04-29-2007, 11:19 AM
Quote: Weigh any of them at the mid-way point and they'll be front-heavy. Even the smallest metal arrowheads will outweigh the horn nock and feather fletchings at the back (though the difference will be less, here, than with the heavier head of a javelin or a spear, obviously.I see, yes, you're right there.
Quote:The IAA don't want javelins flying on a completely flat trajectory and skidding-off the grass to spear some official or spectator.That would not be good for the sponsors, indeed..
However, javelins are primarily flat-trajectory weapons. Plumbatae are mainly curved trajectory weapons, arrows can be both.
Quote:The same principle goes in warfare. The primary function of the head of any projectile (or spear) is to punch through the target, rather than get blunted or split, as the bare wooden shaft might, on its own. But with projectiles, especially, you desire them to be slightly front-heavy, as this prevents them tumbling in flight and not hitting the target with the point first.Agreed. The metal head will do that for you.
Quote:No they are not. You are talking about different things. All trajectory weapons have a metal head (the're weapons, after all) but that's not 'weighted'. The weight of the pilum and the plumbata is added to gain the force to punch through armour.Vortigern:1bdk5j49 Wrote:The difference between arrows and spears (hastae) on the one hand, and pila and plumbatae on the other, is that they are weighted. This weight gives them different qualities, and much more force is put on the joints between head and shaft.They are all weighted. The plumbata most of all and the arrow least.
Quote:The javelin requires a larger weight in its head, to keep it flying front-first, as it doesn't have the fletchings. The plumbata is an interesting case. How do you throw yours? By holding it at the back of the shaft, behind you, and pointing backwards? Right. And you fling it (either over- or under-arm - it doesn't matter which) past your head with your arm passing through 180 degrees. Thus the plumbata is also passing through 180 degrees.The javelin has a weight in its head? The head is the weight. The trick to keep it flying front-first without the tail overtaking it does not lie in the weight of the head, but in the technique of throwing it. With pila you don't have that problem because it's much slower and the weight is attached much further down. With the plumbata it is higher up, which is why the plumbata needs flights.
The throwing of the plumbata is mostly not 180 degrees, but 360 degrees, to give it more speed. And like shooting slings, it's the trick to let it go when it has all that speed exactly in the direction that you want it to go. if you do it right, the tail will hardly wobble or not at all, like with the javelin.
Quote:You are thus not only giving it lateral motion butNo, that's the flights kicking in, preventing the rotational spin that's started by the heavy front. the stabilising flights actually prevent the tail overtaking the head. Like you said above:
imparting rotational kinetic energy to it. That is, if it did not have the lead weight to over-ride its rotational momentum upon leaving your hand, it would continue to spin, end-over-end in mid flight, losing speed and either dropping short of the target or hitting the target at any angle other than head-on. Notice that slight 'wobble' as it first leaves your hand and settles into its trajectory? That's the lead weight kicking-in and correcting the rotational spin, which would otherwise cause the problem mentioned above. 8)
Quote:it has the added benefit of the fletchings, which, coupled with its higher speed of flight, give it a large 'rudder' effect and a longitudinal spin which prevents 'end-over-end' spin (the thing we're trying to avoid).
Quote:Agreed! If they land neatly head-on, they'll stay in one piece. The socketed head makes no difference there over the tanged one - the latter has enough strength from the lead weight to prevent the shaft being split.Vortigern:1bdk5j49 Wrote:No, no. That's the point (the metal one ). So long as the projectile hits squarely (point-first) then the impact goes directly through the axis of the head and the shaft, lengthways, just how it's designed to do. The problem only comes when it hits at an 'angle-off' and imparts a lateral strain on the joint between head and shaft. That's when it's liable to break.ambrosius:1bdk5j49 Wrote:It doesn't really matter what angle they land at, though, as long as the force of impact is straight through the head and into the shaft.And this is exactly what happens with a plumbata - when the head hits the target (or the ground), the weight plus shaft will 'overtake' the head, thereby forcing it to bend or break. A well-poured weight should protect the shafted as well as the tanged joint from that force.
Quote:As we discussed with tanged versus socketed heads, both will direct the force of impact straight through the head and shaft on target and force the two together. But a slight 'angle-off' on the impact will tend to split the shaft with the tanged head, while the socketed head actually provides a uniform force on the shaft and compresses it inside the socket, which helps to prevent the wood splitting. :wink:Like I said, the lead weight prevents the shaft being pressed downwards onto the tanged point where it would be split.
However, both experience a sideways forced, that wants to 'bend' the shaft and head.
Is the socket stronger? I would like to test that.
So far, I assume that most plumbatae have tanged heads because these are cheaper and easier to make.
Quote:You should always do that as long as you don’t know. It's called science. Scientists who do not assume when they do not know are not doing their job. I know assuming is not popular with modern media :wink: but that's not what we mind very much about here.Vortigern:1bdk5j49 Wrote:So far however, I assume...hock: You should never do that. 8)
Btw, I would love to see some pictures of you testing your plumbatae.
Robert Vermaat
MODERATOR
FECTIO Late Romans
THE CAUSE OF WAR MUST BE JUST
(Maurikios-Strategikon, book VIII.2: Maxim 12)
MODERATOR
FECTIO Late Romans
THE CAUSE OF WAR MUST BE JUST
(Maurikios-Strategikon, book VIII.2: Maxim 12)