Taming the Onager

[LCorneliusScaeva]

Almost everybody is agreed that Ammianus has simply missed out the cross-timbers, needed to make a solid frame.

Maybe Ammianus didn't miss the cross timbers. He did say the side pieces were put together like a frame saw. Here's a picture of a frame saw, complete with cross pieces.

[url:8xoyqovt]http://www.traditionalwoodworker.com/popup_image.php/pID/2037[/url]

[P. Clodius Secundus]

The late Eric Marsden called this observation “ridiculous” and suggests that Ammianus was “confused” since the frame must be solid. That accusation itself is baseless. Using only mortise and tenon joinery on the crossbeams a perfectly solid frame can easily be held together by the cross tension of the spring bundle alone.

Slightly unfair to Marsden, Randi. What he meant was that the machine cannot simply be two side timbers with strong ropes to hold them together/apart. Almost everybody is agreed that Ammianus has simply missed out the cross-timbers, needed to make a solid frame. (In case you think this point is obvious, the French scholar Jacques Fontaine managed to sketch the machine without cross timbers, so that the ropes really are all that holds the sides apart!)

Duncan,
I don't think I'm being unfair to Marsden at all. My comment is directed at his Note #4.

"As far as the onager is concerned, this last phrase is ridiculous. The ground frame of the onager must be quite solid whether the spring is fitted or not. Probably Ammianus is still confused by thought s of the frame-saw, in which it is to some extent true to say that the tightening ropes B (in Fig. 2) are 'compagem, ne dissiliat, continentes'.

He has already addressed the structure of the framework in the previous three comments figures. This comment appears directed solely at whether or not the machine can be held together by the tension of the bundle alone. My model quite easily demonstrates that this is perfectly feasable. It also allows the engine to be easily dissassembled and transported. My Punkin'Chunkin' compatriots have indicated that they use as little hardware as posiible to hold their engines together because it causes more failures than good joinery techinques. The one area where they often resort to using fasteners is on the buffer framework, which as De Reffye and I have indicated is not neeeded. It was Marsden who was unfair to Ammianus in calling his description "riduculous" and "confused".

[P. Clodius Secundus]

This past weekend I had the honor of launching my first projectile from a De Reffye type onager. Several years ago one of my Legion Mates built an onager based very closely on Marsden's version of Schramm's original design. Though solidly constructed, the weapon never lived up to expectations. It had a nasty tendency to knock itself apart every time we used it. For all the fury of it's discharge, the range remained unimpressive. After years of repair and modification the builder asked for my opinion on what could be done to alleviate the problem. That is what prompted me to re-read Ammianus and to look seriously at the De Reffye onager. He has now rebuilt the weapon so that it roughly resembles a De Reffye. The un-necessary and counterproductive buffer frame is gone and the arm now swings much further forward and down onto a ramp with a large padded buffer that simulates the turf pile Ammianus described. The change in performance was immediate and obvious. With little pre-tension in the spring bundle and not much twisted into the skein it matched or exceeded it previous best. With more twisting it soon doubled the old range. With the addition of a bent-arm and some additional tweaking I believe that much greater improvement is possible. At the end of the day we loaded the machine back on the trailer without having broken anything but our old records.
We are still digesting the information we learned from those tests, but our attempts to establish a safe and efficient crew drill have suggested a possible answer to one of the nagging questions that remained in Ammianus' writings. He states that when it is time for shooting, a stone is placed in the sling and then the arm in winched back. How can this be? Surely the stone would fall out or the sling get caught in the winch ropes. Modern crews usually ignore this as they do the rest of the text and simply load the projectile into the sling once the arm is drawn fully back. It's easily done with a small projectile, but would be much more difficult with a boulder weighing fifty or more pounds. Upon reflection I realized that he did not specifically say that the sling had to be hooked up to the arm when the projectile is loaded. Wouldn't it make more sense to place the stone in the sling on the ground behind the engine and then draw the arm back to it? Once the arm is back it would be relatively easy to lift the sling ropes and hook them onto the arm. That way there is no projectile and sling dangling in the way, the weapon remains unloaded until just before firing, and the crew only has to lift the projectile a few inches. This would also allow for inspection/replacement of the sling between rounds and adjustment of the sling length to correct the fall of the shot. In the absence of other contemporary sources we must accept Ammianus at face value and try to rationalize, within reason, his description, or consign ourselves to the realm of conjecture.

