Why don't wings have dimples?

[Dancing Fingers]

Hi all,
I always wanted to build my own airplane but the time and money has
eluded me. So I've decided to design and build my own recumbent trike,
with farings. This brings me to my question, if golf balls have
dimples, to help them sail further, why don't wings -- especially for
STOL aircraft? Would putting dimples in my faring reduce my wind
resistance?
Just curious.
Chris

[Capt. Geoffrey Thorpe]

"Dancing Fingers" > wrote in message
ups.com...
> Hi all,
> I always wanted to build my own airplane but the time and money has
> eluded me. So I've decided to design and build my own recumbent trike,
> with farings. This brings me to my question, if golf balls have
> dimples, to help them sail further, why don't wings -- especially for
> STOL aircraft? Would putting dimples in my faring reduce my wind
> resistance?
> Just curious.
> Chris
>

Dimples work on round things under a relativly narrow range of reynolds
numbers (a function of speed, size and properties of air) by helping keep
the boundry layer attached. Golf balls happen to fit into that range and
have the right shape. Gliders sometimes use "turbulator" tape to trip a
laminar boundry layer and make it turbulant so it will stay attached
longer - but the placement is critical (and only works if you have a very
laminar wing to begin with).

So, if you are having boundry layer seperation problems due to the shape of
your fairing aft of the maximum "thickness", then dimples or other boundry
layer devices may or may not help but most likely they will not.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Bill Daniels]

"Dancing Fingers" > wrote in message
ups.com...
> Hi all,
> I always wanted to build my own airplane but the time and money has
> eluded me. So I've decided to design and build my own recumbent trike,
> with farings. This brings me to my question, if golf balls have
> dimples, to help them sail further, why don't wings -- especially for
> STOL aircraft? Would putting dimples in my faring reduce my wind
> resistance?
> Just curious.
> Chris
>

You may hear stories of the "Golf Ball Effect" improving performance of
aircraft - usually from those trying to sell hail damaged aircraft.

bildan

[jbaloun]

When air moves past a rotating sphere or cylinder the surface friction
can induce a rotational component into the airflow. This shifts the
pressure distribution and causes a net lift. The lift allows a golf
ball to achieve a longer flight. The dimples 'dirty' the surface and
increase this rotational effect.

Lift on a wing can be considered in different and equivalent ways. Some
of the ways to look at lift from a wing are:
-Deflection of the ambient air is a mass pushed down which results in a
force up on the aircraft.
-Faster airflow on the upper surface and slower airflow on the lower
surface create a pressure difference and lift.
-The wing induces a circulation in the ambient air which can be
directly related to lift.

It is interesting to note that a vortex in free air must be closed.
Just like a common smoke ring. But the wing is finite. The vortex peels
off the wing in an approximately elliptical distribution across the
span and is left behind both wing tips as the aircraft flys away. Aside
from friction eventually stopping the circulation a few minutes after
the aircraft is passed, theoretically the vortex continues back behind
the flight path all the way to the runway where the plane took off
where the first inch of movement of the wing began a very small vortex
and very small lift.

A baseball pitcher gets a similar effect when the spinning ball does
not sink as fast as it should thus fooling the batter. On the other
hand a knuckle ball appears to stagger like it was drunk and makes the
batter queasy. eww!

James

Dancing Fingers wrote:
> Hi all,
> I always wanted to build my own airplane but the time and money has
> eluded me. So I've decided to design and build my own recumbent trike,
> with farings. This brings me to my question, if golf balls have
> dimples, to help them sail further, why don't wings -- especially for
> STOL aircraft? Would putting dimples in my faring reduce my wind
> resistance?
> Just curious.
> Chris

[[email protected]]

Dancing Fingers wrote:
> Hi all,
> I always wanted to build my own airplane but the time and money has
> eluded me. So I've decided to design and build my own recumbent trike,
> with farings. This brings me to my question, if golf balls have
> dimples, to help them sail further, why don't wings -- especially for
> STOL aircraft? Would putting dimples in my faring reduce my wind
> resistance?
> Just curious.
> Chris

Because wings are'nt supposed to spin, or hook, or slice.
MadDog

"The early bird may often get the worm,
but it's the second mouse that gets the cheese".

