RCU Forums - Golf ball dimples

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RE: Golf ball dimples

Anybody remember the car Richard Petty drove in the 1968 Daytona 500?
1968 Road Runner...basically a shoe box on wheels...but with a VINYL Top :D
Theory was that the pebbly surface would be less draggy...

I think there's a YouTube vid of it?
I know there was a Glory Days episode...1/2 hour highlights (pre SPEED TV )

The Ford guys cleaned their clocks anyway :D[8D] with the Torino and Cyclone...

RE: Golf ball dimples

I wasn't upset or offended. Not sure you meant to respond to my post. Having seen golf balls arc up from the back spin, I have a hard time believing the drag is more important than the lift. Any measured results on this?

RE: Golf ball dimples

Dimples cause the relative airflow that influences the ball be more turbulent, stickier and generate more surface drag. This causes the relative airflow around the non-spinning ball to stay attached longer before leaving the ball. This causes the ball to leave a smaller wake and generate less dynamic drag than a smooth ball with a more laminar flow. Because dynamic drag is the most prevalent reducing it reduces over all drag.



When the ball is hit with a spin things get more complicated. The relative airflow that influenced the ball while moving through the air is affected dramatically by the balls movement while in the air (rotation). Dynamic drag mostly opposes the balls linear motion while surface drag opposes the balls rotational motion.



Aircraft have reached speeds of 250mph while flying around the earth using drag exclusively as a means of horizontal acceleration. A lot of people may not know that drag in some circumstances can actually oppose motion but even while opposing one motion drag can cause another motion. When you pull a canoe paddle through the water the drag on the paddle is in the forward direction generating the thrust the canoe needs to propel itself. The drag from a powered prop causes the plane to tend to rotate around the propeller axes. The non-aerodynamic drag between a tire and the ground cause the rotating tire to move linear and this is very similar what is happening to the spinning golf ball.



If a spinning golf ball were to be pushed into the ground it would produce a dramatic linear force, if a spinning golf ball were pushed into the air by its linear motion in would produce a much less dramatic linear force that makes it curve called the Magnus effect inaccurately referred to as lift or Magnus lift. The Magus effect is caused by surface drag, dimples increase surface drag and therefore the Magnus effect, and this is not a coincidence





If the Magnus effect is caused by surface drag why is it called lift or Magnus lift? Well that’s a very good question and hear is the answer. Although texts state that the Magnus effect is caused by the ball spinning and the more it spins the more effect is caused, when determining the aerodynamic force that causes it the very large and obvious fact that the ball is spinning is intentionally and totally ignored. For this force to be lift you would have to determine it from the relative airflow caused by the balls linear motion through the air when in fact the relative airflow that is influencing the ball is made up of the balls linear and rotational motion. Calling this force lift is based on the false premise that the ball is not spinning. Not very scientific but it shows the amount of skew of actual occurrence that is acceptable when writing formula. Drag is in the direction of the relative airflow that caused it, and the drag from a spinning ball going through the air opposes its rotation as well as it linear motion, how many directions is that? When the even surface drag around the spinning ball starts to become uneven it also starts to become more linear and this is the cause of the Magnus effect.

RE: Golf ball dimples

For a nice picture and short definition:

http://en.wikipedia.org/wiki/Magnus_effect

RE: Golf ball dimples

Quote:

ORIGINAL: Sport_Pilot

I wasn't upset or offended. Not sure you meant to respond to my post. Having seen golf balls arc up from the back spin, I have a hard time believing the drag is more important than the lift. Any measured results on this?

Thanks for the link Darock. It seems it is not cut and dried to call it "lift", but since Wikipedia does, I'll go along with it. I think we all understand the same thing, we're just explaining ourselves differently. Here's what the Wikipedia article that Darock linked says about the force:

"For a smooth ball with spin ratio of 0.5 to 4.5, typical lift coefficients range from 0.2 to 0.6.".

So the question still stands. Does the "lift" force have more effect on the distance the ball travels than the effect of reducing dynamic or overall drag?

Any one have data on the drag coef's of a smooth golf ball verses a dimpled one?

RE: Golf ball dimples

I have seen balls hit downward from a small clif gain altitude. If you top the ball the foward spin will push the ball down. I have seen these hit with the edge of the club, go up and quickly go down. The latter is very dramatic as any duffer will acclaim. This is sililar to a sinker in baseball.

RE: Golf ball dimples

I've personally experienced the same thing, but I'm still not sure that this force actually carries the ball foward linearly more than the effect of reduced drag and resulting velocity. I guess a better way to ask the question is this:

If a smooth ball and a dimpled ball were both hit with exactly the same force, direction, angle of inclination, etc., but with absolutely no spin, would the dimpled ball go farther, and if so, how much?

RE: Golf ball dimples

After this I guess the next question would be:

If you could a hit another smooth ball and a dimpled ball with all variables equal but with a perfect back spin, which would go farther?

