Hi Everyone,

Just to let you know a mathematician has join the crew working on the wiki.

His name or at least handle is Lohho. He's not a forum member but I can tell you he's been doing some great work for us in the Physics department.

Anyway if you'd like to have a look at what he's been doing.  
Check out his:
http://www.slinging.org/wiki/index.php?title=Viscosity&rcid=741

and

http://www.slinging.org/wiki/index.php?title=Form_Drag

Both excelent work.

nightweave

Nice work!

Wiki main page updated with his stuff.

Hi. I've been out for some days, so please excuse me for not answering before.

I've just completed the "viscosity" entry. Now I'm going for the "Reynolds number" section :P . I hope I'll cover a good part of these fundamental and arguably boring definitions in a manner that is useful, meaningful and as simple as possible. After all, thorough definitions of these physical notions can be found in physicsworld and the wikipedia.

In the physics section of the slinging wiki, the part that I feel is more important and open is the problem of the bullet's spin.

After watching the splendid nightweave's images of the sling release, I think that the casting style, the hand position during the final stage of the cast, and the grip are key factors to determine the bullet spin. In the case of an spherical bullet the spin is somehow secondary, since it only causes a Magnus effect. But when firing glandes, the right spin is the difference between a stable and an overturning bullet.

Being able to predict and control the bullet spin is fundamental. I think I understand the basic cause of the bullet spin, and I devised a formula that should work, but I'm not sure of being right. At least, I think that the explanation (the bullet being dragged by the pouch during relese, because of a difference in tension between the chords of the sling) is consistent with the images that we have, but I think that more experimental data should be gathered.

Well, since the problem of bullet spin is (as far as I understand) highly hypothetical, I have not written about it in the wiki. So I better get back to work with the Reynolds number  ::) .

Welcome lohho,
glad that you are willing to handle the maths.
It is way above my head, but I like the idea that what is being said is right.

Willeke

lohho,

Welcome to the message boards.

Just to let you know I got a chance to sling a prototype of a roman gland today. Oh what fun I had. It was interesting to see the tumble put on the projectile sadly I didn't have my camera or film guy close at hand otherwise I would have posted that for you. Next chance I get, I'll post pictures and film if I have anything worth while.

I can tell you it was tumbling, actually it was more of a really strong wobble and really fast. Left point first then woble to right point first then wobble back to left point first. I never actually tumbled end over end.

Also lost at least two of the nine prototypes. I'll have more later.

nightweave  

It is great that you have started experimenting with glandes! I've been trying to get some pictures of slow-moving, colored balls, but my technique for taking images is greatly behind yours. The best I got was a translucid yellow blur against the background  :( . I'll try using indirect lighting against a dark background.

The problem of wobbling would be mitigated, I think, if the glande could be cast with little jaw and rifle spin. That is quite beyond my slinging ability. There is also a problem with wobbling: the formula for the air resistance in this case should be quite more complicated, and the bullet sould move with a strange trajectory ??? . I've been wondering if the ancient military slingers used a casting style that was optimal for the bullet stability.

lohho,

Movement tracking requires specialised equipment most of the stuff I have seen so far has been with the naked eye, camera with 3 photo's per second or video set at PAL, Australia uses PAL (25 FPS) which means that I don't get the detail I want on film. I have coloured my balls in quarters to make the movement more obvious, this is a something you might want to try.

Lucky for me I have a very consistent throw even if not very powerful in the figure eight. This at least makes it easy for the camera and video operators to film the release.

I have asked my video guy to send me the AVI of the film instead of giving me a DVD of it as it's useless in that format for study. If it's small enough I'll put it up as is, but I figure it'll have to be done as mgp so we can get it over the Internet. (This is the tennis ball stuff by the way.) I'll send you a copy if you like.

I agree slinging for consistent rifle roll would be interesting. (If a little above my skill level at this point in time.) I have changed my grip once to see what happens I might revert it and see what difference that makes to the projectile now that I have some glands to practice with. I the case of the tumble I think I'll have to paint each half of my glands contrasting colours and see what evidence I can come back with for you on the wobble, if its an rotation or just a wobble.

I know tumbling bullets are illegal under the Geneva convention as they do mutilating damage. Maybe this is what the slingers of old were looking for??? Hard to say without testing what kind of impact damage each projectile would do... hmmmm there's another project for me, maybe later when I have good evidence for the wiki.

Thanks for the extra information, I'll work on getting you what you need to continue with your pages. (I'll let my camera and video guy know you appreciate thier work as well.)

nightweave  

Welcome lohho, and thank your for your contributions to the wiki!

Chris