[Ron Webb]

Actually, Vortex Generators on wings are a common device for increasing
usable angle of attack, on everything from supercubs to airliners.

The idea is similar to your golfball dimples. Cause turbulence in the air
flowing over the wing, thus allowing it to continue to follow the wing
surface a bit longer.

There is some engineering data in the NACA web library. This was all I found
with a quick search, but there may be more.
http://naca.larc.nasa.gov/reports/1954/naca-rm-e53l15/naca-rm-e53l15.pdf





"Dancing Fingers" > wrote in message
ups.com...
> Hi all,
> I always wanted to build my own airplane but the time and money has
> eluded me. So I've decided to design and build my own recumbent trike,
> with farings. This brings me to my question, if golf balls have
> dimples, to help them sail further, why don't wings -- especially for
> STOL aircraft? Would putting dimples in my faring reduce my wind
> resistance?
> Just curious.
> Chris
>

[Philippe Vessaire]

Dancing Fingers wrote:

> if golf balls have
> dimples, to help them sail further, why don't wings

because birds hav'nt....

--
Pub: http://www.slowfood.fr/france
Philippe Vessaire ҿӬ

[Alan Baker]

In article om>,
"Dancing Fingers" > wrote:

> Hi all,
> I always wanted to build my own airplane but the time and money has
> eluded me. So I've decided to design and build my own recumbent trike,
> with farings. This brings me to my question, if golf balls have
> dimples, to help them sail further, why don't wings -- especially for
> STOL aircraft? Would putting dimples in my faring reduce my wind
> resistance?
> Just curious.
> Chris

First of all, golf balls have dimples because in order to create lift
they need to influence the air passing by them with the golf ball's
spin. The dimples help to make the air slow down beneath the ball and
speed up above it; creating downward flow.

Wings produce that downward flow with their shape.

[[email protected]]

> > Dancing Fingers wrote:
>
> > if golf balls have
> > dimples, to help them sail further, why don't wings



> Philippe Vessaire wrote:
>
> because birds hav'nt....



Dang.

That's a lot of feathers for the fellow to have to glue to his wings.

Daniel

[[email protected]]

A few years ago someone was marketing a perforated tape to stick on
your propeller leading edges to act as vortex generators, improving
thrust and therefore performance. I have never seen any of this stuff
on a prop, and don't know if it was worthwhile or just another of the
gimmicks to get a poor pilot's money. Anybody else see it?

Dan

[Ron Wanttaja]

On 12 Jun 2006 06:07:26 -0700, wrote:

> > > if golf balls have
> > > dimples, to help them sail further, why don't wings
>
> > Philippe Vessaire wrote:
> >
> > because birds hav'nt....
>
> Dang.
>
> That's a lot of feathers for the fellow to have to glue to his wings.

"Fortunately, I keep my feathers numbered for just such an emergency."
- Daffy Duck

Ron Wanttaja

[Alan Baker]

In article >,
Ron Wanttaja > wrote:

> On 12 Jun 2006 06:07:26 -0700, wrote:
>
> > > > if golf balls have
> > > > dimples, to help them sail further, why don't wings
> >
> > > Philippe Vessaire wrote:
> > >
> > > because birds hav'nt....
> >
> > Dang.
> >
> > That's a lot of feathers for the fellow to have to glue to his wings.
>
> "Fortunately, I keep my feathers numbered for just such an emergency."
> - Daffy Duck

Foghorn Leghorn.

