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Context

I have a group of people with super strength and the durability to withstand its use. The super strength does not come with super weight/mass so they can't lift cars or punch through walls. They wear heavy armor made of sapphires to get more weight. I haven't defined an exact limit to their strength, I now see that could be problematic for my question.

My world is medieval-ish, but does not have problems with creating or maintaining high levels of heat. It also has plants that cannot be broken or cut, but can still flex. Other then being incapable of breaking, the plants retain their real-world properties.

I'm focusing on the material the bow is made of, and keeping it travel-sized.

Question

With all this in mind, what would the bow be made of, and how powerful would it be?

I know normal bows can break arrows. I did some research and I think a straight, unbending, unbreakable, arrow would be best. Am I right, or are there other criteria?

How powerful would it be? (Could it match low or mid-powered guns? How far would it shoot? What could you shoot through?) I don't need science, just an estimate.

Assuming the person were trained in its use, how practical would this even be? (The bow is not intended for warfare, but for individuals to use against a variety of things, eg. bandits, people with armor, large animals. Sorry it's not very specific, my people are dimension travelers so they could run up against almost anything.)

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch ♦
    Dec 10, 2021 at 13:18

6 Answers 6

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The Same Materials as now

Historically, bows were made mostly of a single piece of wood, laminated woods, or combinations of wood, fiber (plant/animal), or horn (most notably the mongol composite bows).
But in most cases, the material is not the limiting factor, but the strength of the user. In theory, bows could be incredibly strong - but no one would be able to use them.

So the actual question is:

How would those bows look like?

Mostly like they do now, except:

  • thicker: doubling the thickness increases draw weight eightfold. a two-finger thick yew bow can reach 200 pounds draw weight, easily. Let's assume we add 25% thickness, and we're close to 400pounds.
  • broader: it's basically like using two bows in parallel. Power scales linear, but you don't increase the maximum material stress. So make our bow three times as wide, while still being just a bit thicker, and we're in the ballpark of 1200 pounds - with a mostly traditional flat bow design, only beefed up.
  • so together, your bows would be a big, tapered plank with a grip in the middle.

Concerning your plants that cannot be broken or cut - well, here you break the system twice. It could make an infinitely strong bow, but if it can't be cut, it can't be processed.

Why not steel?

There were, historically, longbows of steel. Their problem is that they're heavier, much more expensive and less efficient than their wood counterparts. And even in modern times, other materials are superior (fiberglass, carbon).

But given steel was used in a similar weapon:

Why not crossbows?

Crossbows were ideal to offset the drawbacks of steel bows - it's very easy to make a very strong, short bow of steel if you don't care about its efficiency. And when you can just draw a crossbow, you can use a lever or winch - so it does not matter how strong it is. 2000 pounds draw weight were uncommon, but realistic.
But the main benefit that crossbows provide - being able to shoot with them without being incredibly string - is kind of pointless when you are, well... incredibly strong.

Concerning your other questions:

  • unbendable arrows - No. Because of the archers' paradox, you want arrows to bend around your bow, so you can shoot straight (unless you have a modern, high-tech bow with central arrow rest).
  • power - even regular bows can match mid-powered guns. They didn't fall out of favor in warfare because they didn't deal damage, but because they're hard to use, need extensive training, and you can't take as much ammunition with you. Plus: rate of fire.
  • range - traditional composite bows in eastern Asia hold the record of ~1km maximum range. with our "superbow" I suggest twice the range is possible. However, effective range is much less dependent on strength, but on the archers dexterity.

How I know this:

hand-crafting historic bows is one of my hobbies, as is devouring books on any topic in huge quantities. I recommend the Traditional Bowyer's Bible for facts and inspirations.

Addendum for modernity:

If you're not strictly stuck to medieval technology, then a fiber-backed compound bow will be the weapon of your choice - no matter if you're arming a man made of cotton candy or superman.

