deflex and reflex theory

[Halfbow]

  I don't think a hornbow or fiberglass bow could hold up to not twisting with that design. Not too hard to brace but once braced the string is under a huge amount of tension. Too much for a bow to stand up to. Maybe with the very small working limb area it might make it. I bet it would be a screamer.

To make sure I'm understanding you right, if you had a highly reflexed asiatic design vs the highy reflexed deflex design I drew, tuned the reflex in each to get you the same string tension, you'd expect the asiatic design to be more stable than the deflexed design? Why?

Is it because in the design I drew, at brace the limb follows the string so closely, just not quite touching for such a length? I could see that being problematic. I also imagine it would be okay without getting too ridiculous with limb width... But if it did turn out to be a problem, I have some ideas about how to fix it.

The ultra-reflexes horn bows are pretty interesting. They don’t have a particularly impressive force-draw curve, but are extremely efficient due to the small bending area and minimal flex in the outer part of the arms. Much of that unbraced reflex goes away during a conditioning process while it is strung where the bow it tortured into a stable braced position. When unstrung after shooting, most of that reflex is gone.

Alan

I did not know that! That is interesting. So all the pictures of unbraced bows with touching or nearly touch tips.. those bows have never been braced? Why do you think they went through the effort to build them that way? I imagine that even with horn, it's best not to take an intense amount of set?

[Stick Bender]

I have never tried a bow to that exstream but guys on the horn bow side have tried it ,I think BowEd is posting one there soon ,I credit him on a lot of my knowledge on D/R design ,I have made a couple 64" bows posted below that have extream early draw weight ,I cringe to string , you could easely get hurt if it went wrong but they are among my fastest bows the problem with highly reflexed D/R & angular bows is you have to brace higher to keep from flipping the string so there is always a ballance point , what hasn't been discussed in detail here is front view profile by altering it you can control the bend, also I have found that D/R bows that unwind with less stiff tips may not be the best in FPS but they are very accurate user friendly bows the one I posted earler is by far my most accurate hunting bow it hade no wedges , I think it would be easer & quicker to exsperment with bamboo backed wood bows with adjustable forms vs having to make a new form every time !

[Halfbow]

Stick Bender, I didn't mean to belittle the work that goes in to making glass bows. I just meant science is easier. Fewer variables and more consistent results.

Yeah in my early bow making days, I had a quite reflexed bow flip on me so hard it jammed my wrist. Could've been worse, I've read historic accounts of people dying while trying to string highly reflexed asiatic warbows. High reflex and instability can be scary as hell. And they definitely tend to be less accurate. Less forgiving. But I'm on conceptual mission for the fps here. 

In light of these stability concerns, I will whip up a new design idea. Will have to wait until later though.

[Stick Bender]

No worries I didn't take it as belittling I was just saying adjustable form vs individual forms is easier and wood/bamboo bows are more economical to make , it makes exspermenting easeier !

[Badger]

No worries I didn't take it as belittling I was just saying adjustable form vs individual forms is easier and wood/bamboo bows are more economical to make , it makes exspermenting easeier !

  That is a nice bow you posted, I bet it is fast. Bows like that have tons of pressure pushing outwards at brace, like if you set the bow on one end and just pulled straight down on the string it would be extremely tight.

[Badger]

  I don't think a hornbow or fiberglass bow could hold up to not twisting with that design. Not too hard to brace but once braced the string is under a huge amount of tension. Too much for a bow to stand up to. Maybe with the very small working limb area it might make it. I bet it would be a screamer.

To make sure I'm understanding you right, if you had a highly reflexed asiatic design vs the highy reflexed deflex design I drew, tuned the reflex in each to get you the same string tension, you'd expect the asiatic design to be more stable than the deflexed design? Why?

Is it because in the design I drew, at brace the limb follows the string so closely, just not quite touching for such a length? I could see that being problematic. I also imagine it would be okay without getting too ridiculous with limb width... But if it did turn out to be a problem, I have some ideas about how to fix it.

The ultra-reflexes horn bows are pretty interesting. They don’t have a particularly impressive force-draw curve, but are extremely efficient due to the small bending area and minimal flex in the outer part of the arms. Much of that unbraced reflex goes away during a conditioning process while it is strung where the bow it tortured into a stable braced position. When unstrung after shooting, most of that reflex is gone.

Alan

I did not know that! That is interesting. So all the pictures of unbraced bows with touching or nearly touch tips.. those bows have never been braced? Why do you think they went through the effort to build them that way? I imagine that even with horn, it's best not to take an intense amount of set?

  Halfbow, I am not talking about string tension as you pull the string but tension pushing outwards trying to pull the limbs together.

[Halfbow]

Halfbow, I am not talking about string tension as you pull the string but tension pushing outwards trying to pull the limbs together.

Yes I know. String tension at brace, right? Could be measured by inserting a hanging scale in to the string like this:


That's what I've been talking about. Do we agree that very reflexed asiatic horn bow designs also have very high string tension at brace?

[sleek]

I wonder what that tension is, and how it compares to other bows. If a bow could be made that duplicates the string tension of a horn bow, throughout its draw length, seems its performance could be duplicated in wood only.