>
> Ron Wanttaja

[[email protected]]

Capt. Geoffrey Thorpe wrote:
>
> ...
>
> Dimples work on round things under a relativly narrow range of reynolds
> numbers (a function of speed, size and properties of air) by helping keep
> the boundry layer attached. Golf balls happen to fit into that range and
> have the right shape. Gliders sometimes use "turbulator" tape to trip a
> laminar boundry layer and make it turbulant so it will stay attached
> longer - but the placement is critical (and only works if you have a very
> laminar wing to begin with).
>
> So, if you are having boundry layer seperation problems due to the shape of
> your fairing aft of the maximum "thickness", then dimples or other boundry
> layer devices may or may not help but most likely they will not.
>

So maybe you could use dimples on fairings, fuselage or struts,
especially
if the struts are circular tubing, eh?

--

FF

Lots of aviation stuff for sale cheap:

http://groups.google.com/group/rec.aviation.marketplace/msg/a084cb0d234406ed?dmode=source&hl=en

[[email protected]]

Dancing Fingers wrote:
> Hi all,
> I always wanted to build my own airplane but the time and money has
> eluded me. So I've decided to design and build my own recumbent trike,
> with farings. This brings me to my question, if golf balls have
> dimples, to help them sail further, why don't wings -- especially for
> STOL aircraft? Would putting dimples in my faring reduce my wind
> resistance?
> Just curious.
> Chris

I read a story about NASA research of wings with thousands of tiny
holes that suck air into them on the top of the wing. Apparently they
aid in laminar flow, but there were concerns with the holes clogging
too easily with dirt.

Dean

[Capt. Geoffrey Thorpe]

> wrote in message
ups.com...
>
> Capt. Geoffrey Thorpe wrote:
>>
<...>
> So maybe you could use dimples on fairings, fuselage or struts,
> especially
> if the struts are circular tubing, eh?
>
> --
>
> FF

Could be. Somewhere or another I saw some wind tunnel data on golf balls
that nicely showed how the flow remained attached further around the back
side (no spin was involved - just a reduction in the wake). But you would
have to find out what the range of Reynolds number this works for...

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Dancing Fingers]

Thanks everyone for the great answers vto my silly question.
Capt. Geoffrey Thorpe wrote:
> > wrote in message
> ups.com...
> >
> > Capt. Geoffrey Thorpe wrote:
> >>
> <...>
> > So maybe you could use dimples on fairings, fuselage or struts,
> > especially
> > if the struts are circular tubing, eh?
> >
> > --
> >
> > FF
>
> Could be. Somewhere or another I saw some wind tunnel data on golf balls
> that nicely showed how the flow remained attached further around the back
> side (no spin was involved - just a reduction in the wake). But you would
> have to find out what the range of Reynolds number this works for...
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.

[Dancing Fingers]

Does anyone know of a good simulation program where you could play with
dimples on a large hot dog shape, just to see what happens.
Just more curious.
Chris
Dancing Fingers wrote:
> Thanks everyone for the great answers vto my silly question.
> Capt. Geoffrey Thorpe wrote:
> > > wrote in message
> > ups.com...
> > >
> > > Capt. Geoffrey Thorpe wrote:
> > >>
> > <...>
> > > So maybe you could use dimples on fairings, fuselage or struts,
> > > especially
> > > if the struts are circular tubing, eh?
> > >
> > > --
> > >
> > > FF
> >
> > Could be. Somewhere or another I saw some wind tunnel data on golf balls
> > that nicely showed how the flow remained attached further around the back
> > side (no spin was involved - just a reduction in the wake). But you would
> > have to find out what the range of Reynolds number this works for...
> >
> > --
> > Geoff
> > The Sea Hawk at Wow Way d0t Com
> > remove spaces and make the obvious substitutions to reply by mail
> > When immigration is outlawed, only outlaws will immigrate.

[Montblack]

("Alan Baker" wrote)
> First of all, golf balls have dimples because in order to create lift they
> need to influence the air passing by them with the golf ball's spin. The
> dimples help to make the air slow down beneath the ball and speed up above
> it; creating downward flow.
>
> Wings produce that downward flow with their shape.


How about a dimpled spinner?

Your choice - slice or draw.


