Dimpling on arrows

[Fuzzy]

I used to play golf. Badly. I played again recently and it got me thinking about dimples and turbulence.

Golf balls are dimpled. The dimples create tiny pockets of low pressure in flight that allow the ball to travel faster and, if well hit, straighter. (This also allows you to radically curve the ball too). Bernoulli's principle at work, essentially.

What would happen, then, if you were to apply the same technology to an arrow? The folowing is a thought experiment:

Imagine two arrows: arrow 1 has a point. The head of the point remains sharp; the rest is covered in tiny dimples. The shaft is similarly dimpled, with an undimpled area at the back for fletches etc. Arrow two is identical to arrow one apart from the dimpling.

When shot, these arrows spin, like all arrows. They both move forwards and rotate about their long axes. If you're a non-compounder, they moving significantly from side to side due to "paradox".

Ignoring the relatively massive drag effect of fletchings (which, if they are fletched the same, should cancel out), what, if any, is the difference between these two arrows?

Arrow 2 flies normally, but...

Arrow 1 is generating low-pressure spots as it moves forwards and rotates. I imagine that the point is where this effect would be most marked, although the same effect must apply along the length of the arrow too. I reckon this arrow will:

Move marginally faster through the air due to these low pressure areas.

Rotate faster, as the effect of those low pressure spots also apply in the direction of spin.

Might move slightly in the direction of lateral spin.

Might also suffer increased drag from side-to-side movement as the airflow is more disturbed (dimples again).

What do you think? Fluid dynamicists especially welcome - and if anyone has a physics modelling package and some spare time to play with, I'd be fascinated at the results.

 

[007]

I don't know about the shaft, but that is certainly the argument put out by New Archery Products QuikFletch QuickSpin ST Arrow Vanes


Did a quick search on dimpled arrows and found these links...
'dimpled' arrows faster? - TradTalk Forums
Vaneless arrow shaft - Patent 5971875


[edit]
Fluted arrow - Patent 6595880
found this.... Fluted arrow shafts?? Maybe I'm going bonkers..

From: Omar Almaini <[email protected]>
Subject: Fluted arrow shafts?? Maybe I'm going bonkers..
Date: 5 Feb 1996 16:51:20 GMT

After reading the surreal debate on the advantages or otherwise
of drilling holes in your riser (I was tempted to post something
like "the holes are without doubt the strongest part of your bow
with the remarkable property that they actually weigh less as they
get larger...") I had an uncanny flashback to the page of an archery
catalogue that I bought years ago just as I started archery.

Is it just me, or does anyone else remember a weird and wonderful arrow
called the Fluted Arrow Shaft which wasn't quite cylindrical but had
an indented groove along the side. I can't remember the advantages
claimed for these arrows but I presume the design made them stiffer
which allowed the weight to be reduced, smaller diameter etc..

I'd love to know if anyone has shot these arrows and what finally
became of them. Does anyone think they were a good idea? Ahead of its
time maybe??

Or maybe I'm going completely mad and just dreamt the whole thing....


Omar

From: [email protected] (John Dickson)
Subject: Re: Fluted arrow shafts?? Maybe I'm going bonkers..
Date: 6 Feb 1996 09:56:30 GMT

[snip]

Hi Omar,
No, you're absoloutely right, fluted shafts did exist and in
field archery they were quite popular around 1985-1987....even
Mackenzies in Edinburgh sold them!

A few problems which I know of (other than those listed by "Olympic
Question"...some people have wierd names ;-)

They are a bugger to straighten because of the flute.

You get ###### off because every now and then you don't get a
line-cutter because you have a flute where you would have got it with a
trad. shaft!

They carve chunks out of your pressure button if you set the nock the
*wrong way*.

They seemed to peform pretty well though but not necessarily any better.

I think they were supposed to be more difficult to bend but now things
are getting vague!

Ahh the days when Severns had Nishizawas in the catalogue...not too
mention... gasp... swing bars ;-)


John Dickson,(aka Stretch)

From: olympic question <[email protected]>
Subject: Re: Fluted arrow shafts?? Maybe I'm going bonkers..
Date: 6 Feb 1996 03:05:57 GMT


Re fluted shafts- Yes you are right on both counts but the
company went under due to poor sales,fleching the arrows were a
problem because of the flutes leaving a gap under the vane and
whistling during flite.Also carbons made their debut in 3-D abuot
the same time,I don't think that they are around anymore.

