The Ballista

“Stacking” is what we call it when the draw weight hits a point during the draw back where it starts to increase very rapidly. Responding to a question about stacking by John Payne, I came up with this blurb about how it seems to work with inswingers.  At least, how it seems to work with Firefly.  With catapults, everything is a situation.

There are two types of stacking.  The usual archery type that has to do with the angle between the string and the limb at full draw, and another type that has to do with the spring saying “Oh! now I’ve hit a wall. My fibers are getting stubborn.  I’m not going to budge so easily anymore.”  (Not bad for a talking spring, huh?)

The first type is easy to understand.  Imagine an ordinary limb on a hand bow at full draw.  The more you pull it back the closer the limb and string get to forming a straight line.  In other words a straight line pull.  That’s like pulling on an anchored chain.  Not move so much.  Here’s a rough idea of how this type of stacking works on an inswinger.

The second type of stacking, the springs “hitting the wall” phenomenon, is only something you can judge by how much the draw weight goes up and at what point that happens during the draw back.  With an inswinger I don’t think the first stacking issue (the archery one) starts to take effect until we get beyond 100 degrees.   Therefore:  If your stacking is happening at 100 degrees or less then you are probably hearing the spring talking to you.  This sort of thing is more likely with a short fat spring, rather than a taller, skinny one.  It’s certainly something to be aware of if the draw weight skyrockets all of a sudden.  Back off.  Play with it.  At some point you will have to say, “That’s enough for this framework I’ve built.  I will not ever draw it back any further than this.”  Whatever that draw length happens to be.  That is what I did with Firefly.  Fortunately by the time I made the decision  to enforce a ban on further draw back, she was performing at the level we see today.  I would be pretty nervous about going any further.  Too many bends and breakages for one lifetime.

In her current configuration, Firefly clearly shows the spring type stacking.  That is why I’m keeping her at 45 degrees of limb rotation.  There are a lot of advantages here.  If it’s done right, little things like:  faster cocking times, more compact machines, and hopefully, the highest velocity Dura bolts possible out of authentic geometry.   With catapults, everything’s a situation. What a grand hobby! It’s all just tickety-boo when you find the right combo.

….or so you think, at least for a while….

Neighbor Richard may have scared-up a suitable range for us to test Firefly at intermediate distances.  (200, 300, 400 yards.)  A recce seems in order. Fingers full crossed on this one.

The Lyon ballista has sharp 90 degree edges on the top of it’s crossbars.  If Firefly has shown us one thing it is that these edges would quickly cut through any spring that had the misfortune to be stretched over them.

Ergo:

With the Lyon machine, at least, there had to be an additional piece with a properly radiused top surface to make contact with the spring. Take that as a given. Sharp edges are anathema in this area.

Therefore:

The extra part that would have this radius on it would have to be there for some additional reason , otherwise they could have just radiused the top of the crossbar and called it a day.

What could that additional reason be? Some higher order scheme placed in the exact spot a wedge tensioning system would need to do it’s work.  Hmm?  …With the correct type of modelling it may be possible to make a compelling case for the Lyon machine being a type of wedge machine*. It seems the most logical explanation for having a flat surface on the top of the crossbar.

Ergo:

Phoenix, our reconstruction of the Elenovo ballista, will take her cue from the Lyon crossbars and be a wedge machine. At least, she’ll try very hard to be one.

*See: Marsden, Greek and Roman Artillery. Philon is quite the champion for wedge machines.

There is no final verdict possible in this game of iron frame catapult reconstruction.  No matter how well done, there will always be contingents of armchair theorists ready to rip into any modern attempt at making an “authentic” machine.  It really is a fools game trying to hold up any one design as the preeminent candidate for scholarly acceptance, whatever that is. Might as well dump chum into a shark tank.   Agreement is no longer possible because there are so many careers and threads of opinion at stake.  Inswinger or outswinger? Barring a definitive archaeological find, there will never be a winner. The waters here are just too deeply muddied by all the thrashing around.

Going back to my hobby now.   Thankfully, very few people ever read this blog.  I like the quiet of not being judged by paper know-it-alls with limited shooting experience.

On the other hand, I’m in a mood.  Let’s smack back at the poor dears anyway.

If, by the slimmest of chances, there is a partisan from the outswinger camp reading this labyrinth of a blog, here is something you might want to consider:  if an idiot like me can make an iron frame inswinger perform at levels so much higher than any iron frame outswinger, are you really saying I have accomplished something the ingenious Romans could not have, all with the exact same artifact geometry? Do you really think the Romans did not see the same performance potential in their own parts, just as many of us have done? Of course, they weren’t exactly artifacts back then were they?  They were an integral part of an engineering triumph made by ancient craftsmen who put their reputation on the line trying to develop superior machines.   When it comes to catapults, superior is superior in any epoch.

