Possible Benefits Of Zero Brace Heights

For discussion related to primitive bows.
Tim Baker
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Tim Baker
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Joined: May 23rd, 2005, 6:22 am

June 12th, 2018, 8:55 am #21

Tuomo.e:
 
That was a lot of work. Thanks again. It's clear that a low-braced taut string yields extra stored energy. A reflexed straight bow at low brace should yield similar numbers. I've used a version of you second-option testing, but at this location don't have a worked in zero-set or somewhat reflexed bow, so instead used a "1,000-shot" wood bow with 1.5" of string follow, which permits two bad options: brace it at 1.5" and have a no-tension string, or put moderate tension in the string and see it pull the bow into a higher brace height. In either case the early draw weight advantage of taut low bracing is lost, so further testing on hold till an appropriate bow is available. Degree of tip advance is a good measure of limb strain, such testing on hold too. 
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French Crow
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French Crow
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June 12th, 2018, 1:46 pm #22

Low string tension and low stress in limbs when strung: that reminds me some deflex recurve bows I made, such as this one:

That design allows convenient brace height and the FD curve climbs quickly in the first inches of draw.
Bruno
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Patrick St M
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Patrick St M
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June 12th, 2018, 4:21 pm #23

Repeated for emphasis:
"  The Yukon bow used a lashed on piece of wood to achieve brace height without really stringing the bow.   That clears the hurdle of having the bow at zero brace height.  You need somewhere to get your hand on the bow and string clearance on the loose.   Plus the string would crack like a whip if it was slapping on the whole length of the bow on the loose"
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Tim Baker
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Tim Baker
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June 12th, 2018, 10:45 pm #24

French Crow: 
 
That's a good design for fairy high bracing. It would be efficient once braced high enough for relatively high string tension.
 
Try to do something different with bow design and the bow gods are going to mess with you: The closer a bow gets to no-string-tension bracing the lower it's FPS per stored energy. After release of a normally-braced bow, as string and arrow approach brace position, slight forward tip motion works to generates ever greater string tension, pulling the string ever straighter, yielding ever faster arrow acceleration. But a low-brace-tension string is unable to pull the string to such tension, low acceleration resulting in those last half-inches of travel when arrow speed is being topped off. So for a near-zero brace height bow to be efficient it mush have high string tension at brace height. This creates some challenges.  But argue back if you see holes in this.
 
Patrick St M:
 
I took that feature simply as a wrist protector at the time, but it's been ages, so I can't remember if the bow was deflexed, the string straight at brace, resting on or just above that protecting stick, or if the stick actually elevated the string near its nocking point when braced, the string not straight; if so, this would prevent normal final acceleration of the arrow, possibly a conscious trade off for comfort. The bowmakers in that challenging and low-population part of the world were possibly the most innovative design experimenters of all time. Thanks for the reminder.
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Patrick St M
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Patrick St M
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June 13th, 2018, 12:46 am #25

The bow in this plate looks to be barely bending and most of the brace height is due to the bridge.
https://www.archerylibrary.com/books/po ... ate02.html
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Tim Baker
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Tim Baker
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June 13th, 2018, 3:03 am #26

Patrick St Ma:
 
Big thanks for that. No arrow weighs given, but assuming about equal grain weight for all then the Yukon bow is the slowest per drawweight of all, which you'd expect given that it has a functionally slack string. Sure would like to known the arrow weights and draw lengths. My Pope literature is elsewhere; do you know if such stats were given?
 
I may have held that particular Pope bow in my unworthy hands, but that's another story. Thanks again for the information.  
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Patrick St M
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Patrick St M
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June 13th, 2018, 11:25 am #27

The bows tested all shot the same 320 grain  30 inch arrow. This bow was only drawn 25 inches however despite being 68 inches long.   Not sure why.

 The stats are all in Hunting with the Bow and Arrow.  You can access that through the online Archery Library.
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Tim Baker
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Tim Baker
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June 16th, 2018, 9:14 am #28

Patrick St M:
 
Re the Archery Library site you posted the link to: It's a treasure trove of classic archery knowledge, and it seems few know about it. Me, for instance, before your link. It took ages and piles of dollars for me to locate and acquire the physical books now available there free. Somehow everyone seriously interested in natural-materials bows should be made aware of the site. I'll begin mentioning it whenever appropriate. Thanks again for the link.
 
https://www.archerylibrary.com/
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Patrick St M
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Patrick St M
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June 16th, 2018, 11:18 am #29

Tim, definitely.  I love to get my hands on actual books when I can but having all of those old books at the touch of a keyboard is really neat.
 I've frequently mentioned it but not too many people  seem to use it as a resource.
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