06-13-2008, 09:33 PM
Quote:Your original comment interests me though. You say the 'forward' sloping stop proved more efficient. More efficient than what? Presumably the vertical stop? But, more efficient in what sense? Longer range, higher accuracy, better load throwing capacity, Less arm breakages?Yes / not necessarily / not sure what you mean / probably (but that's down to the size of the buffer).
Theoretically, of course.The problem is that De Reffye's design has never been taken up. Marsden seems to have been unaware of it -- from memory, he doesn't mention it anywhere. And everyone has tended to follow the design tried and tested over 25 years by the Ermine Street Guard. So there has been no history of practical testing, and hence no opportunity to tweak the design.
Michael Lewis's theory is published in an obscure mathematical journal. (Hart, V. G. & M. J. T. Lewis, "Mechanics of the Onager", Journal of Engineering Mathematics 20, 1986, pp. 345-65 -- good luck finding that one!)
He (and his mathematical collaborator) found that, unlike the ballista, the onager cannot be defined by a nice simple mathematical formula. As you have probably realised, there are a number of variables: arm length, arm thickness, sling length, finger angle, and buffer angle. We have no idea about any of these!
Lewis tested a De Reffye-style model versus a Payne-Gallwey-style model (note: not full-size machines), and found that, all variables being equal, the De Reffye generally gave a longer range. Might be worth investigating -- but it would be expensive!!
hock:
