Plausibility check for a setting - Iron Giants

[Simon_Jester]

The problem then is that the climbers must scale the wall. For one, that makes them much more vulnerable to attack by defenders dropping things on them, or to any vaguely competent patrols the defenders have circling the tower and looking at the walls.

Also, by the time you've scaled the wall you might as well just come in the old-fashioned way- why bother drilling a hole through the top of the wall? That's even more difficult when you're dangling from one hand from a steel pick driven precariously into a cast-iron wall cladding while trying to beat a hole in the wall with your fists and feet.

[To tell the truth, I'm not sure such heavy beings COULD drive picks into a metal surface with enough force to hold up their weight, even given their great strength, unless they have picks made of uncommonly hard and tough metals]

[krakonfour]

The problem then is that the climbers must scale the wall. For one, that makes them much more vulnerable to attack by defenders dropping things on them, or to any vaguely competent patrols the defenders have circling the tower and looking at the walls.

Also, by the time you've scaled the wall you might as well just come in the old-fashioned way- why bother drilling a hole through the top of the wall? That's even more difficult when you're dangling from one hand from a steel pick driven precariously into a cast-iron wall cladding while trying to beat a hole in the wall with your fists and feet.

[To tell the truth, I'm not sure such heavy beings COULD drive picks into a metal surface with enough force to hold up their weight, even given their great strength, unless they have picks made of uncommonly hard and tough metals]

They don't have to be putting their whole weight on the picks, I mean, they could just dent the outer layer of metal, drive the pick in diagonally and use it to grip the edge of the dented wall. The pressure would be spread along the edge of the dent. Plus, 1:5 ratio means the slope is about 12 degrees.

Climbing is pretty fast. If they can jump 12m, and the wall is 300m high, then they will take around 40 seconds to scale it. The real limitation is how fast they can go through a wall several meters thick.

I think I can derive an answer from the rate jackhammers can go through various materials.

Lol, I can just imagine the scene. The alarm is sounded and the defenders rush to their posts, looking up and trying to fire at the raiders scampering up the walls. Seconds later, the attackers group up in one spot, and half of them raise their shields, catching the spears thrown at them. There is a moment of silence... and RATATATATATATATA! The attackers coordinate their punches to drive through the stone wall and break in.

[Borgholio]

Humm... what if the GRB was artificially caused, by an enemy? That would explain why the beam was much more power than it should have been (there are no nearby unstable stars that can cause this, not to the extend of the climate disaster I mentioned), and why humanity fled the solar system entirely despite only Earth being hit: They were scared of the new superweapon striking again.

The Death Star uses more power in a single shot that our sun produces in 7,000 years. A few second long GRB contains more energy than our sun produces over it's entire 10 billion year lifetime.

Hard to imagine any civilization creating an artificial GRB that produces anything near the power of a natural one.

[Simon_Jester]

They don't have to be putting their whole weight on the picks, I mean, they could just dent the outer layer of metal, drive the pick in diagonally and use it to grip the edge of the dented wall. The pressure would be spread along the edge of the dent. Plus, 1:5 ratio means the slope is about 12 degrees.

I'm really not clear on the part where these guys can just casually dent pieces of metal with sufficient force that they can use a pick to hold themselves in place, supporting a weight of many many tons, in hurricane force winds.

I mean, this is still a nearly vertical wall, right?

Climbing is pretty fast. If they can jump 12m, and the wall is 300m high, then they will take around 40 seconds to scale it. The real limitation is how fast they can go through a wall several meters thick.

...Real humans have a high jump of about two meters, and take a LOT more than six times forty seconds to climb 300 meters.

I don't think you're being realistic about the biomechanics of scaling a (nearly) vertical wall. If you try to do it hastily, these guys are so darn heavy that they'll either break the picks, or the pick will skid off the metal surface, leaving them with no handholds, and they'll fall to their deaths.

Also, if the massive wall could be scaled in a minute or two, there isn't really any point in building it in the first place. Just build a much shorter, squatter structure (which will also handle massive wind better). If the walls are twenty feet thick everywhere, except perhaps the roof (which can be actively guarded), then that counters this "climb the wall hundreds of times faster than a human could, then just effortlessly punch through four feet of rocks" tactic pretty nicely.

I think I can derive an answer from the rate jackhammers can go through various materials.

I'm not at all sure that the rates are as high as you think.

Also, jackhammers DO take time to punch through a stone wall, and are not designed to punch through the wall horizontally. They break up the rock above them, which slides down and threatens to dislodge the climber. Also, they have one hell of a recoil force, which is not what you want when precariously clinging to the side of a cliff.

Lol, I can just imagine the scene. The alarm is sounded and the defenders rush to their posts, looking up and trying to fire at the raiders scampering up the walls. Seconds later, the attackers group up in one spot, and half of them raise their shields, catching the spears thrown at them. There is a moment of silence... and RATATATATATATATA! The attackers coordinate their punches to drive through the stone wall and break in.

Except this is... stupidly unrealistic in my opinion.

[madd0ct0r]

Clad ignition you say? Electromagnetism say I

[krakonfour]

No idea what madd0ct0r meant, but thanks Simon_Jester for making me rethink things from scratch.

How does a settlement come to be?
First we need a prospector to find a radioactive source that can be mind. Whether it is a natural vein, a nuclear reactor buried under hundreds of meters of earth or a weapons depot, he'd use something akin to geiger counter to locate it.

The guy then has to gather a group of workers and build their first, temporary installations. The material? Well, the ground around them!

Then they start digging straight down. A finalized tunnel would be a zigzagging line straight down to the nuclear resource. Each step would include a winch to haul minerals up from the bottom and relay it to the next winch.

The earth and rock dug up would make the perfect material for the first walls. In fact, they would simply have to throw the dirt out of hole and it piles up into neat mounds around the mine's entrance. Kind of like ant-hills. Compacted earth is fairly resistant to impacts, and only a thin shell is needed to make it withstand the constant wind erosion.
Within the crater formed by the earth walls, the group would install the centrifuges for nuclear enrichment, as well as the furnaces for purification before enrichment. These need to be powered somehow... wind-power. On top of the industrial base, they'd place a roof made of hard rock, with a hole through it to drive shafts through it. The shafts are turned by windmills are placed on top of towers to avoid being destroyed by flying debris. The towers double as observation posts and glider launch platforms.

The last step is convenient because the miners would hit bedrock by the time they need to build a roof, so the materials are just there waiting for them.

Once the nuclear fuel supply is set up, secondary industries become necessary. Metalwork, research and whatever need an extension above the ground. A space will be cleared next to the tower, dug into the earth walls. It will be placed behind the tower, in the wind's trailing direction.

The final step would be to properly reinforce the earth walls and increase the height and width of the tower to increase energy production. The design would end up being like this:


Living quarters would be inside the tower for three reasons:
-Ventilation is much easier.
-The industrial base is more important, so it takes up the underground space which is more easily defended.
-Increasing population means that to increase the room available, you build a new level in the tower instead of digging a new one into the ground, both weakening the foundations and taking up more time and energy.

[krakonfour]

Any now on how this structure would be attacked:

At a distance!
All I had to do was open a few tabs on medieval siege warfare and calculate a few trebuchet size and projectile speeds.

The defenders fire javelins with 116.5kJ of energy and 117m/s speed. From a height of 300m, they can travel up to 1500m. At this distance, they are travelling slowly (down to 40m/s) but the angle of their fall means they can penetrate the weaker top armor of a suit.
The attackers ideally want to stay out this range. They can do that by hurling projectiles with enough force to cover this distance and still damage the walls.

I went to various trebuchet simulations and reached this:
16m tall, 16m long arm, 4m short arm (20m beam of metal).
The projectile is 375kg. It impacts with about 4MJ of force, and travels a distance of about 2.2km. It is an iron cylinder 20cm in diameter and 1.5m long, with fins to stabilize it.

The counter weight is a box containing 133 projectiles. Each projectile fired is filled back in with stones that were excavated to dig in the trebuchet against recoil. The structure is about 10 tons, for a total of 60tons package weight.

Of course, this won't be fired from 2km away, not if they want to hit anything with the wind. It'd be fired just out of the defender's reach, for much greater force and accuracy.

The attackers would carry this assembly and set it up outside of the defender's range. Since they weigh 60 tons, and the armor suits weigh 10 tons, then a group of 10 raiders (total lift capacity 220 tons) can carry two of these with a full complement of shells.
They would first fire very light shells to measure the wind and distance, before beginning the bombardment. Preferably, they would do so with the wind to their backs, to increase their range and decrease the inaccuracies caused by the wind
.
The defenders would have spotted them in the mean-time and starts to fire with its longest range armament. They might have trebuchets of their own. The problem is, they are firing at a small target (enemy trebuchet 1.5km away vs a gigantic tower sitting still) and against the wind.

The defenders can also move out with their own troops and stop the attackers from setting up. The problem is, out in the open, the raiders are on equal footing with the defenders and they might have better equipment and training, allowing them to overwhelm a larger force. Also, the attackers in that situation can throw their own javelins before the defenders meet them in battle, then run away and repeat. The defenders are tied to the place they are guarding.

If all goes well for the attackers, the wall is breached and they can mount an attack. The defenders would move the civilian population underground, out of the tower, leaving only armored warriors above ground. The defenders regain the upper hand when the attackers move within range to attack, but the latter are hoping that their bombardment was enough to thin the guards.

The assault is mounted. They climb over the wall, dodge the defender's javelins and enter a breach in the walls. They then proceed down the corridors, killing those in their way, until the defenders are all underground or dead. A large attacking force would move in the destroy the stone roof of the mine, a smaller force would scavenge the tower and surrounding area for goods to steal.

PS: I did say the prevalence of the wind was included in the setting for a reason. That reason is projectile accuracy.
These monsters can throw pretty much anything with destructive force over very long ranges. I however want a setting where the main form of combat is exchanging lance blows and hammer falls in hand-to-hand combat. So, I included the win so that it would mess with anyone trying to rely exclusively on throwing weapons.

[Simon_Jester]

Any now on how this structure would be attacked:

At a distance!
All I had to do was open a few tabs on medieval siege warfare and calculate a few trebuchet size and projectile speeds.

The defenders fire javelins with 116.5kJ of energy and 117m/s speed. From a height of 300m, they can travel up to 1500m. At this distance, they are travelling slowly (down to 40m/s) but the angle of their fall means they can penetrate the weaker top armor of a suit.

I'm still dubious of ~100 m/s speeds for a thrown weapon- mostly because of the implications for how fast their arms and legs can move. Atlatls might help.

Honestly, I wouldn't consider a spear moving at those speeds to be much of a threat to well designed armor- it isn't fast enough to act like an armor-piercing shell, and their metallurgy can't be that good.

The attackers ideally want to stay out this range. They can do that by hurling projectiles with enough force to cover this distance and still damage the walls.

I went to various trebuchet simulations and reached this:
16m tall, 16m long arm, 4m short arm (20m beam of metal).
The projectile is 375kg. It impacts with about 4MJ of force, and travels a distance of about 2.2km. It is an iron cylinder 20cm in diameter and 1.5m long, with fins to stabilize it.

Bombarding the enemy with catapults from that range is a waste of metal and time; the darts aren't going to hit a damn thing. Also, trebuchets are not good at throwing an actual dart in any case, given the way they throw things overhand.

The counter weight is a box containing 133 projectiles. Each projectile fired is filled back in with stones that were excavated to dig in the trebuchet against recoil. The structure is about 10 tons, for a total of 60tons package weight.

Not worth the trouble to carry around, then. In real life, medieval siege engines weren't all that effective, but at least the bulk of them could be made from wood that was harvested locally. Here, it's all got to be carried around everywhere, and it's bulky and clumsy as all get out.

Of course, this won't be fired from 2km away, not if they want to hit anything with the wind. It'd be fired just out of the defender's reach, for much greater force and accuracy.

How much? I thought you said javelin range was over a kilometer, and so far you haven't even thought about what happens if the defenders build giant-ass crossbows on the walls of their own stronghold.

The attackers would carry this assembly and set it up outside of the defender's range. Since they weigh 60 tons, and the armor suits weigh 10 tons, then a group of 10 raiders (total lift capacity 220 tons) can carry two of these with a full complement of shells.

Remind me again how they carry 22 tons apiece without falling over on their asses? Carrying a load heavier than your own body is hard, even if you have the muscles to hold it up.

They would first fire very light shells to measure the wind and distance, before beginning the bombardment. Preferably, they would do so with the wind to their backs, to increase their range and decrease the inaccuracies caused by the wind

Light bolts won't fly the same way heavy ones do in the wind; they'll be deflected a lot more.

The defenders would have spotted them in the mean-time and starts to fire with its longest range armament. They might have trebuchets of their own. The problem is, they are firing at a small target (enemy trebuchet 1.5km away vs a gigantic tower sitting still) and against the wind.

Since hitting the tower doesn't really accomplish anything, and the only meaningful target for the attacking siege engine is the defenders' own bodies and engines, this is more like a tie than you think.

Or they could just, y'know, send out a party of their own men to get rid of this tiresome group of ten 'raiders.' Presumably a tower like this would contain a lot more than ten capable warriors.

The defenders can also move out with their own troops and stop the attackers from setting up. The problem is, out in the open, the raiders are on equal footing with the defenders and they might have better equipment and training, allowing them to overwhelm a larger force.

