The Ballista

I imagine that most catapult gurus would object to this Mk. X  limb on purely “historical” grounds.  After all, it’s a pretty easy target when you only see it as a snapshot frozen in time and divorced from the larger development continuum.

This is all a work in progress, and these highly effective limbs are just one of several iterations yet to come.  Knowing the performance characteristics of a cabled backed design will provide a useful base line of comparison for when we test some steel strapped versions in the future.   That sinew strapped limbs similar to this could likely have been rendered in ancient times, is enough of a signpost for now.

If you don’t know how much fast you can get, you may be tricked into settling for something slow.  Prototype development is not about making the last thing first.

It has been noted by some, that Firefly is a tad over-engineered.   Compared to what?, we would like to know.  As our machine appears to be the only one generating authentic levels of performance (shooting 800 meters across the Danube etc.),  perhaps it would be more accurate to suggest that all other modern reconstructions of her size and class are actually under-engineered.  Firefly was never intended to be put on parade at a reenactment event and nit-picked by all those worthies that have already assembled a keen vision of what a late model, iron framed Roman machine must have looked like,  (although surely they appreciate our accurate dimensional reconstruction of the Orsova artifacts).  Firefly was made largely as a test bed, and in that sense I suppose she is a dither or two overwrought.  Her talents are weighted more to the shooting range, and generating all the events and observations that have been so painstakingly presented in this journal.

Little things like:

Repeated groupings of three and more consecutively fired Dura bolts inside a twenty foot circle at a range of 880 yards;  firing a flight bolt 1,000 yards (okay, 998 yards, but near enough to that iconic distance);  understanding that the authentic, 7 1/2 degrees of rotational discrimination in the washers is just about the right fineness of control needed to preload the spring bundles into a state of balance; observing how the aerodynamic pressure on a truly fast moving Dura bolt stabilizes it much more quickly than a regular straight sided shaft; proving the necessity of angle struts to make the machine rigid enough for heavy draw weights; demonstrating that with an inswinger there is plenty of power potential in 45 degrees and less of arm rotation, and from this realizing that the original Orsova machine could have been as short as 5 feet, rather than Firefly’s 7 1/2 feet;   proving that a sliding trigger block is a practical and desirable alternative to a long and awkward slider of conventional design, and also showing how this might be a viable interpretation of certain depictions on Trajan’s column;   having a muscular appreciation for the cocking effort;   punching 1/2″ diameter holes through 1/4″ steel plate;  taking a  quarter-kilo bolt up to 400 feet per second;  generating 2,000 foot pounds of muzzle energy;  having multiple witnesses observe the parabola of a half-kilo bolt as it travels an estimated 300 yards up into the air, and a carefully measured, 820 yards downrange; putting 11 consecutive shots through a two inch hole at fifty meters; seeing how easy it is to swap bowstrings and use one with a pouch to fire 400 gram lead glandes at over 300 feet per second, and then using the same pouched string to fire loads of grape shot;  demonstrating that a modular, pre-wound torsion spring can be installed into a field frame in less than half an hour;   dealing with chaffing issues on the spring;  understanding where the potential wear points and weak spots are in the machine when under repeated heavy loads; tuning the machine to eliminate all traces of erratic bolt flight;  dealing with the whip arch in the bowstring at the moment of firing and preventing it from tangling under the stock; demonstrating how the two holes in the kamerion were likely used to support a front sight;   having multiple witnesses observe what an authentically flat trajectory with a heavy bolt actually looks like;  having multiple witnesses observe the very high precision and long range of Firefly’s indirect fire;  tuning the bundles so that the limbs sweep in the correct plane;   showing that by firing Firefly for a couple of hundred shots on a broken strand in one of the bundles that waxed 1/4″ , 3 ply cordage does not necessarily unravel or lose power by the diminisment of a single strand, (an obviously important consideration for the muggins that has to work the maintenance shift);  making and testing ten different variations of limbs to arrive at something fast and reliable;  enduring multiple limbs breakages and risking life and limb in that process;  using an experience and work bench methodology to achieve results rather than a limited mathematically based one, (ie. the way the Romans would have done engineering);  providing lots of evidence that the Orsova artifacts make much more sense kinetically when configured as an inswinger rather than a outswinger.   And finally,  let’s not forget our current project:  modelling the propulsion characteristics of both sinew and nylon torsion springs so that accurate predictions about the performance of original machines can be made with modern reconstructions.

