The Ballista

To the best of my knowledge this catapult project is different from any others you may have heard about.  For a historically defined machine of this class and size, the one you see below is the most comprehensively tested, powerful, long-ranged, and accurate shooting ballista made since ancient times.  No brag, just fact.* Her name is Firefly. This blog is a journal of how she came to be. 

Click for video: 000142 (2)       Click for another vid:  00017(1)

The impressive work of the Pumpkin Chunkers may seem like an obvious counter to this bold claim.  However,  they are working with an unlimited class of machine that is not concerned with matters of historical fidelity.  This journal details the day to day efforts it took to make a formidable, Fourth Century Roman ballista that did not stray outside the dimensional constraints of the artifacts it is based on.

Like any modern catapult reconstruction, Firefly is not a perfect duplication of the original machine.  Which is hardly possible as there are no intact ancient catapults,  just rusty old bits and pieces, and a few original texts that are inadequate in explaining how these machines achieved their reputedly high performance.

Firefly is in a ongoing state of testing and refinement. Many of you with a bent towards reenactment will no doubt find areas where she is not particularly convincing.  That is to be expected as Firefly is not a machine built primarily for display purposes.  As much as anything, she should be considerd a “proof of concept” shooting machine.  A historical test bed, if you will.   Perhaps polished a little more than is strictly necessary, but that’s a personal issue……

A word about my sometimes flippant tone — I’ve only got so much happy in me for this kind of trial and error marathon.  I find a certain amount of glibness necessary to keep buoyant after so many setbacks. Hopefully it doesn’t belie too much of the actual work.

And with that, here is the continuing saga of Firefly and our new machine, Phoenix…..

Nick Watts,  September 2015

* Believe it or not,  I really would appreciate it if someone would refute this claim.  Numbers, please.  Comments section is open.

What follows is essentially a set of field notes and facetious contemplations.  You will need a sieve.  If this wordy, highly detailed, maze of a blog is not to your taste, please try the following website for a more concise presentation:

http://alexisphoenix.org/ballista.php    

The two postings below will provide newcomers a glimpse into what this project is all about. They are a little older and are presented out of sequence. For the latest postings please go to the menu on the right and check out our other categories. Day one of the project defines the historical origins of this device and is easily accessible by clicking in the archives.   Actually reading through the rest of the days — that will take some stamina….

My old friends, Brian and Frank, were on hand for our first successful attempt at shooting a twelve shot group at Firefly’s maximum range.   They took some nice photos of our set up.  Here we see the newly installed Mk. X limbs just before being put into action for the first time.  (Click to enlarge.)

And next, here is a shot of that space blanket reflector we needed for the laser range finder. (Which worked extremely well, we are pleased to report.)

There happens to be a rock outcropping overlooking our firing line and Brian was able to get a good vantage point for this next video.  It takes some sharp eyes to catch the trace of that bolt across the screen, but it is there.  Click for vid:  20120918143324(2)(1)

From atop the rock, Brian and Frank were able to see the entire flight of the bolt out to it’s 800 yard endpoint.  Apparently, witnessing the scale of that arching trajectory in person is quite impressive.  It leaves me a bit jealous as I’m the muggin’s that always has to operate the machinery.  The most I get to see looks something like this:  Click for vid.   20120918144301(1)

But I ain’t complain’.  At least we got some data this time.  These next two charts show how the dispersion of the shots appeared when we finally went downrange to take some measurements.

This first one shows the overall range of the shots in yards and their dispersion to scale.  Bolt weight is 521 grams.  (Click to enlarge)

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And this second image shows the dispersion of the shots up close and to scale, with the shots numbered in the sequence in which they were fired, their distance from the firing line, their muzzle velocity,  and the angle that they were found sticking in the ground. (Click to enlarge)

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A quick analysis of these 12 shots reveals the following:  Shots numbers 1, 2 & 3 can be discarded when determining the overall group size for the simple reason that the wooden wedge I used to secure the tail of the machine had been inserted from the wrong side and fell out during use.  (Although 2 & 3 do seem to have all fallen very close to one another.  Something is going on here, so maybe the machine didn’t shift position after all.)   Anyway, the wedge issue was easily fixed and shooting resumed without further incident.   Shot number 7 we can call a flyer due to gusting winds at the time of firing.  The remaining 8 shots can be considered valid from a shooting standpoint, and basically fell inside a 60 foot radius.    That is just about enough precision to hit your average three story Mc’Mansion  at almost half a mile.  Not bad, but I know we can do better.