Fighting does not work that way; being better trained does not make you a match for several times your numbers. Besides, don't the guys who built this giant-ass tower have their own equivalent of the oh-so-super-leet raiding parties?

If all goes well for the attackers, the wall is breached and they can mount an attack.

The weapons described will not be able to breach the walls, or at least not any part of the wall that can be reached practically in a hurry. The upper curtain walls of the 'tower' might be vulnerable, but they're hard to reach and the defenders can rush men to cover any breaches from the inside.

Of course, that is yet another argument for the 'fortress' looking like a big, low-slung structure with walls filled in with rubble and a thin layer of solid cladding; they'd soak up glorified catapult darts so well that they'd never manage to crack the wall. More or less exactly what real people did during the age of gunpowder as catapults were replaced by cannons.

The defenders would move the civilian population underground, out of the tower, leaving only armored warriors above ground. The defenders regain the upper hand when the attackers move within range to attack, but the latter are hoping that their bombardment was enough to thin the guards.

A bombardment of solid shot will have basically no chance of actually killing any meaningful number of the guards. Even if the guards stand out in the open, a few hundred rocks or spears landing amidst them won't hit more than a few of them by chance.

The assault is mounted. They climb over the wall, dodge the defender's javelins and enter a breach in the walls. They then proceed down the corridors, killing those in their way, until the defenders are all underground or dead. A large attacking force would move in the destroy the stone roof of the mine, a smaller force would scavenge the tower and surrounding area for goods to steal.

This plan is only going to work if the defenders are so much comically weaker than the attackers, both man for man and in terms of their intelligence and planning ability, or so outnumbered that it begs the question of how they ever build such a gigantic fortress in the first place.

In other words, you haven't planned a battle; you've planned an execution. It only works if the target isn't really trying to fight back with any intelligence or strength.

[krakonfour]

Any now on how this structure would be attacked:
I'm still dubious of ~100 m/s speeds for a thrown weapon- mostly because of the implications for how fast their arms and legs can move. Atlatls might help.

Honestly, I wouldn't consider a spear moving at those speeds to be much of a threat to well designed armor- it isn't fast enough to act like an armor-piercing shell, and their metallurgy can't be that good.

That's 360km/h for the tips of the fingers. World record for a baseball throw is 169km/h, and that's with flesh and bones. I'm thinking for iron beings using electric linear accelerators for muscles won't have a problem going 210% faster. Plus, their arms are 60% longer, so the actual muscle contraction speed is no that much more than the maximum a human can do.

Back to the armor penetration characteristics of a spear containing 200kJ of energy: You have to put things in perspective. They smash through plates of steel by concentrating their energy on a high-strenght metal on the tip. The tip can be tiny, it just has to withstand the impact forces. The rest of the spear's mass ploughs through the fissure created and strike the occupant of the armor.

Longbow shots are made of wood and they can go through 2mm of high quality steel with a measly 160 joules of energy. Even perfectly made armor has an upper limit set by the material properties of the steel it is made up of.

Also, suits of armor weighing tons have to be made of lower quality, high carbon steel due to cost reasons. The tip of the spear can be of much higher quality in consequence.

I used various 30mm cannons and low velocity tank gun shell penetrations to gather an esimate:
-400g AP round @ 188kJ penetrates 50mm at point blank
-37mm Pak 36 L/45, 685g, 745m/s, 190kJ penetrates 64mm at point blank

All values are in RHA-equivalent

Low quality steel therefore requires over 50-60mm of thickness to stand up to a 200kJ projectile of 30mm diameter.

[krakonfour]

Bombarding the enemy with catapults from that range is a waste of metal and time; the darts aren't going to hit a damn thing. Also, trebuchets are not good at throwing an actual dart in any case, given the way they throw things overhand.

Indeed. They are going to shoot from much closer than that however.
To solve the Trebuchet trajectory problem, I was thinking of a system that slides the dart down a rail, similar to a barrel, as it is dragged along by the sling. Better yet, the dropping weight could pull a length of rope which is connected through gears to another length of rope, forming a slingshot-type structure that fires a projectile down a tube, but I wonder how many ropes can handle 4MJ of energy.

Not worth the trouble to carry around, then. In real life, medieval siege engines weren't all that effective, but at least the bulk of them could be made from wood that was harvested locally. Here, it's all got to be carried around everywhere, and it's bulky and clumsy as all get out.

Right again, but at that age, they were shooting rocks that had less strength than their target material... they shattered on impact and dissipated most of their energy. Also, the angle of their fall gave most targets naturally sloped armor anyway...

As for the clumsiness, well, these giants throw around 20ton weights so something weighing 10tons can't be too hard to set up.

How much? I thought you said javelin range was over a kilometer, and so far you haven't even thought about what happens if the defenders build giant-ass crossbows on the walls of their own stronghold.

I did, but not exactly crossbows. I mentioned a defending trebuchet.
The defenders have two problems: their accuracy is much lower than the attacker's, and they cannot move.

The attackers fire down the wind, and they can reposition if they are under strong fire.

[krakonfour]

Remind me again how they carry 22 tons apiece without falling over on their asses? Carrying a load heavier than your own body is hard, even if you have the muscles to hold it up.

Maybe having muscles they can adjust down to the millimeter helps? The whole issue with carrying something heavier than you is the center of gravity that moves outside of your body. I'm sure that can be dealt with...

Light bolts won't fly the same way heavy ones do in the wind; they'll be deflected a lot more.

Yes, but you'll get an exaggerated and thus much easier to read wind strength. I don't know how artillery ranging is done, but I think the techniques apply here.

Since hitting the tower doesn't really accomplish anything, and the only meaningful target for the attacking siege engine is the defenders' own bodies and engines, this is more like a tie than you think.

I'm going to argue this point. A dense projectile containing over 4MJ of kinetic energy striking unmortared walls WILL have an effect.

Modern kinetic penetrators have about 12MJ, and they go through 6m of steel. Iron/Stone has the same density ratio.
I tried finding bunker busters with similar masses and energy, but the smallest one I could find was the Mk48 bomb with 42MJ of impact energy. That one went through 2m of reinforced concrete or 6m of compacted earth.
Scaling here can't be recommended, but here's what I have:
-Common stone has 7MPa of compressive strength, concrete has 28MPa, reinforced concrete has 40MPa.
-A dart with 10 times less energy will go through 1m of limestone.

If these darts dig through 1m of stone wall each time they hit, then the bombardment has a non-negligible effect on the masonry.

Or they could just, y'know, send out a party of their own men to get rid of this tiresome group of ten 'raiders.' Presumably a tower like this would contain a lot more than ten capable warriors.

A lot more is about a hundred. I did say the population sizes were small.
If it turns out that your men are nearly as capable as the raiders, then they'll just run way.

Fighting does not work that way; being better trained does not make you a match for several times your numbers. Besides, don't the guys who built this giant-ass tower have their own equivalent of the oh-so-super-leet raiding parties?

A small colony does not have a superb industrial base, and much less the money needed for high-grade steel and high-temperature furnaces.
This means that the suits they wear can be of much lower grade steel than those of the attackers... or even be made from relatively soft iron. In that case, their spears are blunt and their armor nearly useless. The enemy, if funded by a proper colony, will have the best weapons and armor capable of defleting strikes all day long. An analogy would be the introduction of the Tiger I tank in 1942 or the King Tiger near the end of the war. Their armor and weapons completely dominated the opposition, however ingenious it was. Another example is hordes of PzIII tanks grinding to a halt in the face of a single KV-1 tank.

Of course, that is yet another argument for the 'fortress' looking like a big, low-slung structure with walls filled in with rubble and a thin layer of solid cladding; they'd soak up glorified catapult darts so well that they'd never manage to crack the wall. More or less exactly what real people did during the age of gunpowder as catapults were replaced by cannons.

A low thick structure would not have the room for a decent industrial space, nor the capability to place its windmills far above the ground where it will be damaged.
An attacker can approach much closer because you do not have the advantage of a well-placed firing and observation platform, and then proceed to take the time to set up a large upwards-firing trebuchet. The projectile will strike straight downwards time and time again with good accuracy, demolishing whatever the wall thickness is over time.

A bombardment of solid shot will have basically no chance of actually killing any meaningful number of the guards. Even if the guards stand out in the open, a few hundred rocks or spears landing amidst them won't hit more than a few of them by chance.

Yes, but they won't have the protection provided by intact walls in the end. Alse, they are relatively compacted inside the sructure despite their low numbers because there is just not enough quality stone to cover the entire thing if it were much larger.

In other words, you haven't planned a battle; you've planned an execution. It only works if the target isn't really trying to fight back with any intelligence or strength.

Maybe. I'll work the numbers more.

[madd0ct0r]

seige - could the attackers just smash the windmills and pick off the defenders when they come out to repair it?

[Simon_Jester]

Maybe having muscles they can adjust down to the millimeter helps? The whole issue with carrying something heavier than you is the center of gravity that moves outside of your body. I'm sure that can be dealt with...

If the load is physically large and the winds are as great as described, it may be physically impossible to avoid having the center of mass (and pressure) move outside your body. It will also be very hard to avoid stumbling and falling in the face of unforeseen inconsistencies in the ground.

Light bolts won't fly the same way heavy ones do in the wind; they'll be deflected a lot more.

Yes, but you'll get an exaggerated and thus much easier to read wind strength. I don't know how artillery ranging is done, but I think the techniques apply here.

Artillery ranging uses consistent-type projectiles for each shot, because otherwise you don't learn anything from THIS shot that can be translated to the next shot without doing differential equations in your head.

It also uses precision machinery, so you can repeat the same action with the gun and get the same result. Catapults are unlikely to be this precise.

Since hitting the tower doesn't really accomplish anything, and the only meaningful target for the attacking siege engine is the defenders' own bodies and engines, this is more like a tie than you think.

I'm going to argue this point. A dense projectile containing over 4MJ of kinetic energy striking unmortared walls WILL have an effect.

Nothing that a properly designed wall can't handle almost indefinitely. The combination of metal cladding and loose rubble fill is almost ideal for this, because either the impactor will fail to penetrate the cladding (possible but unlikely), or it will succeed and wind up buried harmlessly in the rubble. You can't break meaningful holes in a wall that's already broken.

The biggest danger would be that punching holes in the outer bit of the curtain wall at the base could cause a general collapse, but such a collapse would not be very useful for a small party trying to gain entry, because the wall would collapse outward into a ramp of rubble. And these iron giants don't cope well with treacherous footing. Nor is this likely to happen after only a few hundred impacts.

Modern kinetic penetrators have about 12MJ, and they go through 6m of steel. Iron/Stone has the same density ratio.

Modern kinetic penetrators also move several times faster, which makes a very large difference. Projectile dynamics are very different at 100 m/s than they are at 1000 m/s.

If these darts dig through 1m of stone wall each time they hit, then the bombardment has a non-negligible effect on the masonry.

Bear in mind that under no circumstances will you be able to hit the exact same point on the wall repeatedly, so your attack is scattershot all over its surface.

A lot more is about a hundred. I did say the population sizes were small.
If it turns out that your men are nearly as capable as the raiders, then they'll just run way.

Abandoning their equipment? Good enough- that counts as a victory. Encumbered by their equipment, they have no chance of escape.

Fighting does not work that way; being better trained does not make you a match for several times your numbers. Besides, don't the guys who built this giant-ass tower have their own equivalent of the oh-so-super-leet raiding parties?

A small colony does not have a superb industrial base, and much less the money needed for high-grade steel and high-temperature furnaces.
This means that the suits they wear can be of much lower grade steel than those of the attackers... or even be made from relatively soft iron. In that case, their spears are blunt and their armor nearly useless. The enemy, if funded by a proper colony, will have the best weapons and armor capable of defleting strikes all day long.

Why would a colony that can't even afford a decent ironworks be building massive, hundred meter stone towers in the first place?

You might as well just come out and say "my model of warfare is based on a predatory military elite from a long-established and wealthy society, preying easily on the helpless, feeble, and impoverished colonies recently established around it." This is why I keep saying you're not describing a battle plan, you're describing an execution.

Of course, that is yet another argument for the 'fortress' looking like a big, low-slung structure with walls filled in with rubble and a thin layer of solid cladding; they'd soak up glorified catapult darts so well that they'd never manage to crack the wall. More or less exactly what real people did during the age of gunpowder as catapults were replaced by cannons.

A low thick structure would not have the room for a decent industrial space, nor the capability to place its windmills far above the ground where it will be damaged.

In that case, the solution is trivial. Build a curtain wall ten meters high 100 or more meters across, which will contain any reasonable industrial facilities. Any tower that needs to be built is located in the center of this. Attacking the tower directly accomplishes nothing as long as the roof of the 'main building' from which the tower rises can be defended, unless you can collapse the tower, which is much easier said than done.

Attackers will have to scale the curtain wall (and find defenders ready to repel them, plus exposing themselves to missile weapons from the tower defenses) and then repeat the whole thing to get into the tower.

No "upward-firing trebuchet" will work in this case, because the enemy can see you perfectly well- but they cannot easily create a breach in your walls which will permit anyone to enter.

An attacker can approach much closer because you do not have the advantage of a well-placed firing and observation platform, and then proceed to take the time to set up a large upwards-firing trebuchet. The projectile will strike straight downwards time and time again with good accuracy, demolishing whatever the wall thickness is over time.

