TL3+1 Mechanical Artillery

[Icelander]

Originally Posted by Ze'Manel Cunha

Compound bows, especially compound Xbows make for some significantly increased firepower which scale up in siege weaponry.

It is possible that someone might develop such weapons as TL3+2 gadgets, probably unreliable and extremely expensive. The lack of the materials that modern compound bows use would mean much less efficiency, of course.

Originally Posted by Ze'Manel Cunha

Nitroglycerin and other explosives, as well as Greek Fire and other incendiaries, are all completely different development path tracks from gunpowder, giving you the bang and burn without the chemical propellant guns.

Such alchemical explosives exist, but are off-topic as not being mechanical artillery.

Rest assured, however, that a profligate commander could opt to shoot glass spheres filled with explosive liquid and/or greek fire from his trebuchets.

[Ze'Manel Cunha]

Originally Posted by Icelander

It is possible that someone might develop such weapons as TL3+2 gadgets, probably unreliable and extremely expensive. The lack of the materials that modern compound bows use would mean much less efficiency, of course.

You don't get modern compound bows, but you can still easily machine steel wheels and such, they aren't as light as TL 8 plastics, but they can hold the same stresses, just a bit heavier and more expensive due to being hand made.

[Sam Baughn]

Smaller size, greater rate of fire and improved accuracy might make the use of artillery for purposes other than sieges somewhat viable. Bolt throwers used as field artillery is something of a fantasy trope.

More accurate artillery would also probably make it more likely that siege engines (including artillery) would be successfuly targeted the defender's artillery. This implies that there could be an arms race of siege engines designed to avoid or survive artillery strikes, either through being heavily armoured or mobile enough to get out of the way before the defenders can calculate how to hit it.

[Icelander]

Originally Posted by Perfect Organism

Smaller size, greater rate of fire and improved accuracy might make the use of artillery for purposes other than sieges somewhat viable. Bolt throwers used as field artillery is something of a fantasy trope.

Exactly! But I need plausible benchmarks of performance for them.

How much range would be too much? How small could one make a stone thrower that was still powerful one to make an effective weapon against a wooden ship?

[Polydamas]

Originally Posted by Icelander

In the real world, the invention and widespread adoption of gunpowder quickly made it impractical to continue the advancement of mechanical artillery. No matter how much spring steel ('crossbow' steel) and any number of pulleys and windlasses might have improved lower tech scorpions, arbalests, mangonels and onagers; it would ultimately have been less effective than bombards and cannon.

In a world where gunpowder is rare, unavailable or restricted, however, like many fantasy worlds, this does not apply. Faerun, for example, is a mature TL3+1 in many areas, with functionning TL3+2 gadgets in some areas.

So, how might the artillery devices in GURPS Low-Tech be improved by one or two tech levels of extra design and better materials? Has anyone gone over those tables and wondered?

All ideas welcome. Worked out stats even more welcome.

Better springs for torsion artillery. Low-tech ones have capacity X for storing energy, and change properties with the humidity; special materials might store more energy or be unaffected by changes in humidity.

More metal parts in general should allow lighter, more durable machines. We see this happen with Roman torsion artillery, and the Romans and Hellenistic Greeks were as rich as many TL 4 societies.

Cheaper and better naptha/Greek Fire for ammunition obviously.

In the past few decades, engineers have shown that gravity trebuchets are more efficient if you mount them on wheels or let the axle roll back and forth as the weight drops. Ideally, the path of the dropping weight should be as close to vertical as possible. These were impractical for full-sized engines historically (and the "rolling axle" design required modern physics, materials, and modelling) but might be invented in a TL 4-5 setting with divination and superior craftsmanship and materials.

[sir_pudding]

Originally Posted by Polydamas

and the "rolling axle" design required modern physics

Really? That seems very unlikely, as it is a mechanics problem and should be solvable with Newtonian physics. What modern physics does it need?

[Anthony]

Originally Posted by Icelander

Exactly! But I need plausible benchmarks of performance for them.

How much range would be too much? How small could one make a stone thrower that was still powerful one to make an effective weapon against a wooden ship?