Montblack

[Peter Dohm]

"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
...
>
> > wrote in message
> ups.com...
> >
> > Capt. Geoffrey Thorpe wrote:
> >>
> <...>
> > So maybe you could use dimples on fairings, fuselage or struts,
> > especially
> > if the struts are circular tubing, eh?
> >
> > --
> >
> > FF
>
> Could be. Somewhere or another I saw some wind tunnel data on golf balls
> that nicely showed how the flow remained attached further around the back
> side (no spin was involved - just a reduction in the wake). But you would
> have to find out what the range of Reynolds number this works for...
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>
>
I've seen a video of that, but don't recall where. However, I believe that
you have it backward--the flow detaches earlier (from the non-spinning golf
ball) and reduces the drag.

I am not quite sure how that might relate to wings and propellers; but I
suspect that they (wings and props) are two radically different, and
possibly opposite, phenomena.

Peter

[Peter Dohm]

"Alan Baker" > wrote in message
...
> In article om>,
> "Dancing Fingers" > wrote:
>
> > Hi all,
> > I always wanted to build my own airplane but the time and money has
> > eluded me. So I've decided to design and build my own recumbent trike,
> > with farings. This brings me to my question, if golf balls have
> > dimples, to help them sail further, why don't wings -- especially for
> > STOL aircraft? Would putting dimples in my faring reduce my wind
> > resistance?
> > Just curious.
> > Chris
>
> First of all, golf balls have dimples because in order to create lift
> they need to influence the air passing by them with the golf ball's
> spin. The dimples help to make the air slow down beneath the ball and
> speed up above it; creating downward flow.

I believe that you have the effect exactly backward. The spin, which should
only be significant using the more steeply pitched irons; slows the relative
speed over the "top" of the ball and causes it to remain attached longer,
while the air flowing under the bottom breaks away more quickly, which would
result in a slight net lift. It also explains why a "slice" curves as it
does--which is why a smooth ball would have improved my game. :-(
>
> Wings produce that downward flow with their shape.

Exactly.

Peter

[Peter Dohm]

> wrote in message
oups.com...
>
> A few years ago someone was marketing a perforated tape to stick on
> your propeller leading edges to act as vortex generators, improving
> thrust and therefore performance. I have never seen any of this stuff
> on a prop, and don't know if it was worthwhile or just another of the
> gimmicks to get a poor pilot's money. Anybody else see it?
>
> Dan
>

I remember it, but haven't seen it since and don't recall who made it.

I believe that there was also an article in "Experimenter", now renamed
"Sport Pilot", regarding a gent who had drilled a line of dimples (or
perhaps two) along the low pressure face of both blades of his prop at
approximately the thickest point. He did achieve his goal with regard to
static RPM and cruise RPM, as well as cruise speed for the particular
aircraft. However, IIRC, some baseline data was not recorded and the
article did not include the precise description and placement of the
dimples; with the result that a general inference was not reasonable.

Peter
Where's John Ronz when we need him?

[Capt. Geoffrey Thorpe]

"Peter Dohm" > wrote in message
...
>>
> I've seen a video of that, but don't recall where. However, I believe
> that
> you have it backward--the flow detaches earlier (from the non-spinning
> golf
> ball) and reduces the drag.
>
> I am not quite sure how that might relate to wings and propellers; but I
> suspect that they (wings and props) are two radically different, and
> possibly opposite, phenomena.
>
> Peter

Ok, now you've done it. You are going to make me look this up...

http://www.fi.edu/wright/again/wings.avkids.com/wings.avkids.com/Book/Sports/instructor/golf-01.html
description and a drawing...

http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml
with a little math and some graphs

http://turb.seas.ucla.edu/~jkim/sciam/0197moinbox3.html
plots drag as a function of Reynolds number for a golf ball and a smooth
sphere - a good starting pont if you want to dimple your nosegear strut to
reduce drag - just figure you your own Reynolds number...

