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First, an engineering view of the double bow.
The Penobscot bow / Wabanaki bow / Mi'kmaq (double) bow is an advanced version of
a cable-backed bow with very different mechanics. It's different in its performance from bows that simply use wider or thicker limbs or more limbs.
photo uploaded by "Judson"/"Judson127", taken from here
Mechanical engineers learn that everything can be considered to be a spring; even a solid block of steel is a spring. We can apply a force to it and it will either compress or elongate. We usually cannot see the tiny change in its dimensions, but it happens. Its
spring constant simply requires a powerful force for very little change of its dimensions. Spring steels in coil spring shape make it much easier to experience how steel yields to mechanical forces.
A bow can be considered a spring as well - you pull harder, it yields more - and just like a spring, it stores energy in the process. This energy can be released for the purpose of accelerating the arrow (or with an arrow guide, the dart).
Bows (and many other spring arrangements) have no spring constant, though; the amount of force required to pull the arrow back by one more centimetre depends on how far you already pulled it back. The bow design doesn't simply compress or elongate, but changes its shape as it yields to the pulling force (the string notches approach each other).
The ideal bow design would accelerate the arrow with about the same force regardless of how far it's still drawn (but that's not feasible). The force must not be excessive (or the user couldn't draw and hold the drawn bow well or at all) and should not be low (for the sake of accelerating the arrow well).
This cannot be done with a single spring; you need a set of springs (or a more complicated design such as the recurve or composite bows) to approximate this ideal.
Springs of different spring characteristics can be arranged to create a non-linear spring curve; this way compressing or elongating by a certain distance doesn't require the addition of the same force regardless of how much the spring system has already been manipulated.
The double bow is such a two-spring-ish system in spirit. The small front bow is not just an overly elaborate way of making the bow stiffer; it actually modifies the spring curve (requires more force to draw at first, thus also accelerates the arrow more) as
a parallel spring, and by consensus of double bow users, it does so in an advantageous way compared to a self bow of equivalent technology. You get more performance out of such a bow for the same maximum (28" draw) draw 'weight' than with an otherwise equivalent technology self bow.
That, by the way, is the reason why people who create double bows with the front bow almost as long as the main bow either didn't get what the design is meant to accomplish or are merely trying to create a bow that can make do with poor material (poorly suitable woods). A proper performance double bow has a short front bow that gets fully drawn fairly soon in the drawing motion.
(BTW, the Penobscot double bow is supposedly not really "ancient", supposedly it's just over a hundred years old - I doubt this, but don't have sources that mention it earlier.)
edit: I decided to add this link, asthe author there actually shows a diagram with force-draw curves. The Penebscot double bow design essentially leads to a quicker rise in draw strength on the first centimetres (inches) of draw. During the shot, the arrow gets accelerated with more force when it's forward that much again. / I also cleaned up the text above a bit.
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Second, this video on African martial arts (unrelated to double bows):
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Third, some general remarks on non-firearm weapons:
It's amazing how after some study one becomes mostly able to tell the way a weapon was meant to be used by merely looking at it, including some requirements for the associated armour.
Curved blades typically require a relatively high quality material because they almost never have two edges, and one edge could quickly become dull in an extended battle. Curved blades are especially meant for cutting, so holding a good blade is important (harder edge allows for a sharper edge) and difficult (harder edge ~ more brittle edge).
The one exception I'm aware of are the bronze age sickle swords, and their users were probably prepared to sharpen their weapon with a grindstone on their own as in agricultural use of sickles.
Curved blades are never made for thrusting into the body; they are made for cuts and slashing motions. The cutting motions may include a pushing and pulling motion, but only to cut along the side of the target. The pushing cut isn't really an option with forward-curved blades such as sickles, romphaia or falx.
Straight blades can be built for thrusting into organs, but don't necessarily have the point for it (Celtic swords were largely limited to slashing, as the point was often dull). Very fine points give away the intent to penetrate an armour type that's not very good against thrusting attacks (typically mail), and are thus uncommon in areas where such armours that are vulnerable to thrusting attacks are rare (example East and South Asia).
An extreme case are the smallswords and the like - straight sword-like blade weapons meant exclusively for thrusting with the point, without a shard edge. These continued to be in use after mail armour fell out of fashion in almost all of Europe (Balkans excluded). Frankly, my suspicion is that they were optimised for light weight, as respectable sidearms that aren't too much of a burden on their user.