Well, it's unlikely that you can get a trebuchet much better than modern floating-arm designs. In general, you need a total kinetic energy no less than to 0.5 * range * weight (and better than 50% efficiency is unlikely, so go with range * weight), and you need a structure strong enough to handle that, plus adequate energy storage. Counterweights have total energy storage of (fall distance) * (counterweight weight), elastics have a total energy storage of 0.5 * (volume) * (ultimate tensile strength)^2 / (young's modulus); typical steel with 400 MPa tensile strength and 200 GPa young's modulus stores 400 kJ/m^3 or 50J/kg or 16 ft-lb/lb. Including all hardware, I'd put a lower limit of around 0.2 lb per ft-lb stored energy. There's also an upper limit to how fast any such design can reasonably propel a payload, we might up the limit to around 3,000' at TL 3+1.

Let's say we want to propel 25 lb to a range of 2,000', which is equivalent to the small hinged trebuchet in Low-Tech, and we're assuming 50% efficiency, so we need 50,000 ft-lb, for a 10,000 lb device (compare 17,500 lb in LT).

Now, winding this trebuchet requires 50,000 ft-lb energy, modified by the efficiency of your crank, and a human can reasonably sustain about 100 ft-lb per second for a medium period of time, so winding it should take no less than 500 man-seconds, and probably more like 1,000 man-seconds; one shot per minute requires a crew of 17 (LT manages one shot per 5 minutes with a crew of 25), so there's quite a bit of range for improvement here.

[Icelander]

I have a number of tactical roles for mechanical artillery and I was wondering what kind of designs would best fill them and, of course, what stats to assign to them.

First, I need some kind of substitude for cannon on ocean-going ships. Sailing technology is at late TL4 and some TL5 prototypes exist. But apart from magic*, nothing in Low-Tech can reach out at ranges of up to a mile. Also, trebuchets seem like they'd be troublesome on shipboard, what with their height interfering with rigging and catching the wind.

So, ideally, I'd need a stone thrower that does not need to be tall to function. This means using springs instead of counter-weights, I suppose. The weight, well, certainly it would help to have a small model of no more than a ton or two, a medium model of no more than 5 tons and a heavy model that could be up to 10 tons.

Also, an anti-personnel weapon for very long ranges. Something to use when heroic archers with imbuements or mages with long ranges curses are able to attack at extreme range and you want to have a change at disrupting them. I suppose it would be a gigantic crossbow on a tripod or swivel, shooting an aerodynamic bolt that is too small to work on buildings or ships, but which can play havoc on human targets. Or, of course, large monsters.

*Which, while capable of such feats in the right hands, is more usually seen wielded by mages who are at their best within 100 yards.

[Anthony]

Originally Posted by Icelander

So, ideally, I'd need a stone thrower that does not need to be tall to function. This means using springs instead of counter-weights, I suppose.

Low-tech springs will tend to require large amounts of horizontal space, though depending on your assumptions about magic things like Essential Wood bows may make sense.

Originally Posted by Icelander

Also, an anti-personnel weapon for very long ranges.

An issue with very long ranges is time of flight. A move of more than 100-150 is rather unlikely for mechanical artillery. 150 is enough to hit a target a mile away (as long as you're using something dense and reasonably streamlined) but time of flight would be 15 seconds or so, which won't hit a human target except by luck.

[Polydamas]

Originally Posted by sir_pudding

Really? That seems very unlikely, as it is a mechanics problem and should be solvable with Newtonian physics. What modern physics does it need?

Well, calculus and Newtonian kinematics (with mathematical ideas like energy, force, and so on) are modern by definition. My Realmslore is at default, but I don't think they have scientific physics or calculus there. I also think there may have been computer simulations involved in inventing or perfecting the floating arm design, although they wouldn't be strictly necessary.

Icelander, what do you mean by a substitute for cannon? I think the trifecta of cheap cannon, truck carriages, and sturdy ships drove European warships in one direction. A TL 4-5 society without those might develop warships in another! Indian and Chinese naval warfare at TL 4 might be a profitable area for research ...