Then we could compare the numbers and know which force actually has more effect.

RE: Golf ball dimples

And how much less if spinning foward from the top, and how much more if spinning foward from the bottom.

Surely there are some imperical measurements out there. It would be a good college aerodynamics project.

RE: Golf ball dimples

back about 18 years ago top flite, the golf ball manufacturer, not to be confused with e-flite experimented with pimpled golf balls, what they found is that the pimples make the ball travel even further than a dimpled ball, but it becomes very VERY sensitive to hook and slice issues on the drive. the application for us modelers, might be what effect would oversize rivet lines have on our planes? could they do the same for us....

RE: Golf ball dimples

If I remember correctly, Richard Petty also had a car with golf ball dimples in the roof. I do remember the vinyl top car.

RE: Golf ball dimples

Quote:

ORIGINAL: Sport_Pilot

Now that you have read a few web pages on this. Tell me how much the drag is, how much that slows the ball down, and how much lift is created from the spinning ball.

Sport_Pilot,

No web pages needed until you asked for numbers. I just found some nominal values for the coefficient of drag: the laminar CD for a sphere is 0.4 - 0.47, and the turbulent CD for a sphere is 0.2. The page I found didn't give a Reynolds number, but we could reasonably say that the drag is roughly cut in half for turbulent flow. This effect is pretty obvious if you go to a driving range and hit some old range balls that have had the dimples worn away. You can easily notice the difference in distance between the older balls and the newer ones. This effect was discovered in the old days of golf, when gutta-percha balls (which were smooth at first) were observed to fly further after they had become scuffed up by the grooves of the clubs. The phenomenon involved is well documented.

Another web page gave an estimate for the coefficient of lift for a typical initial velocity and rate of spin of a golf ball: this CL was estimated to be 0.134. This would be turbulent value, and would obviously start decreasing immediately, as the forward velocity and rotational velocity start decaying. I don't know what the laminar value would be, so I can't compare, but it wouldn't be zero. This is a lot of lift, and also contributes to the distance that a golf ball flies, as well as whether it hooks or slices.

banktoturn

RE: Golf ball dimples

Quote:

ORIGINAL: hugger-4641

After this I guess the next question would be:

If you could a hit another smooth ball and a dimpled ball with all variables equal but with a perfect back spin, which would go farther?

Then we could compare the numbers and know which force actually has more effect.

hugger-4641,

The dimpled ball would go further, which is why they put dimples on them.

banktoturn

RE: Golf ball dimples

As far as auto makers using dimples on a production car, ever look under some German cars? My wife's Volkswagon EOS has dimples on the entire undercarige. The car gets great gas mileage with a 2.0L Turbo. Seems to do just fine. Steve

RE: Golf ball dimples

By numbers I mean actual measured values. There are a lot of numbers made up by proffessors used simply as examples, or test problems, then picked up as fact, when it never was fact.

RE: Golf ball dimples

Quote:

ORIGINAL: Sport_Pilot

By numbers I mean actual measured values. There are a lot of numbers made up by proffessors used simply as examples, or test problems, then picked up as fact, when it never was fact.

Those darn professors! The CD numbers in my post are measured values, and I've found several web pages with similar values. I haven't found clear references to measured lift values, and the one in my post seemed to be calculated using an equation for the lift due to the Magnus effect.

banktoturn

RE: Golf ball dimples

Quote:

ORIGINAL: banktoturn

Quote:

hugger-4641,

The dimpled ball would go further, which is why they put dimples on them.

banktoturn

Yes, I think we all agree on that, the question is which force contributes the most, "lift" from the spinning (magnus effect), or reduced loss of velocity due simply to reduced drag from the dimples?

RE: Golf ball dimples

Quote:

ORIGINAL: hugger-4641

Quote:

ORIGINAL: banktoturn

Quote:

hugger-4641,

The dimpled ball would go further, which is why they put dimples on them.

banktoturn

Yes, I think we all agree on that, the question is which force contributes the most, ''lift'' from the spinning (magnus effect), or reduced loss of velocity due simply to reduced drag from the dimples?

hugger-4641,

I don't know for sure, but my guess is that the dimples are more important. I base this guess on 3 things: 1) my observation that very worn range balls don't fly as far as new ones (a very obvious difference, when witnessed), 2) balls marketed as "distance" balls tend to have lower spin rates, and 3) the aspect ratio of a golf ball is so low that generating a lot of lift causes a big drag penalty.

banktoturn

RE: Golf ball dimples

I tend to agree on this, but it would be neat to have some data to support the opinion. Somebody send this to Myth Busters!!!;)

RE: Golf ball dimples

Quote:

ORIGINAL: banktoturn

Quote:

ORIGINAL: hugger-4641

Quote:

ORIGINAL: banktoturn

Quote:

hugger-4641,

The dimpled ball would go further, which is why they put dimples on them.

