engineering geekery

Paradoxes of Sword Design

cross-sections of six swords near the guard
Cross-sections of six swords near the hilt. From Peter Johnson’s talk “Paradoxes of Sword Design” at Arctic Fire 2012 https://youtu.be/nyAc5HbUuqw?t=2630

In February, I started to think seriously about swords after sketching the swords from Ghalekuti (which I will blog about one day). I am the “armour” sort of historical fencing person not the “swords” sort (thanks Steve Muhlberger) and I don’t have access to many originals in good condition. A group of European and American bladesmiths and engineers have been thinking about how to describe swords and how they want to move. The names I know best are Michael Tinker Pearce, Vincent le Chevalier, and Peter Johnsson; other people would mention Angus Trim and George Turner.

Swords are simple objects, but designing a specific sword requires trading off all kinds of goods against one another. The longer sword is more of a nuisance to wear and slower to draw, the stiffer sword may not be as effective in cutting, the more complex hilt limits how the weapon can be held. These seemingly simple objects hide a lot of engineering that you can slowly train your eye to see and your arm to feel.

This is a topic where not much has been formally published, but two great web resources are “Understanding Blade Properties” by Patrick Kelly and Peter Johnsson’s talk “Paradoxes of Sword Design” from Arctic Fire 2012 (warning: YouTube). Peter Johnsson is probably the most charismatic speaker discussing these ideas today and he has his own theory of how the medieval cruciform sword was designed. Because his talk is 80 minutes long and on a scary Google website I want to call out two things which I noticed.
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How Much Does the Protection of Low-Tech Armour Vary?

A selection of images from tactical displays in Star Wars: A New Hope
Despite all of our technological terrors, we still can’t predict the outcome of hand-to-hand combat very well. Graphic courtesy of Dr. Mike Reddy 2013 https://doctormikereddy.wordpress.com/2013/02/26/javin-java-battle-of-yavin-tactical-computer/

Designers of roleplaying games who are interested in learning how the real world works, and not just studying other people’s stories and games, usually put a lot of thought into the combat mechanics. One old argument is about how to handle the performance of armour. Fairly early on (sometime in the 1970s or 1980s?), the idea of a damage roll was combined with the idea that armour could provide a penalty to damage. However, this tends to bother people whose archetypical combat involves modern firearms and armoured vehicles or kevlar body armour.

Bullets and shells have a very predictable ability to penetrate armour, and modern industrialized, standardized-tested armour has a very predictable ability to resist it, and the damage-roll-minus-armour model tends to let some things get through which should be stopped. While sometimes this can be abstracted away (“eh, maybe those few points of damage represent bruising”) other times that is difficult to justify (“did the shell explode inside the tank or outside? Did the Deathly Dagger of Draining touch his flesh or not?”) One solution to this is to treat both penetration and resistance as more or less fixed, then generate the effect of the wound based on their interaction. GURPS fans often refer to this as armour-as-dice, because armour can be treated as reducing the predictable number of damage dice which the attacker rolls instead of the variable results of that roll.

However, models which treat penetration and resistance to penetration as more-or-less fixed tend to make people who are more interested in combat with hand weapons uncomfortable. In this post, I would like to explore what we know about how much the ability of hand-made armour to resist weapons can vary, even within a given piece of a known form and quality. If you want, you can skip to where I sum up.

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