The Ballista

I got my dander up on this 400 fps mythogical barrier bit, cranked up the preload 7 1/2 degrees all stations, and labored through a series of six shots with one of our new 397 gram bolts.  In feet per second the velocities were 385, zero (i.e. no reading), 386, 385, 383, and 365.

This last was cause enough for a pouty moment, complete with lower lipped roosting platform and everything. However, for one glorious moment we seem to have topped 2000 foot pounds of energy. 2,026 fpe is fairly smoking for this contraption.  PDW was up to 5500 lbs @ 38″ DL

On inspection of the port side bundle, a broken rope was discovered.  It appeared that in the outer most layer of the spring, a piece of 1/4″ , 3 strand nylon line had parted directly over the apex of the crossbar.

Oops!

…. Think I’ll go spend forty days and forty nights in the desert.

New spring meditations are in order.

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Update: Repairs to that broken rope in the spring seem possible. Our sky date is still on.

This afternoon, I made up four of these items to use as piles on a set of flight bolts. Clearly this design is not meant to represent an authentic style of Roman bolt head. The purpose is narrow. They are designed only to be cheap, aerodynamic, and to weigh 128 grams. This is the same weight as on the head of that 377 gram bolt I’ve been shooting lately; call it 5,818 grains, if you like, it’ll be all the same to Firefly when we get her pointed at the sky.

This first round of flight testing is just meant to set a baseline utilizing some projectiles that are not overly fancy. Dura bolts and the like can be shot for range later. The intent right now is to take that 360 feet per second performance we’ve been getting, and just take everything out for a field trip as soon as possible.

Hopefully before the end of the world. …… Which, I believe, is scheduled for the first Tuesday, month after next.

That doesn’t leave a lot of time, does it?

Clearly I’m dodging the central issue here — making bolts.

I’ve got to admit, I find myself getting a bit sick of all this engineered intensity. That is to say, mucking around with catapults in the backyard can get even the most ardent adventurer down, if he doesn’t exercise some moderation in the matter.

I mean, what does it get you? A gold watch for meritorious achievement in the field of catapult research? A patch with crossed duras blazoned on it? Buying your comission by dint of service performed; always that fading glow of self admiration when the action inevitably ceases.

Pregnant pause, ensues.

….It’s not like we’ve got bleachers here. Standing ovations are just not in the cards when you work alone. There are no cheering sections when you are inside the bubble, cut off from the greater throng of humanity……

And as the pity party reaches its crescendo…

….Snivel, snivel. Blub, blub.

Wait for it…

…..sob, sob , sob….

Trembling fingers reach for a tissue, while a sly eye glints at the camera.

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Of course, this is all rubbish. The trick is: allowing yourself to believe that you don’t care, just long enough to perform some act of public embarrasment (like all this nonsense I am scribbling now) and then, when your true self catches up with you (the one that actually does care) it has some freshly manufactured shame to help get up a head of steam. Motivation is the heart-throb of any endevour.

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And the next morning:

Chasened by the stunned silence from his worldwide audience, the catapult maker drifts back into his workshop and picks up his tools with a groan. He coughs and grumbles, dreams of the great outdoors, and vows to never make another catapult ever again.

Soon, however, the sounds of a lathe can be heard emanating from behind closed doors.

His day has begun.

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Melodramatic chords, ensue.

My first lesson in the pursuit of truly idiotic arguments came at the hands of Linda Dean. She was a spitfire of a girl, and not someone to be brooked in matters of opinion regarding the nature of felines. Cats were her thing. After more than half a century, I still remember the thrashing she gave me for taking exception to the notion that “pussy cats do ride bicycles”.

Linda and my-own-self, shortly before my humiliating defeat at the hands of a ….girrrl!

One cannot expect to triumpth in every ill conceived spat that comes along, but I must admit, I was utterly unprepared for the level of ferocity she was about to unleash. As I remember, it was a hot summer’s day and Linda had been quite insistent all morning that Pussy Cats could ride bicycles. She had seen it on the telly just the night before.

Ever equipped with my steel bladed, trap of a mind, I had opposed her on every point. Yes, they might be able to fit in the basket, but no, they were not at all suited to pedaling. Yes, cat’s had good balance, but riding a bicycle required hands to grip the handle bars didn’t it? But she had seen it with her own eyes, and on the BBC too. As far as she was concerned, that was an end to it.

Would that I had heeded.

Now it so happened, that on the day in question, Linda was in possession of a plastic lemon. The kind that holds juice concentrate, and was the envy of every post war English kid in need of a small, reliable water pistol to stuff in his pocket. Somewhere in the middle of my most earnest exposition on how felines were constitutionally unsuited to pedaling, my young companion exploded into a fit of screaming rage. I can still see that vivid flash of yellow as her cudgel smashed into my precious, upturned nose. My world was, for a moment, nothing but plastic lemon. … Funny how I can still recall the little dimples in its surface.

