Composite Longbow

[Yooper Bowyer]

I'm toying with the idea of building a composite longbow to see how it works.  Basically it would be an exaggerated holmegard with horn/sinew laminated on the inner limb, stiff outer limbs, and a lot of reflex.  Something like this was mentioned in TBB 4, and a similar pattern was posted here a while back.

I don't know of it being made historically, which means it might not work, but the concept seems sound. 

What kind of horn works well for bow limbs?  I know where to find cow and bison horns, though it would be ~ $50 for enough.

Thanks,

[bownarra]

Buffalo horn. I wouldn't use anything else. The cow horns can delaminate.
The TBB bow idea is good but there are quite a few things that you would need to modify.
You can't have that much reflex in the bending limbs. They will delaminate. If you look at most composites they have little if any reflex in the bending areas. They are glued up straight in htis area, any reflex is just from the sinew. Also you can't make the limbs all that wide because of the poisson effect. 1 1/2 would be about the max, otherwise without mega draw weight the limbs will be too thin.
I've made a couple of bows along the lines of this design and when you keep it within the realms of possibility (rather than a fantasy bow ) they work very well indeed. Mine shoots 10gpp over 190fps (from memory) and also loves light arrows. A 300 grain arrow is well over 200fps with zero handshock. Anybody who I have let shoot these bows hands it back with a look of surprise
I will post a picture if you want.

[sleek]

Buffalo horn. I wouldn't use anything else. The cow horns can delaminate.
The TBB bow idea is good but there are quite a few things that you would need to modify.
You can't have that much reflex in the bending limbs. They will delaminate. If you look at most composites they have little if any reflex in the bending areas. They are glued up straight in htis area, any reflex is just from the sinew. Also you can't make the limbs all that wide because of the poisson effect. 1 1/2 would be about the max, otherwise without mega draw weight the limbs will be too thin.
I've made a couple of bows along the lines of this design and when you keep it within the realms of possibility (rather than a fantasy bow ) they work very well indeed. Mine shoots 10gpp over 190fps (from memory) and also loves light arrows. A 300 grain arrow is well over 200fps with zero handshock. Anybody who I have let shoot these bows hands it back with a look of surprise
I will post a picture if you want.

OF COURSE WE WANT PICS, WE ALL WANT PICS!

[Yooper Bowyer]

Thanks for the input.

Do you mean American Bison or water buffalo?  I've read that cow from northern climates is ok.  There are Scottish highland cattle down the road, but maybe I'll save cow for experimental mini bows.  Bison horns are only ~14" long, so the working limb would have to be even shorter unless I try to cut out a spiral scale and boil it flat.

I understand you can counter the poision effect by rounding the corners.  I wouldn't need much reflex in the working limbs at all, even a very slight angle in the inner limbs would lead as much reflex as I can handle while stringing.  I would probably aim for a long draw bow rather than a high reflex bow.

[Pat B]

Water buffalo

[Yooper Bowyer]

I just found gemsbok horns online, surpassingly inexpensive, how would those hold up? 

[mmattockx]

Also you can't make the limbs all that wide because of the poisson effect.

Can you explain why the Poisson effect would be a problem on this style bow as opposed to other styles of bow?

I will post a picture if you want.

That's a silly question, of course we want pictures.


Mark

[sleek]

Whats the poison affect?

[scp]

I would love to see a composite bow with less than 14 inch long working limbs and more than 14 inch long siyahs.

[mmattockx]

Whats the poison affect?

Poisson, named after French mathematician Simeon Poisson. It is the effect where a material changes dimension perpendicular to the direction it is loaded in. Think of pulling on a rubber band, as it stretches in length it gets narrower in width. Also, when you squash a rubber block it expands in width.

This affects bows with wide, flat limbs because the back is being stretched while the belly is being compressed. This means the back surface is trying to get narrower while the belly wants to get wider. The end result is the limb cups towards the back when bent. You can easily see the effect by drawing a bow with wide rectangular section limbs on the tillering tree and putting a straight edge across the back of the limb.


Mark

[sleek]

Whats the poison affect?

Poisson, named after French mathematician Simeon Poisson. It is the effect where a material changes dimension perpendicular to the direction it is loaded in. Think of pulling on a rubber band, as it stretches in length it gets narrower in width. Also, when you squash a rubber block it expands in width.

This affects bows with wide, flat limbs because the back is being stretched while the belly is being compressed. This means the back surface is trying to get narrower while the belly wants to get wider. The end result is the limb cups towards the back when bent. You can easily see the effect by drawing a bow with wide rectangular section limbs on the tillering tree and putting a straight edge across the back of the limb.


Mark

FASCINATING! Glad I asked, and thank you for answering!

[Yooper Bowyer]

So, what kind of horn works, and which is best?

[Pat B]

Gemsbok horn will work but water buff is what most Asiatic horn bows are made with. Goat will work well too I think.

[Yooper Bowyer]

Thanks,

I found both at a pretty fair price. I think I'll go with gemsbok so I can avoid the uncurling etc.

[WhistlingBadger]

Whats the poison affect?

Poisson, named after French mathematician Simeon Poisson. It is the effect where a material changes dimension perpendicular to the direction it is loaded in. Think of pulling on a rubber band, as it stretches in length it gets narrower in width. Also, when you squash a rubber block it expands in width.

This affects bows with wide, flat limbs because the back is being stretched while the belly is being compressed. This means the back surface is trying to get narrower while the belly wants to get wider. The end result is the limb cups towards the back when bent. You can easily see the effect by drawing a bow with wide rectangular section limbs on the tillering tree and putting a straight edge across the back of the limb.


Mark

Interesting!  I never thought about that in relation to bows, but it makes sense.  Thanks for explaining.