A small group of raiders has no chance of doing such a thing, as this would require an immense supply of both time and ammunition for them to operate unmolested. Under no realistic conditions of warfare is that practical.

You cannot engage in siege warfare unless you have an army strong enough to defeat the garrison in open battle.

This rule does not change; it really is that simple. If your force is insufficient to win against an enemy force in open battle you cannot hope to break that same force when it is in strong fortifications. That's... sort of the point of fortifications, you see.

A bombardment of solid shot will have basically no chance of actually killing any meaningful number of the guards. Even if the guards stand out in the open, a few hundred rocks or spears landing amidst them won't hit more than a few of them by chance.

Yes, but they won't have the protection provided by intact walls in the end. Alse, they are relatively compacted inside the sructure despite their low numbers because there is just not enough quality stone to cover the entire thing if it were much larger.

i don't think you're visualizing the damage the walls experience- you should picture a huge structure with a few pinholes poked in it, not a normal structure blasted to rubble and craters. Thus, it will provide excellent cover for the defenders right up to the end, given the practical scale of the bombardment.

I mean seriously, divide the target area by the number of rounds you are firing- it should be obvious that you won't come anywhere near saturating the target, and without that you have no real chance of seriously weakening the garrison.

In other words, you haven't planned a battle; you've planned an execution. It only works if the target isn't really trying to fight back with any intelligence or strength.

Maybe. I'll work the numbers more.

I think part of your problem is a lack of context. No number of kinetic energy calculations can substitute for a realistic appreciation of what it means to be in a structure of this scale under bombardment, from the history of actual warfare.

[krakonfour]

Humm... what if the GRB was artificially caused, by an enemy? That would explain why the beam was much more power than it should have been (there are no nearby unstable stars that can cause this, not to the extend of the climate disaster I mentioned), and why humanity fled the solar system entirely despite only Earth being hit: They were scared of the new superweapon striking again.

The Death Star uses more power in a single shot that our sun produces in 7,000 years. A few second long GRB contains more energy than our sun produces over it's entire 10 billion year lifetime.

Hard to imagine any civilization creating an artificial GRB that produces anything near the power of a natural one.

I was thinking triggered rather than actually storing and releasing the energy artifically. Or maybe a portion of a natural blast was redirected by grazing-angle lenses or something.

If the load is physically large and the winds are as great as described, it may be physically impossible to avoid having the center of mass (and pressure) move outside your body. It will also be very hard to avoid stumbling and falling in the face of unforeseen inconsistencies in the ground.

Constant winds means that the ground is very smooth and sandy. Otherwise, the warriors would never run at their top speed.
Also, there is not reason why the weight can't be shared between two or more carriers. Each other can carry 20 tons individually, but placing 40 tons on two person's shoulders is better from a stability point of view.

I've tried analyzing just what makes carrying something equal or superior to your own bodyweight so difficult.
The answer lies in the way we walk. We basically trip ourselves, then bring our other foot forward and straighten out body. It's the little muscles that act on the pitch and yaw of the foot that keep us from falling in any other direction.

Let's say we accidentally shift ourselves 5 degrees to the right. The imbalance in newtons, for a 1.8m tall man weighing 75kg, is about 1.5 Newtons, assuming center of gravity is halfway. Our leg muscles can easily exert that force and compensate for the imbalance. (I used a pendulum to model this).

Now let's imagine we get the same imbalance, but while carrying 100kg. Holding that weight at waist level won't do anything to our center of gravity. The imbalance has to be compensated by 17.5 Newtons of force, which is 11.6 times greater than if we weren't carrying anything.

The muscles quickly tire, or are overwhelmed, and the constant balancing mechanism will cease the function.

Artillery ranging uses consistent-type projectiles for each shot, because otherwise you don't learn anything from THIS shot that can be translated to the next shot without doing differential equations in your head.

It also uses precision machinery, so you can repeat the same action with the gun and get the same result. Catapults are unlikely to be this precise.

I concede the point about ranging shots, but are you sure that this design is as inaccurate as a field-built wooden trebuchet?

Nothing that a properly designed wall can't handle almost indefinitely. The combination of metal cladding and loose rubble fill is almost ideal for this, because either the impactor will fail to penetrate the cladding (possible but unlikely), or it will succeed and wind up buried harmlessly in the rubble. You can't break meaningful holes in a wall that's already broken.

The biggest danger would be that punching holes in the outer bit of the curtain wall at the base could cause a general collapse, but such a collapse would not be very useful for a small party trying to gain entry, because the wall would collapse outward into a ramp of rubble. And these iron giants don't cope well with treacherous footing. Nor is this likely to happen after only a few hundred impacts.

I don't think you understand what 'goes through half a meter of rock' means. It means it packs as much punch as a kilo of TNT. That's 4 sticks, and demolition crews use that amount to go through 4 ton of rock.
Since this is solid shot, the energy is transmitted into a cone starting from the point of impact and spreading until it reaches the back of the wall. The volume affected is equal to how much energy the projectile has divided by the yield strength (in kJ/kg) of the material.

A round figure I found was 30kJ/kg needed to crush the rock and displace it.
Our darts are disrupting 133kg of rock. Since the target is supposed to be rubble, not solid rock, and since it is not held together by mortar (what would they make it out of?), AND we only need a partial destruction of the grain's structure for the section to collapse... then it is safe to say that sizable chunks are being blasted out of the wall.

As to the effects of each shot... these darts are not going through the walls as they would through a metal plate. If the target was a metal plate, then it's deform plastically once the kinetic energy overcomes its yield strength. The result is neat hole with metal bent outward. A few shards from the center fall off; spallation.
A closer example to the effect I envision is that of a cannonball going through a thick wooden deck. Because most of the energy and momentum is transmitted to the wooden target (the cannonball has lots of energy but poor penetration), we can assume a very elastic collision. A large amount of wood blasts out the back of the target at high speed, killing occupants behind it much like a frag grenade would do. In this case, the projectile strikes the wall, and rock blasts out the back, hitting many more targets than a clean penetration would do.

A method to estimate that effects is to use the 50cm of penetration. At the very least, it means that a hole the diameter of the solid shot and half a meter deep is going to be excavated into the wall. The displaced material has to go somewhere. If I'm guessing correctly, and that 50cm of penetration takes into account the perpendicular displacement of the rock, then the only outcome possible is for 4600cm3 of rock to blast out the back of the wall. It would bear a momentum and energy equal to what is left over from the shot after some of it is used to penetrate the wall.

Of course, this is only an estimate. In real conditions, a very large section of the back wall would fly out, many times the volume excavated by the projectile. The velocity however would by much lower. Like bowling pins, striking the first pin would transmit the momentum to two others behind it, until we have a much larger number of bowling pins (volume of rock) flying out the back.

Modern kinetic penetrators also move several times faster, which makes a very large difference. Projectile dynamics are very different at 100 m/s than they are at 1000 m/s.

I am aware of that. Enough to not mention shockwaves or plastic deformation of the penetrator.

Bear in mind that under no circumstances will you be able to hit the exact same point on the wall repeatedly, so your attack is scattershot all over its surface.

Medieval trebuchets were already obtaining an accuracy of 6x6m at a distance of 180m. Modern trebuchets (with metal hinges) have an accuracy of about 3m at 100m.

Why would a colony that can't even afford a decent ironworks be building massive, hundred meter stone towers in the first place?

You might as well just come out and say "my model of warfare is based on a predatory military elite from a long-established and wealthy society, preying easily on the helpless, feeble, and impoverished colonies recently established around it." This is why I keep saying you're not describing a battle plan, you're describing an execution.

Oh, they do have decent ironworks. The problem is that iron, however well you smith it, just does not have the same resistance as high-grade steel. That requires certain ingredients you cannot get in a world devoid of most organic life, more specifically, the coke needed to reach high temperatures. It's a material scarcity, not lack of skill.

[Simon_Jester]

I was thinking triggered rather than actually storing and releasing the energy artifically. Or maybe a portion of a natural blast was redirected by grazing-angle lenses or something.

Anyone capable of building or operating on that scale would be better advised to attack our planet directly- less work to achieve the same result.

If the load is physically large and the winds are as great as described, it may be physically impossible to avoid having the center of mass (and pressure) move outside your body. It will also be very hard to avoid stumbling and falling in the face of unforeseen inconsistencies in the ground.

Constant winds means that the ground is very smooth and sandy. Otherwise, the warriors would never run at their top speed.

Constant winds blowing over sand mean dunes and sandstorms which impair visibility, making it suicide to run so fast. There are a lot of features that won't just cease to exist like that: rocks exposed by the blowing wind, unexpected patches of soft sand or other bad footing, and so on.

It is simply not realistic to imagine a humanoid being running at high speed while carrying a mass significantly greater than its own bodyweight in its arms. If you want to do that, get a rickshaw.

Also, there is not reason why the weight can't be shared between two or more carriers. Each other can carry 20 tons individually, but placing 40 tons on two person's shoulders is better from a stability point of view.

Still dangerous- the toughness you've implies is not so great that people can't be crippled by dropping loads like this when the walkers lose their bearing.

Now let's imagine we get the same imbalance, but while carrying 100kg. Holding that weight at waist level won't do anything to our center of gravity. The imbalance has to be compensated by 17.5 Newtons of force, which is 11.6 times greater than if we weren't carrying anything.

The muscles quickly tire, or are overwhelmed, and the constant balancing mechanism will cease the function.

That sounds right- though how did you calculate the angles involved, and did you factor in the way the muscles in the body operate? For example, the muscles of the lower back routinely require forces of thousands of newtons while carrying heavy loads; that's why so many people go around with bad backs from trying to pull those muscles too hard.

Artillery ranging uses consistent-type projectiles for each shot, because otherwise you don't learn anything from THIS shot that can be translated to the next shot without doing differential equations in your head.

It also uses precision machinery, so you can repeat the same action with the gun and get the same result. Catapults are unlikely to be this precise.

I concede the point about ranging shots, but are you sure that this design is as inaccurate as a field-built wooden trebuchet?

If it wasn't assembled using precision machinery and operated under controlled conditions, it won't be accurate enough. Even Napoleonic cannons aren't, and they have a higher muzzle velocity, a firing mode that is inherently easier to make accurate, and so forth. Moreover, you have 200 mph crosswinds messing things up.

I don't think you understand what 'goes through half a meter of rock' means. It means it packs as much punch as a kilo of TNT. That's 4 sticks, and demolition crews use that amount to go through 4 ton of rock.
Since this is solid shot, the energy is transmitted into a cone starting from the point of impact and spreading until it reaches the back of the wall. The volume affected is equal to how much energy the projectile has divided by the yield strength (in kJ/kg) of the material.

A round figure I found was 30kJ/kg needed to crush the rock and displace it.
Our darts are disrupting 133kg of rock. Since the target is supposed to be rubble, not solid rock, and since it is not held together by mortar (what would they make it out of?), AND we only need a partial destruction of the grain's structure for the section to collapse... then it is safe to say that sizable chunks are being blasted out of the wall.

The problem here is that what's going to happen is that the impactor penetrates the cladding, then punches into a mass of rubble, which it "disrupts" into... a mass of rubble. Which is still being held in place by the cladding. Result? No significant change.

You can make this even more effective by just dumping an assload of sand into your rubble fill (since you imply that sand is readily available from all the wind erosion). This makes it very hard to destroy the wall- much as earthen ramparts with sloped facings were highly resistant to fire from siege guns during the gunpowder era.

The point is, if it's a realistic threat to have guys setting up mechanical artillery with effect comparable to Napoleonic siege artillery, the obvious counter is to design your fortifications to resist Napoleonic artillery. This is hardly impossible.

A method to estimate that effects is to use the 50cm of penetration. At the very least, it means that a hole the diameter of the solid shot and half a meter deep is going to be excavated into the wall. The displaced material has to go somewhere. If I'm guessing correctly, and that 50cm of penetration takes into account the perpendicular displacement of the rock, then the only outcome possible is for 4600cm3 of rock to blast out the back of the wall. It would bear a momentum and energy equal to what is left over from the shot after some of it is used to penetrate the wall.

If the wall is made like real walls of this thickness (as opposed to being a solid construction of dressed stone blocks, which is stupid), then it has a vast amount of interior volume acting as a "crumple zone" to absorb the displaced material. You are modeling the wall as a rigid object, when this is simply not the case. Broken-up rocks and sand can compress quite a bit when struck forcefully.

Of course, this is only an estimate. In real conditions, a very large section of the back wall would fly out, many times the volume excavated by the projectile. The velocity however would by much lower. Like bowling pins, striking the first pin would transmit the momentum to two others behind it, until we have a much larger number of bowling pins (volume of rock) flying out the back.

Except that if you actually (for instance) fire a cannon into a thick wall that consists of dressed stone faces holding together a mass of rubble, it doesn't do that. The wall swallows the cannonball without a burp. You only have any chance of breaching the wall when you've pounded on it so long that the outer face is in danger of falling apart structurally, and that takes a long time if the outer face of the wall isn't vertical.

Bear in mind that under no circumstances will you be able to hit the exact same point on the wall repeatedly, so your attack is scattershot all over its surface.