Before going on this field trip I only had time to put four shots through Firefly after the new limb installation.  I suspect the bundles are still moving towards a stable equilibrium and that this is causing some of the velocity variation we are seeing in the above chart. Looking at the shots in numerical order it does seem as if there is a gradual decrease in velocity and range that tends to stabilize at the end of the string.    Unfortunately the chrono showed error readings with the last few shots, but if we consider only the last five consecutive shots it is clear from the chart coordinates that the group size shrinks to something like a 30 foot radius, which seems pretty darn good to me.  I certainly wouldn’t want to be standing inside that circle if some hotshot ballista crew were taking potshots at me from half a mile away.

Today’s tests show that this level of precision would make machines of this type effective against massed adversaries to the full extent of their range.  I have no doubt that with lighter bolts of the Dura pattern,  Firefly’s  maximum range could exceed 1,000 yards. With a bit more tuning the heavier 521 gram bolts we are shooting here should clear 850 yards with ease.  Given how hard it was to extract the bolts from the ground, and considering their average 10 1/2″ of penetration into the packed and dry topsoil, it seems clear they would have been brutally effective on cavalry and lightly armoured troops.

Also of interest:  The shooting session had varying winds from zero to eight knots and was less than ideal for our purposes.  Because time was limited for my two compatriots, we took to the field with a minimum level of tuning on the new Mk. X limbs. There appears to be some asymmetry in the way these limbs are tracking in their planes relative to the deck of the machine, the starboard limb rising perhaps an inch high and the port limb a similar amount low. All fixable by more tuning.  Apart from that, the limbs behaved brilliantly, with no observable curvature at full draw, and sacrificing only perhaps 15 fps from the 1/2 pound increase in their weight from the spreaders and extra bindings etc.  This we should be able to make up, and more, when we final tune the machine.  The average velocity with the 521 gram bolts we are using in this test is 308 feet per second.  All shots were fired with a launch angle of 44 degrees.

And to give some more scale to the proceedings, here is a video with Brian acting as a human laser reflector as we map out the position of the bolts in our group.  Click for vid:  20120918151232(1).   Frank was kind enough to drive back to the truck and retrieve my binoculars that have an internal compass in them.  This made measuring the angles out to each shot a snap, and combined with the laser range readings off Brian’s chest, plotting the locations of these twelve shots only took a few minutes.

In this next video we can see the laser range finder in action as it takes a reading back to the reflector at the firing line.   Click for vid:  20120918150853(1).    The rock outcropping mentioned before is visible on the horizon line of the field we are standing in, just to the right of center screen and at the end of the video.  For reference, that tiny dot to the left of the outcropping  and in the middle of the screen, is the truck and radar reflector.  Can’t see it?  Well it looks a very long way away when seen in person too.

Here is a quick pan across the field of carnage.  click for vid:  20120918153451

And finally, a couple of photos of the new Mk. X limbs sharing the full draw weight of 5,000 lbs.

Note the lack of  bending as compared to those snapshots of the Mk IX’s from a few days ago.  I wonder if it is a good thing that shooting Firefly is not quite as terrifying as it used to be.   No doubt the Catapult Gods will keep me apprised about all that.

This stalwart group of time travelers has just braved wind and cold and bumpy roads to witness this Sunday’s ballistic recreation from the Fourth Century.    On the left is George Baumgardner, on the right is Dr. Walter Henze, and in the middle, our beloved and intrepid lab assistant: the Rebecca.   Richard Rough, who has been out on these jaunts with us before, was also present to observe our attempt to poke holes in the sky and bring home some fresh data.

The small size of this group of shots is remarkable.   They were all fired consecutively from a carefully positioned 44 degree launch angle.  George and Walter’s bolts are only 13 feet apart, while the average range for these  shots is  790 yards.    So at this range Firefly is tossin’ them into a 20 minute of angle group.  This is exactly the kind of performance I’ve been dreaming about these last four years.  To the gunnies out there, 20 MOA at 800 yards is pretty lame to be sure, but I don’t recall anyone recording that kind of performance from a modern reconstructed ballista before.