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    $\begingroup$ I don't buy that crossbows would be useless if you were incredibly strong. In fact, if you could actually use a crossbow without needing all the supporting mechanisms (winches etc.) to draw them, I would expect you would basically be able to remove all the drawing mechanisms, leaving only the actual bow limbs and string, and just rapidly fire it by hand - being left with a very tiny and maneuvrable yet incredibly powerful steel mini-bow. Is there any reason this wouldn't work? Moreover, is there any reason scaling this up to a steel bow wouldn't work? Efficiency doesnt matter here, only power. $\endgroup$
    – Boris
    Dec 9, 2021 at 17:42
  • $\begingroup$ if you take a crossbow and remove the "drawing mechanism" - you have a tiny bow with a short draw length. but: the energy put into the arrow (=the damage) is dependent on draw weight times draw length (simplified). so the longer the draw, the more power. that's why a crossbow, when compared with a longbow of the same draw weight, has less power $\endgroup$
    – Franz Gleichmann
    Dec 9, 2021 at 17:48
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    $\begingroup$ also, when you want something small, then you'd upscale a mongols (or koreans) composite bow. they combine a very short, strongly curling bow, laminated from sinew, wood and horn, with stiff levers, called "siyah". they're incredibly hard to make, though, compared with "primitive bows". $\endgroup$
    – Franz Gleichmann
    Dec 9, 2021 at 17:53
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    $\begingroup$ Firearms didn't become stronger than bows until the Kentucky Rifle (and, arguably, even then not until the Minie ball), but they replaced bows long before that. Really goes to show that the factors OP is asking about weren't all that relevant for why bows disappeared from military usage in the first place. +1, good synopsis on the downsides of bows. $\endgroup$
    – Michael W.
    Dec 9, 2021 at 18:15
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    $\begingroup$ @MichaelW. some bonus info: english longbowmen weren't just the most dreaded, but also the most expensive type of medieval foot soldier. even in terms of caloric intake - if you're training all day long to shoot a 150-200# bow, you just burn a freaking lot of energy - meaning you eat a freaking lot of food. and they need that intense training to keep firing ~6 shots per minute in a battle that can last hours. bonus fact #2: even a "entry-level" sports bow with 20# can easily punch through a kevlar vest. $\endgroup$
    – Franz Gleichmann
    Dec 9, 2021 at 18:30
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I'm not an engineer, but I would guess you could make bows out of spring steel, like used in the suspension of cars. It is intentionally made to be used for springs; deform by bending to store energy, and when released return to its original shape without any deformation, and can take many tons of weight.

The problem I see is the bones and flesh of your heroes; I'm not sure how much pressure an arm bone or the hand bones can take before crushing or breaking. So even if the muscles can pull a bow that takes tons of strength, can their arm bones, shoulders, etc withstand those tons of pressure without breaking?

for reference, here is Kevin Fast breaking the world record for heaviest vehicle pulled: About 100 tons.

Kevin Fast Breaking World Record, 2017

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    $\begingroup$ pulling a 100-ton vehicle != exerting 100 tons of force. You can pull arbitrarily big things with arbitrarily small force, as long as you use good enough lubrication and you're patient enough. In case of pulling a car, you just need to overcome the static rolling friction once and then the dynamic rolling friction semicontinuously - and those are specifically designed to be low. $\endgroup$
    – John Dvorak
    Dec 9, 2021 at 12:32
  • $\begingroup$ @JohnDvorak Well you have a lot of inertia to overcome as well, which requires a continuous force. But if you like, substitute weight-lifting, Paul Anderson lifted 6270 pounds. The point being, human bones can withstand that level of pressure, so maybe we could have a 3-ton bow. $\endgroup$
    – Amadeus
    Dec 9, 2021 at 14:41
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    $\begingroup$ Required Secondary Powers are a thing (as is TVTropes), basically it's the get out clause for the bones needing to be up to strength without having to state it explicitly $\endgroup$
    – Separatrix
    Dec 9, 2021 at 15:02
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    $\begingroup$ @JohnDvorak's point is good though, even a puny human can push a 2-tonne car. And as for moving a boat, with no friction to worry about, that's easy. It's a pity we can't get timing data for Kevin Fast's feats. Then we could estimate the force he's actually exerting. Deadlift records and the like really are probably more relevant. $\endgroup$
    – Chris H
    Dec 9, 2021 at 17:11
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    $\begingroup$ And note that spring steel crossbows are a thing, so the bow part is easy. $\endgroup$
    – Chris H
    Dec 9, 2021 at 17:12
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Crossbows

I don't know from the top of my head what materials are best for bows. The idea is simple enough, but the materials and composition is difficult. The bow needs to be sturdy with a bit of flex, while the string needs to be able to flex much more with tension to store energy. The string needs to be able to be used a ten to hundred times for it to be useful as well. Too much hassle, so I'll look at a proxy that does pretty much what you want. A crossbow. That means we can learn a lot from what other people already found out for us.

A crossbow is a device created to reduce the effort of drawing and holding the string. There's versions that still need to be manually drawn, but more interesting are the ones that need a winch or other mechanism to be drawn. In very simple terms these remove the strength limit and place the limits in the material.

A quick search shows me the strongest crossbow is a heavy 880 lbs (400kg) windlass crossbow. I'm guessing the lbs isn't the actual weight but a power measure. The crossbows were designed so you could more easily have power and accuracy over long distances. This particular one was probably most used on ramparts to allow the weapon to rest on something, as it's still heavy to hold and aim.

