vs everything else
« Reply #91 on: November 08, 2017, 04:02:41 pm »
Badger, not trying to over simplify, but when you speak of high energy storage, is that pretty much indicated by the "fat FD curve"?

Offline Badger

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Re: Pyramid vs everything else
« Reply #92 on: November 08, 2017, 10:04:33 pm »
  Willie, yep that's what it is. Just a fat FDC.

Offline willie

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Re: Pyramid vs everything else
« Reply #93 on: November 08, 2017, 10:09:25 pm »
BTW, I have read you mention a few times about changing the way you tiller ELB's now, but I must have missed where you describe what those changes were, (or perhaps you haven't said). Have you been tillering them more elliptical?

Offline Badger

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Re: Pyramid vs everything else
« Reply #94 on: November 08, 2017, 10:31:07 pm »
  Somewhat more elliptical but I also have the outer limbs pretty stiff, just showing very slight flex.

Offline willie

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Re: Pyramid vs everything else
« Reply #95 on: November 08, 2017, 10:52:24 pm »
Thanks Steve, apparently those improvements could be considered to improve energy efficiency rather than energy storage? Not sure what you meant earlier how....
Quote
Many of the things that increase energy storage will also reduce efficiency.
Does, for instance, increasing reflex in a given design reduce efficiency or add hysteresis?

Offline Badger

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Re: Pyramid vs everything else
« Reply #96 on: November 09, 2017, 01:00:10 am »
Thanks Steve, apparently those improvements could be considered to improve energy efficiency rather than energy storage? Not sure what you meant earlier how....
Quote
Many of the things that increase energy storage will also reduce efficiency.
Does, for instance, increasing reflex in a given design reduce efficiency or add hysteresis?

  Willie, adding reflex will always increase the risk of adding set which increases hysteresis. Depending on the design it could increase efficiency. Lower string angles at brace will normally tend to boos efficiency. Reflexed bow will often also have lower string angles but not necessarily.

Offline JW_Halverson

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Re: Pyramid vs everything else
« Reply #97 on: November 09, 2017, 06:38:03 am »
Again I'm miffed,thought whe were talking about straight stave bows?kinda all over the map.

Absolutely.  Without parameters, defining better or best is impossible. I mean, would I pick a record holding flight bow to go on a river of no return Alaskan bush hunt? Would I pick an Agincourt replica longbow to sit in a tiny groundblind? Or funnier yet, carry Marc's fiberglass and plastic horse manure fantasy Penobscot abomination to an Agincourt reenactment!!!

The question, as it stands now, is only marginally more defined than just the question "what is best?"  Someone out there loves chocolate pudding more than bows, so obviously chocolate pudding is best and bows just plain suck.

That being said, there is a post doctoral graduate study level of education going on in this thread, that is the only reason I follow this thread when it seems to show up annually!  And it shows up annually, almost like clockwork.

Carry on.
Sawdust.  It's man glitter.

Offline Badger

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Re: Pyramid vs everything else
« Reply #98 on: November 09, 2017, 07:10:26 am »
    John, actually the bows I have done best with in flight were exactly the kind you would take on an Alaskan bear hunt. They are low stressed and very reliable. 5 or 6 years ago this might not have been true. I could make my tips a bit thinner but I prefer to keep them beefy enough to use for other things besides flight.

Offline joachimM

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Re: Pyramid vs everything else
« Reply #99 on: November 09, 2017, 12:50:40 pm »
Can I get a clarification about these attributes?

Energy storage = clear what it is. But more means sending a heavy arrow faster?
Energy efficiency = what? Pulling for example 100# but getting 120# in the arrow? Or is it a smoother draw?

Energy storage: the area below the force-draw curve. Actually, the area below the curve is the expended energy by the archer. A fat draw curve is convex. A bow that stacks has (near the end of the draw) a concave curve. Hence it stores less energy than expected for the draw weight.