Sean

Re: Fluted arrow shafts?? Maybe I'm going bonkers..
From: Hywel Owen <[email protected]>
Date: 1996/02/06
Ah yes!
I remember them well.... they were pretty awful! You had to make
sure the nocks has exactly the same orientation with respect to the
flutes, or your button would be pressing either on a 'ridge' or a
'trough', thus sending the arrows left or right. Another reason they
fell from favour was that the alloy they were made from was pretty
poor - and you couldn't straighten them easily, of course!

 

[TJ Mason]

It might make the arrows easier to pull from the boss when wet.

 

[Staffan]

Something like this?

 

[Fuzzy]

Thanks, that's exactly it. (No dimpling on the rest of the arrow I see). What point is that? (Also thanks to 007, I now have some research to do).

 

[grimsby archer]

Doesnt the effect due to dimpling on golf balls have a lot to do with the backward rotation of the golf ball in flight?
If you were able to hit a golf ball so it travelled throught the air without spinning, or so that it spun "forward" it wouldnt get the lift.
Arrows dont spin in that way. They spin along their length, so lift would be in the wrong plane.

 

[Yew Selfbow]

Interesting question.....
my first thoughts are ..... a golf ball is a sphere so it has an infinite number of axes around which it can rotate....
an arrow has a single axis and can only rotate about that single axis...
I don't know if this is significant
interesting thread though ..

 

[Fuzzy]

The dimples themselves don't make the ball spin - they just magnify the effect by amplifying the pressure differences. Balls can spin in any direction depending on how they're hit.

If you want to see a non-rotating example of the low pressure effect, look on the bottom of racing boat hulls. Those are dimpled to create pockets of low drag in exactly the same way.

 

[007]

To be perfectly honest, I would say, due to shaft rotation, that the dimples would have more of an effect on any crosswinds than the arrow going forwards. It may make them better for windy condidtions, much like a slimmer arrow is better than a fatter one.

This is a good article on arrow dimpling Aerodynamics in Sports Equipment, Recreation and Machines - Golf - Instructor and a very good video here Golf Ball - Dimple Dynamics, Super-computer simulation


On a side note: VIDEO: Mythbusters test golf ball-like dimpling effect on fuel economy (*Spoiler Alert!*) — Autoblog

 

[Staffan]

Thanks, that's exactly it. (No dimpling on the rest of the arrow I see). What point is that? (Also thanks to 007, I now have some research to do).

Have to admit I don't know anything about he arrow or how it performed..
I stole the picture from a Swedish archery forum.. It was part of an April fools joke... :cheerful:

 

[gtek]

The concept has been thoroughly tested and discredited. That doesn't seem to stop it coming up every 10 years or so from armchair theoriticians who haven't gotten the word....

 

[geoffretired]

Are the fletchings that have one roughish surface( quikspins, I think)using a similar principle?

 

[wychcraft]

The dimpling on golf balls appears to reduce drag by keeping the airflow "attached" to the ball for longer as it passes the ball. Because of this, the empty space behind the ball is reduced in size, so the drag effect of this low pressure area is reduced.

I'd expect no effect for arrows, since the drag area is so much smaller, especially as nocks are slightly streamlined anyway rather than the chopped off shape fo a ball. Besides, the effect of the vanes on the airflow should exceed any effect from dimpling. If anything, you *want* laminar flow as long as possible over the length of an arrow, you don't want to disrupt it if you can help it.

As for quickspins, i expect they introduce spin by *adding* drag rather than reducing it, they certainly seem to be slower.

 

[007]

the quick spins most probably DO add drag, however they claim to create lower pressure on one side of the vane, which it what supposedly causes the increased spin rate.

 

[whiz]

Ah, multiple posting across several forums.
No problem. You've been answered on AF.

 

[007]

Ah, multiple posting across several forums.
No problem. You've been answered on AF.

So he has
Arrow and Dimpling - Archery Forum - Australia's archery related forum

 

[whiz]

And just because a vane manufacturer claims something, doesn't mean that they've proven it.

 

[007]

very true.

 

[disbloke]

The flick and groves on Quickspins do increase spin by creating a low pressure zone, however the increased spin also creates drag which can cause a more pronounced parachute effect on longer distances. The same occurs with spinwings but the increase in drag is minimised by the nature of the Mylar materiel and the vane profile itself which is why a spinwing and ep16 vane will impact in much the same position. There are a whole load of other very good reasons why the top recurve shooters use spinwings though.

 

[jimlee]

I don't know if dimpling would help with arrow flight at all, but I recon it would make a hell of a racket as it goes over the rest.

Cheers, Jim