Large handguards tend to be associated with no use of shields, or use of shields very unwieldy (pavise) or very small (buckler). Handguards can then help protect the hand when you cannot do it with a shield. An exception is the customary retention of large handguards along with late medieval plate armour, but one should keep in mind that swords were sidearms and thus also (if not primarily) used when the wearer wasn't fully geared up.
Blunt weapons such as maces and hammers (also hammer components in weapons such as the pollaxe) were either an extreme budget solution (clubs) or a response to very effective armour. Blunt force can even be effective against plate armour and equivalent helmets when blades and pointy weapons fail. The latter are usually built to be nimble in their use and thus quite lightweight. Axes and blunt weapons require a lot of mass where it matters the most; at the end of a pole or short shaft.
Single-handed weapons that are quite long among their kind (mace, sword, sabre) tend to be cavalry arms. Their increased length compensates for poor riding skills* or a loss of dexterity caused by the user's armour.
Lances and pikes were usually held low, while spears were held high (if used single-handedly) for a greater choice of movements.
Polearms with oval pole cross section and/or dedicated axe head, spike or blade elements (examples pollaxes, halberds, naginatas) were meant for slashing and/or swiping movements. This in turn indicates that they were meant for two-handed use, and thus lead to an emphasis on good armour protection for the user, since shields would be quite impractical.**
Javelins are particularly interesting; the very light ones were used in great quantity by dedicated skirmishers and cavalry, while the more elaborate ones such as the famous Roman pilum (no doubt the most advanced and most capable javelin design ever despite lacking an
amentum or
spear thrower) were carried in small quantity (one or two per legionary; that's still up for debate). The pilum's purpose was threefold; a demoralising/shocking salvo, disabling shields by sticking to them (making them unwieldy and enabling the enemy to push the shield sideways) and finally an emergency use as a spear, particularly against cavalry.***
Spears are capable weapons for one-on-one situations unless the enemy has good armour. Their use was typically rooted in at least one of three motives; poverty (spears as versatile budget option), horsemen threat (spears as anti-horseman weapon,**** obviously not helpful against missile horsemen) and third, disciplined forces employing closed order tactics (example Greek phalanx).
As with swords, the width of the spear tip usually indicates whether a spear was meant for use against armoured opponents or not. A wide, leaf-shaped spear tip would be for use against unarmoured opposition (example
iklwa), or for the hunt. Boar spears and some other spears had some guards to limit penetration.
Particularly short stabbing blade weapons such as the Spartan short xiphos versions or Germanic seax were associated with very restricted close quarters combat, such as fighting in a phalanx or shield wall where the gaps between shields and the air above could be used for very short stabbing motions. Another use for such short sidearms was on board of warships (for boarding actions), usually with a blade that's well-suited to slashing (which makes it useful for cutting tows).
Likewise, the design of shields allows conclusions about their use.
S O
defence_and_freedom@gmx.de
*: Not all horsemen were good at horsemanship games and thus capable of picking
stuff up from the ground while riding, so they needed longer weapons to
strike targets lying on the ground. That in turn is important because to simply lie on the ground is a reasonable approach to protect oneself from a cavalry charge; horses will avoid to step on such irregularities to avoid injury.
**: This requirement finds in exception of the very late halberd-ish weapons such as partisans of the firearms era, about 17th and first half of 18th centuries. The same applies to bayonets. The requirement may not be met because of economical reasons, but two-handed polearms were rare when good body armour was unaffordable unless the use of powerful halberd-like weapons made it quite pointless anyway (example Japanese warrior monks with Naginatas).
***: The pilum slowly fell out of use when the longer spatha sword gradually replaced the gladius sword. The disciplined Roman infantry (even auxiliary infantry) was able to resist shock cavalry with disciplined closed order formations (horses don't run into spear tips, but the don't run into shield walls either) and a longer sword made the need for some spear-ish weapon against cavalry less pressing. There may thus have been such a relation between the rise of the spatha and the decline of the pilum (in favour of plumbata and cheaper simple javelins). Alternatively, the increased use of light javelins by horsemen may have led to a better opinion about them, eroding the pilum's role. Last but not least, the late imperial Western Roman infantry faced much more cavalry and actual spears became much more common in service again. Spears and pila don't go well along because spearmen tend to keep close formation, whereas pila require some more space for the user to throw. In the end, the pilum+gladius combination was unique to late Republican and early Imperial Rome, and a hugely successful approach that seemed to have been suboptimal in other times and places.
****: Long straight swords could be used to deter cavalry as well (Pallasch
weapons were used by cuirassiers of the 18th century almost as if they
were spears).
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