Efficiency is how much of this energy is actually transferred upon the arrow. The arrow is not the only thing that needs to be moved, the limbs also need to return to their original position, which also requires energy. And there are energy losses within the bow, friction between wood fibers so to say. This is hysteresis. Dick Baugh explains it well here: http://www.primitiveways.com/Bow_and_Arrow_Efficiency.pdf and here http://www.primitiveways.com/Bow%20and%20Arrow%20Efficiency-2-16-11.pdf
To cut a long story short: with a 50# 28" draw and a straight force-draw curve, a 500 grain arrow could theoretically fly a touch over 200 fps, at 100% efficiency. In reality, most bows aren't 70% efficient, and shooting 170 fps is already very good.

Some designs store more energy, some are less efficient.


 
Tillering is easy. Problems arise when a bowyer thinks he's right and the wood is wrong.

Offline DC

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Re: Pyramid vs everything else
« Reply #100 on: November 09, 2017, 12:54:11 pm »
Actually, the area below the curve is the expended energy by the archer.

I'd never thought of it that way. That's a good one. :)
Vancouver Island

Offline Badger

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Re: Pyramid vs everything else
« Reply #101 on: November 09, 2017, 02:39:51 pm »
Can I get a clarification about these attributes?

Energy storage = clear what it is. But more means sending a heavy arrow faster?
Energy efficiency = what? Pulling for example 100# but getting 120# in the arrow? Or is it a smoother draw?

Energy storage: the area below the force-draw curve. Actually, the area below the curve is the expended energy by the archer. A fat draw curve is convex. A bow that stacks has (near the end of the draw) a concave curve. Hence it stores less energy than expected for the draw weight.

  Good post and a good piece written by Dick Baugh. Energy storage is very straight forward, all about geometry while efficiency relies heavily on the bowyer. I did some work on the hysteresis issue a few years ago hoping to be able to pin it down and find out much more closely how much we actually dealing with. The test I came up with was based on a real simple concept but a pain to do on a regular basis. It simply establishes the virtual mass of the bow and then tracks how the virtual mass seems to change with lighter and heavier arrows. In reality the virtual mass should stay about the same as it does in synthetic material bows. This clearly illustrates that hysteresis is the culprit that causes the VM to change with the speed of the bow limbs. Hysteresis is time sensitive so it is easy to see how it is affected. Over straining the wood is the main cause of this and is very provable. 

Efficiency is how much of this energy is actually transferred upon the arrow. The arrow is not the only thing that needs to be moved, the limbs also need to return to their original position, which also requires energy. And there are energy losses within the bow, friction between wood fibers so to say. This is hysteresis. Dick Baugh explains it well here: http://www.primitiveways.com/Bow_and_Arrow_Efficiency.pdf and here http://www.primitiveways.com/Bow%20and%20Arrow%20Efficiency-2-16-11.pdf
To cut a long story short: with a 50# 28" draw and a straight force-draw curve, a 500 grain arrow could theoretically fly a touch over 200 fps, at 100% efficiency. In reality, most bows aren't 70% efficient, and shooting 170 fps is already very good.

Some designs store more energy, some are less efficient.

Offline Morgan

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Re: Pyramid vs everything else
« Reply #102 on: November 09, 2017, 02:52:04 pm »
Holy cow you guys really get technical! There’s no way I can wrap my head around a lot of the stuff discussed. I have a hard enough time making two limbs bend right. I do want to try a pyramid from a stave one day when I have a straight stave to work with.

Offline Selfbowman

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Re: Pyramid vs everything else
« Reply #103 on: November 09, 2017, 05:45:55 pm »
Well I have been busy and so have you guys.  :) it's been interesting for sure. Work has been in my way! These warm discussions bring us to try harder at perfecting our work. Proving someone else wrong! I don't know about everyone else it makes me work harder and I learn from it if my hardhead allows me to. Arvin
Well I'll say!!  Osage is king!!