On a comment to My carrier pigeons have been replaced by spoons: how can I send messages? I joke about creating a network of trebuchets to launch spoons.

Is it realistic?

My concerns:

  • How far will it be launched?
  • Would the spoon resist the impact?
  • Is a trebuchet accurate enough?
  • Is it affordable for a medieval king? I will first make a single route of 25km. (No industrialization or Chinese factories in my universe.)
  • What would be the speed of this message?
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    I love that now we're just discussing spoons here. I imagine a king could afford a few trebuchets though. – J0hn Aug 9 at 14:07
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    It might be rather expensive. You would need someone to retrieve the spoon and load the next trebuchet after every launch, meaning the message would be rather slow. In addition, the shape of a spoon and the relative inaccuracy of a trebuchet would make it rather hard to make a functional system of trebuchets for that purpose – Cubemaster Aug 9 at 14:14
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    On a side note, we're having a very fun trebuchet and cannibal spoon conversation in chat – AndyD273 Aug 9 at 15:20
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    New spoon tag :P? – Midnightas Aug 9 at 19:42
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    Currently there are a maximum of three questions that fit the requirements, but we can work on that! – wizzwizz4 Aug 10 at 11:43
up vote 28 down vote accepted

So a few things first; Spoons are not very heavy. Spoons are not aerodynamic.

A trebuchet is great when you want to throw a 90kg stone over 300 meters. You could potentially throw a lighter load further, but it takes a bit of juggling to get maximum distance.

The more mass something has the harder it is to get moving, but once moving are harder to stop, which is why most trebuchets sending very heavy messages used enemy castle walls as backstops.
A smaller load is easier to get moving, but will be affected by air resistance and wind more.

The dimensions of the trebuchet are also a huge factor.
The length of the arm, the counterweight mass, the counterweight drop distance, the projectile mass, pivot height... Just going bigger does not guarantee better real world results.

The average spoon weighs around 25 g, and due to the thin convex shape would be more susceptible to drag than a more sphereical object such as a ball or rock.

You can use the Virtual Trebuchet to design a trebuchet that can throw a light object, but getting more than 300 meters is hard, and that's assuming a spherical object, not a spoon.

If you start plugging numbers into the VT, you'll see that there is diminishing returns when it comes to weight. A 1kg object will travel further than a .5kg object. Increasing the mass of the counterweight can help some, as can increasing the lengths of the arms, but each has diminishing returns as well.

Getting an actual distance of more than 300 meters might be possible if you were throwing a spherical spoon in a frictionless vacuum, but real world results will not be as good.

Accuracy will also not be great, especially if there is wind.

If there is any kind of underbrush or long grass then finding a single wayward spoon is going to be difficult. But because it is so light it should slow down enough before hitting the ground to resist the impact just fine.

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    +1 for "very heavy messages": "Do you think these boulders could be her passive-aggressive way of breaking up with me?" – browly Aug 9 at 19:07
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    @browly Less passive, more aggressive, if you ask me... – AndyD273 Aug 9 at 19:32
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    Maybe you just need bigger spoons. – Ghotir Aug 9 at 20:36
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    @browly if that's passive-aggressive, then what the hell does active-aggressive look like? – DonQuiKong Aug 10 at 7:17
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    @DonQuiKong Passive aggressive - she just shoots your general direction. Active-aggressive - she's aiming at you – Alexander von Wernherr Aug 10 at 7:36

Range

Trebuchet ranges vary quite a lot, from a bit under 100 meters to as far as 300-400 meters. "Siege crossbows" could have ranges of 500-1000 meters. Therefore, I think ~500 meters is a reasonable target. Today, Warwick Castle's trebuchet can hurl a 13 kg projectile 250 meters at 190 kph. If you were to redesign it to throw a lighter object - like a spoon - those numbers would increase dramatically.

Cost

Alexios I is thought to have had trebuchets, or similar weapons, and they were certainly used in the 13th century. Now, keep in mind a couple things:

  • Alexios was an emperor and was fairly powerful.
  • His empire was at war, and war means more funds diverted to . . . war.
  • Alexios liked inventing new weapons.

Therefore, for a rich, war-like emperor, this is a more plausible scenario, especially if these trebuchets have military applications (and they do - they're trebuchets, after all).

Theoretical speed and range

I used this trebuchet calculator to get some results. Though I was limited by the calculator itself, I used the following parameters:

  • Counterweight arm length: 10.5 ft (3.2 m)
  • Projectile arm length: 10.5 ft (3.2 m)
  • Counterweight mass: 98.5 lbs (44.7 kg)
  • Projectile mass: 0.5 lbs (0.23 kg)

The resulting speed was 2381 ft/s (726 m/s), and the range was 176881 feet (53.9 km). I suspect the stresses here would be too much for the machine, so I toned things down to a counterweight mass of 49.5 lbs (22.5 kg). The result was a speed of 1182 ft/s (360 m/s) and a range of 43425 feet (13.2 km). This means you'd only need two trebuchets to travel the full 25 km distance . . . assuming that the spoon survived. Which I doubt it would. 1182 ft/s is a lot for a poor spoon.

