Earlier compound bows?

[fdsa1234567890]

What is the earliest date that a compound bow seems plausible? While they were only created in the 1960s(TL7) in reality(as noted in GURPS High-Tech), could they be plausible in TL4 or TL5?

The obvious reason for this was that guns more or less made bows obsolete, but it seems like they could have evolved in this fashion if guns did not exist as in the real life tech tree.

[Fred Brackin]

The simple machines invovled in the compound bow are about TL2. The necessary light and strong materials probably aren't. Then there's some precision machining that would be difficult to duplicate by hand.

[Anthony]

Originally Posted by fdsa1234567890

What is the earliest date that a compound bow seems plausible?

I'm not sure when the required math became available, but you need lightweight, low-friction axles, cams, and cord, and based on the progression of clockwork, you're probably looking at late TL 4 (post-gunpowder) for it to be particularly viable.

[jacobmuller]

I remember reading that the Romans could have had firearms. Inefficient, black-powder, clunky, unreliable, but a legion armed with SMG*s, even inaccurate, and comparatively short ranged, would have been "possible".
*Spear-machine-gun.
So clunky, unreliable TL2 compound bows - not as good as TL4, not as good as modern, but better than the basic? Possible. TL4, plausible.

[Anthony]

Originally Posted by jacobmuller

I remember reading that the Romans could have had firearms.

That's being pretty generous -- there are a bunch of technologies that need to be invented and they weren't particularly close.

Originally Posted by jacobmuller

So clunky, unreliable TL2 compound bows - not as good as TL4, not as good as modern, but better than the basic? Possible. TL4, plausible.

A poor quality compound bow is worse than a self bow, because every cam is costing you energy. With modern axles that energy loss isn't large, but with TL 2 machining... the likely result is something that's heavier, more expensive, less accurate, and less powerful.

[Pursuivant]

Given the need to attach cams to bow limbs in a way that keeps a high draw-weight bow from exploding at full draw, you either need really well-developed composite bow technology or very good spring steel.

The cams would have to be made out of metal, as would the inert parts of the bow.

If you were willing to accept a very low draw weight to avoid overstressing the bow limbs, you could conceivably have wooden or composite compound bows at TL1 - as soon as you get the concepts of the spoked wheel, the block and tackle, and the recurve bow. They'd be little more than toys, however.

A hunting-weight compound bow could be based on a crossbow, with spring steel arms and lightweight steel cams, but wooden grip and risers. That would be firmly late TL3/ early TL4. Cams date back to the 3rd century BCE or earlier, and the Chinese used them for crossbow triggers, so all the ingredients were there.

[Verjigorm]

Originally Posted by Pursuivant

Given the need to attach cams to bow limbs in a way that keeps a high draw-weight bow from exploding at full draw, you either need really well-developed composite bow technology or very good spring steel.

The cams would have to be made out of metal, as would the inert parts of the bow.

If you were willing to accept a very low draw weight to avoid overstressing the bow limbs, you could conceivably have wooden or composite compound bows at TL1 - as soon as you get the concepts of the spoked wheel, the block and tackle, and the recurve bow. They'd be little more than toys, however.

A hunting-weight compound bow could be based on a crossbow, with spring steel arms and lightweight steel cams, but wooden grip and risers. That would be firmly late TL3/ early TL4. Cams date back to the 3rd century BCE or earlier, and the Chinese used them for crossbow triggers, so all the ingredients were there.

I wanna touch on this: Medieval steel prod crossbows had pathetic power strokes of 5" or so, and from playing with Doug Cole's spreadsheet for bows, increasing that power stroke to 12 or 15" the performance rapidly improves.

Todd Cutler has a video on you tube about this as well, and he notes that due to the slag inclusions, medieval steel was inconsistent and unreliable, and the last thing you would want is for a kilo or two of steel under that much tension to snap and fly back into your face.

[Anthony]

Originally Posted by Verjigorm

I wanna touch on this: Medieval steel prod crossbows had pathetic power strokes of 5" or so, and from playing with Doug Cole's spreadsheet for bows, increasing that power stroke to 12 or 15" the performance rapidly improves.

There's no guarantee that you can increase the power stroke, because the maximum draw length depends on the properties of the elastic medium (essentially, your goal is for the elastic medium to be stretched to its yield strain minus some safety margin, and this gives a radius of curvature of (front to back thickness) / (maximum strain)).

One of the problems with Doug's spreadsheet is that it has a lot of unnecessary calculation. The total draw energy of a well designed bow is just equal to (total mass of elastic medium) * (max safe energy storage of elastic medium), and there's a lot of tradeoffs you can make between draw length, bow length, and bow thickness that really aren't going to change the end result.

[Verjigorm]

Originally Posted by Anthony

There's no guarantee that you can increase the power stroke, because the maximum draw length depends on the properties of the elastic medium (essentially, your goal is for the elastic medium to be stretched to its yield strain minus some safety margin, and this gives a radius of curvature of (front to back thickness) / (maximum strain)).

One of the problems with Doug's spreadsheet is that it has a lot of unnecessary calculation. The total draw energy of a well designed bow is just equal to (total mass of elastic medium) * (max safe energy storage of elastic medium), and there's a lot of tradeoffs you can make between draw length, bow length, and bow thickness that really aren't going to change the end result.

The uneven quality of medieval steel pretty much always meant you were going to be unable to get close to the yield, consistently, due to slag inclusions. This also influences early guns, as iron was used to make early cannon, and it was poor for that, due to the smelting process. If the process used produced enough heat to liquify the iron, then the slag floats to the top and forms a layer on top, or runs off and can be relatively easily separated, producing a more homogeneous and consistent process.

[Pursuivant]

Originally Posted by Verjigorm

The uneven quality of medieval steel pretty much always meant you were going to be unable to get close to the yield, consistently, due to slag inclusions.

That's why I suggested late TL3/early TL4 for a hypothetical steel limbed low tech compound bow. It's the earliest you're going to get anyplace close to good enough steel.

The limbs for such a bow would require state of the art metallurgy and lots of extra work to remove carbon and slag inclusions. You could possibly, maybe, get such steel with secret European alloying techniques (to get a bit of Magnesium, Chromium, or Vanadium in the mix) but Japanese style smelting and forging techniques which resulted in purer steel.