Before we get to the data, here is the only video we could get of the parabolic flight path of a 521 gram heavy bolt.  I believe it is that same bolt that Walter is standing next to.  The footage shows only the first two seconds of it’s ten second journey, so it takes some pretty quick eyeballs to see it at all .   Click for video:  20121104130331(1).

Here is a snapshot of the three types of bolts we tested today.  The red one weighs 521 grams and is 36″ long.  The blue is 340 grams and 29 1/2″ long.  The orange is 276 grams and 21 1/2″ long.

Here is a scale chart showing an overview of all the shots in today’s shooting.  Click to enlarge.

And here is a closer look at the actual landing zone for the three different types of bolts we were testing today.

The reds, on the left, are the “heavies” we’ve been testing over these last few postings.  They form themselves into two distinct groups.  Numbers 1, 2 & 3 were fired at the beginning of the session when we had a 6 mph tail wind; while shot numbers 4, 5  & 6 were  fired at the end of the session when the tail wind had dropped to 3 mph.  This latter group is the one seen in the above photo that fell inside a 13 foot diameter circle.   It makes sense that the higher wind speed caused the greater dispersion of shots 1, 2 & 3.  Average velocity for the “reds” was 315 fps.

The oranges, on the right,  are the same orange bolts we used on the last field trip and can be considered functional duplicates of the famous Dura Europos bolt from the Third Century.  What caused them to string out in such an even fashion is unknown.  We’ll blame the wind.  I suppose, to a certain extent, we should also thank the wind for helping give us the longest shot Firefly has made to date:  947 yards.  It looks like it is going to take either a hefty gale from the south, or at least some more innovation, to get us striking beyond the 1,000 yard mark.   (Which, of course, is a meaningless,  arbitrary goal we probably shouldn’t be spending too much time on…. more — blah, blah, blah.)  Average velocity for the “oranges” was 360 fps.

The blues, in the middle, are something new.  They are the same as the orange Dura Europos bolt, except 6″ longer, and with heavier heads that boosts their weight to 340 grams.   They very neatly dropped themselves into a 20 foot diameter circle at an average range of 934 yards.  Not bad for the new kid on the block.  Average velocity for the “blues” was 348 fps.

Also of interest is the increased depth of penetration now that the ground has been thoroughly soaked with rain.

This heavy “red” bolt  has an overall length of 36″ and  has buried itself  to a depth of 18″.  When the ground was dried out over the summer these same bolts penetrated 10″ on average.  It should be noted that the ground on our firing range has a uniquely homogeneous consistency with no rocks or other anomalies.  It is some pretty fine grained stuff and, now that it has been wetted down, the bolts show amazing consistency in how far they penetrate.  The “blues” penetrated 15″ , and the “oranges” did 14″.   I am not sure what any of that means, but we record the fine quality of our target medium in deference to the large amounts of “moondust” we all must eat when the roads around here get dried out and driven over by big trucks with lumpy tires.   More yum than you can possibly imagine!

And, finally,  some photos to brighten up the page.

A “blue” looking pretty for the camera at the 895 yard mark.

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And demonstrating the dispersion of the three shots in the “blue” group,  in the foreground we see George standing next to a bolt at the 904 yard mark,  while Walter and  myself are standing by ones back at the 896 yard mark.

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And here the humanoids mark  the longitudinal positions of those lightweight orange bolts, the furthest of which made it out to 947 yards.

(Sorry! No photo of you Richard.  Are you camera shy?)

That truss arrangement is just about enough to give a fella ideas.

That’s cutting it as close as I dare on the acuteness of that string angle at full draw.

An inswinger’s bowstring is prone to interfering with the projectile fins when we try and stretch too much limb rotation out of them.

The 65 degrees of limb rotation, seen above, is about as much as can be managed with Phoenix, and still have her limbs be as long as reasonably possible.   This limitation is very deliberate.  The type of torsion spring I am making,  seems to yield it’s best performance with short limb rotations of 50 degrees or so.   Firefly convinced me of this to the point I decided to embrace the principle and make Phoenix as compact as possible.  The shorter limb rotation means I can get away with a stock length that is perhaps 18″ shorter than would otherwise be possible with some kind of 110 degree, over-rotating, specimen.

Short, sharp, and violent in it’s stroke, our ballista limb needs to be both light and immensely strong.  All this mock-up work is being done to help intuit how much weight we can trim away from the limb irons.

