Bow design and development

[Stick Bender]

Thanks Ben good to know , do your remember where it failed (where the weak areas) working limb ?

[Bayou Ben]

Yeah most of these see a lot of stress mid limb.  Leaving it full width past mid limb should help. 

[Stick Bender]

Im waiting for your results on your latest, I was thinking I have the sled for the supper lam now the power lam & wedges combined in one lam it would simplify things a bit , also thinking quad lam maple/osage maybe 66in. ? Im just not sure on the tapper rate given the other design is shallow so Im waiting on you pionering....lol

[Halfbow]

Good examples Half, Take example C for instance. With all that reflex it would have a very high early draw weight. But the geometry isn't such that would allow for a gradual build up of weight so it would simply need to be tillered down in weight which would put that reflex far beyond the point of deminishing returns.

I'm not sure what you mean here. We know it's 50lbs at full draw, and you say it would have a high early draw weight. What would you expect the f/d curve to do between the high early draw weight and 50? I'm not sure where the need for tillering it down comes in.

The profile certainly isn't ideal. Add some good recurves and it will store a lot more energy. But that's true for all 3 bows.

[Badger]

Half, if you tillered the bow out to look like the other bows in the pic I think it would loose most of the high early draw weight long before you reached full draw. It would end up flmsy and unstable and if you did manage to get shots out of it the efficiency would be poor because the limbs would be too thin and prone to distortion. If it was tillered out like a horn bow with short working limbs all that would change except wood won't tolerate the short working limbs.

[Halfbow]

Yeah I certainly wasn't picturing wood for this thought experiment. Even with the full limb working evenly, you'd need an impressive material to take as much bend as bow C without breaking down quickly. But not an unrealistic one. As you know, materials that bendy exist. I was imagining a modern material, since we are discussing why modern bows are so uniform. If I were to try to make this a real life experiment with wood, the reflex would be way way toned down.

Given the set up (that all bows are 50lbs) we can immediately know that when unbraced, bow A is much stiffer than bow C. Bow C has lighter and more flexible limbs. But once they're all braced, bow C is stiffest. By which I mean, it's the hardest to get to bend farther.

I'm not understanding where a lack of stability would come in. There are no recurves to be pulled out of line. (I liked the way the paper linked by willie talked about this) With a recurve, because the tips point away from you, the string tension will have an amplifying effect on any sideways deviation. This pulls things out of line and encourages twist. But with a long bow profile like we're talking about, the string has a correcting effect. If any part of the bow gets a funny idea and wants to step out of line, the string will pull it right back in. And it will correct extra hard on bow C, due to the high string tension.

One type of stability that I could imagine being different is.. it may be more sensitive to where you hold the bow. Put your hand lower and the lower limb will bend more, higher and the higher limb will bend more. I could see bow A being less sensitive to inconsistency there.

I think we probably just need a real life experiment. 

[Badger]

Half, one of the big challenges that modern longbows face when adding over 3" reflex is that they become unstable at brace. They will rock back and forth. Reducing working limb is the only way to counter it. Wood bows are the same way if they have too much working limb and reflex.

[DC]

I'm thinking that any time the tips are in front of the handle(fulcrum) you can have a tendency for twist. The self correcting doesn't take place until after the tips pass the handle. But even then if your limb wants to twist, say due to uneven thickness, the tips will still amplify the twist. Had this happen the other day. The tip was starting to twist at about half draw. The limb felt a little thicker on one side and a couple of scrapes later, no problem. That was actually the first time I'm managed to fix a twist that way. 

[Halfbow]

Half, one of the big challenges that modern longbows face when adding over 3" reflex is that they become unstable at brace. They will rock back and forth. Reducing working limb is the only way to counter it. Wood bows are the same way if they have too much working limb and reflex.

Ok so if I'm understanding you right, it sounds like do mean the second kind of stability I mentioned. Where the top and bottom limb will too easily trade off bending more? If so, then I'm on board.