Medieval trebuchets were already obtaining an accuracy of 6x6m at a distance of 180m. Modern trebuchets (with metal hinges) have an accuracy of about 3m at 100m.

Modern trebuchets are not doing this by throwing aerodynamic darts in a hurricane-force wind, at ranges you have quotes as being up to a kilometer or more.

You might as well just come out and say "my model of warfare is based on a predatory military elite from a long-established and wealthy society, preying easily on the helpless, feeble, and impoverished colonies recently established around it." This is why I keep saying you're not describing a battle plan, you're describing an execution.

Oh, they do have decent ironworks. The problem is that iron, however well you smith it, just does not have the same resistance as high-grade steel. That requires certain ingredients you cannot get in a world devoid of most organic life, more specifically, the coke needed to reach high temperatures. It's a material scarcity, not lack of skill.

You're missing my point. The question you should ask is "if this little community is so feeble, so lacking in numbers and equipment, that it cannot produce armor and weapons of real value... what the hell are they doing constructing massive stone fortresses requiring them to move hundreds of thousands of tons of rock, yet providing virtually no security against the UBERLEET RAIDERS from the next town over?"

This does not represent a stable equilibrium.

[krakonfour]

Anyone capable of building or operating on that scale would be better advised to attack our planet directly- less work to achieve the same result.

Maybe Humanity at that time could oppose an enemy fleet sent their way? Maybe they could stop everything up to the energies involved in a GRB, for which they had no defense?
I don't want to dwell on the question right now. I might as well go down the old 'nuclear winter' backstory.

Constant winds blowing over sand mean dunes and sandstorms which impair visibility, making it suicide to run so fast. There are a lot of features that won't just cease to exist like that: rocks exposed by the blowing wind, unexpected patches of soft sand or other bad footing, and so on.

Well, they can't actually run at anything approaching 100km/h, they're going to be leaping. The cheetah is the closest thing I found running at these speeds. Their stride length is up to 8m long.

If we move over to our running giants, based on top human sprinters, 50% of the impulse in each stride is vertical.
http://www1.arielnet.com/start/apas/stu ... etcher.pdf - Page 27
The drag force at 100km/h for a 2m squared frontal cross-section, Cd: 1.1 is 22.5kN, so the force exerted is at least equal to this.

In other words, with each step, the giant jumps with 22.5kN of force for a total of 50kN average exerted over the course of a step. On a side note, the giant is producing 400kW and skin surface temperature is 300 degrees C.

Using the hip as a hinge for a 1.5m long leg, the ground contact time is 0.09s, half of which is spend accelerating.Using F=ma, I deduce that each giant flies for 0.4s between steps, covering about 8m. Working backwards, the step frequency is 2.04Hz.

What am I trying to prove?

Don't know, it's just interesting to calculate. My initial intent was to see if the Iron giant had enough time to gauge the terrain before the foot landed for each step, and it seems it can. The reaction speed necessary to run at all means 0.49 seconds is enough before each step to visually analyze the terrain ahead and gauge whether they're hitting a pit or a jutting rock.

Going back to the cheetah, how does the animal ever attempt to run at 100km/h with so much debris around?

It is simply not realistic to imagine a humanoid being running at high speed while carrying a mass significantly greater than its own bodyweight in its arms. If you want to do that, get a rickshaw.

Of course they wouldn't run with so much weight in their arms. They don't have enough horsepower! Also, there is no practical need to do so. Before the assault, there is no need to hurry.

Still dangerous- the toughness you've implies is not so great that people can't be crippled by dropping loads like this when the walkers lose their bearing.

I don't understand...
If we're speaking toughness, these guys can drop from dozens of meters safely and trip over at top speed without hurting themselves. They are after all a big lump of walking iron.

That sounds right- though how did you calculate the angles involved, and did you factor in the way the muscles in the body operate? For example, the muscles of the lower back routinely require forces of thousands of newtons while carrying heavy loads; that's why so many people go around with bad backs from trying to pull those muscles too hard.

I didn't factor in how the muscles are arranged, whether there are any ligament tensions or lever actions within the joints or anything, just the end result from a mechanical point of view. I mean, the foot has a certain width and we're mostly adjusting using the flat part under the toes. I just modeled the body as a pendulum and calculated the sideways force from being titled at 5 degrees.

If it wasn't assembled using precision machinery and operated under controlled conditions, it won't be accurate enough. Even Napoleonic cannons aren't, and they have a higher muzzle velocity, a firing mode that is inherently easier to make accurate, and so forth. Moreover, you have 200 mph crosswinds messing things up.

There's no way for me to find out the accuracy of the launching mechanism without actually building it.... I think the closest real-world equivalent, factoring in the wind, would be unguided rockets fired from WWII planes. If I could get data on those, I'd be able to guesstimate something.

The problem here is that what's going to happen is that the impactor penetrates the cladding, then punches into a mass of rubble, which it "disrupts" into... a mass of rubble. Which is still being held in place by the cladding. Result? No significant change.

You can make this even more effective by just dumping an assload of sand into your rubble fill (since you imply that sand is readily available from all the wind erosion). This makes it very hard to destroy the wall- much as earthen ramparts with sloped facings were highly resistant to fire from siege guns during the gunpowder era.

The point is, if it's a realistic threat to have guys setting up mechanical artillery with effect comparable to Napoleonic siege artillery, the obvious counter is to design your fortifications to resist Napoleonic artillery. This is hardly impossible.

The problem with rubble is that it is bad at spreading the force of impact to the rest of the rubble due to the infinitely lower contact area between particles compared to a solid rock face. The sectional density is much lower too, so if a penetrator can go through 50cm of solid rock, then it can go through 2 or 3m of rubble riddled with air-gaps. Also, the amount of rubble blasting out of the back is much greater, since less of the momentum is transferred to the rest of the wall's mass and more is retained in the displaced debris.
In short, the effects of a successful penetration are more devastating. And while yes, a rubble-filled wall has the great advantage of being self-healing to an extent, it is bad at actually standing up to a thin penetrator.

I don't see a downside though to a sloped rampart and sand-filling for increased resistance.

If the wall is made like real walls of this thickness (as opposed to being a solid construction of dressed stone blocks, which is stupid), then it has a vast amount of interior volume acting as a "crumple zone" to absorb the displaced material. You are modeling the wall as a rigid object, when this is simply not the case. Broken-up rocks and sand can compress quite a bit when struck forcefully.

Namely, the maximum load for specimen W1 was 372.1 kN, with
vertical shortening of 1.55 mm (Point 1). The collapse occurred later, with a load of 267.99 kN and vertical shortening of 5.29 mm (Point 2).
From: http://www.civil.ist.utl.pt/~rbento/tmp ... 12_253.pdf

They use rubble limestone walls and tested their reaction to compressive forces. The initial height was 70cm, so a compression ratio of 0.0022 at best doesn't sound very flexible. Steel rods in the same situation compress with a 0.000027 ratio.

What I'm trying to say is that the rubble is more likely to crumble and shoot out the back than absorb the shot like putty.

Except that if you actually (for instance) fire a cannon into a thick wall that consists of dressed stone faces holding together a mass of rubble, it doesn't do that. The wall swallows the cannonball without a burp. You only have any chance of breaching the wall when you've pounded on it so long that the outer face is in danger of falling apart structurally, and that takes a long time if the outer face of the wall isn't vertical.

Yes, you are right. It would take a lot of shots to make the rubble-filled wall collapse. However, in the mean time, each impact is causing spallation and shooting cones of ejecta. I'd like your sources/work on how you arrived to the conclusion that the cannonballs have no effect on the walls.

Modern trebuchets are not doing this by throwing aerodynamic darts in a hurricane-force wind, at ranges you have quotes as being up to a kilometer or more.

Indeed. I'll get back to the accuracy as mentioned above.
Here's a simple calculation on how much the shells could be deflected if they are shot from 1km:

325kg shell, made of 8000kg/m3 iron.
Length 50cm, diameter 32cm. Let's assume we have a 200mph wind blowing directly sideways to the direction of travel.

Projectile cross-section to the wind: 0.16m2
Wind force: I'll use the method detailed here: http://www.wikihow.com/Calculate-Wind-Load, using a Cd:0.8 for the shell. I get 2.83N.

The shell stays approximately 11 seconds in the air, based on the trebuchet simulator.
Sideways acceleration: 0.088m/s2
Sideways movement at impact: 8.8m

This means that even if the wind switched completely from one side to another, the effect on the shell is small enough to still hit the same section of a wall. Of course, the attackers will place their backs to the wind, and real life winds do not blow 200mph one way then another while the shell is still in flight.

You're missing my point. The question you should ask is "if this little community is so feeble, so lacking in numbers and equipment, that it cannot produce armor and weapons of real value... what the hell are they doing constructing massive stone fortresses requiring them to move hundreds of thousands of tons of rock, yet providing virtually no security against the UBERLEET RAIDERS from the next town over?"

This does not represent a stable equilibrium.

There are three types of battles, and all are the result of uranium fuel scarcity.
Imagine we have a successful community. They mine a lot, their population grows. Very quickly though, they will not be able to feed their entire population, not with the small average size of the uranium depot. A typical find is an ancient power station, buried underground. Today's power stations hold only 25 tons of uranium for the 1300MW class.

So, their needs grow. Two possibilities open up. Either they become rich enough to buy the fuel from other communities, or they have to resort to stealing it. If they are rich enough, they are going to mount armed and armored trade caravans to sell metalworks and minerals in exchange for the precious fuel, and these caravans will be attacked in the open. That's one type of battle.

If they are struggling, they will resort to expelling some of its members, either in glorified long-term scouting missions or by modifying the penal law... whatever the reason, these outcasts will have to group up to survive and mount new towers of their own. These are the poor, new communities trying to defend themselves. Only these guys have enough time on their hands and the desperation to search for the faint radioactive signals of an underground nuclear fuel depot.

A final option is to resort to attacking weaker communities and taking their resources. This is where the well-equipped, well-trained armed forces come from, raiding new communities in a form of 'predatory' warfare.

After the trade attacks and the raids, we have the organized battles.
These happen when rich towers group up and try to find another solution other than raiding the neighbourhood to exhaustion. There are no real countries because any clan can break the contract and hole himself up in his tower for years. These federations organize massive invasion parties and try to take over control of opposing conglomerates. Only they can gather the manpower and resources to break a siege and permanently occupy other communities.

So that's how the situation is.

PS: Do you find this setting interesting?

[Simon_Jester]

Actually, there wasn't much wrong with the gamma ray burst- the issue is simply determining how much of the atmosphere it burnt off.

Well, they can't actually run at anything approaching 100km/h, they're going to be leaping. The cheetah is the closest thing I found running at these speeds. Their stride length is up to 8m long.

If we move over to our running giants, based on top human sprinters, 50% of the impulse in each stride is vertical.

I don't deny they can run at whatever speed you claim over a race track- they're basically machines, and they can be as strong and tough as you like. Doesn't bother me.

My point is that running across country, while encumbered with very massive pieces of equipment, is basically impossible. Raiders carrying such heavy gear will be reduced to something like a walking pace, just by the necessity of not falling on their faces and scraping them at car-accident speeds every time they encounter an unexpected feature in the ground.

Likewise, the sheer physical mass and bulk of the iron-dudes means that they don't climb as well as humans on bad footing, such as a sand dune or a loose pile of rubble. They slip more, slide more, and might even sink right down into a deposit of soft sand, never to be seen again unless they can sink to the bottom and (somehow, eventually) find their way out onto rockier ground.

[And yeah, if there's that much sand, there are sand dunes in some places]

Don't know, it's just interesting to calculate. My initial intent was to see if the Iron giant had enough time to gauge the terrain before the foot landed for each step, and it seems it can. The reaction speed necessary to run at all means 0.49 seconds is enough before each step to visually analyze the terrain ahead and gauge whether they're hitting a pit or a jutting rock.

Going back to the cheetah, how does the animal ever attempt to run at 100km/h with so much debris around?

Well for one, it's running on relatively open ground. For another, it's not carrying objects heavier than its own body weight. That's the important part- I don't deny that your iron-dudes can run fast; my point is that it beggars the imagination that they can both run fast and carry loads massively larger than their own bodies at the same time.

If nothing else, the shifts in posture they'd need to counter "I'm about to hit a jutting rock, move my foot" are going to often be mutually exclusive with the shifts they need for "I'm carrying half the weight of a twenty-ton steel girder on my shoulder." Which is a good recipe for having the girder swing and take your fool head off, because you're running at car-accident speeds that can actually do that to metal objects.

Of course they wouldn't run with so much weight in their arms. They don't have enough horsepower! Also, there is no practical need to do so. Before the assault, there is no need to hurry.

But in that case, if the raiders are forced to flee (even temporarily) because they've been attacked by ten times their numbers of enemy warriors, they can run away but they must abandon their equipment in place.

Also, moving slowly while carrying heavy equipment increases the risk of being spotted by enemy patrols, who can run at whatever speed they wish.

And no, if this is going to come down to hand to hand, having superior armor and weapons won't save these guys if they're outnumbered five or ten to one. If nothing else, they'll get mobbed and wrestled into helpless positions.

There's no way for me to find out the accuracy of the launching mechanism without actually building it.... I think the closest real-world equivalent, factoring in the wind, would be unguided rockets fired from WWII planes. If I could get data on those, I'd be able to guesstimate something.