banktoturn

hugger-4641,

I don't know for sure, but my guess is that the dimples are more important. I base this guess on 3 things: 1) my observation that very worn range balls don't fly as far as new ones (a very obvious difference, when witnessed), 2) balls marketed as ''distance'' balls tend to have lower spin rates, and 3) the aspect ratio of a golf ball is so low that generating a lot of lift causes a big drag penalty.

banktoturn

As long as we are all guessing
-try this guess
A worn golf ball may not store as much energy (from the club) .
old balls may lose some of their "bounce"
(Don't we know it)
Distance balls MAY flatten more when hit by the club and therefore may not be set into rotation as easily as a harder ball-which MAY thru the angle of club contact - tend to ratate faster from the impact
If that concept is too hard to grasp-consider hitting a steel sphere . the contact area of th ball will remain smaller and therefor (I love college talk), the "english" put on th ball will be more than that put on a softer surface -which flattens before going into motion
My next slide please.

RE: Golf ball dimples

Quote:

1) my observation that very worn range balls don't fly as far as new ones (a very obvious difference, when witnessed),

The dimples also contribute to the magnus effect. Baseballs were produced for a while without stitching, but taken off the market because they would not curve or sink, or at least not as much.

RE: Golf ball dimples

Already done. MB tested the fuel economy of a car clean, dirty, and with dimples. Dimples was the best.

Quote:

ORIGINAL: hugger-4641

I tend to agree on this, but it would be neat to have some data to support the opinion. Somebody send this to Myth Busters!!!;)

RE: Golf ball dimples

Quote:

ORIGINAL: dick Hanson

Quote:

ORIGINAL: banktoturn

Quote:

ORIGINAL: hugger-4641

Quote:

ORIGINAL: banktoturn

Quote:

hugger-4641,

The dimpled ball would go further, which is why they put dimples on them.

banktoturn

hugger-4641,

I don't know for sure, but my guess is that the dimples are more important. I base this guess on 3 things: 1) my observation that very worn range balls don't fly as far as new ones (a very obvious difference, when witnessed), 2) balls marketed as ''distance'' balls tend to have lower spin rates, and 3) the aspect ratio of a golf ball is so low that generating a lot of lift causes a big drag penalty.

banktoturn

As long as we are all guessing
-try this guess
A worn golf ball may not store as much energy (from the club) .
old balls may lose some of their ''bounce''
(Don't we know it)
Distance balls MAY flatten more when hit by the club and therefore may not be set into rotation as easily as a harder ball-which MAY thru the angle of club contact - tend to ratate faster from the impact
If that concept is too hard to grasp-consider hitting a steel sphere . the contact area of th ball will remain smaller and therefor (I love college talk), the ''english'' put on th ball will be more than that put on a softer surface -which flattens before going into motion
My next slide please.

It's a reasonable guess that the older balls may not get as much energy from the club. I suppose we could rely on the initial observations of smooth gutta-percha balls versus scuffed ones, to eliminate that possibility.

Your guess as to the mechanism by which distance balls acquire lower spin rates doesn't happen to be the one that the ball manufacturers give, but it doesn't really matter. The salient observation is that balls intended to fly farther are designed to spin more slowly.

I'm also guessing that you don't really like college talk any more than you like spelling and punctuation. I suppose that was a little irony. Nicely done.

banktoturn

RE: Golf ball dimples

[quote]ORIGINAL: banktoturn
Your guess as to the mechanism by which distance balls acquire lower spin rates doesn't happen to be the one that the ball manufacturers give, but it doesn't really matter. The salient observation is that balls intended to fly farther are designed to spin more slowly.

Salient:
Does the ball actually spin more slowly by design intent?
or
does the ball spin more slowly because the energy imparted by the club , is better transferred into forward motion
Sorta like a super ball.
Energy is a tricky thing
you have to account for all of it
the energy could either be used for
A- rotation
or
B- forward motion
You can't have yer Kate n Edith too.
Perhaps someone has wind tunnel documentation which prooves otherwise.
Anyone?
.

RE: Golf ball dimples

[quote]ORIGINAL: dick Hanson

Quote:

ORIGINAL: banktoturn
Your guess as to the mechanism by which distance balls acquire lower spin rates doesn't happen to be the one that the ball manufacturers give, but it doesn't really matter. The salient observation is that balls intended to fly farther are designed to spin more slowly.

Salient:
Does the ball actually spin more slowly by design intent?
or
does the ball spin more slowly because the energy imparted by the club , is better transferred into forward motion
Sorta like a super ball.
Energy is a tricky thing
you have to account for all of it
the energy could either be used for
A- rotation
or
B- forward motion
You can't have yer Kate n Edith too.
Perhaps someone has wind tunnel documentation which prooves otherwise.
Anyone?
.

That's a viable guess, but legal golf balls are restricted in terms of their initial velocity when leaving the club head. With that limitation, the spin can be chosen independent of the linear velocity to optimize the distance.

Either way, I don't think a wind tunnel would proooove anything about the energy.