That's enough. Didn't find the picture I was looking for. But I see
references to both the reduction in wake and Magnus effect that converts the
spin into lift. Apparently both contribute to the increase in range. (and
the drawings I've seen show the boundry layer staying attached longer as I
thought.)

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Alan Baker]

In article >,
"Peter Dohm" > wrote:

> "Alan Baker" > wrote in message
> ...
> > In article om>,
> > "Dancing Fingers" > wrote:
> >
> > > Hi all,
> > > I always wanted to build my own airplane but the time and money has
> > > eluded me. So I've decided to design and build my own recumbent trike,
> > > with farings. This brings me to my question, if golf balls have
> > > dimples, to help them sail further, why don't wings -- especially for
> > > STOL aircraft? Would putting dimples in my faring reduce my wind
> > > resistance?
> > > Just curious.
> > > Chris
> >
> > First of all, golf balls have dimples because in order to create lift
> > they need to influence the air passing by them with the golf ball's
> > spin. The dimples help to make the air slow down beneath the ball and
> > speed up above it; creating downward flow.
>
> I believe that you have the effect exactly backward. The spin, which should
> only be significant using the more steeply pitched irons; slows the relative
> speed over the "top" of the ball and causes it to remain attached longer,

No. It doesn't. Golf balls spin with a rotation such that the bottom is
moving forward and the top is moving rearward.

> while the air flowing under the bottom breaks away more quickly, which would
> result in a slight net lift. It also explains why a "slice" curves as it
> does--which is why a smooth ball would have improved my game. :-(
> >
> > Wings produce that downward flow with their shape.
>
> Exactly.
>
> Peter

[Ron Wanttaja]

On Wed, 14 Jun 2006 05:20:31 GMT, Alan Baker > wrote:

> > I believe that you have the effect exactly backward. The spin, which should
> > only be significant using the more steeply pitched irons; slows the relative
> > speed over the "top" of the ball and causes it to remain attached longer,
>
> No. It doesn't. Golf balls spin with a rotation such that the bottom is
> moving forward and the top is moving rearward.

Not the way I play... :-)

Ron Wanttaja

[Peter Dohm]

"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
...
> "Peter Dohm" > wrote in message
> ...
> >>
> > I've seen a video of that, but don't recall where. However, I believe
> > that
> > you have it backward--the flow detaches earlier (from the non-spinning
> > golf
> > ball) and reduces the drag.
> >
> > I am not quite sure how that might relate to wings and propellers; but I
> > suspect that they (wings and props) are two radically different, and
> > possibly opposite, phenomena.
> >
> > Peter
>
> Ok, now you've done it. You are going to make me look this up...
>
>
http://www.fi.edu/wright/again/wings.avkids.com/wings.avkids.com/Book/Sports/instructor/golf-01.html
> description and a drawing...
>
> http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml
> with a little math and some graphs
>
> http://turb.seas.ucla.edu/~jkim/sciam/0197moinbox3.html
> plots drag as a function of Reynolds number for a golf ball and a smooth
> sphere - a good starting pont if you want to dimple your nosegear strut to
> reduce drag - just figure you your own Reynolds number...
>
> That's enough. Didn't find the picture I was looking for. But I see
> references to both the reduction in wake and Magnus effect that converts
the
> spin into lift. Apparently both contribute to the increase in range. (and
> the drawings I've seen show the boundry layer staying attached longer as I
> thought.)
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>
>
It looks like I misremembered as well, since all of them show the flow
remaining attached further around the dimpled ball. However, the
explanation of top spin under "How a Golf Ball Produces Lift" in the first
link does introduce a problem, since the result of Magnus Effect seems
(intuitively) reversed from the separation issue. The author's description
of the direction of lift is consistent with the description under "Hook and
Slice" which I know (regrettably) to be absolutely true.

So all of the articles agree on a couple of points, and appear to have
obtained the same photo for publication. However the Magnus Effect, while
well known to be true to every golfer (usually in a detrimental way) appears
to be backward in some sense.