I premise this attempt by accepting the well known idea that late model Roman ballistas utilized iron strips and bowstring hooks on their limbs.  Therefore, at this stage, the existence of full length, limb irons, is a non-negotiable tenant of this project.  Puzzling the geometry at full scale, is my focus at the moment.

Phoenix’s full size spring mock-up has allowed me to make a start on the limb design.  There will be many cogitations on these parts before I can be confident that the limb is as light as possible, yet amply strong to handle heavy draw weights (3,000 lb.  at least, I’m hoping),  all the while exploring the historical utility of steel tension straps and steel end hooks for the bowstring.

That piece of steel, nestled up against my fake limb, is actually the prod for a small 200 lb. crossbow.  The prod is about 3/16″ thick, and seems about the right size to be a rudimentary model for the tension straps.

Gazing at it for hours on end helps bend my visualizations around what’s absolutely needed and what is not.  When it comes to limbs, the more “not” you can generate, the faster you can go.

The value of full scale mock-ups cannot be underestimated at this stage of spring development.

I’ll ponder on what I’m seeing here, for awhile.

No doubt all that’s needed is to deepen that scallop in the butt of the limb by a small amount.  That should provide enough clearance to prevent the spring chaffing on the straight stanchion as it is now.

In torsion catapults,  spring size really does matter.   ….So vital to keep our springs as girthful as possible!

So that’s 166 feet worth of 1/4″,  3 strand, nylon rope, going through a hole that is 2.630 inches in diameter.  This later is the same size as the hole in the field frame that the spring passes through.

After a year or more of dormancy, the Phoenix project has started to stir again.

With mock-ups for the springs and limbs,  I am figuring the clearances needed inside the field frames for everything to operate smoothly.

The above photo gives some idea of how the wedge system will work.  The wedges shown here are just softwood.  Ipe seems like a good choice for the final version.  The wedges will need to resist some pretty massive crushing forces from the spring.

The spring being made in the above photo will probably not be used to power the final machine.   It is just another mock-up to help verify the limb design.  When the cord wrappings fill up the circle in the template, the spring will be ready to install in the field frame for a first real look at the clearances involved.  We want the spring to be as large as possible and still work within the field frame.  Also it is important to make the limb as thick as possible where it goes through the spring.  This will not only make the limb stronger at it’s weakest point, but will also force the two haves of the spring apart and so increase the leverage acting on the limb and make it’s action more powerful.

I have decided to put the Phoenix project on hold for the rest of the summer as there are more pressing concerns right now re: house building for my daughter.   Many thanks to those folks who have taken an interest in this project, and I’ll be back at it probably sometime in November.   Email dead for the duration.  Cheers,  Nick.

Two degree, counter-posed wedges, seem like a good starting point for our first attempt at an adaption of Mr. Philon’s souped-up torsion machine.

Those extra long wedges will be trimmed to length after the fine tuning is completed.   For experimental purposes the washers will also be capable of fine rotational adjustments.  There are 16 holes in the washers, each 22.5 degrees apart.   There is a 3 hole pattern in the vernier plate*,  with each hole set 15 degrees apart, so that the washers that control spring rotation can be locked down every 7 1/2 degrees.   The second set of three holes is so that there can be two locking pins for each station.   Next will be the radiused pusher bar that sits on top of the wedges.  And then on to springs and limbs.

*Counter plate, or counter washer, if you will.  I prefer “Vernier plate” as the Ampurias finds, whose geometry we are mimicking here, seem to contain the first deliberate use of a logarithmic scale similar to a modern day Vernier.

The notches and locking holes on Phoenix’s washers are complete.

Quite the labyrinth of mechanical possibility ain’t it?

Except for the locking holes and notches for the crossbars, the washers are about finished.

Why “modiolus of doom”?  Because right now I need some kind of hairy provocation to keep this project alive.

Time has a way of elongating, right before it runs out.  You think you have all the time in the world to finish something, and then …. Blam!… you’re done.  The meter runs out.  Which leaves the Catapult Gods smirking at you for the rest of eternity.   Damn their temporal omnipotence anyway!

Also, my laptop is getting hinky.  Email is down.  Correspondence not possible until I get it fixed.

…If I get it fixed.  A hermit-like submergence seems somehow linked to my ability to self-motivate.  Go figure.