[Aulus Perrinius]

A Laudes from me

[Justin of the New Yorkii]

Actually, the first thing that would pop into my mind would be an F1 car!!! lol: :lol:

I stand corrected. I should have been careful to specify normal people :lol:
This sort of supports my point about Ammainus writing for a genral audience. Here in the U.S. even if I were to say race car most would probably think of a NASCAR stock car instead of an F1.

Or if you're really hardcore, Craftsman Truck. :lol:

[P. Clodius Secundus]

Or if you're really hardcore, Craftsman Truck. :lol:

I guess the truck series would be more appropriate since the whole bent-arm idea is a result of my research to build a mule cart, the Roman version of a "deuce-and-a-half"army cargo truck. The best part of our recent testing was that now we can say that like Aitor Irirarte's experiments with the Cheiroballistra, we've seen the same weapon configured two radically different ways. Apart from historical context, the upright buffers on the Payne-Gallwey and Schramm types are poor engineering. If anyone needs further convincing they can talk to this weapon's builder. He was a true convert the moment we shot the new version. He's already working on a slightly bigger one encompassing the lessons learned.

[Gaius Longius]

Hi Randi,

Thanks for posting this as it has answered a number of questions that had been bugging me for a while.

Interestingly there appears to be a picture of what you are describing at the bottom of this page:
http://www.roman-empire.net/army/onager.html apparently in the Muzeo della Civilta in Rome.

Keep up the good work.

Regards,

Gary.

[P. Clodius Secundus]

Interestingly there appears to be a picture of what you are describing at the bottom of this page:
http://www.roman-empire.net/army/onager.html apparently in the Muzeo della Civilta in Rome.

Yep, That's a model of De Reffye's original design. There are several of them out there. The buffer ramp is a compromise to avoid having to pile up turf/sod. It doesn't significantly interfere with the function of the machine, so no harm done. He had it pretty much right (except for the arm) until Sir Ralph Payne-Gallwey came along and turned it into a mangled mangonel. One good feature of the bent-arm design is that because the arc of the arm is rotated forward, steeper at release and closer to the ground when it strikes the buffer, the sod pile or ramp doesn't have to be as tall/steep.

[Gaius Julius Caesar]

I realise this will probably sound a bit foolish, but here goes....

What is the evidence for piling sods up to act as a buffer for the arm?
It just seems, well, a half assed engineering effort for a portable weapon, and also totaly restricts your field of fire..... :?

[P. Clodius Secundus]

I realise this will probably sound a bit foolish, but here goes....

What is the evidence for piling sods up to act as a buffer for the arm?
It just seems, well, a half assed engineering effort for a portable weapon, and also totaly restricts your field of fire..... :?

Nothing foolish in asking a valid question. The evidence, like almost everything we know about onagers comes directly from Ammianus' text. As with most things, the Devil is in the interpretaion. Once they add a buffer frame, those who choose to follow Payne-Gallwey and Schramm are stuck with a bit of a problem. What do you do with the sod or bricks in the text? Ammianus clearly states that the buffer is spead out in front of the arm on top of the pile. They ignore that and place them underneath the whole engine to absorb the recoil. There's just one hitch, the only design that's likely to produce any sort of significant downward energy is the De Reffye. If they had enough vertical force to shatter masonry under the frame they would certainly have destroyed the wheels that these same experts love to add.
We know that cutting and stacking sod was a familiar task for the Roman Army, so building the pile would be easy.
These were portable weapons, but more like siege mortars than field guns. Haul then in, set them in place, and batter down the walls. A wide field of fire isn't really needed to keep hitting the same spot. The wall is that way. Find the range and bash away. Also, what restricts your field of fire works both ways and protects the engine as well. When you trust Ammianus, ignore the convetional "wisdom", apply a little imagination, and think things through it eventually makes sense.

[Gaius Julius Caesar]

Thanks, I guess that makes sense.
I honestly haven't read any of the sources about artillery, and just the mentions of them in the accounts of caesar and others in translations.
I suppose it is logistically more practical to just lug the essential parts, and then dig up a buffer at the location, instead of hauling it there with you.

[Koyuncu]

Sorry but it seems the image posted by OP is gone. Could anyone fix it? Thanks in advance.

[Robert]

This help you?

[Koyuncu]

Thank you so much Robert.

(In case you think this point is obvious, the French scholar Jacques Fontaine managed to sketch the machine without cross timbers, so that the ropes really are all that holds the sides apart!)

I tried hard to imagine that but failed! Could you please share any definition or an image of it?

[Robert]

Best thank P. Clodius Secundus (Randi Richert), as he is the one that made this excellent drawing. I was going to build one, but that project fell through when the workshop of the Liburna was disassembled and the wood was "reclaimed". Have fun!