For the moment, this appears to have moved from my Solved Problems List to
my Unsolved Problems List.

Peter

[Peter Dohm]

"Ron Wanttaja" > wrote in message
...
> On Wed, 14 Jun 2006 05:20:31 GMT, Alan Baker > wrote:
>
> > > I believe that you have the effect exactly backward. The spin, which
should
> > > only be significant using the more steeply pitched irons; slows the
relative
> > > speed over the "top" of the ball and causes it to remain attached
longer,
> >
> > No. It doesn't. Golf balls spin with a rotation such that the bottom is
> > moving forward and the top is moving rearward.
>
> Not the way I play... :-)
>
> Ron Wanttaja

Wait. That was my line!

Peter

[cavelamb]

Peter Dohm wrote:

> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
> ...
>
>>"Peter Dohm" > wrote in message
...
>>
>>>I've seen a video of that, but don't recall where. However, I believe
>>>that
>>>you have it backward--the flow detaches earlier (from the non-spinning
>>>golf
>>>ball) and reduces the drag.
>>>
>>>I am not quite sure how that might relate to wings and propellers; but I
>>>suspect that they (wings and props) are two radically different, and
>>>possibly opposite, phenomena.
>>>
>>>Peter
>>
>>Ok, now you've done it. You are going to make me look this up...
>>
>>
>
> http://www.fi.edu/wright/again/wings.avkids.com/wings.avkids.com/Book/Sports/instructor/golf-01.html
>
>>description and a drawing...
>>
>>http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml
>>with a little math and some graphs
>>
>>http://turb.seas.ucla.edu/~jkim/sciam/0197moinbox3.html
>>plots drag as a function of Reynolds number for a golf ball and a smooth
>>sphere - a good starting pont if you want to dimple your nosegear strut to
>>reduce drag - just figure you your own Reynolds number...
>>
>>That's enough. Didn't find the picture I was looking for. But I see
>>references to both the reduction in wake and Magnus effect that converts
>
> the
>
>>spin into lift. Apparently both contribute to the increase in range. (and
>>the drawings I've seen show the boundry layer staying attached longer as I
>>thought.)
>>
>>--
>>Geoff
>>The Sea Hawk at Wow Way d0t Com
>>remove spaces and make the obvious substitutions to reply by mail
>>When immigration is outlawed, only outlaws will immigrate.
>>
>>
>
> It looks like I misremembered as well, since all of them show the flow
> remaining attached further around the dimpled ball. However, the
> explanation of top spin under "How a Golf Ball Produces Lift" in the first
> link does introduce a problem, since the result of Magnus Effect seems
> (intuitively) reversed from the separation issue. The author's description
> of the direction of lift is consistent with the description under "Hook and
> Slice" which I know (regrettably) to be absolutely true.
>
> So all of the articles agree on a couple of points, and appear to have
> obtained the same photo for publication. However the Magnus Effect, while
> well known to be true to every golfer (usually in a detrimental way) appears
> to be backward in some sense.
>
> For the moment, this appears to have moved from my Solved Problems List to
> my Unsolved Problems List.
>
> Peter
>
>

Will forward your Unsolved Problem to Mary Shafer (NASA).

Maybe the Lift Demons have a clue?

[cavelamb]

Peter Dohm wrote:

> "Ron Wanttaja" > wrote in message
> ...
>
>>On Wed, 14 Jun 2006 05:20:31 GMT, Alan Baker > wrote:
>>
>>
>>>>I believe that you have the effect exactly backward. The spin, which
>
> should
>
>>>>only be significant using the more steeply pitched irons; slows the
>
> relative
>
>>>>speed over the "top" of the ball and causes it to remain attached
>
> longer,
>
>>>No. It doesn't. Golf balls spin with a rotation such that the bottom is
>>>moving forward and the top is moving rearward.
>>
>>Not the way I play... :-)
>>
>>Ron Wanttaja
>
>
> Wait. That was my line!
>
> Peter
>
>
Oh well. The net effect is the same...