I could go on.  But what’s the point?  If your definition of “authenticity” in an experimental archaeology project doesn’t include factors like this, it is clear our wavelengths are never going to merge.

I’ve been thinking about some discussions I had with Samuli Seppanen about trying to find out the relative power of sinew vs. nylon in a torsion spring.   As I recall, we were agreed that it should be possible to work out a ratio between the propulsive qualities of the two materials by using a pair of small, identical catapults — one powered by nylon, and the other by sinew.   This seems like an important enough question that it could stand to have a couple of different researchers probing it.  I have some fixturing and tests  in mind that should establish that ratio with adequate precision to make a reasonable prediction about how well Firefly’s torsion springs would perform if they were made out of sinew rather than nylon.

This is important because I have noticed a repeated criticism from some quarters, that if experimental archaeology can’t be counted on to demonstrate what a torsion machine can do when powered by sinew, then the whole exercise is “pointless”.  In a certain narrow way, I suppose this is true.   However, it has always seemed to me that any serious inquiry into the potential of a sinew based machine  would need to be predicated on some baselines established with a fully developed nylon powered machine of unquestionable power and performance.  Without that, there is no way to really know if all the other aspects of the machine (ie. the strength to weight ratio of the limbs, frame strength, rigidity, draw weight etc.)  have been taken to an optimum level.  It’s not like it is practical to do that kind of extensive research with something as rare and precious as a matched pair of full sized sinew torsion springs.  However, a small enough torsion spring made from sinew, maybe something the size of a 4″ blunt cigar, now that’s a happening thing! …

I have tried to be  careful in this blog to never openly state that Firefly’s ballistic performance is necessarily an accurate analog for a sinew powered machine.  It is perhaps the most obvious of objections to complain that because  modern reconstructions are powered by nylon,  they have no useful contributions to make.   In Firefly’s case, it might be helpful for any critics to remember that she is a work in progress.

Just because I was in the mood, I decided to take off on a little expedition this afternoon in search of that missing flight bolt from a few weeks back.   (See posting, “A bolt too far”)   We had  tried our best to bust 1,000 yards with a 276 gram (4,259 grain), scale replica of the famous Dura-Europos bolt.  The last we saw of that exotic bird it was ripping out of Firefly at 375 feet per second.  Here, again, is a quick video of that shot.  Click for Vid.   20121107135533(1)

We searched for that bolt for a couple of hours right after the video was taken.  To no avail, of course.  Gary and I had looked for it on a second occasion back when we were “wabbiting”.   And again, no luck.    Today I had a new strategy to try.

The last few times we’ve taken Firefly out, when we got around to working on the downrange end of the data, I was getting a little lunk-headed in the sensitivity department.   Probably I needed sugar.  Today I was properly fueled and rested for the task of finding the bolt.     …. And, I was wearing my magic moccasins.

Experience has taught me that when I am looking for something in a natural setting,  beyond fixing the object’s appearance in my mind, it is best to melt into that setting by shedding any desire to find anything, and just letting course and direction be dictated by wherever the moccasins choose to go.  The eyes do the rest by relaxing and almost casually observing the area being walked over.  Believing yourself to be lucky, also seems to help.

After about twenty minutes of padding over the damp earth and falling deeper and deeper into this purposeless trance, a flash of orange registered somewhere in my subconscious.  A more deliberate squint at the ground four yards ahead, revealed this peeking out of a clump of grass.   The rains must have flattened the grass enough to make it visible because it sure seemed like we’d been over that area before.

