The Ballista

Okay, this is weird.  The blog post that follows just popped itself out of the archives and redated itself to the present.  Probably my fat fingers teasing me again.  I’ll not correct the error and just figure providence gets a say here too.  Here it is, ancient in it’s own right:

— I have been guilty of certain apriori approaches in the development of Firefly that have caused a lot of unnecessary effort.  Perhaps the greatest of these has been my fixation on protecting the field frames and the kamarion from the shock of the limbs crashing home.  Originally I had assumed that leather buffers would be a good idea to prevent damage to the machine from so much energy having  to be absorbed by the framework.  Great idea, until the leather buffers broke down and caused endless problems with bowstrings breaking as they absorbed all the shock.

After the buffers I moved on to heavy bronze hardstops intended to spread the load over a greater area of the stanchion,  I really thought I was on to something because now the limbs had a positive stopping point and the bowstrings were well protected from the limb shock by simply adjusting their length so that they were just long enough not to be over stressed.  The frames showed no damage with these bronze hardstops, so obviously this approach was working.

This phase with the bronze hardstops lasted quite a while.  Eventually my  desire to increase the limb rotation past 90 degrees caused the removal of these  pretty bronze parts, and with it (for reasons I don’t remember) my concerns about frame damage.

When we have experienced the pain of all the things that didn’t work we are ready to learn. —

Increasing limb rotation beyond 90 degrees?  Because, you know, back then I’d dreamed there were fabulous kinetic riches to be had with an extra long power stroke.  Oh! the innocence of the young!

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 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.

It seems that every time I look at someone else’s vision of how an inswinger must have looked, the machine is invariably striking a pose with it’s limbs showing dramatic amounts of rotation and, presumably, extra long draw lengths.  This cool painting by Mr. Dominic Andrews shows what I’m getting at:

Have they never heard of stacking?   The leverage angle between the bowstring and the limb becomes so nearly like a straight line it’s just not possible to pull it back any more.  The springs are at maximum strain just when there is minimal draw back power to get them that way. There is a fundamental illogic about that arrangement.   Anyway, Firefly wasn’t having any of this over-rotated hype.  A short, intense, 45 degrees of limb rotation is where she found her power.  I’ve heard the theories about how, with inswingers, long draw lengths and big rotations are better for throwing heavier objects.  Maybe so, but there didn’t seem to be anything to it when Firefly was set up that way.  Of course, Pumkin Chunkin ain’t exactly her forte.

I don’t always believe things just because mathematicians tell me they are true.  Real world modelling has to count for something too. Maybe the math isn’t big enough.  Of course, in fairness, maybe the modelling isn’t big enough either. Be that as it may, with Phoenix, I’m sticking to Firefly’s proven strategy for nice flat trajectories with Dura bolts:  45 degree limb rotation with an extra-extra taut resting bowstring, along with all the rotational pre-tension that implies.  Locking in a couple of tons of linear stretching first, makes an excellent foundation for all the rotational stuff you are going to have to spend so much time foolin’ with, if you want to birth a balanced and powerful machine.

And if that all sounds a little bit serious, that’s because it is.  (Rant alert)  There is just too much work in this hobby to go down any more fruitless paths.  If someone from the school of super-duper rotations wants to show us how to shoot an authentically weighted Dura Europos bolt a thousand yards from an actual machine (as Firefly has done), then we are all ears.  In the meantime, my experience with Firefly (here we go again) warns that the stacking from big rotations would require a low rotational pre-tension to achieve full draw, which causes the bowstring to be loose when in the just fired, at rest position.  This lack of tension in a resting bowstring is coincidental with sluggish velocities — not at all the thing after so much work is put into dreamin’ big.

The particular game I’m playing does not favor the Hamish approach:

On the subject of accuracy and precision, this graphic just about says it all.

Firefly’s long range shooting has so far been typified by that sketch on the upper right.  While it is true that on a calm day she has enough precision to repeatedly hit something the size of a Volkswagen bus at half a mile,  it is doubtful she could do so unless the driver first parked his rig in the middle of an established pattern.  The Romans would have had to engage in some clever maneuvering to get their foes into a pre-determined kill zone for this type of long range ballista fire to be effective.  Pre-sighted artillery would be the trick.  High-precision machines like Firefly could act similar to long range booby traps, just waiting for someone to step into their “beaten” ground.  Half a dozen machines trained on the same spot might well nobble Otto….. if he could just be persuaded to pause by that big oak tree….

On our fifty yard shop range, where Firefly’s peep sight can be utilized, the performance is much like the sketch in the lower right.  Accuracy and precision makes all sorts of trick shots possible. For example, back in October of 2011,  we had good luck juicing apples perched atop pumpkins. (Unfortunately, Firefly remains hidden in the shop because we had no way to move her back then.)  Click for video:  2011102711243911

When she is dialed in, Firefly can do this kind of duty with monotonous regularity.  Such is the nature of precision and accuracy when they are combined.

And not to forget the coconut balanced on top of a wine bottle.   That is, a full wine bottle, certain to incur the wrath of the Rebecca if it gets broken.

Click for chunks of flying coconut:   201110221249222

Center shot,  just like in the movies.  Except, of course, this is real.

Firefly will very reliably toss all of her bolts into a 2″ circle at 50 yards.  When the wind is calm she can shoot 3 consecutive bolts into a 156″ circle at 800 yards.  Those two data points I have good confidence in because they have borne up under repeated testing. Other intermediate distances have been difficult to experiment with because the bolts keep shattering when they impact the available backstops.  But I am determined to get a decent 150 yard group before winter hits, even if I have to sacrifice the eight remaining projectiles I have left.

In the sketch below, I included a speculative 4″ group at 100 yards.  (Not enough data yet to be really sure. That’s why it’s marked in red. Possibly dodgy.  Probably should disregard.)

MOA = minute of angle.

Click to enlarge:

Just for fun, I thought I would put it to all the math people that are not reading this, how they would predict the group sizes at the other ranges based on the 50 yard and 800 yard results. Firefly will be filling in the blanks with more testing, so there will be real world corrections and corroborations.  (Yeah, I know, that’s all sounds a bit squeaky clean doesn’t it?)

And here’s a photo of that 156 inch group at 800 yards.  (Actually 790 yards, but round numbers are good enough at this stage.)

And here is one of the many 2 inch groups we knocked out on our small shop range.

That flyer was a sighting shot, while the ragged one hole group was made by 7 bolts fired consecutively at 50 yards.  The highly authentic Roman uniform and helmet were just a lucky find from Goodwill.

I’ve put the winch battery on to charge.  Which can mean only one thing.

A somewhat suitable hillside has been found with a 300 yard range attached.  More testing as soon as it rains a bit.

It is all range land, not yet despoiled with “no trespassing” signs.   I suppose I should track down the owner and ask for permission….

Here is a 360 degree view of an earlier version of Firefly,  made old school with the radio playing and everything.  Click for vid:   20101231224828 .

It gives a feel for the machine not seen in other pictures taken of her.

The smoke ridden hills of the Okanogan have finally been scrubbed clean by a nice bout of rain. Which can only mean one thing for ’ems of us wot got itchy trigger fingers.  Must ride the hills in search of a hill.  A nice soft hill with no sharp edges.  They are around, but usually locked away behind barbed wire and unfriendly signs that say things like “No catapults allowed” or “Keep your frigging catapult out of my pasture”, or some such.  Bet the Romans didn’t have this problem.