And then came the blood. Blood all over me, blood all over her, and perhaps what I remember most, blood dripping down the sides of all that curved yellow plastic. At first I was too stunned to wail, or make a fuss. But that didn’t last long. I booed, she ran, and I guess that was an end to it. Other than the shame. That stung for a quite a few days.

It wasn’t until later that I realized two things. Girls that smack you in the chops often steal your heart. And if they drop their little, yellow, plastic lemons, that is one rearmament program it is best to keep hidden for awhile.

Before our little shop-bound catapult can pummel the skies with flight bolts, there are a few developments yet to make. Appropriate projectiles, appropriate fixturing for transport, appropriate field to use for a range, appropriate measuring gear, appropriate cameras, appropriate lighting, appropriate this …appropriate that …

“appropriate, appropriate”…

It sounds like one of those “modern” parents fussing over junior.

You come to hate that word sometimes.

Shot # 37 was fired in the late afternoon with the same settings and stats as the previous shot. Velocity 360 fps. As before, with a 5818 grain bolt, that’s 1700 foot pounds — near enough. Here’s a vid of the kinetics. 20120615174130(1) . To my ear, that sounds markedly faster than anything the MK VIII’s ever plopped out. It would be interesting to know if trimming the bolt weight by say a quarter, will get us into the magic kingdom; 400 feet per second ain’t impossibly far away. But even if it doesn’t, this trajectory already looks flat enough to do some serious work.

In the world of ancient Rome, converted muscle power was the only way to generate this kind of flat trajectory, armour busting, impact. This next vid gives a taste of what that work-out must have looked like; although their efforts at the winch were undoubtably more rapid than what this old gezzer can manage. Click here: 20120608134124(1)

Now if there were two geezers at it…

You-know-who has been leveling charges of cowardice aganist me. Wincing poltroon that I am, I suppose I’m supposed to increase the bottoms, again. (..Shake, shiver, snivel.)

…..Again? again and again? Could more pre-load on the springs, turn 362 into 382? And if that is the case, would lightening the projectile push us over that mythical 400 fps boundary? The mind reels at the glory of it all. Perhaps I could get a seat with the CG’s themselves.

But who am I kidding. I’m much happier as a struggling mortal. I know my lot. “Feet per second” do not take things on charge. You are supposed to earn them by the sweat of your brow.

BTW, that hand-winch is starting to look a lot like a medieval torture device. Still, one or two shots a day should see ‘er done. At least enough for me to take a vacation from catapulterneeering for a while.

One of those stalwart legionaries perched on my shoulder whispered me a chide today. “Stop being such an effing pussy. So what if you break your little baby? It’s not like you get to take it with you.”

I took him to mean that I should crank up the pre-load and increase the draw length a notch. And so, I did.

Shot # 36. Velocity shot up to 362 fps with a 377 gram (5,818 grain) bolt. Not quite cartwheels yet, but at least worth a headstand or two. 7 1/2 degrees was added to both bottoms. DL was back at 38″, PDW soared to 5,000 lbs. Effort to cock is getting a bit much for me. Yes I know!, it really is time to haul out the Warren winch and let a gang of electrons do the work.

In the meantime, this happy increase puts us in a party mood. 1692 foot pounds. Hmm-hmm good! I’ll rate that as enough zippity-do-dah to go test for maximum range.

… Now, where did I put that Jack Daniels? ….

Shot #35 went ahead with both top washers tightened 7 1/2 degrees each. Velocity with the 377 gram bolt was a disappointing 336 fps, only 2 fps improved over the previous shot. PDW is now at 4800 lbs with the 35.75″ DL. It seems best not to take the pre-load any higher with these long limbs for reasons stated perviously. I will take a few more shots at this maxed-out setting, just to confirm the new baseline, and then get ready to permanently shorten these long limbs down to the same length as the MK VIII’s.

Something I have not mentioned yet is that Firefly is back to her old accuracy standards, these last few shots formed a 2″ group at 55 yards, which seems a bit odd given the tweaks we have been introducing; but who’s complaining, right? Also, those new bowstring nocks made from glue saturated whippings, are doing a fine job of hanging on to the bowstring at the end of the power stroke. I have left off using those restraining straps on the bowstring loops, and while the straps do provide some extra measure of safety if a limb were to break, I would like to establish once and for all if they are really essential for reliable operation of the machine.

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Some consequences ride on the back of a turtle, others are more fleet of foot. Either can cause disruption if your imagination is not up to the task of perceiving them. Training is essential, but it’s not quite the same thing as a well developed sense of how to anticipate trouble. In the machine shop, “anticipate” has saved my hide more than once. It’s what makes fear useful.

Shot #34 recieved 7 1/2 degrees of extra twist in the bottom washers. TS let back 1 MRU. Draw length is our new standard 35.75″. Hopey/changey continuium got a boost by having the velocity jump back up to 334 fps. The last shot at this draw length was only 301 fps. Does this mean if I add another 7 1/2 degrees to both top washers there will be a similar 33 fps increase with shot #35?

….gives me goosebumps just thinking about it.