To summarize, they were miserably inaccurate. Very effective at demoralizing the enemy, but not good at all for missions like blowing up a hardened point target. Sometimes they got lucky.

The problem with rubble is that it is bad at spreading the force of impact to the rest of the rubble due to the infinitely lower contact area between particles compared to a solid rock face. The sectional density is much lower too, so if a penetrator can go through 50cm of solid rock, then it can go through 2 or 3m of rubble riddled with air-gaps. Also, the amount of rubble blasting out of the back is much greater, since less of the momentum is transferred to the rest of the wall's mass and more is retained in the displaced debris.

The cladding on the rear face of the wall acts as a spall liner. Rubble fill wouldn't work if you were dealing with cannonballs of this mass because it's not practical to build to the requisite thickness- but for something like this, with workers who can casually lift ten ton loads, hell yes it's practical to drop in a "rubble fill" mixed up of hundred pound rocks, then pour sand and gravel down to fill in the chinks and act as cushioning.

In fact, this is probably a lot easier than building the wall out of dressed stone blocks, because the giants will find dressing stone to make it nice and square to be a laborious and annoying task, while just lifting the rocks is relatively easy.

What I'm trying to say is that the rubble is more likely to crumble and shoot out the back than absorb the shot like putty.

I'd honestly think the sand fill would help a lot with that. Also, building a sturdy, well-buttressed back wall- it's not just a loose pile of rubble we're talking here, it's two dressed stone walls, the outer one slanted and possibly clad in metal, with rubble in-fill between them. This is the model used by real castle and city walls that were resistant to some pretty impressive mechanical siege artillery, modified for cannonball resistance.

Or that's my picture.

Now, cards on the table, I am not a structural engineer. Are you?

Yes, you are right. It would take a lot of shots to make the rubble-filled wall collapse. However, in the mean time, each impact is causing spallation and shooting cones of ejecta. I'd like your sources/work on how you arrived to the conclusion that the cannonballs have no effect on the walls.

Mostly just the observed ability of brick and earthen ramparts to absorb cannon fire; look at the trace italienne fortress designs and their ability to resist cannon fire for prolonged periods.

Stone will shatter more easily than brick, which is a serious problem IF you expect the structure to sit there for weeks taking hundreds upon hundreds of rounds. But given the constraints of these operations, I don't really expect that.

The shell stays approximately 11 seconds in the air, based on the trebuchet simulator.
Sideways acceleration: 0.088m/s2
Sideways movement at impact: 8.8m

The real problem is that since these are darts, the wind will tend to cause them to tumble (think about it, how do you keep an arrow flying on course when the airflow is, in its frame of reference, coming in at a significant angle away from its nose/tail), and lose speed very rapidly. If you can stay precisely upwind and the wind does not shift it's not much of a problem. But modest angular shifts in the wind, given that the wind moves as fast or faster than the darts do, are going to be an issue.

If they are struggling, they will resort to expelling some of its members, either in glorified long-term scouting missions or by modifying the penal law... whatever the reason, these outcasts will have to group up to survive and mount new towers of their own. These are the poor, new communities trying to defend themselves. Only these guys have enough time on their hands and the desperation to search for the faint radioactive signals of an underground nuclear fuel depot.

A final option is to resort to attacking weaker communities and taking their resources. This is where the well-equipped, well-trained armed forces come from, raiding new communities in a form of 'predatory' warfare.

The practical problem here is twofold. One is that the desperate groups may well build an entirely different category of home base than the strong ones. Rather than create huge, laborious stoneworks that seem to pose no serious deterrent to an UBERLEET RAIDING PARTY, they would tend to do whatever is possible to conceal their home base.

Another is that it would probably be less work for the strong central community to just colonize the outlying sources itself than to raid them.

PS: Do you find this setting interesting?

The setting is interesting, I just think certain parts of your picture of their means of warfare are unrealistic.

[krakonfour]

Actually, there wasn't much wrong with the gamma ray burst- the issue is simply determining how much of the atmosphere it burnt off.

No ozone layer? Perfect! Make this setting even more barren, flooded with UV and hostile to radio communications!

I don't deny they can run at whatever speed you claim over a race track- they're basically machines, and they can be as strong and tough as you like. Doesn't bother me.

My point is that running across country, while encumbered with very massive pieces of equipment, is basically impossible. Raiders carrying such heavy gear will be reduced to something like a walking pace, just by the necessity of not falling on their faces and scraping them at car-accident speeds every time they encounter an unexpected feature in the ground.

A logical consequence indeed. The amount of force they will be putting into each step is going to be the difference between their maximum output and the load.

And.... sh*t. All my drag force formulae are wrong by a factor v. I'll work with the correct v^2 factor then rewrite my previous calculations to correct for the v^3 I was using.
In simple terms, a 50kN step can withstand a drag force generated at speeds of 700km/h, not 144km/h. At 966 degrees C core temperature, they are producing 400kW thermal energy and 140kW of useful energy, running at a stupid speed of 1172km/h.

Let's imagine they are carrying 20 tons and that they drop by half a meter with each step. This means that they are putting out 98kJ with each step.
Their power production capacity is limited by their waste heat removal capacity. Radiation removes up to 78kW if the skin temperature is 300C, pretty much a maximum I'm assuming touch sensors can resist. The rest has to be convected through airflow, meaning it is dependent on wind speed.

We know that just standing around will give you an automatic 93m/s windspeed to cool down with. Thermal calc says that's 127kW for a total of 205kW dissipated. Working backwards, the useful energy is 110kW. The problem is that the force of the wind is 11kN.

The step frequency is therefore 1.2Hz, giving an 11km/h walk speed with such a load.

You can see how important waste heat management is. Toying around with the convection calculator, I find that each extra m2 facing the wind removes 59kW. Alse, drag force is directly linked to the drag coefficient, so I think that the armored suits will be some kind of winged, streamlined things designed to cut through the wind and radiate a maximum amount of heat.


Likewise, the sheer physical mass and bulk of the iron-dudes means that they don't climb as well as humans on bad footing, such as a sand dune or a loose pile of rubble. They slip more, slide more, and might even sink right down into a deposit of soft sand, never to be seen again unless they can sink to the bottom and (somehow, eventually) find their way out onto rockier ground.

[And yeah, if there's that much sand, there are sand dunes in some places]

Don't know, it's just interesting to calculate. My initial intent was to see if the Iron giant had enough time to gauge the terrain before the foot landed for each step, and it seems it can. The reaction speed necessary to run at all means 0.49 seconds is enough before each step to visually analyze the terrain ahead and gauge whether they're hitting a pit or a jutting rock.

Going back to the cheetah, how does the animal ever attempt to run at 100km/h with so much debris around?

Well for one, it's running on relatively open ground. For another, it's not carrying objects heavier than its own body weight. That's the important part- I don't deny that your iron-dudes can run fast; my point is that it beggars the imagination that they can both run fast and carry loads massively larger than their own bodies at the same time.

If nothing else, the shifts in posture they'd need to counter "I'm about to hit a jutting rock, move my foot" are going to often be mutually exclusive with the shifts they need for "I'm carrying half the weight of a twenty-ton steel girder on my shoulder." Which is a good recipe for having the girder swing and take your fool head off, because you're running at car-accident speeds that can actually do that to metal objects.

Of course they wouldn't run with so much weight in their arms. They don't have enough horsepower! Also, there is no practical need to do so. Before the assault, there is no need to hurry.

But in that case, if the raiders are forced to flee (even temporarily) because they've been attacked by ten times their numbers of enemy warriors, they can run away but they must abandon their equipment in place.

Also, moving slowly while carrying heavy equipment increases the risk of being spotted by enemy patrols, who can run at whatever speed they wish.

And no, if this is going to come down to hand to hand, having superior armor and weapons won't save these guys if they're outnumbered five or ten to one. If nothing else, they'll get mobbed and wrestled into helpless positions.

There's no way for me to find out the accuracy of the launching mechanism without actually building it.... I think the closest real-world equivalent, factoring in the wind, would be unguided rockets fired from WWII planes. If I could get data on those, I'd be able to guesstimate something.

To summarize, they were miserably inaccurate. Very effective at demoralizing the enemy, but not good at all for missions like blowing up a hardened point target. Sometimes they got lucky.

The problem with rubble is that it is bad at spreading the force of impact to the rest of the rubble due to the infinitely lower contact area between particles compared to a solid rock face. The sectional density is much lower too, so if a penetrator can go through 50cm of solid rock, then it can go through 2 or 3m of rubble riddled with air-gaps. Also, the amount of rubble blasting out of the back is much greater, since less of the momentum is transferred to the rest of the wall's mass and more is retained in the displaced debris.

The cladding on the rear face of the wall acts as a spall liner. Rubble fill wouldn't work if you were dealing with cannonballs of this mass because it's not practical to build to the requisite thickness- but for something like this, with workers who can casually lift ten ton loads, hell yes it's practical to drop in a "rubble fill" mixed up of hundred pound rocks, then pour sand and gravel down to fill in the chinks and act as cushioning.

In fact, this is probably a lot easier than building the wall out of dressed stone blocks, because the giants will find dressing stone to make it nice and square to be a laborious and annoying task, while just lifting the rocks is relatively easy.

What I'm trying to say is that the rubble is more likely to crumble and shoot out the back than absorb the shot like putty.

I'd honestly think the sand fill would help a lot with that. Also, building a sturdy, well-buttressed back wall- it's not just a loose pile of rubble we're talking here, it's two dressed stone walls, the outer one slanted and possibly clad in metal, with rubble in-fill between them. This is the model used by real castle and city walls that were resistant to some pretty impressive mechanical siege artillery, modified for cannonball resistance.

Or that's my picture.

Now, cards on the table, I am not a structural engineer. Are you?

Yes, you are right. It would take a lot of shots to make the rubble-filled wall collapse. However, in the mean time, each impact is causing spallation and shooting cones of ejecta. I'd like your sources/work on how you arrived to the conclusion that the cannonballs have no effect on the walls.

Mostly just the observed ability of brick and earthen ramparts to absorb cannon fire; look at the trace italienne fortress designs and their ability to resist cannon fire for prolonged periods.

Stone will shatter more easily than brick, which is a serious problem IF you expect the structure to sit there for weeks taking hundreds upon hundreds of rounds. But given the constraints of these operations, I don't really expect that.

The shell stays approximately 11 seconds in the air, based on the trebuchet simulator.
Sideways acceleration: 0.088m/s2
Sideways movement at impact: 8.8m

The real problem is that since these are darts, the wind will tend to cause them to tumble (think about it, how do you keep an arrow flying on course when the airflow is, in its frame of reference, coming in at a significant angle away from its nose/tail), and lose speed very rapidly. If you can stay precisely upwind and the wind does not shift it's not much of a problem. But modest angular shifts in the wind, given that the wind moves as fast or faster than the darts do, are going to be an issue.

If they are struggling, they will resort to expelling some of its members, either in glorified long-term scouting missions or by modifying the penal law... whatever the reason, these outcasts will have to group up to survive and mount new towers of their own. These are the poor, new communities trying to defend themselves. Only these guys have enough time on their hands and the desperation to search for the faint radioactive signals of an underground nuclear fuel depot.

A final option is to resort to attacking weaker communities and taking their resources. This is where the well-equipped, well-trained armed forces come from, raiding new communities in a form of 'predatory' warfare.

The practical problem here is twofold. One is that the desperate groups may well build an entirely different category of home base than the strong ones. Rather than create huge, laborious stoneworks that seem to pose no serious deterrent to an UBERLEET RAIDING PARTY, they would tend to do whatever is possible to conceal their home base.

Another is that it would probably be less work for the strong central community to just colonize the outlying sources itself than to raid them.

PS: Do you find this setting interesting?

[/quote]The setting is interesting, I just think certain parts of your picture of their means of warfare are unrealistic.[/quote]

[Simon_Jester]

We know that just standing around will give you an automatic 93m/s windspeed to cool down with. Thermal calc says that's 127kW for a total of 205kW dissipated. Working backwards, the useful energy is 110kW. The problem is that the force of the wind is 11kN.

The step frequency is therefore 1.2Hz, giving an 11km/h walk speed with such a load.

And much faster than that they become stupidly vulnerable to balance issues.

I mean... seriously, have you ever carried a big piece of furniture? This isn't just about energy calculations, unless you're familiar in detail with the biomechanics of humanoid bodies, which I know I'm not. People trip and fall when running fast over open ground. Especially when their attention is divided between managing a very heavy load and running very fast.





Aside from that you didn't actually respond to anything I said, so I'll just wait for a bit.

[krakonfour]

Actually, there wasn't much wrong with the gamma ray burst- the issue is simply determining how much of the atmosphere it burnt off.

No ozone layer? Perfect! Make this setting even more barren, flooded with UV and hostile to radio communications!

I don't deny they can run at whatever speed you claim over a race track- they're basically machines, and they can be as strong and tough as you like. Doesn't bother me.

My point is that running across country, while encumbered with very massive pieces of equipment, is basically impossible. Raiders carrying such heavy gear will be reduced to something like a walking pace, just by the necessity of not falling on their faces and scraping them at car-accident speeds every time they encounter an unexpected feature in the ground.

A logical consequence indeed. The amount of force they will be putting into each step is going to be the difference between their maximum output and the load.