This was made of ash (tree), steel and linen. With enough heat and knowledge definitely something they made in medieval times. Still this thing would be poor to use as an actual bow. Though more skill is needed to draw, hold and aim a bow, bows were still very good as they could fire much more rapidly. To use this as a bow, I would increase the metal bow like part in the front to a normal bow size. Make it more sturdy/thick to withstand the extra forces involved thanks to leveraging effects. Add the linen string. Ash is likely not needed anymore.

This is if course theoretical, but in my view a close proxy to what the limit of medieval material can do.

The problem then is the arrows. Bolts are often shorter, which allows them to withstand more forces without breaking. That being said, they often shot wooden arrows and bolts with a possible added iron/steel tip. It is simply too costly to make them all fully out of iron/steel. If you make yours fully out of steel the arrows will likely be fine. Other people can comment on of the wobble of iron/steel arrows is still sufficient for the arrow to stay accurate.

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    $\begingroup$ "880lbs" is the force needed to fully draw the string; equivalently, it is the maximum force applied to the bolt throughout its travel. $\endgroup$
    – Logan R. Kearsley
    Dec 9, 2021 at 12:35
  • $\begingroup$ There were medieval and renaissance crossbows significantly heavier than 880 lb. -- I've seen YouTube video of one with about a 1500 lb. prod, and the strength of the wood between the prod and the trigger lock is the only significant limitation on this (once you're willing to use a winch to draw the cable). If you use other material (even mild steel, for instance) you could build up to several tons (tonnes) of draw weight. Diminishing returns sets in, though; all you gain between 800 lbs and 1500 lbs is ability to cast a heavier bolt. $\endgroup$
    – Zeiss Ikon
    Dec 9, 2021 at 17:58
  • $\begingroup$ One thing: the string does not hold the power. Its the flexing of the (cross)bow that stores the power and releases it into the projectile when firing. $\endgroup$
    – Demigan
    Dec 10, 2021 at 4:58
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The ballistics of bows are incredibly complicated - even compared to firearms, where they already sometimes seem more art than science...

However, a few things to consider:

The velocity of the arrow is limited by how fast the limbs of the bow can return to their initial state. This in turn is dependent on may factors, including the material the bow is made from and its mass. Typical maximum velocities range from around 55 m/s to 125 m/s. The higher figures are from compound bows and gain advantage from the cams. This means every bow has an ideal arrow mass - lighter arrows won't go any faster, have less kinetic energy, and just mean more energy being absorbed by the bow limbs; possibly damaging them. Heavier ones will be slower with little extra kinetic energy. The important lesson is that maximum velocity is a property of the material of the bow, not its draw weight.

This leads us to a limitation of accuracy of bows vs firearms - bullets travel much faster so their potential for long range accuracy is much greater. The limit of accurate shooting for bows is going to be 100m to maybe 150m. Beyond that the curved trajectory of the relatively slow arrow is going to mean that you are using indirect fire - literally raining arrows down from above which is never going to be as precise as aiming directly at the target.

Second, bows with very high draw weights suitable for super-humans are going to shoot very heavy arrows. This is a good thing for penetration - heavier projectiles penetrate better all other factors being equal.

Armour penetration is about the only thing that will change at the target however.

Bows with 70lb draw weights will already shoot clean through an unarmoured target with the same body mass as a human at 20m. That is with broadheads. Nobody really shoots arrows optimised for penetration at living targets anymore, but just for the sake of argument lets say 30m. I don't know at what distance a long bow with twice the draw would reliably accomplish the same feat, but safe to say, significantly further. We are now approaching the range limit of practical accuracy. Our super heavy arrows can probably do the same thing past the limit of accuracy, but the maximum damage you can do the target is shoot an arrow straight through it which the lesser bows can already do at practical distances.

The heavier bows will penetrate armour better, but again, in the absence of anyone having tested 400lb draw weight super bows it is very difficult to say how much better... How much do we need?

Breast plates and helms of high quality mediaeval armour could reliably defeat long bows. Other parts of the armour, and cheaper armours provided some protection (lethal wounds became survivable ones - an arrow in the lung became an arrow in the meat of the chest).

If we doubled the momentum of the arrow, which is quite possible, then I would find it plausible that the best armours would offer partial protection, with lesser armours providing little protection, except at long range. This would put the super bows on a par with early firearms, but still far behind even early breach loading rifles. That said, opponents would rightly fear anyone wielding one of these bows...

A note on arrows: it turns out that arrows actually need to be flexible, so unbending is not a desirable property. If the arrows need additional support during firing, then an arrow guide can be used to provide additional support.