After that it didn’t take long to set up the laser range finder and get a reading back to the 750 yard marker.   It was telling me that the bolt had traveled exactly 250 yards beyond the marker, which I had difficulty swallowing as that would put the range of the shot bang on 1,000 yards.    However, a quick check of the angle indicated we were 9 degrees to the left of the marker.  Plotting this out when I got back to my computer revealed that, after this correction, the overall range of the shot was actually 998 yards.

So, technically at least, we haven’t busted 1,000 yards yet.  Clearly, the Catapult Gods are out there, always keeping the mortals in check and from rising above their station.

And from our never ending blooper reel, we have this event that occurred several weeks ago.  The footage was taken by our good friend and neighbor, Richard Rough.

Click for video,  blooper 3

A slick new serving on the bowstring and an injudicious use of lubricant, caused this dizzying little tumbler as the string slipped under the bolt.  Now you see,  “..why with the steel helmet, already yet?”

Sometimes it all starts with a mental photograph.  The memory of a vision, perhaps.   A snapshot rendered only in the mind, but somehow, a recorded image none the less.

The more the image is accessed, the stronger it becomes.   And then, one day, you just pick up a tool and start to make the damn thing.   Metal chips begin to fly, and iron and steel brighten under the torch.    Wood shavings drop to the ground.   Occasionally a little blood is shed, so the band-aid tin gets stuffed full with new recruits.

By constant reference the image deepens and matures as more and more details are completed.  Finally, one day, you can reach out and touch that vision.  It has become corporeal.  A created “thing” that sits in a circle of it’s own construction debris; all the parts of it that are not, as it were.

Only then are you free.

The oil drum in this next video is sitting directly on the 750 yard marker.   Headwinds of up to 11 mph have reduced our normal range by 30 yards or so.   Generally speaking, when it is this windy, any stuffed rabbits we might chance to meet just laugh at us and go on about their business.   Click for vid.   20121110134512(4)

However, occasionally we get close enough to make their ears twitch.  Click for Vid.   20121110134512(1)(1)

Lovers of all thigs soft and cuddly will be relieved to hear that no stuffed “wabbits” were harmed in any of today’s range exercises.

A snip from that first video shows a heavy 521 gram bolt steaming in at maybe a fifty degree angle.   Probably the FOC balance point of the bolts effects how steeply they descend.  Those blue Dura’s we captured on video from a few days ago were closer to sixty degrees.

When the wind dropped to 4 mph, this pattern overshot our long-eared friend by 31 yards, the furthest striking at the 781 yard mark.

Today’s high jinx were accomplished with the help of Mr. Gary Davis.  Who is, most decidedly, not a “wabbit”.

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Well, now that we’ve had our fun, it’s time to buckle down to the larger question.  What next?

Because this is such a one-sided project,  and the input of any who might quibble and distract is excised at every turn, I find myself in the position of the perfect tyrant, and have narrowed the possible choices down to three.   To wit:  I could sit in my armchair all winter and let the workshop rot by entropy;  I could start work on a handheld version of a Roman inswinger;  or I could get on and build Phoenix, an updated version of Firefly that would be shorter, yet much more powerful.  There is also factor X: unknown for not having thought of it yet.

The astute reader may have observed that I believe there is value in taking certain lines of inquiry to beyond the mere extreme, and Phoenix would certainly be that.   For me this is a motivational tactic as the maintenance and good order of the shop requires the sustained use of imagination as well as elbow grease.  In some ways it doesn’t matter what the subject matter is that activates the brain in a tactical fashion (being in the moment as some might say) so long as it provides a focus of interest to mitigate the depressing accumulation of dulled tools and metal chips.   There is an underlying irony when precision is surrounded by filth — it is just the nature of metal working to be janitorialy intensive;  in a one man shop, without an over-arching mission, the prospects for survival diminish as soon as the spring winds down.     ….. But, I digress.