And.... sh*t. All my drag force formulae are wrong by a factor v. I'll work with the correct v^2 factor then rewrite my previous calculations to correct for the v^3 I was using.

Let's imagine they are carrying 20 tons and that they drop by half a meter with each step. This means that they are putting out 98kJ with each step.
Their power production capacity is limited by their waste heat removal capacity. Radiation removes up to 78kW if the skin temperature is 300C, pretty much a maximum I'm assuming touch sensors can resist. The rest has to be convected through airflow, meaning it is dependent on wind speed.

We know that just standing around will give you an automatic 93m/s windspeed to cool down with. Thermal calc says that's 127kW for a total of 205kW dissipated. Working backwards, the useful energy is 110kW. The problem is that the force of the wind is 11kN.

The step frequency is therefore 1.2Hz, giving an 11km/h walk speed with such a load.

You can see how important waste heat management is. Toying around with the convection calculator, I find that each extra m2 facing the wind removes 59kW, so adding radiator fins is needed. Also, drag force is directly linked to the drag coefficient, so I think that the armored suits will be some kind of winged, streamlined things designed to cut through the wind and radiate a maximum amount of heat.

Here are my redone calculations:
A naked giant with no armor, drag coefficient 1.1, frontal cross-section 2m2, producing 90kW of useful power without extra cooling, can run up to 101km/h.
A giant wearing a full suit, running against the wind, frontal cross-section 4m2 with drag coefficient 0.5 (this one has 0.51, producing 200kW of useful power, can run up to 198km/h, but the weight or the armor reduces this speed in a way that is too difficult to calculate for now (I have to integrate the up/down motions of the suit and the power it consumes, remove it from the available power, then rework the speed with the remaining power before doing everything again with a new frequency for the suit's motions...)

A giant running in a proper lightweight speed suit, area 3m2 and Cd 0.3, driving the core up to 1100C, runs up to 258km/h.

Likewise, the sheer physical mass and bulk of the iron-dudes means that they don't climb as well as humans on bad footing, such as a sand dune or a loose pile of rubble. They slip more, slide more, and might even sink right down into a deposit of soft sand, never to be seen again unless they can sink to the bottom and (somehow, eventually) find their way out onto rockier ground.

[And yeah, if there's that much sand, there are sand dunes in some places]

I've been trying to look up the effects of long-term wind erosion and the end result is invariably desert pavement. This gets flattened into a hard, flat surface that crumbles. Also the temperature is cold, so there is little temperature difference between day and night that splits up stones easily.
Here's a picture of the landscape I envision:


Cold, desertic, rocky.

And they'll never sink through the sand like that!
If they are standing in small-grained sand, and sink in until their entire foot is covered in sand, I can assume that the full area of the foot is in contact with the sand instead of just their sole and heel.
Foot length is about 1/7 of height, so based on that, I got a foot area of about 0.09m2. Standing on two feet, they have 0.56kg/cm2 ground pressure. That's 7.8psi, about the same as a human on flat ground, and half of that of an M1 Abram tank (15psi). With full armor on, they have about 5-10 tons to distribute, with the minimal shoe size being 0.11m2. The ground pressure would then be 32-64psi. That's a lot, yes, but in comparison, we have horses at 25psi and mountain bicycles at 40psi.
I think that they would wear larger shoes if they wore armor on...

Well for one, it's running on relatively open ground. For another, it's not carrying objects heavier than its own body weight. That's the important part- I don't deny that your iron-dudes can run fast; my point is that it beggars the imagination that they can both run fast and carry loads massively larger than their own bodies at the same time.

If nothing else, the shifts in posture they'd need to counter "I'm about to hit a jutting rock, move my foot" are going to often be mutually exclusive with the shifts they need for "I'm carrying half the weight of a twenty-ton steel girder on my shoulder." Which is a good recipe for having the girder swing and take your fool head off, because you're running at car-accident speeds that can actually do that to metal objects.

Of course. They don't run when carrying heavy weights, they walk quickly. In fact, if they went full power to carry the girders, they'd still only be moving at an entirely manageable 20km/h, but then they'd overheat terribly.

But in that case, if the raiders are forced to flee (even temporarily) because they've been attacked by ten times their numbers of enemy warriors, they can run away but they must abandon their equipment in place.

Also, moving slowly while carrying heavy equipment increases the risk of being spotted by enemy patrols, who can run at whatever speed they wish.

And no, if this is going to come down to hand to hand, having superior armor and weapons won't save these guys if they're outnumbered five or ten to one. If nothing else, they'll get mobbed and wrestled into helpless positions.

That's possible. Another possibility is that the attackers will one-shot the defenders one by one as they approach, which takes a minimum of 30 seconds in open ground. In a case of overwhelming attack power, the defenders either wear very heavy suits or very light suits.
If they wear heavy suits, they will stand up to the aggressor's shots, but will never be able to catch up and will forever stay under fire without being close enough to return fire effectively. If they wear light suits, they will quickly catch up with the raiders, but will lose a member of their team with each hit. 5-10 ratio might not cut it in these conditions.

To summarize, they were miserably inaccurate. Very effective at demoralizing the enemy, but not good at all for missions like blowing up a hardened point target. Sometimes they got lucky.

Yeah, but just how inaccurate? How far away would they reliable hit the same wall? Same section of a wall? Same crater in the wall?

The cladding on the rear face of the wall acts as a spall liner. Rubble fill wouldn't work if you were dealing with cannonballs of this mass because it's not practical to build to the requisite thickness- but for something like this, with workers who can casually lift ten ton loads, hell yes it's practical to drop in a "rubble fill" mixed up of hundred pound rocks, then pour sand and gravel down to fill in the chinks and act as cushioning.

In fact, this is probably a lot easier than building the wall out of dressed stone blocks, because the giants will find dressing stone to make it nice and square to be a laborious and annoying task, while just lifting the rocks is relatively easy.

Lol it'd be like peeling potatoes for them. Cut cut cut then chuck over the shoulder.
I understand where you're coming from. Cladding the entire internal surface of the wall with metal, especially when metal is a trade product, is going to be damn expensive. Maybe they'll create safe rooms, lined with iron instead.

Also, I looked up trace italienne fortresses and damn they are beautiful.

What I'm trying to say is that the rubble is more likely to crumble and shoot out the back than absorb the shot like putty.

I'd honestly think the sand fill would help a lot with that. Also, building a sturdy, well-buttressed back wall- it's not just a loose pile of rubble we're talking here, it's two dressed stone walls, the outer one slanted and possibly clad in metal, with rubble in-fill between them. This is the model used by real castle and city walls that were resistant to some pretty impressive mechanical siege artillery, modified for cannonball resistance.

Or that's my picture.

Now, cards on the table, I am not a structural engineer. Are you?[/quote]

Not even structural engineers have medieval castle building in their books!
The design does look sound. It's the set-up they use to test bunker-buster penetration, the first layer simulates a rock cover, then the second layer is the actual concrete with compacted earth in between.

I real some articles on star-forts designed to resist cannon fire, and one of the aspects of the design was deflecting cannonballs by presenting a sloped surface. Since the attack could come from any direction, it gave them the star-shaped appearance. However, in this setting, the prevailing direction is wind-ward. I'd think the defenders would exploit this and make a diamond-shaped fort, with the pointed edges facing the wind and the flatter edges to the sides, because no same artillery would fire against a side-ways wind.

The real problem is that since these are darts, the wind will tend to cause them to tumble (think about it, how do you keep an arrow flying on course when the airflow is, in its frame of reference, coming in at a significant angle away from its nose/tail), and lose speed very rapidly. If you can stay precisely upwind and the wind does not shift it's not much of a problem. But modest angular shifts in the wind, given that the wind moves as fast or faster than the darts do, are going to be an issue.

Maybe, just maybe, if the rails on the design I presented before can become fully enclosed and turn into some sort of rifled barrel, then we could spin the parts and stabilize them that way.

The practical problem here is twofold. One is that the desperate groups may well build an entirely different category of home base than the strong ones. Rather than create huge, laborious stoneworks that seem to pose no serious deterrent to an UBERLEET RAIDING PARTY, they would tend to do whatever is possible to conceal their home base.

Another is that it would probably be less work for the strong central community to just colonize the outlying sources itself than to raid them.

Concealing an uranium mine with the giant windmills needed to power the refineries is going to be hard, especially so in a mostly featureless landscape. The stoneworks DO pose a threat to raiding parties. They might not be impervious to attack, but they do make each raiding operation costly. There's a reason a rich community does not send out its entire army each time it goes attacking the weaker neighbourhood: it costs too damn much to supply and repair the high grade steel that is damaged in each attack. So it sends a few, and hopes to get back more in value than it paid for the operation.

The stoneworks are dirt cheap in comparison. When your labor force is a bunch of desperate machines that never eat or sleep and can chuck around huge blocks of stone, you will be able to complete the tower quickly, and repair it in even less time.

I also mentioned the heavy-suit approach above.

If all the defenders put on their heaviest armor and slowly trodded their way to the opposition, they can force the raiders to leave their equipment behind and escape. The raider's losses are zero, but the cost is great. If the rich community sends out too many raiding operations where is could not simply rush the defenders and get away, then it won't be rich anymore.

[krakonfour]

I accidentally hit 'Submit' instead of preview while I was in the middle of writing, so sorry for the earlier post.

[Simon_Jester]

Here are my redone calculations:
A naked giant with no armor, drag coefficient 1.1, frontal cross-section 2m2, producing 90kW of useful power without extra cooling, can run up to 101km/h.
A giant wearing a full suit, running against the wind, frontal cross-section 4m2 with drag coefficient 0.5 (this one has 0.51, producing 200kW of useful power, can run up to 198km/h, but the weight or the armor reduces this speed in a way that is too difficult to calculate for now (I have to integrate the up/down motions of the suit and the power it consumes, remove it from the available power, then rework the speed with the remaining power before doing everything again with a new frequency for the suit's motions...)

A giant running in a proper lightweight speed suit, area 3m2 and Cd 0.3, driving the core up to 1100C, runs up to 258km/h.

I strongly suspect he's going to trip and fall running at these speeds, unless he can find very good ground to run on. He'd probably be better off riding a wide-tired bicycle with an aeroshell to reduce drag.

The problem here is that you're very good at handling 'static load' problems, in other words at drawing a free body diagram and balancing the forces exerted on something. I have considerable respect for that. But you're mostly not considering more complex aspects of the problem when dynamic loads start turning up- such as the effect of the foot-to-ground force on the ground itself, whether or not the iron guy's foot will skid when he strikes smooth rock at 200 km/h, things like that.

I've been trying to look up the effects of long-term wind erosion and the end result is invariably desert pavement. This gets flattened into a hard, flat surface that crumbles. Also the temperature is cold, so there is little temperature difference between day and night that splits up stones easily.
Here's a picture of the landscape I envision:

Okay, within reason- but there are always going to be soft spots, patches of gravel sheltered by tiny dips in the terrain, and so on.

In a lot of places you'll get things like salt flats that are ideal for high speed running (there's a reason they test rocket cars out at Bonneville), but the point is that any irregularity in the ground will have very painful consequences if you run into it at 200-250 km/h.

Also, people may try to deliberately create belts of such irregularities around their own homes, out to a distance of several kilometers- the equivalent of sowing caltrops in medieval warfare, to discourage your enemies from running at excessive speed in or around your stronghold.

Standing on two feet, they have 0.56kg/cm2 ground pressure. That's 7.8psi, about the same as a human on flat ground, and half of that of an M1 Abram tank (15psi). With full armor on, they have about 5-10 tons to distribute, with the minimal shoe size being 0.11m2. The ground pressure would then be 32-64psi. That's a lot, yes, but in comparison, we have horses at 25psi and mountain bicycles at 40psi.

There's got to be something wrong with a calculation that gives a giant iron man the same ground pressure as a human being on his feet... one of us is missing something, very probably me.

That's possible. Another possibility is that the attackers will one-shot the defenders one by one as they approach, which takes a minimum of 30 seconds in open ground. In a case of overwhelming attack power, the defenders either wear very heavy suits or very light suits.

If they wear heavy suits, they will stand up to the aggressor's shots, but will never be able to catch up and will forever stay under fire without being close enough to return fire effectively. If they wear light suits, they will quickly catch up with the raiders, but will lose a member of their team with each hit. 5-10 ratio might not cut it in these conditions.

I don't expect these guys to be able to make ranged weapons consistently lethal on every throw- no real army ever accomplished that, even without armor. Given room to spread out, skirmish, bob and weave, they cover ground fast enough to limit casualties from ranged weapons- carrying a large shield will also help, and the shield can be cast away in melee.

When it comes down to hand to hand combat, the greatest advantage of the numerous side is that they can literally say "OK, you two, use your weapons to parry and bind his weapon, while we two circle behind, flip him over and stick a spear in his back." If they fight with any real competence and coordination, it won't matter that the UBERLEET RAIDER's weapon can kill them with one hit; if one armored man with a sword fights four or five or ten unarmored men with swords, he's going to lose unless they screw up by the numbers.

To summarize, they were miserably inaccurate. Very effective at demoralizing the enemy, but not good at all for missions like blowing up a hardened point target. Sometimes they got lucky.

Yeah, but just how inaccurate? How far away would they reliable hit the same wall? Same section of a wall? Same crater in the wall?

