Artillery range, 1st Century AD

[Paullus Scipio]

Just as a matter of interest on what can be achieved, Baatz calculated ranges for stonethrowers allowing for 'wind resistance' of over 400m ( see for example the chart reproduced in Duncan Campbell's "Greek and Roman artillery") based on an initial launch velocity of 70 m/227 ft per second. I know many of us follow fellow RATter Joel's threads on his 'inswinger' catapult as it steadily climbs in power, toward velocities almost double this (425 ft/130 m per second) - for a bolt-shooter.

This has been achieved with just four years of 'tuning'.....what might a late Roman catapult be capable of after 6-700 years of development? hock: hock:
The videos of this machine in action are truly impressive.....

[Warhammer1]

With the onagers action so close to the treb, one should be able to add an additional acceleration component by optimizing the design. Naturally velocity would favor the higher energy potential of an increased rotation, so that a hole in the ground is dug in which the arm, sling and projectile can rest in a semi vertical positon with the sling containing the projectile hanging almost vertically also and resting on the ground. By placing the projectile so that it rests outside the axis, upon release the heavy projectile under gravitational force will swing sideways as it is lifted with the motion creating an "incidence" of parametric resonance, which in turn can add considerable to the net velocity. Extra (swinging) motion of the projectile is set into play during the early part of acceleration and where the most acceleration is attained. It also changes the release point (delayed).

While I cant be sure, parametric resonance occurs within the action of a whip, and also a fly fisherman seeks out parametric resonance in his cast so that the smooth slow and steady motion of the rod accelerates the almost weighless fly at the end of the string resulting in a distance not attainable by other means.

Many years ago I read an physics honors thesis by a Matthew Covington attending U of SC in which he theorized that an N-levered trebuchet/catapult, should be able to attain supesonic capabilities provided it had certain characteristics that would cause it to act in a manner similar to the cracking of a whip. Much like the sine wave that is set up in a whip where the amplitude of the sine wave constantly diminishes in length and height, and at the very end of the stroke a violent whipping motion causes the tip to accelerate past the speed of sound whereby a sharp crack is heard (mini sonic boom).

I have designed the needed components as he has described, but there is a very large difference between a single arm powering a string, and TWO arms that SHARE a common string. It is quite a challenge to build a two armed ballista that would act in such a way. I have had to devise a way to impart that last whipping motion to the string or rope, as it cannot be easily done while connected to two separate arms moving in opposite directions. My answer is to simply impart that violent whipping action to both of the ballista "arms" - each in an opposite direction.

Thus at the end of the stroke substantial acceleration in the string must occur. I now apply my knowledge to ballista/catapult designing, and trying to get Nick on the same page as me. His craftsmanship is far superior, and he has a whole workshop of tools. I have only a vise, a pipe and hammer that I use to bend metal rods into differnet shapes and configurations which are then welded at the local smithy. Its one thing to do things on a small scale, where the complexity and difficulty increase expedentially where both size and power used is increased by many multiples.

Mistakes and failures have been my greatest learning tool, and Nick my greatest sounding board for new theories and providing secondary confirmation of my intial experiments and findings. Without Nicks help I could never hope to prove my Orsova design theory with any conviction.

W.

Dug in with a sod pile in front of it, this would be a perfect application for a DeReffye onager. Particularly one with a properly bent arm that flattens out the trajectory and increases the forward velocity of the ball. Too bad there's little evidence to place them back in Philon's era.

Oh, but there is. (Philon, Pol. 3.10.) And Michael Lewis' tests with a small scale model showed that varying the sling length and pin orientation effectively adjusts the trajectory. He was able to shoot on a fairly flat trajectory, rather than the "lobbing" that everyone seems to expect.