I recently saw a NOVA episode where several experimenters working in the field of animal intelligence, had put upwards of twenty years into investigating how homing pigeons accomplish their amazing feats of navigation.  Seeing as how the Firefly project has only got 4 1/2 years into it,  any whining on my part is just whimpering for lack of direction.  Ruts abound on country roads such as these.

But at least I see now how these back-roads of investigation can take a decade or two to complete.   A quaint notion, to be sure.

Here we are popping off a blue.  That is: one of our blue-tailed Dura’s that weigh 340 grams and are 28 1/2″ long.  This particular one is being ejected from the machine at 359 feet per second.

Click for vid.   20121107141039(2)

The bowstring has been caught close to the apex of its whip arch.

This is shot number two in a three shot sequence, in which two bolts landed within 10 feet of each other at the 884 yard mark, and, due to headwinds, there was a third that fell 20 feet short of that.  The same sequence we showed last Wednesday.

I wonder if any sharp-eyed Romans mused on how closely the arch in their kamerion matched the “whip arch” in their bowstrings. Now, that’s nerdy.

Observe, if you will, the fine lines and streamlined appearance of our latest analog for the famous Dura Europos bolt.

Our older version, on the bottom,  looks sluggish and fat in comparison.  The new bolt is made from an old martial arts staff, and while we don’t know for sure what exactly the wood is, clearly it’s much more dense than the ash we have been using.  This allows these two bolts to weigh exactly the same (276 grams),  while giving the new one a 3/16″ smaller diameter.  This will be our final, all out attempt to bust 1,000 yards before the weather turns bad.

In keeping with that goal, the fins are much thinner; made from .01″ thick phospor bronze sheet, as  compared to the .062″ thick polyethelene we have been using.  It’s a springy material, and of negligible weight.  Kinda looks pretty too.

Yesterday morning, this sleek, little, race horse of a dart found itself pointed at the sky with a very big machine behind it.   And in a 375 feet per second flash, it was gone …..

Click for vid.  20121107135533(1)

…… never to be seen again.

Even now, it lurks in the underbrush.  Or perhaps has burrowed it’s way completely underground,  waiting for some future archaeologist to uncover it and ponder why they were using ballistas back in the early 21 st century.  Of course, it may not seem out of place at all.  Einstien’s admonition about bow and arrows will likely make more sense by then.

One of the advantages of precision shooting is that it gives you the nerve to risk your expensive video camera down at ground zero.

The first of these vids. is a little dark and it may be difficult to discern one of our  “blue” bolts dropping out of the sky.  If you allow your eye to relax on the sky in the area that the incoming action is occurring,  it will all become clear if you play it on loop for a dozen times or so.  (If you are looking for Hollywood theatrics in your falling ballista bolts, this is all going to be profoundly underwhelming for you.  It is, however, absolutely real.)

Click for vid.  20121107150929(2)

Click for vid.  20121107150929(5)

Click for vid.  20121107150929(4)

Range of the furthest shot is 884 yards, the second shot falls ten feet shorter and is in line with it.  The third shot, again lines up, but falls shorter at the 880 yard mark.  The projectile is a 28 1/2 ” long, Dura style and weighs 340 grams. Muzzle velocity is averaging 362 fps.  There was a 3 mph headwind with today’s shooting.

The  middle video picked up the streak of the incoming bolt in two locations in this next snapshot.   A classic example of  plunging fire.  Don’t see anything? Click on the photo to enlarge.

As near as I can measure it,  when we plaster these videos up on the big screen, it looks like these whistling darts are coming in at a 60 degree angle.   Rome’s enemies must have hugged their walls pretty close.  This kind of unstoppable and unpredictable attack must have made the besieged feel vulnerable and edgy.  Basic psy/ops type stuff.  If you can’t go out into the open for fear of fast moving pointy things falling on your head,  it makes it hard to get your chores done.  And if your chores go undone ……

…..well, that’s always the beginning of the end,  isn’t it?