Note that the craters made in the expected type of wall aren't necessarily that large...

The cladding on the rear face of the wall acts as a spall liner. Rubble fill wouldn't work if you were dealing with cannonballs of this mass because it's not practical to build to the requisite thickness- but for something like this, with workers who can casually lift ten ton loads, hell yes it's practical to drop in a "rubble fill" mixed up of hundred pound rocks, then pour sand and gravel down to fill in the chinks and act as cushioning.

In fact, this is probably a lot easier than building the wall out of dressed stone blocks, because the giants will find dressing stone to make it nice and square to be a laborious and annoying task, while just lifting the rocks is relatively easy.

Lol it'd be like peeling potatoes for them. Cut cut cut then chuck over the shoulder.

The problem is in making the cuts precisely enough for the stones to be fitted without mortar. You just said they don't have any mortar, which makes rubble fill a LOT more appealing, because it vastly decreases the amount of precision work involved in fitting together stones to make a large, thick wall.

I understand where you're coming from. Cladding the entire internal surface of the wall with metal, especially when metal is a trade product, is going to be damn expensive. Maybe they'll create safe rooms, lined with iron instead.

Possibly. On the other hand, you don't need metal cladding on the inside for the inside to act as a spall liner. Just having heavy buttressing and a slightly slanted wall which acts to hold the rubble down and in place helps. By the time you get far enough through the wall that the rubble fill is bumping up against the back, you're no longer trying to contain a fast-moving impact, you're trying to tamp down a large but slow movement of a great mass of rocks. Not quite the same problem as containing the spallation fragments from steel AP rounds hitting steel armor.

Also, I looked up trace italienne fortresses and damn they are beautiful.

Also highly resistant to cannonballs, and cannonballs of the 1500-1800 era are roughly as destructive as these guys' mechanical artillery. Question: would you happen to be an American?

What I'm trying to say is that the rubble is more likely to crumble and shoot out the back than absorb the shot like putty.

I'd honestly think the sand fill would help a lot with that. Also, building a sturdy, well-buttressed back wall- it's not just a loose pile of rubble we're talking here, it's two dressed stone walls, the outer one slanted and possibly clad in metal, with rubble in-fill between them. This is the model used by real castle and city walls that were resistant to some pretty impressive mechanical siege artillery, modified for cannonball resistance.

Or that's my picture.

Now, cards on the table, I am not a structural engineer. Are you?

Not even structural engineers have medieval castle building in their books!
The design does look sound. It's the set-up they use to test bunker-buster penetration, the first layer simulates a rock cover, then the second layer is the actual concrete with compacted earth in between. [/quote]Right. Well, you might have looked up castle walls before you got too into this, since your guys are essentially building castles.

Seriously though, that's the key idea- to understand that since cannonball-equivalent mechanical artillery is a realistic threat, fortifications will be designed to resist such artillery, and such designs are very much possible.

I real some articles on star-forts designed to resist cannon fire, and one of the aspects of the design was deflecting cannonballs by presenting a sloped surface. Since the attack could come from any direction, it gave them the star-shaped appearance. However, in this setting, the prevailing direction is wind-ward. I'd think the defenders would exploit this and make a diamond-shaped fort, with the pointed edges facing the wind and the flatter edges to the sides, because no same artillery would fire against a side-ways wind.

Yes- the real point I made in talking about star forts (which is the English name for the trace italienne design) is that the walls resist cannon fire much, MUCH better than a stereotypical curtain wall of vertical dressed stone would. Here, you'd use rubble of rocks and sand in place of dirt to build up the substance of the walls, but it's the same basic idea.

The practical problem here is twofold. One is that the desperate groups may well build an entirely different category of home base than the strong ones. Rather than create huge, laborious stoneworks that seem to pose no serious deterrent to an UBERLEET RAIDING PARTY, they would tend to do whatever is possible to conceal their home base.

Another is that it would probably be less work for the strong central community to just colonize the outlying sources itself than to raid them.

Concealing an uranium mine with the giant windmills needed to power the refineries is going to be hard, especially so in a mostly featureless landscape.

Why not conceal the uranium mine, then move the ore to another location for refining? Say, one on top of a mountain? Or one that's in the middle of rough, broken terrain that slows down raiders operating in the immediate environs of the fort, so that they will be intercepted and attacked by patrols when they try to make their escape.

The stoneworks are dirt cheap in comparison. When your labor force is a bunch of desperate machines that never eat or sleep and can chuck around huge blocks of stone, you will be able to complete the tower quickly, and repair it in even less time.

This I acknowledge, but I do suggest that you consider alternate strategies the groups might pursue- for example, they might explore ways to build windmills that don't rely on huge, highly visible towers. They might find a way to power their refinery with guys on bicycle-equivalents, and not bother with windmills at all.

If all the defenders put on their heaviest armor and slowly trodded their way to the opposition, they can force the raiders to leave their equipment behind and escape. The raider's losses are zero, but the cost is great. If the rich community sends out too many raiding operations where is could not simply rush the defenders and get away, then it won't be rich anymore.

As long as this is recognized, then good quality fiction is preserved and all is wellish.

[krakonfour]

I strongly suspect he's going to trip and fall running at these speeds, unless he can find very good ground to run on. He'd probably be better off riding a wide-tired bicycle with an aeroshell to reduce drag.

It's more likely that this is going to be a burst speed, than a sustained velocity. It's still nice to know what the upper limit is.

Speaking of wheeled vehicles, there are some in this setting. They are used to carry loads in caravans. As for personal locomotion, well... The Flintstones?

Okay, within reason- but there are always going to be soft spots, patches of gravel sheltered by tiny dips in the terrain, and so on.

In a lot of places you'll get things like salt flats that are ideal for high speed running (there's a reason they test rocket cars out at Bonneville), but the point is that any irregularity in the ground will have very painful consequences if you run into it at 200-250 km/h.

Also, people may try to deliberately create belts of such irregularities around their own homes, out to a distance of several kilometers- the equivalent of sowing caltrops in medieval warfare, to discourage your enemies from running at excessive speed in or around your stronghold.

That's something I totally forgot. Deliberately messing up the terrain to the defender's advantage. I think something like camouflaged pits and scattered debris would be more effective than moats. A caltrop trying to penetrate an iron foot isn't going to happen.

There's got to be something wrong with a calculation that gives a giant iron man the same ground pressure as a human being on his feet... one of us is missing something, very probably me.

The giant's foot increases in area with height, and the average giant is nearly double that of a human (3m vs 1.75m). I also used the full skin surface area under the foot, claiming it was partially sunk into sand to maximize contact area. On a hard, flat surface, it's going to be around 2-3 times higher.
Anyhow, they're going to be wearing shoes with a much greater area than their bare feet.

I don't expect these guys to be able to make ranged weapons consistently lethal on every throw- no real army ever accomplished that, even without armor. Given room to spread out, skirmish, bob and weave, they cover ground fast enough to limit casualties from ranged weapons- carrying a large shield will also help, and the shield can be cast away in melee.

Ah yes, I detailed in earlier posts that the most likely lethal hit was a chest penetration, which has a great amount of armor on top of it. I was exaggerating with the one-shot-per-kill thing, real life conditions are far from perfect. The giants might be able to launch javelins with the exact same speed and angle with each throw (machines!), but factors they cannot influence decrease their hit ratio.

The best way to approach a firing squad is at a slanted angle. This is the best balance between closing the distance and making the opponent deflect the shots against the wind.

Carrying a discardable shield is an interesting tactic, but we also have the vast realm of mecha warfare to rely on. The aim of this setting is creating interesting combat, so coming up with quirky tactics to amaze the audience is part of the job.

When it comes down to hand to hand combat, the greatest advantage of the numerous side is that they can literally say "OK, you two, use your weapons to parry and bind his weapon, while we two circle behind, flip him over and stick a spear in his back." If they fight with any real competence and coordination, it won't matter that the UBERLEET RAIDER's weapon can kill them with one hit; if one armored man with a sword fights four or five or ten unarmored men with swords, he's going to lose unless they screw up by the numbers.

Even less that is needed. A superior-armed force can stall an enemy at long range indefinitely. At close range, the fight boils down to a matter of skill, because even a rudimentary, soft iron spear or club can still penetrate a weakpoint or bash in armor, however thick.

Note that the craters made in the expected type of wall aren't necessarily that large...

About 50cm by 50cm. If they hit a collapsible rubble wall or dirt filling, the opening will close up. If they hit a solid surface, the cracks will provide an entire weakened section to capitalize on.

The problem is in making the cuts precisely enough for the stones to be fitted without mortar. You just said they don't have any mortar, which makes rubble fill a LOT more appealing, because it vastly decreases the amount of precision work involved in fitting together stones to make a large, thick wall.

I wonder if a metal framework can be used to hold together the stones, or maybe the stones themselves can be carved with grooves that increase the contact area between stones until they hold together by friction.

Another method would be pressure-welding a sheet of metal between the stones.

Possibly. On the other hand, you don't need metal cladding on the inside for the inside to act as a spall liner. Just having heavy buttressing and a slightly slanted wall which acts to hold the rubble down and in place helps. By the time you get far enough through the wall that the rubble fill is bumping up against the back, you're no longer trying to contain a fast-moving impact, you're trying to tamp down a large but slow movement of a great mass of rocks. Not quite the same problem as containing the spallation fragments from steel AP rounds hitting steel armor.

True.
The dirt-cheap solution against spallation is... dirt. Pardon the pun. The soil can be placed against the back of the wall, and would have the thickness to stop any fragments from flying out.

The only problem with all these solutions (sloping, buttresses, anti-spallation layer, inter-wall earth fill, sloped rampart, curtail walls... is that they're going to take up a shitload of space.

Also highly resistant to cannonballs, and cannonballs of the 1500-1800 era are roughly as destructive as these guys' mechanical artillery. Question: would you happen to be an American?

I think their main aim was to return fire and remove the main weakspots (corners) and blindspots of square walls. If we are not going to mount trebuchets on the walls, then some of the more extreme features can be removed. For example, the top of the walls doesn't have to be wide and flat to place cannons on, they can end in ridges instead.

As for me...
I'm of British-French-Algerian-New Zealander origin. Pick your favorite part.

I'd honestly think the sand fill would help a lot with that. Also, building a sturdy, well-buttressed back wall- it's not just a loose pile of rubble we're talking here, it's two dressed stone walls, the outer one slanted and possibly clad in metal, with rubble in-fill between them. This is the model used by real castle and city walls that were resistant to some pretty impressive mechanical siege artillery, modified for cannonball resistance.

I fully agree.
It's just that I find it unlikely that a newly-built community with no metal to spare can integrate all of these features into the walls. Maybe the walls will evolve as they grow richer, and the difference between a rich and poor tower is that one has a simple rubble-fill wall with earthen ramparts, and the other is a dozen meters thick multi-layered wall resistant to just about anything for weeks.

Also, a raiding party will have to scout the tower before-hand. If the defenses are shoddy or newly-built, then they'll attack. If it's just too difficult, then it isn't worth the cost of the tons of iron they'd have to fire to go through the defenses.

I mean, sieges here are nothing like on earth. There can never be the option of starving the opposition into submission, or waiting for disease to take over. The defender's aren't waiting for a relief army to come and help them, and the attackers have come for a hit-and-run affair, not occupation. The actual mechanics of taking over a castle may be historical, but the entire scenario around it can be different.
For example, a determined occupation force numbering in the thousands can stay in place for years if they wanted to, and we'd reach the point where it is easier for the defenders to recycle the darts thrown at them than mining their own supply of ammunition. Even if the windmills are torn off right at the start of the conflict, and no more uranium fuel is produced, they guys can last for a long time. They're got self-breeding reactors after all!

Maybe they'll develop an honor system to avoid year-long sieges costing kilotons of iron shot. Tournaments, or a duel to the death between generals, and situations like David vs Goliath occur.

Right. Well, you might have looked up castle walls before you got too into this, since your guys are essentially building castles.

Seriously though, that's the key idea- to understand that since cannonball-equivalent mechanical artillery is a realistic threat, fortifications will be designed to resist such artillery, and such designs are very much possible.

I'll look into it. Thanks for providing the direction of study.

Why not conceal the uranium mine, then move the ore to another location for refining? Say, one on top of a mountain? Or one that's in the middle of rough, broken terrain that slows down raiders operating in the immediate environs of the fort, so that they will be intercepted and attacked by patrols when they try to make their escape.

It'd add a weak link to the system: transporting the ore from the mine to the refinery-fortress. I can imagine that the machines running across featureless terrain aren't very stealthy, and their tracks will be humongous. Furthermore: heat. A bunch of miners working underground with little ventilation are going to be HOT. A visible column of distorted air, if not smoke, will rise and be visible for kilometers around.

I don't think this setting allows for much stealth.

This I acknowledge, but I do suggest that you consider alternate strategies the groups might pursue- for example, they might explore ways to build windmills that don't rely on huge, highly visible towers. They might find a way to power their refinery with guys on bicycle-equivalents, and not bother with windmills at all.

Poor machines, actually being used as machines...
I'll think up of alternatives.
Something on top of my head is a well-established colony mining deep enough to set up geothermal energy.

As long as this is recognized, then good quality fiction is preserved and all is wellish.

I'm trying to find out how this setting can be turned into a good story. A plot skeleton I have in my head is a lieutenant participating in a joint raiding operation with an allied force. The target is a new tower in the allies 'hunting ground', and the lieut and his platoon are helping for a share of the profits. The allies cause the greatest civilian massacre of recent history (killing civilians when the Iron giant population is so low is understandably horrific), and the lieutenant gets dragged along and kills somebody. The allies are in fact trying to cause a Great War between federated nations, and use the massacre in their back garden as a casus belli by removing their names from the culprits and blaming it on the other guys.
The lieut and his platoon mates now have their names tarnished, and will face the death penalty wherever they go. Feeling guilty despite the events, they split up and try and hide in the neighbourhood. The main character takes up the identity of the guy he murdered as atonement.
He passes the beginning of the war as a mercenary for low-key colonies. His skills are recognized but he is labelled a coward because he deserts whenever a non-combatant dies. He ends up in one of the major cities of the federation attacking his home land. There, he finds his platoon mates again, and together they try and find a way to help their homeland from their position. Some have put down their arms, some actively defend their new home and others just want to be free from their homeland's dictatorship. Tense philosophical discussion on whether to defend your country or not if you disagree with the way it's governed, or whether to fight for a morally right country that uses underhand methods to cause wars.
The lieut steals a suit and fights his way to the frontline to find an answer.

[Simon_Jester]

Plot sounds interesting, good one.

Side note: I wonder if these guys might experiment with actual turbines for wind? They'd be a lot less exposed, and could be placed lower to the ground while still extracting power. High wind velocity makes a many-bladed turbine more practical.

I strongly suspect he's going to trip and fall running at these speeds, unless he can find very good ground to run on. He'd probably be better off riding a wide-tired bicycle with an aeroshell to reduce drag.

It's more likely that this is going to be a burst speed, than a sustained velocity. It's still nice to know what the upper limit is.

Speaking of wheeled vehicles, there are some in this setting. They are used to carry loads in caravans. As for personal locomotion, well... The Flintstones?

A rickshaw would be quite effective, for people who can't handle manufacturing decent gears. A bicycle is a much more efficient means of transportation than any Flintstones-style vehicle could be, simply because it is lighter. A bicycle or bicycle-like vehicle (possibly a quadcycle) powered by pedal action would be every bit as good as a car here, probably better in some ways. And it would almost certainly be more energy-efficient than running or jumping, allowing people to travel fast in cool comfort, with style.

Also, people may try to deliberately create belts of such irregularities around their own homes, out to a distance of several kilometers- the equivalent of sowing caltrops in medieval warfare, to discourage your enemies from running at excessive speed in or around your stronghold.

That's something I totally forgot. Deliberately messing up the terrain to the defender's advantage. I think something like camouflaged pits and scattered debris would be more effective than moats. A caltrop trying to penetrate an iron foot isn't going to happen.

Yes. I mean, if you can run at 100 km/h you can leap a pretty wide ditch. But God help you if someone's been walking around with a heavy shovel chopping irregular foot-wide holes out of the ground you try to run across.

There would probably be gaps in any such field of obstacles, but it'd make a damn good deterrent against anyone trying to run fast near you. Such an obstacle course might be placed in the bits of ground most suitable for planting siege engines- it's a lot less work than building the walls, if you have a good shovel in the first place.

There's got to be something wrong with a calculation that gives a giant iron man the same ground pressure as a human being on his feet... one of us is missing something, very probably me.

The giant's foot increases in area with height, and the average giant is nearly double that of a human (3m vs 1.75m). I also used the full skin surface area under the foot, claiming it was partially sunk into sand to maximize contact area. On a hard, flat surface, it's going to be around 2-3 times higher.
Anyhow, they're going to be wearing shoes with a much greater area than their bare feet.

True, but that will also make them clumsy on their feet- clown shoes are awkward. As to fast running on sand, the problem is that the instantaneous pressure is likely to cause the sand to slide and give way at least a little. A wheeled vehicle can handle having the ground under it give way a bit; a running man has more trouble with that.

Likewise, when climbing rubble or natural rock surfaces, the problem is simply that there are fewer hand and foot holds that have enough structural strength to support the weight of a multi-ton man. You grab a rock to pull yourself up, and instead you pull the rock down onto your head and trigger a landslide that carries you right back down to the bottom.

When it comes down to hand to hand combat, the greatest advantage of the numerous side is that they can literally say "OK, you two, use your weapons to parry and bind his weapon, while we two circle behind, flip him over and stick a spear in his back." If they fight with any real competence and coordination, it won't matter that the UBERLEET RAIDER's weapon can kill them with one hit; if one armored man with a sword fights four or five or ten unarmored men with swords, he's going to lose unless they screw up by the numbers.

Even less that is needed. A superior-armed force can stall an enemy at long range indefinitely. At close range, the fight boils down to a matter of skill, because even a rudimentary, soft iron spear or club can still penetrate a weakpoint or bash in armor, however thick.

I think you exaggerate the "stall at long range" aspect. Especially if we incorporate my idea of systematically making the ground shitty to run on for several miles around the fortress- defender patrols could outmaneuver the raiders, get around behind them faster than they can retreat by exploiting clear lanes through the roughened ground, and come at them from multiple directions.

I wonder if a metal framework can be used to hold together the stones...

If you can work metal in the requisite quantity this is a great idea, and largely nullifies the ability to crack the stones.

Or maybe the stones themselves can be carved with grooves that increase the contact area between stones until they hold together by friction.

Mortise and tenon joints are a common technique in early stoneworking, and still used today in some cases, yes.

True.
The dirt-cheap solution against spallation is... dirt. Pardon the pun. The soil can be placed against the back of the wall, and would have the thickness to stop any fragments from flying out.

Well, there's no topsoil here, only sand and crumbly rock, right? However...

The only problem with all these solutions (sloping, buttresses, anti-spallation layer, inter-wall earth fill, sloped rampart, curtail walls... is that they're going to take up a shitload of space.

The inter-wall fill of rubble and the sloped rampart take up space outside the wall, which is largely irrelevant. The rubble fill in particular is vastly less labor-intensive than building a wall of dressed stone, especially since you can use the fruits of your own mining excavation as rubble.

The anti-spallation layer takes up space inside the wall, but you'd need SOME kind of solid wall in place to hold back the inside of the rubble fill anyway, or it's going to slide down and bury you anyhow. Buttressing that wall takes up space, but is necessary if the wall is to be very high- a near-vertical stone wall fifty feet high isn't particularly stable.

Also highly resistant to cannonballs, and cannonballs of the 1500-1800 era are roughly as destructive as these guys' mechanical artillery. Question: would you happen to be an American?

I think their main aim was to return fire and remove the main weakspots (corners) and blindspots of square walls.

Nonono.

You're looking at the geometry of the walls in terms of where the walls were placed. I'm thinking in terms of the cross-sectional geometry, the structure of the wall itself. My point is that the star forts of the trace italienne were built to resist cannonfire, and their walls could absorb vast amounts of it. Your point is that the walls were laid out in specific ways to avoid blind spots. We're both right, but we're talking past each other.

If we are not going to mount trebuchets on the walls, then some of the more extreme features can be removed. For example, the top of the walls doesn't have to be wide and flat to place cannons on, they can end in ridges instead.

You'd still want a parapet and battlements, and possibly places to mount some kind of very large crossbow. The top of the wall is a good place to stand, keep watch, and shoot at intruders, after all.

I asked if you were American because I live near a (modest) star fort, and was wondering if you'd seen it because it's mildly famous in American history. Many, many SDN-ers are from other countries, but enough SDN-ers are from the US that it's probably the single most likely country of origin.

It's just that I find it unlikely that a newly-built community with no metal to spare can integrate all of these features into the walls. Maybe the walls will evolve as they grow richer, and the difference between a rich and poor tower is that one has a simple rubble-fill wall with earthen ramparts, and the other is a dozen meters thick multi-layered wall resistant to just about anything for weeks.

True. On the other hand, probably the first thing they'd do is build their curtain wall, then heap piles of mine tailings outside it to act as the "rubble fill." The outer retaining wall might not even be added until later, or built to significantly reduced height- so at first, the wall might look like a low stone 'fence' at the outer perimeter of the wall, a talus slope of rubble and mine tailings inside that, and then a high curtain wall on the inner perimeter.

The talus slope would actually be a bitch to climb if the rocks are broken up finely enough, as mentioned- because it just doesn't have the structural strength to support a giant statue's weight.

[krakonfour]

Plot sounds interesting, good one.

It's just a rough first draft. I'll work on it more.

Side note: I wonder if these guys might experiment with actual turbines for wind? They'd be a lot less exposed, and could be placed lower to the ground while still extracting power. High wind velocity makes a many-bladed turbine more practical.

Maybe the richer towers could use this. If fact, it could be an argument as to why a rich community wouldn't need towers: the turbines can be concealed and shielded behind armored walls, with the winds being ducted from the outside through minimal slits in the walls.
Why only rich towers: a working, geared multi-bladed turbine is going to use up a lot of metal and precision craftsmanship to be constructed than a simple windmill.

Humm. I'm seeing poor colonies having a tall, rubble wall reinforced with earthen buttresses, encircling a tower with windmills mounted on it, while rich communities have vast structures standing up to artillery fire, several concentric walls with metal spall liners and very low ducts bringing wind to the turbines inside.

]A rickshaw would be quite effective, for people who can't handle manufacturing decent gears. A bicycle is a much more efficient means of transportation than any Flintstones-style vehicle could be, simply because it is lighter. A bicycle or bicycle-like vehicle (possibly a quadcycle) powered by pedal action would be every bit as good as a car here, probably better in some ways. And it would almost certainly be more energy-efficient than running or jumping, allowing people to travel fast in cool comfort, with style.

A quadcar can mount a much larger cooling system for the rider than an armored suit can, so there's another argument for its use. Though to see huge armored beasts cycling around on this thing strikes me as bizarre:

There would probably be gaps in any such field of obstacles, but it'd make a damn good deterrent against anyone trying to run fast near you. Such an obstacle course might be placed in the bits of ground most suitable for planting siege engines- it's a lot less work than building the walls, if you have a good shovel in the first place.

Humm. A spiderweb tactic: only the spider knows the routes around its web.
As for the places suitable for planting siege engines, it's be in front of the colony, windward, with the secondary spot being directly behind it. Trade routes and relatively clear terrain would cross the colony perpendicularly, where it is hardest to shoot diagonal to the wind.

I realized something this morning too: Going at 200km/h, an iron giant in a full, heavy suit of armor (10 tons) has about 15MJ of kinetic energy. Ramming an opponent might lead to mutual suicide, and these things are going to plough through walls.

Here's another funny calculation: How far would a giant be able to slide of a metal surfboard?
I used this table of values, and came up with the result: 385-765m depending on the surface. Could it be that with a good enough run up, the giants could slide their way over all the potholes?

True, but that will also make them clumsy on their feet- clown shoes are awkward. As to fast running on sand, the problem is that the instantaneous pressure is likely to cause the sand to slide and give way at least a little. A wheeled vehicle can handle having the ground under it give way a bit; a running man has more trouble with that.

Clown shoes won't help
What we need is something akin to a snowshoe, but modified for running by trimming the extension behind the heel and curving the front. Also, the legs are in contact with the ground for approximately 0.09 seconds. Just how much time does the sand have to slide away?

Likewise, when climbing rubble or natural rock surfaces, the problem is simply that there are fewer hand and foot holds that have enough structural strength to support the weight of a multi-ton man. You grab a rock to pull yourself up, and instead you pull the rock down onto your head and trigger a landslide that carries you right back down to the bottom.

D-Day!
The giants would use large sheets of metal to place over the rubble and walk on.

I think you exaggerate the "stall at long range" aspect. Especially if we incorporate my idea of systematically making the ground shitty to run on for several miles around the fortress- defender patrols could outmaneuver the raiders, get around behind them faster than they can retreat by exploiting clear lanes through the roughened ground, and come at them from multiple directions.

Great idea!
The long range stalling is exaggerated too because they just don't hold enough ammunition to kill everyone without resorting to CQC.

If you can work metal in the requisite quantity this is a great idea, and largely nullifies the ability to crack the stones.

Once again, a rich man's thing. It reminds me of the current situation with materials such as titanium. Our cars would be super light and super strong if we used it, and many other things would be much more efficient... but it costs 30-100 times more than steel.

We're both right, but we're talking past each other.

Happens.

You'd still want a parapet and battlements, and possibly places to mount some kind of very large crossbow. The top of the wall is a good place to stand, keep watch, and shoot at intruders, after all.

Maybe pits dug behind the ridges would do.

True. On the other hand, probably the first thing they'd do is build their curtain wall, then heap piles of mine tailings outside it to act as the "rubble fill." The outer retaining wall might not even be added until later, or built to significantly reduced height- so at first, the wall might look like a low stone 'fence' at the outer perimeter of the wall, a talus slope of rubble and mine tailings inside that, and then a high curtain wall on the inner perimeter.

The talus slope would actually be a bitch to climb if the rocks are broken up finely enough, as mentioned- because it just doesn't have the structural strength to support a giant statue's weight.

I'll try and put up a step-by-step construction timetable for a colony's defenses.
Also, the problem with a loose talus slope is that it'll just get blown away by the wind.