[Badger]

Halfbow, I am not talking about string tension as you pull the string but tension pushing outwards trying to pull the limbs together.

Yes I know. String tension at brace, right? Could be measured by inserting a hanging scale in to the string like this:


That's what I've been talking about. Do we agree that very reflexed asiatic horn bow designs also have very high string tension at brace?

  I wouldn't be anywhere near as high as you might find on the design in the diagram. It is not the reflex that makes it high it is the flat profile of the limbs

[sleek]

Halfbow, I am not talking about string tension as you pull the string but tension pushing outwards trying to pull the limbs together.

Yes I know. String tension at brace, right? Could be measured by inserting a hanging scale in to the string like this:


That's what I've been talking about. Do we agree that very reflexed asiatic horn bow designs also have very high string tension at brace?

  I wouldn't be anywhere near as high as you might find on the design in the diagram. It is not the reflex that makes it high it is the flat profile of the limbs

100% agree, and the straighter the limbs are at brace, the higher the string tension.

[Halfbow]

I wouldn't be anywhere near as high as you might find on the design in the diagram. It is not the reflex that makes it high it is the flat profile of the limbs

Ah so I pretty strongly disagree with you there. Not to say that the flat profile of the limbs doesn't matter, but the reflex will be a huge part of the string tension at brace.

I've posted a relevant pic on these forums before.. let me dig it up.



Ok bow C is fanciful, but it works fine to show my point. These 3 bows are the same draw weight. They have identical profiles while braced and at full draw. But they are very different when unstrung.

It should be pretty obvious that bow A will have low string tension at brace. It barely has to bend to get to brace. Imagine the experience of stringing it. If it were any more deflexed, the string would be slack.

Add a bit more reflex to bow A, scrape the belly some, and you get straight bow B. You'd have to use a bit more muscle to string this one. When you string it, you bend the wood halfway to its final full-draw bend. That string is taught.

Just keep going. Adding reflex. Making the limbs weaker to maintain the same draw weight. Hope your materials are real good.

Eventually you get to bow C. To brace bow C, you have to bend the bow like 80% its final bend. That thing is wicked straining to go back. With like 80% of its might. The string tension will be enormous. With this bow, the stress the wood (or more realistically: some other material) feels from brace to full draw doesn't even change that much.

I put it to you that the difference reflex makes to string tension at brace isn't subtle, but huge.

Edit: Disclaimer. I'm not advocating any of these designs, just illustrating a concept.

[Halfbow]

I wonder what that tension is, and how it compares to other bows. If a bow could be made that duplicates the string tension of a horn bow, throughout its draw length, seems its performance could be duplicated in wood only.

I think string tension throughout the draw would be an interesting thing to pay attention to, but I think you'd have a really hard time mimicking a horn bow's string tension with a wood bow. And if you managed it, it would be just one factor of many that effect performance.

[sleek]

String tension is NOT a function of how much the bow has bent.  This is evidenced by string tension drops as the bow is drawn. String tension is a factor of the mechanical advantage offered over the limbs by the angle at the tips, not by how far the tips bent to get to brace.

[Stick Bender]

It would be interesting to see a working proto type of Halfbows drawing or even a milder version I'm not that smart numbers wise but I built enough bows to intuitively know the problems with the build (not saying it can't be done) I'm speaking building ,my guess is there would be stability problems & wood only ,would not work in my mind ,A horn/wood/sinew could take the stress but stability ? , carbon,stabil core,glass,wood would could take it but the problem would lie with material thickness vs stability it would have to have very thin lams & zero taper or max.001  the bend would have to be controled by the front view , the problem in my mind is how to get a stabile bow that's doesn't have a 300 lb draw weight...lol even minor miss alignment  would be exponentially multiplied in stability , deflexing the bow adds issues but it would be a great bow if you could get one to fly would be my guess , but a milder version would defiantly be possible in a short bow !

[Halfbow]

String tension is NOT a function of how much the bow has bent.  This is evidenced by string tension drops as the bow is drawn. String tension is a factor of the mechanical advantage offered over the limbs by the angle at the tips, not by how far the tips bent to get to brace.

When a bow is drawn, there are many factors that change and interact in interesting ways. A substantial one has nothing to do with the angle at the tips, but the angle at the fingers. The one I linked earlier. https://roperescuetraining.com/physics_angles.php The fingers are like the weight in those pictures. The table and the graph show the force multiplying effects of a near straight string. This is a big part of why string tension is higher earlier in the draw, and why draw weight gets higher the further you draw.

The angle at the limb tips plays its part too, though I think people usually measure it in a pretty uninformative way. But yes, sometimes the limb has more leverage over the string than other times and that makes a big difference.

But the thing that's true throughout all of it is: String tension has everything to do with how hard the poor string is being pulled. And how hard the limbs are stressing against it is absolutely a part of that.

When comparing a braced bow to other braced bows, straight string to straight string, a lot of the factors that change around interestingly during draw don't come in to play. Like the angle at the fingers.

All 3 of those bows will end at full draw with the same string tension. They will not begin with the same string tension. Not remotely.

Again this is not to say that other factors don't matter a lot. I'm just saying, let's not discount the effect of reflex here.