Archery Question

[Occhidiangela]

Basically, there are two quantities of importance, the center of mass and the center of pressure.  In the case of something like an arrow or a spear (i.e., long thin objects) the center of mass is just the point where the object balances.  So, for instance, the center of mass of a naked arrow shaft is just the center of the shaft. When the head and the feathers (fletching) have been added, the center of mass is closer to the head of the arrow since the head now weighs more.

The center of pressure is a little more complicated, but essential it is just where the object would 'balance' in the wind.  Think of suspending the item so that it is free to pivot horizontally.  Now let a wind blow on the item.  Move the point at which the item is suspended back and forth until the item has no tendency to line up with the wind.  The place where the pivot is located when this happens is the center of pressure.  In model rocketry, a simple trick is used to determine the center of pressure.  The two dimensional outline of the rocket is cut from uniform carboard.  Where the outline balances is the center of pressure of the three dimensional rocket.  In the case of an arrow, the center of pressure is towards the tail because the feathers have a greater cross section than the arrowhead does, so there's more there for the wind to catch.

Now, once these two quantities are found, 'straight' flight is simple to figure.  An object wants to fly with the center of mass ahead of the center of pressure.  A naked arrow shaft is right on the border.  If launched without a twist, it might go straight.  Firing an arrow, however, always introduces a twist.  To achieve true stability, the center of mass has to be well ahead of the center of pressure.  Normally this is true.

The conclusions from this simple analysis is that at the front of the arrow we want dense stuff and at the back we want fluffy stuff.  Taking a normal arrow, wrapping a bunch of cloth (or grass, or whatever) around the front of the arrow, and soaking it with oil or pitch puts a lot of low density stuff at the wrong end.  So, in addition to putting the fire a little further from the archer, this gives another reason why longer than usual arrows would be needed.  Add to that the fact that a lot more fluffy stuff will be need to be at the back end to regain stability, and the drag on the arrow becomes monstrous.

Were fire arrows occasionally used?  Probably.  But they sure don't sound like a Good Idea for general warfare.

--Pete
[right][snapback]64456[/snapback][/right]

More brain waves working, in re the mixture of art and science. Achery is a "feel" skill, and requires developing muscle memory for different loads.

A couple of ways my brain sees around a few of the technical challenges you mention:

Replace the metal/stone arrowhead completely with a flammable substance. Wicked wax perhaps? You are now handcrafting each arrow, but then, weren't most arrows hand made anyway? Second process needed to be mastered by the fletchers and archers. The risk is no penetrating/piercing/sticking properties with no pointy tip. Solution: slide the tip of flammable goop down the shaft slightly and then, on each arrow, file/sand/whittle the wood a conical point at the business end of the arrow. Perhaps a good way to make them stick in soft wood or thatched rooves. Rebalance of the flights again a must, though the center of mass vs center of pressure should remain in general harmony as before.

Soaking the entire arrow over night in pitch/naptha so that the entire arrow is flammable. Practical application of this sort of technique requires significant training: light-pull-loose, or set your bow on fire, per Doc's comments. One torch per archer, or section. Logisticallly much harder to support than standard archer units. Rags wrapped around the tip of an arrowhead strikes me as a way to bugger the weight and balance problem, or accuracy suffers greatly. COncur with your observation on the significant drag penalty for non aerodynamic rag wraps at the pointy end. Poor accuracy results in generally undirected fire, which is hardly the solution to the problem of setting particular targets alight. As a purely visual/psychological ploy, maybe not so important. Range is still important, as archers are not good melee troops in a general, combined arms engagement.

Check, thanks to all, on the longer arrow and larger feathers at the back, larger control surfaces for a different load. That should also allow for, I think, more stable flight, even in conditions of high wind, again at the cost of increased drag, and thus shorter range expectations on the standard XX pound pull bow the archers are using.

Training. Archers must train with the different sized/shaped arrow to get a feel of proper launch angle for the target geometry that will be applied tactically. Longbowmen did considerable practice to be able to guage distance by eye, laser range finders being scarce during the battle of Poiters, for example. <_<

Some armies have and had better training systems than others. Good training and familiarity with the equipment would go a long way to ensuring tactical utility of the flaming arrow as an option. Not a good ad hoc weapon/tactic.

Since the OSHA madness of modern times was probably not the norm in ancient days, a few guys gooning it up and setting themselves alight was probably considered the cost of doing business in a real battle, by the average aristocratic general, though possibly less so by a merc company captain.

Occhi