Re: Do Ducks have cavalry?

From: donald_at_-e8ASHwujZMj8K2SVoZq8gE405zWkeg52Hv0Yvnaq9tW9fcDf3x1dFcG2wUDrR8VL_Tir
Date: Wed, 12 Dec 2007 11:49:37 GMT


In message <27c976de0712111743l6823f508u6198b3bcbff73367_at_nfRYA5pjn-kB820CDnsafRWFaZqSnSIJI_mlqc6QGsP9dnvB4u9npoC0J8BIEAbbHoc2uLoYJ3JSPObXWVmhv3k-hFwcpdLZw8yJjJEN7KA3NocfNEs6I78SBWUswtnqEckBKg.yahoo.invalid> Grimmund writes:
>On Dec 11, 2007 1:38 PM, <donald_at_uMjJyXkYZPwV3T9P4glpK8wbqGHnmNdRgRD-XG9zX9oATvAnMWtZRgapFnmjHWYNiPZVaz6rLIz3Ao54XouT.yahoo.invalid> wrote:
>
>> However you don't get recoil on ancient weapons.
>
>Practical experience with smaller ones suggests you may be mistaken on that. :)
>
>Ballistae and torsion catapults have significant recoil, scaling up with size.
>
>>The nearest thing
>> I can think of is the trebuchet and with that the counterbalancing
>> weight comes down which is not really recoil.
>
>Trebuchets recoil in a circular motion around the the pivot of the
>throwing arm. This is exaggerated if there's a safety stop on either
>end to prevent the long side of the arm from making a full circle.
>Without a stop, they just swing and slowly dampen out until friction
>stops them.
>
>>Potentially disruptive
>> by making the platform bounce around but not by moving it significantly.
>
>FIRING the trebuchet causes the bucket to swing, and the platform it's
>on to tip fore and aft. If you're moving at the time, I suspect it
>would auger the front end into the dirt. If you're moving at speed,
>that tends to wreck your ride. If you can stop the platform and
>lower it to the ground before firing, you'd probably be OK, as long as
>the ground was solid. Mud or water, not so much.

That's not recoil. Recoil is what moves a one tonne cannon back several metres when it fires a ten kg. ball. AFAIK confined to explosives based weapons.

The movement you are describing is due to the disappation of energy caused by the whole of the energy of the descending weight not being transferred to the projectile. Similarly an onager tends to move forward as the arm hits the crossbar to release the shot. I don't know if there's a special name for those forces.

A properly designed platform can cope with these forces and even recoil. It's mostly dependant on the size of the weapon compared to the platform but also how solidly the weapon is attached to the platform. I believe small cannon were mounted on elephants in 18th Century India. No reason to suppose ballistia couldn't be used the same way.

>> The time spent on regaining control is also trivial in the context of
>> reloading time of such weapons.
>
>Depends on the size of your firing platform, crew, and weapon. The
>different arm length provides leverage in both directions. Depending
>on the relative arm lenghts, 2-3 guys in armor can just *pull* down
>the arm on a half-ton trebuchet; reload time goes pretty quick, 2-3
>minutes. If you've got to *crank* it back down, longer, of course.

Whereas the forces you mention disappate within seconds. Indeed you don't start pulling the arm down until they have. So unless you've upset a living mount you'll regain control quickly enough.

-- 
Donald Oddy
http://www.grove.demon.co.uk/

           

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