I must admit, I am unfamiliar with this being a major concern for modern longbows, but that's interesting. I'd have expected a handle that makes it clear where to hold the bow would be an effective counter for that, but I guess it's a bigger problem than I imagined.

In that case, what would you think of this thought experiment if I had used an extreme holmegaaurd-type design, to the point of them all being hinge bows?

I'm thinking that any time the tips are in front of the handle(fulcrum) you can have a tendency for twist. The self correcting doesn't take place until after the tips pass the handle. But even then if your limb wants to twist, say due to uneven thickness, the tips will still amplify the twist. Had this happen the other day. The tip was starting to twist at about half draw. The limb felt a little thicker on one side and a couple of scrapes later, no problem. That was actually the first time I'm managed to fix a twist that way. 

DC, I think you would find the effect you're talking about is a function of the bow's shape in use. Meaning, the bow's shape at any point from brace through full draw. In regard to twist, bow C is a very stable shape from brace through draw, same as the other 2 bows. You would only see that kind of unstability manifest when trying to string bow C. That bow would be a bear to string (as is any extreme reflex bow). But once you got it, I think you'd be golden in that regard.

[Stick Bender]

Steve I don't know what modern long bow strait ? Your referring to if it's strait type with reflex I don't know but the moderen D/R long bow has no issue with limb rocking as described , if there was a issue as described I think it would be related to design,material or taper rate , about 3 in. in front of the handle is max that I have gone do to increasing brace height  ?

[willie]

I got this from the link you posted

For a cantilever spring, however, the DFC is non-linear, as both the
force and the differential force both increase as the deflection increases.

Can you explain this for me? I think this is something I have wanted to know ever since I started bending sticks

I think what they are trying to say in a fancy way, is that the the cantilever will stack. take a look at the bottom sketch that halfbow  posted in reply 65 for an extreme example.

[willie]

... How're they going to not talk about the angle the limbs come off the riser? And the overall reflex or deflex? The distance the handle is in front of or behind the tips when unbraced. They just seem to start with the assumption that the industry has it perfect. Almost like it didn't occur to them that it's a variable they can play with. Maybe the industry does have it dialed in already, but their failure to mention it makes me think maybe they don't.

Halfbow,
I hope Don doesn't mind me posting a link to a project I started last winter. I have asked myself similar questions, but more to do with arrows for flight shooting.

http://www.primitivearcher.com/smf/index.php/topic,62820.0.html

edit: fixed link, maybe.  look for "shooting fixture" in the flight section

[Halfbow]

Willie, that fixture looks great. I know you were mostly focused on arrows, but did you get any impressions about different setups for bows?

[BowEd]

Halfbow.....To tiller out a bow such as C that you showed it would be like tillering a wildcat.Linear and lateral stability would be an issue especially more so if the bow was very narrow.More width can help with stabilizing.I've been there and done that and it can be done.Quite frustrating really with no added benefit but still very unstable as Badger stated even after tillering it stable.In fact the bow will stack at the end of the draw.Not a desirable thing at least for me.A bow such as C should have retro bent tips pointing straight down the last 6" in the profile you've shown.
A boat shape type profile with the reflex mostly on the outer half of bow and left a bit stiffish will be much easier.With not so much up close reflex to tiller coming from the fades but if reflex is in fades more so should be put in the outer half of limbs yet.
More reflex can be put on the last 6" of these bows here too with a bit more benefit but this profile is easier for me to brace with just a primitive stringer the way it is without the use of tepeliks.They are still very stable bows.The extra reflex on the outer limbs puts more pressure or strain closer to the handle which is flatter profiled which helps stabilize the limbs better.Making static recurves have the same effect of pressure on a self bow.As with most bows the most power on profiled bows like this comes from the innerlimbs to midlimb as it was'nt reflexed on the inner limbs that much to begin with and so it is more stable then.A hard almost impossible trick to do with wood alone bows with over 6 inches of resting tillered out reflex.
Different degrees of reflex here with the background one to tiller yet but when done will show the gradual increase over the other two in front.

[Badger]

Good one Ed! Nice photo!