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Actual long bow is almost maximum what can make without destroing arrow. Problem is with wooble. If make something like "Instant Legolas" then can make stronger bow and fire arrows with no risk of breaking them.

Rifle comparision. Bows are skill related - if have no skill in bows then can compare them to single shot front loaded rifle, same damage, same range. With increased strenght and arrow structure can have bigger range and damage than most rifles. Need think about loading time, "Instant Legolas" can be compared to early IIWW rifles but not to MG or SMG. Noise is an advantage of bow.

Range. Long bow 80kg, 1m arrow can shot up to 300m but forget about precision after 100m

Target comparision:

Bandits can scare, kill with no big problem. On 100m skilled can kill up to 10 people before they run to him.

People with armor on 40m there is no armor against 80kg long bow. Plate mail can be shoted trough.

Large animals if skilled enough(average) can kill elaphant with 80kg long bow. Possibly be killed by elephant before death. Can hunt most land, air and water animals.

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  • $\begingroup$ I did some research and I think a strait, unbending, unbreakable, arrow would be best. I'm I right, or is there other criteria? Like, would it also mess with aim somehow? $\endgroup$
    – Opal
    Dec 9, 2021 at 11:40
  • $\begingroup$ @Opal - an unbending arrow would have serious aim and release issues. The arrow needs to flex in order to fly straight. $\endgroup$
    – jdunlop
    Dec 9, 2021 at 18:32
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Typically bullets have muzzle energy in the order of 10^3 (thousands) of NM. So say the most powerful handguns have around 1200NM of muzzle energy. A 50 cal anti-materiel rifle might ready 10^4 (tens of thousands, say 15000) NM.

Typically a powerful conventional (say hunting) bow might produce 10^2 (hundreds) NM of kinetic energy. So a powerful handgun is sort of 10 times more powerful than a hunting bow. A powerful rifle a hundred times.

Could we make a bow 100 times more powerful than they are now using modern materials (ignoring the ability for a human to draw it). Yes probably.

Leaving the design as it is currently (recurve, compound etc.) I suspect we'd use modern composites such as carbon fibre for extension (the front of the bow, carbon fibre has excellent tensile strength) and some sort of ceramic (or glass), or perhaps titanium for compression (the back of the bow).

What effect would such an arrow have down range? Well it would deliver the same energy as the bullet, so a comparable effect. Though arrows do suffer from much higher wind resistance.

How far would it travel, well that depends on the weight of the arrow. I suspect it would have to be heavier than a normal arrow to cope with the stress it'd have to be made of stronger stuff. Lets go with 400g (just shy of a pound)

If we give an arrow weighing 400g a kinteic energy of 15000 joules (high calibre rifle energy) it will leave the bow at ~300m/s! So we would make an arrow weighing about a pound travel at speeds comparable to a pretty powerful hand gun bullet.

How far would it go at 45 degrees at that velocity? Well it's hard to be precise because of wind resistance, but shooting it at 45 degrees it might go between 5Km and 10Km.

Bear in mind that English Longbowmen were piercing the finest plat armour ever made at a distance of around 200m (somewhere near the end of a longbow arrow's range).

We could reasonably expect such an arrow to pass clean through a car engine.. Or stop a truck.. Just as the Barret 50 cal can.

Enjoyed all that.. hope it helps.

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  • $\begingroup$ Revision : Somewhere between 4 and 8 Km $\endgroup$
    – Richard
    Dec 10, 2021 at 0:48
  • $\begingroup$ there is a weird thing with how bows work that means you can't really increase the speed of the projectile, only the mass of the projectile. how fast materials can flex is already pushed to the limit for existing bows. making bows stronger does not make arrows faster it only lets you use heavier arrows. the bow can't return to shape any faster extra force is just wasted not converted to higher velocity. I made the same mistake. $\endgroup$
    – John
    Dec 10, 2021 at 0:57
  • $\begingroup$ @John Interesting. I kind of don't believe you and believe you at the same time. It seems like an amazing problem to try and tackle. $\endgroup$
    – Richard
    Dec 10, 2021 at 1:02
  • $\begingroup$ @John For fun I re-did a quick calculation.. We could make the arrow weigh at least a kilo (maybe two) if we assume it had sort of 15000J and launched at normal arrow speeds. I wouldn't want to be hit by that. $\endgroup$
    – Richard
    Dec 10, 2021 at 1:08
  • $\begingroup$ I made the same mistake but this is why crossbows even when many times more owerful can't move a projectile faster even of the same distance, the flex speed of a material does not scale much, just the force that flex can generate. this is why medieval crossbows throw bolts the same distance basically regardless of draw weight $\endgroup$
    – John
    Dec 10, 2021 at 1:15

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