There are some things this simulator ignores, however, and tweaking the parameters a bit leads to different results. I also considered a different trebuchet calculator that takes into account the mass and moment of inertia of the arm itself. Here are some of the parameters I used:

  • Length of long and short arms: 10.5 ft (3.2 m)
  • Mass of arm: 10 lbs (4.54 kg)
  • Mass of counterweight: 98.5 lb (44.7 kg)
  • Mass of projectile: .055 lb (24.9 g)
  • Projectile diameter: 0.1 ft (3 cm)

This yielded a distance of 166 ft (50.6 m!) and an initial speed of 88 ft/s (26.8 m/s). Why? Well, it takes into account friction and the mass of the arm itself. Now, if we increase the projectile mass to 0.55 lbs (0.249 kg), we can get a distance of 232 ft (70.7 m).

As some people have suggested, these calculations might be a bit off because the calculators weren't designed to be used for throwing light, non-spherical objects like spoons! They should be more accurate if we use heavier projectiles - which could mean placing a spoon inside a more durable shell. The shell could also protect it a little during landing.

Regardless, we know that trebuchets can chuck things several hundred meters, and if you're willing to strap a spoon onto one of those projectiles, those ranges can be achieved.

Time

theGarz pointed out that reloading and resetting a trebuchet can take a while. I agree that the distance (25 km) could be covered in a very short time; 1.5 to 2 hours is reasonable for a good runner. For the trebuchet to be an efficient mode of communication, you would need to have the turnaround time be very quick, and you'd need the accuracy to be good. Hunting in the woods for a projectile that's gone astray isn't easy. Looking for a spoon in a forest is probably worse than looking for a needle in a haystack.

It's debatable as to how much of an improvement a horse would be over 25 km; 30-50 km in a day might be a reasonable estimate for a horse's stamina unless it specifically trains for this sort of messenger work. Nonetheless, a sort of Pony Express might also be a good option - and more efficient that a trebuchet unless the trebuchet's turnaround time is short.

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    Looking at the two calculators, I believe the reason for the order of magnitude difference is that the first one doesn't seem to take into account for the moment of inertia of the arm, just the counterweight and the projectile. Practically speaking, trebuchets were not used to launch such light weight objects, so its very believable that the models start to diverge at low projectile masses. – Cort Ammon Aug 9 at 14:46
  • I guess that the first calculator is somehow broken: 13km?? For comparison, the WW2 Brandt Mle 27/31 mortar had a range of less than 3km. – theGarz Aug 9 at 14:50
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    @CortAmmon I agree with that. Spoons are pretty different from idealized projectiles in terms of mass and shape. – HDE 226868 Aug 9 at 14:54
  • Also worthy of note that if you did manage to convert all of the mechanical energy of a trebuchet in kinetic energy n the spoon, that doesn't stop wind resistance slowly down the very light spoon very quickly, so the "dramatically increased range" wouldn't be all that increased, it may even be decreased – Blade Wraith Aug 9 at 16:05
  • This looks like it could be a good answer. However, almost nothing is metric (the question asked about a metric length) and I simply can't understand it as I live in a metric country and not using powers of 10 seems ... a lot of effort. There are too many numbers for me to be bothered converting them all as I read. Could you add the metric equivalent for all your values? – CJ Dennis Aug 10 at 1:13

Not really realistic...

How far will it be launched? Would the spoon resist the impact?

300m at maximum with a proper projectile, while the spoon could resist the impact you should put it inside a more aerodynamic shape. Your king would be one of the first users of message encapsulation.

Is trebuchet accurate enough?

It has a reasonable accuracy, I guess 30m at maximum, it was used to aim at specific buildings inside a besieged castle. The trebuchet operators (Gynours) doesn't need to spend a lot of time fetching the launched message.

Is it affordable for a medieval king?

A very rich one can reasonably afford a hundred trebuchet, covering no more than 30km, enough for your first test. Sieges with 20-30 trebuchet were big sieges, still real sieges. NB: just because you can doesn't mean you should, trebuchet are really expensive.

What would be the speed of this message?

If the operators are ready to receive and resend the message you could estimate 3-5 min for every step (with preloaded machines ready to launch). 5 hours at least.

Why would you spend this much money on machines and operators to carry a message in 5h at no more than 30km? Running on feet have more or less the same speed. A couple of mounted postmen will do the job in a fraction of the cost and time.

  • You don't even need to run. I can hike 30km in 5h (assuming the terrain is flat and there's a good service to walk on). Runners can do 30km in 1h30 - 2h. – Abigail Aug 9 at 16:03
  • @Abigail: i've assumed lazy staff... :D – theGarz Aug 9 at 16:10

How about semaphore stations? Smoke signals? Those seem like better choices. Modern semaphores might not be period-accurate, but based on some reading I did, the Greeks used "hydraulic semaphores", and the earliest one was developed in 4th-century BC Greece.

A clever emperor should be able to devise a visual signaling system using stations at line-of-sight distances.

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    This should be an answer to the linked question; this isn't an answer to this one. – wizzwizz4 Aug 10 at 11:52

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