[quote author=curious_aardvark link=1189503844/15#26 date=1208444362]nope - they definitely orient point forwards. It's actually using the same principle as a gyroscope. Because you have  athe main mass spinning central to the main body it uses gyroscopic forces to self orient. You can see this with bi conical shaped rocks as well - they fly point forwards and very straight.

Right just for aussieslinger - here are a couple of better pics of a crossgolf ball a normal golf ball and an egg :-)
You can see here that the cross golf ball is actually more like a normal golf ball squashed into a biconical shape - and both have a much smaller volume than an egg :-)
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C-A has been kind enough to lend me a golf-cross ball to measure and evaluate. Im not sure if the pictures carry across in the above quote but if not just go back and have a look to refresh your memories.

I measured and weighed the ball prior to giving it a good tryout. The manufacturers have most likely attempted to stick to the mass and volume of a standard ball and merely altered its shape.

Golf-Cross Ball  Length = 58.3 mm   Diameter = 39.2 mm   Regular Gof Ball   Diameter = 42.6 mm

Both types weighed around 45 grams and had a volume of around 40 ml. (cubic centimetres)

(For comparison, a 55 gram egg, L= 54.6 mm, Dia= 42.0 mm,  Vol.= 50 ml.)

Here is a link to a good physics based explanation of why golf balls with dimples fly further than ones without despite the fact that they actually increase drag. In essence it works because a golf ball is hit so as to have a very high amount of backspin which creates lift. The dimples accentuate this effect.

http://math.ucr.edu/home/baez/physics/General/golf.html     (Also look up Golf Ball in Wikipedia)

With biconical or ovoid projectiles backspin can't be used or the projectile would "end over end" in flight. Therfore spin must be axial and acts to stabilize the projectile much the same as rifle bullet. So for slinging projectiles it would probably be better not to have the dimples, merely a smooth surface.

I tried to keep the actual throwing test as objective as possible by alternately using the Golf-Cross ball and a regular ball and at least attempting to sling with the same amount of force.

The first few shots were not particularly successful, the placement of the ball in the pouch and hand position during the release is critical and if released badly the ball will not inevitably self orientate. I threw one or two where it flew through the air completely vertically spinning like a top. I also had a couple that actually spiralled in flight. However after only a few shots I got it working.

As expected it does go well and the first thing I noticed was the path was distinctly more parabolic than that of a golf ball with much less sudden drop off. You can see the axis of the ball changing as it travels along its trajectory so it's always point forward with the air flow even around it. Unlike C-A I found that each shot with the Golf-Crosser went further than the regular ball, but not a lot further; no more than 10% extra. As far as accuracy itself, if thrown well it certainly went straight because a small amount of side spin will be overcome when the ball self orientates. After that it goes completely straight. Again not heaps better than an ordinary ball thrown with no side spin.

So whether you find the Golf-ross ball to your liking depends a lot on your slinging style. If you routinely generate lots of backspin then it's unlikely you'll like them much. For rifle spin slingers they are promising. Like all golf balls I find them a little too light; but virtually indestructible so should last forever, but very expensive if you sling in ball losing prone places.

Used as mould for concrete projectiles it should be very good. As to whether it's worth the trouble and expense of acquiring one rather than using an ordinary egg or an Easter egg is debateable.

Cast in lead they would be extremely heavy at almost exactly a pound in weight.

wanderer wrote on May 28^th, 2008 at 10:58am:


I tried the balls in a couple of different parks so initially had to keep the throws down to around 70 - 80 m. as I was scared of losing the ball in the surrounding bushes. In another park throws to a max. of 150 m or so. I'm not a particularly strong distance slinger but if I was ever to top 200 m the golf cross ball would be the one I would do it with.

By using multi-coloured tennis balls I have been able to observe that I always throw with essentially a rifle spin (when throwing Fig.8 or simple overhead). Additionally the ball always breaks to the right when it hits the ground which would be consistent with it spinning clockwise, from my point of view. That's probably why my round golf ball shots don't go as far. They don't get the benefit of the backspin generated lift and have a lower sectional density than the GX balls.

Please correct me if I'm wrong, but did I not read earlier that the dirrection your hand is facing on your release dictates the spin?  I believe that it was that if your hand was facing forward on release it gives a "rifle" spin.  I tried searching for the thread, but couldn't remember what exactly what was said...  I typically cast with my palm facing in toward my shoulder, and that seems to impart a wicked backspin judging from how tennis balls react when they hit the ground.

Aussie wrote on May 30^th, 2008 at 5:48pm:


You are correct, of course. I hadnt spotted that. Curse my feeble brain!

I wonder if the staff-sling could benefit from a small redesign, mounting the cords side by side on a Y shaped end, similar to the design of an elastic slingshot? That way you would get a very consistent release with rifle-like spin. Would the accuracy improve?

I'll try again...

BUMP

I would have with pleasure such a ball.
I would pour him to me in lead.