It is no accident that a modern inswinger can be built so effectively around functional duplicates of a Kambestrion and Kamarion that have been lying dormant in the ground these many centuries.  To see this you just have to turn away from the view that history is solely an exercise in “interpreting” the textual evidence from dead languages. Arguments based only on appeals to authority just don’t cut it in this game.  These machines are deeper than that. Think CSI rather than Henry Higgins and you’ll have the jist of it.  If you are lost, always go back to the hard evidence.  The artifacts are the hard evidence.

Here is something undeniable for you to chew on, the sight and sound of an authentically powerful iron frame ballista going off.   Click for vid: canyon 3     As an inswinger, Firefly simply demonstrates the inherent mechanical logic of the artifacts themselves — the hard evidence given it’s most dynamic and compelling interpretation from a shooting standpoint.  In other words, the kind of performance success any weapons development program strives for.  Perhaps the outswinger faction of this teapot tempest undervalues the idea of superior ballistics.  It’s very doubtful that the Romans were similarly unambitious.

If you are interested in the difference between hard evidence and soft evidence, here is the definition I prefer. It is copied from this website:  htmhttp://www.av8n.com/physics/authority

The Value and Limitations of Soft Evidence

There is a huge difference between hard evidence and soft evidence. Reliance on authority, credentials, and reputation is near the top of the soft-evidence scale. If you don’t have any hard evidence, you ought to be guided by the best available soft evidence. However: remember that the top of the soft-evidence scale remains far below the bottom of the hard-evidence scale.

Not convinced? Perhaps a shooting contest  could settle the matter?

Well that worked a treat.  Clearly they are all won over.  Back to my machine now.

There are likely huge advantages to a wedge machine* in expedient conditions.  Linear tensioning (the most preserving of the spring) can be accomplished by a couple of guys with sledge hammers.  Wedges could be available in different degrees of angularity.  The smaller the angle on the wedge, within reason, the more powerful will be it’s effect in leveraging the steel spreader bar away from the flat-topped crossbar (as in the Lyon artifact).

If the machine is brought into a shooting condition, and then tuned to make the bolt shoot nice and straight by using only the driven wedge method**, then after this it should be possible to rotate the washers with a powerful spanner an additional 180 degrees and turn a nicely balanced lazy ballista into a nicely balanced high velocity bolt shooter. Preservation of balance is the key. It is an axiom discovered during our work with Firefly that a balanced machine does not lose it’s balance if additional washer rotations are performed equally on both sides of the machine. This would help explain the unfathomably coarse 180 degree of washer adjustment on the Lyon machine.  The wedges do the balancing, after which a single pre-determined rotation of all the washers puts the machine into high power mode.  These higher power levels are determined by how much strain is put into the springs originally with the wedges.

Using wedges and sledge hammers for linear stretching and balancing, followed up by a single twist of 180 degrees in the all the washers equally, would provide maintenance crews with easy and repeatable service protocols that are built right into the basic design.  There seems to be some clear synergies between a wedge machine and the modular spring concept we worked out with Firefly.  They should work very well together.

Because our current plan for Phoenix utilizes Vernier plates that can easily lock down 180 degrees of twist, we can test the above scheme simply enough, while retaining our conventional approach to tuning if needed.

* The ancient author Philon describes the wedge machine.    See Marsden, Greek and Roman Artillery.

**There is no more nuanced a way of fine tuning a two armed ballista that by actually shooting it and carefully observing the flight of the bolt in the first few feet. Bolt flight is, after all, the final arbiter.  If the tail kicks left, then the left spring is acting a tad more powerfully than the right spring.  (Or vice versa, of course.)  A wedge machine would be brought into balance only by driving the wedges deeper and never backing them out as this would be an awkward and unpredictable endeavor.  Sneaking up on balance points ain’t that difficult once you get the knack for it.

Unabashed in their rectilinear machine-edness, the scheme for Phoenix’s take-apart tangs and loops and wedges, starts to take shape.  Additional wedges under the tang, also slotted for the vertical keys, will be the next step.

Whatever this reconstruction is about, it clearly has nothing to do with authentic, Fourth Century Roman blacksmithing.  In this analysis, the ability to explore certain specific ballista designs is valued more highly than discovering the intricacies of ancient metalworking techniques;  interesting though they no doubt are.  Even so, I am careful not to make anything that could not be made with standard blacksmithing.  The deep slotted holes seen here could be made at the forge by hammering two halves of the tang around a pair of mandrels, and then forge welding the halves together. Something I do not have the time to mess with anymore. Either way, machined or smithed, the end result forms a close mechanical analog of what the original probably looked like. It helps us to zero in on what works, what doesn’t work, and if we are lucky, what works really well.  (This latter, can and does happen: witness the whole concept of an inswinger itself.  “Working really well” seems apt.)  And that, I believe, is all anyone in this EA gig is actually doing; filtering through the good, the bad , and the sometimes sublime.

