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Elapid

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texturized golf balls fly farther than smooth-surfaced ones when they have dimples of a certain size/shape due to reduction of surface friction, turbulence, etc. iirc.

i don't want to tip my hand too early, but i have some ideas that may change things...

has anyone done any research along these lines?
 

Fore Check

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It's my understanding that the fins and other objects that are necessarily on the surface of the airframe act in a similar fashion as golf ball dimples as far as breaking up the skin friction of the air over the airframe.

I also suspect that the dimple effect is only noticable on certain shapes: i.e. noticeable on a sphere (golf ball) but not on a spear or rocket shape.



That said, actual rocket competition results have proven that a mirror smooth finish, completely void of any irregularities (even the gap between the nose cone and airframe and aiframe spirals) can be the difference when all else is equal in altitude and duration events. That tells me that the smoother, the better in rocketry.
 

Micromeister

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Your Right on Forecheck!
Some time ago, I did an study on a babys butt smooth finish and a Granite like finish to see if there could be any difference.
long story short the smooth finished model consistantly got much better Tracked and 5% closed altutudes.
I think these tests were discussed in another thread here a few months ago. here's a pic of the two models used in those tests.
 

SecretSquirrel

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For years I joked around with people that I gould get better gas mileage out of their cars by giving the sheet metal that dimple finish with a ball peen hammer.

Now I see one auto maker is doing that to the underside of a car.


Hey! Somebody owes me money!

:D
 

Micromeister

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They only owe you if you were going to dimple the underside. topside will only slow you down:D
 

Elapid

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which changes the dynamic...

what i have in mind is something different, but similar...i'm not tipping my hand just yet...

what i have in mind isn't gonna be cheap, but it is an old and proven design...just not from rocketry.

nuff said...
i'm gonna speculate some more...

first i have to look at the NAR rule book.
:D
 

SecretSquirrel

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Originally posted by Micromister
They only owe you if you were going to dimple the underside. topside will only slow you down:D
Actually, I was just looking for an excuse to beat on the car with a hammer.
;)
 

moocrew

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what about rifiling (spelling?)
I've seen this done somewhere (on a rocket) ill see if i can dig up the article.
But the way it was designed was there were slots actaully cut INTO the body of the rocket..or mounted on i think. This caused the rocket to have that same rifle effect as a bullet coming out of the muzzle of a gun.

Im not sure if it would increase the flight height seeing as how its moving vertically and not horizontally. But this would help it fly a little straighter wouldn't it?
You guys understand what Im saying right?...or do i sound like a dummy again? lol :kill:
 

Sirius Rocketry

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Logged on to this thread too early. Took a ball-peen to my van and although it looks like a golf ball now, I still could not make the fairway!

Now I have a dented van I still have to put $2.24 gas in, and a caddie who does not want to haul my gas can!

Seriously, I always wanted to understand the dimple on the golf ball thing, is there anyone who can present a really good explanation?
 

DynaSoar

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Originally posted by Elapid
texturized golf balls fly farther than smooth-surfaced ones when they have dimples of a certain size/shape due to reduction of surface friction, turbulence, etc. iirc.

i don't want to tip my hand too early, but i have some ideas that may change things...

has anyone done any research along these lines?
Research was done on golf balls and printed years ago in SciAm. It might have some pointers for you.

I've been thinking of something similar, but it has to do with dolphins. They have low drag because they exude very thin hairs of which linearize the flow at their skin.

So, a rocket with hair?
 

Silverleaf

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As a 6 handicapper, I've long studied golf balls - simply because the one you don't use, is always the best flyer - at least it is until you tee it up, then it magically morphs into a slicing banana. 8)

Golf + Rocketry = hand in hand

The dimples reduce the drag on a golf ball by redirecting more air pressure behind the golf ball rather than in front of it.

In addition, the dimples change the levels of pressure by bringing the main air stream very close to the surface of the golf ball. The dimples increase the turbulence in the layer of air located next to the surface of the ball. This high-speed air stream near the ball increases the amount of pressure behind the ball-thereby forcing the ball to travel farther.

There are two types of flow around an object: laminar and turbulent. Laminar flow has less drag, but it is also prone to a phenomenon called "separation." Once separation of a laminar boundary layer occurs, drag rises dramatically because of eddies that form in the gap.

Like I said, Golf and Rocketry go hand in hand - though I tend to find more rockets than golfballs.

Turbulent flow has more drag initially, but it also has better adhesion, and therefore is less prone to separation.

Therefore, if the shape of an object is such that separation occurs easily, it is better to turbulate the boundary layer (at the slight cost of increased drag) in order to increase adhesion and reduce eddies (which means a significant reduction in drag). Dimples on golf balls turbulate the boundary layer.

Check this link for more info:

http://www.adsources.com/GOLF/GOLFINFO/golfpa2.htm

Hope that helps,
 

Stymye

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I remember a little while back an invento student came up with a golf ball with dimples around just the middle of the ball..and if made an amazing difference in keeping a straight path...the golf association? immediately changed the rules to outlaw the ball
..it made that much of a difference?
 

Elapid

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af a little is good, more is better!

dolphins!
hairy rockets!
now i'm feeling you!

first on my list is to build a small wind tunnel with my digital scale hooked to a rocket-holding fixture

piece of cake!
i have lots of tubing that won't work well for rockets for air straighteners...
now i have an excuse to buy a fog machine!
:D

dude...i'm either gonna make this work or find out why it doesn't...
;)

that's the plan, though.
build identical rockets with different surfaces and see which has the lowest drag.

first i have to mail in my Sporting Code cupon
 
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