Golf balls?

[nerobro]

given the shape of a sphere, you want to release the boundry layer smoothly and as soon as possiable. Remember tha in flight a paintball's boundry layer can wrap all the way to the back of the ball before it rips off and hte other side swings in. the point I was trying to make was to have something there to kick the boundry layer off and provide a smooth seperation of flow. This is the same reason that the new corvette has a sharp edge around the back of the car. And why the VW bug is getting a wing.

[aut911]

so what you are saying is

that the dimples basically make the golf ball, more aerodynamic? meaning a golf ball with dimples will fly a little bit farther than one without?

aut911

[nerobro]

The dimples KEEP hold the slipstream to the ball. So when it's spinning it changes the lift charecteristics of the ball. Golf balls are dense, and they can use whatever lift they can get. More lift means more range with a golf ball. that isn't true with a paintball.

the ball isn't more aerodynamic, it just makes more lift ;-)

[Skunk_werkes]

nerobro: I think I might be mis-understanding you, but... Concerning conventional paintballs, the boundary layer separation is just a lil bit past the mid point, the boundary layer does not adhere all the way to the back. Your quite right when you say that the dimples also aid in the creation of lift, but there are aerodynamic advantages to having a dimpled non-spinnig golf ball.
If you'd like to discuss automotive aerodynamics, we could do so in greater detail, but please email me ([email protected]), I've actually written a paper on it (automotive aerodynamics), and attended a few lectures by Aiolos (one of the Worlds largest makers of aerodynamic/acoustic/and hydrodynamic test chambers) so I'm always up to a good discussion.

aut911: Yes, that's right. A golf ball actually has a lower Aerodynamic coefficient of friction then does a similar smooth ball. I'll look up the numbers for a conventional golf ball, but off the top of my head I remeber that the Cd of a sphere is 1.2

I'll work on those diagrams tomorrow, along with some math on dimpled paintballs.

Cheers,
Shaun Martin.

[BlackVCG]

In order to find the Cd (Drag Coefficient) of a sphere, you first need to find the Reynolds number of your sphere.

This is acheived by taking the velocity of the object multiplied by the diameter of the sphere and that quantity divided by the kinematic viscosity of the substance your sphere is moving through. In the case of a golf ball or paintball, it would be air.

So...

Nr = (vD)/y

Where v = velocity of sphere
D = Diameter of sphere
y = kinematic viscosity of substance sphere is traveling through

From this you can find the Cd based on a Cd vs. Nr graph.

From there, you can find the drag force by using this equation...

Fd = (ACd)(pv^2/2)

Where A = Reference area, which is the Cross sectional area of the sphere in the middle
p = Density of substance
v = Velocity
Cd = Drag Coefficient

Your Cd is different based on the Reynolds number of your sphere. In the end a sphere with a rough surface usually has about half of the drag force as a smooth sphere.

[Testarosa]

Small bore, Large bore, Dimples, No Dimples,- In my oppinion, paintballs go were they want.

[BlackVCG]

skunk_werkes-

What happened to the charts and math?

[AGD]

Boundary layers, Reynolds numbers AHH it makes my heart sing! Only on AO would you get such a worthy discussion.

If I remember right the dimples on the golf balls INCREASE the size of the boundary layer which without any other effects increases the CD. BUT spongier boundary layers allow the laminar flow to stay attached longer past the mid point of the ball so the overall CD goes down. The other effect of this is the spin on the ball gets its lift from the percentage of laminiar flow sticking to the top of the ball. bigger BL->stickier LF -> more LF area -> more lift.

Love this stuff,

AGD

[sniper1rfa]

not size, thickness. thats what i learned anyway, could be (probably is) wrong.
i also bet you get little eddies in the dimples acting almost like bearings. that would be nifty.