Hats off to Mr. Aitor Iriarte for his classic paper The Inswinging Theory.  The basic design seen above is from that paper.  Here is his famous paper:  iriarte

In the deepest parts of an investigation there is a theme we often fail to see, blinded as we are by disparate facts. When the underlying pattern finally emerges there is a breathless innocence — letting go of what we thought we knew.  Istina.

Happy birthday 63 year old me.

Now that the head Elf has shot his bolt, so to speak, it’ll be no more shootin’ for a bit.  He be resolved to thump on his Kamarion awhile.  Click for vid.  fork forge

While her majesty watches on.  Unamused.

The graphic below shows 3 solid data points that record Firefly’s group size at 3 different ranges from 3 different shooting expeditions. Everything is shown to scale. Click to enlarge.

It is interesting to note that the recent 48″ group @ 300 yards, fits right on the line of dispersion between the 50 yard and 790 yard results.  This is another indication of the consistency and validity of this rate of dispersion @ 19 MOA. When I extrapolate the group size for other ranges it looks like this:

Click to enlarge.

The pink numbers on the bottom represent the extrapolated group sizes in inches at the yardages indicated.  The results at the 50, 300 and 790 yard ranges are carefully measured test results from actual shooting.  I have high confidence in their repeatability under light wind conditions.

For anyone interested in how these late model iron frame ballistas in the Lightning class could have performed under ideal conditions at typical combat distances, all of this should be a very good indication.  In their own way, I have no doubt those grunts in the tower where the Orsova machine was mounted, would have achieved similar or better results.

Here is one last video from our 300 yard shoot the other day.  It shows the aiming and firing sequence in better detail.  If you put your fast eyeballs on, the bolt profile is clearly visible against the blue sky.  Click for vid.    canyon 3

A snip showing the bolt just ejected from the machine:

The urge to shoot some intermediate range groups was finally slaked today.  I have become resolved to the idea that the bolts that get lost and shattered in these exercises are just the price of generating new data.

Three consecutively fired bolts hit in a four foot group at 300 yards.  A forth bolt we can consider a flyer, and hit outside the main group by another three feet.  The bolts have been placed upright to indicate where they struck.  As usual they shattered on impact and left their steel heads buried in the dirt about a foot and a half.  These are the same 520 gram bolts that go 800 yards when pointed at a 45 degree angle.

I decided to keep any ballista shooting activities on our own property for awhile. Here is the set-up overlooking our canyon.

The machine relies on my shoulder to steer it into a proper sight alignment.  The release pressure feels a bit like a double action revolver with a 20 pound trigger.  Stiffish, but smooth. Click for vid.  canyon 2

Considering that each shot had to be individually aimed with the peep sight, I am pretty happy with a four foot group at 300 yards. Firefly is a bit wobbly on that back strut,  this is not exactly bench rest technique here.  Added to that is the fact that my eyes are not as good as they used to be.  I suspect a younger me could have plopped those shots into a three foot circle without much trouble.  But we won’t go there.  I’m just saying there is much more precision going on with Firefly than my abilities as a shooter can fully realize these days.

It’s too bad there is such a high attrition rate with the bolts.  Eight were fired today. Two are MIA. (These were probably burrowers.  Oona was unwilling to find them due to prickly pear all over the bloody place. Ain’t no fool that one.)  Four were DOA. Two were lucky and seem undamaged. You wouldn’t think it would be so hard to find a nice soft hill somewhere! The first four shots were just sighters to try and land them in a soft patch (not so much, apparently).

—– In these next two videos the way the camera is focused makes the target hillside seem way, way closer than it actually is.  The photo at the bottom of this post gives a better idea of what 300 yards actually looks like. —–

So, with all that small print in mind, here is shot number one of our three shot group across the canyon.  You can just make out the dust kicked up when it lands.  Click for vid.     canyon 1

And here is shot number four.  Click for vid.  canyon 4      This one is much more difficult to see. Here’s a map of all four shots to help pinpoint it:

Shots 1 , 2 and 3 fit neatly inside a four foot circle. Shots number 2 and 3 were not caught on video due to poor planning on my part.  (Must remember to set up a second camera next time.) Shot number 4 was called a flyer because I was having a technical issue with my front sight having moved. Here’s a final video of that boorish little moment with me trying to set it back upright.   Click for vid.  canyon 5

And here is a final pic showing the approximate bolt path and landing spot in the shade of that pine tree 300 yards away.  The size perspective here is just about the way it looks in real life. The tip of that crayon line where it intersects the shadow is about the same relative size as the four foot circle we are shooting into.  That should give some idea of the machine’s inherent precision.

With performance like this, the lethal sniping potential available to the Romans with a Lightning class ballista* should be self evident. The myriad ways they could have chosen to utilize such devices beyond obvious pitched battle scenarios, is best left to the imagination.

* The Lightning ballista is from an ancient description of a miraculous bolt shooter by some shy dude called “Anonymous”.  See Marsden, Greek and Roman Artillery.  I suspect that the Orsova machine was of this ilk.