[Capt. Geoffrey Thorpe]

"Peter Dohm" > wrote in message
. ..
>
> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
<...>>
> http://www.fi.edu/wright/again/wings.avkids.com/wings.avkids.com/Book/Sports/instructor/golf-01.html
>> description and a drawing...
>>
<...>
> So all of the articles agree on a couple of points, and appear to have
> obtained the same photo for publication. However the Magnus Effect, while
> well known to be true to every golfer (usually in a detrimental way)
> appears
> to be backward in some sense.
>
> For the moment, this appears to have moved from my Solved Problems List to
> my Unsolved Problems List.
>
> Peter

Dunno, looked OK to me. If the ball is flying across your screen from right
to left think of an airfoil moving from right to left, low pressure on top,
circulation has to be clockwise in this view to accelrate the flow across
the top and decelerate it around the bottom -

"1877, British scientist P.G. Tait learned that a ball, driven with a spin
about a horizontal axis with the top of the ball coming toward the golfer
produces a lifting force. This type of spin is know as a backspin."

That would be clockwise in a view where the ball is moving from right to
left...

Note: Have you ever seen a drawing or wind tunnel picture where the object
was traveling from left to right or the air was moving from right to left?
How did we become so consistant?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Capt. Geoffrey Thorpe]

"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
news:HvednScQQ67J5A3ZnZ2dnUVZ_oGdnZ2d@wideopenwest .com...
>
>
> "Peter Dohm" > wrote in message
> . ..
>>
>> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in
>> message
> <...>>
>> http://www.fi.edu/wright/again/wings.avkids.com/wings.avkids.com/Book/Sports/instructor/golf-01.html
>>> description and a drawing...
>>>
> <...>
>> So all of the articles agree on a couple of points, and appear to have
>> obtained the same photo for publication. However the Magnus Effect,
>> while
>> well known to be true to every golfer (usually in a detrimental way)
>> appears
>> to be backward in some sense.
>>
>> For the moment, this appears to have moved from my Solved Problems List
>> to
>> my Unsolved Problems List.
>>
>> Peter
>
> Dunno, looked OK to me. If the ball is flying across your screen from
> right to left think of an airfoil moving from right to left, low pressure
> on top, circulation has to be clockwise in this view to accelrate the flow
> across the top and decelerate it around the bottom -
>
> "1877, British scientist P.G. Tait learned that a ball, driven with a spin
> about a horizontal axis with the top of the ball coming toward the golfer
> produces a lifting force. This type of spin is know as a backspin."
>
> That would be clockwise in a view where the ball is moving from right to
> left...
>
> Note: Have you ever seen a drawing or wind tunnel picture where the object
> was traveling from left to right or the air was moving from right to left?
> How did we become so consistant?
>


oops, didn't read far enough:

"The dimples also help in the generation of lift. By keeping the flow
attached, the dimples help promote an asymmetry of the flow in the wake.
This asymmetry can be seen in Figure 5. In this figure, the smoke shows the
flow pattern about a spinning golf ball. The flow is moving from left to
right and the ball is spinning in the counter-clockwise direction. The wake
is being deflected downwards. This downward deflection of the wake implies
that a lifting force is being applied to the golf ball."

This is inconsistant with my thinking and inconsistant with the top of the
ball moving towards the golfer as described earlier on the page...

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[cavelamb]

Capt. Geoffrey Thorpe wrote:

>
> oops, didn't read far enough:
>
> "The dimples also help in the generation of lift. By keeping the flow
> attached, the dimples help promote an asymmetry of the flow in the wake.
> This asymmetry can be seen in Figure 5. In this figure, the smoke shows the
> flow pattern about a spinning golf ball. The flow is moving from left to
> right and the ball is spinning in the counter-clockwise direction. The wake
> is being deflected downwards. This downward deflection of the wake implies
> that a lifting force is being applied to the golf ball."
>
> This is inconsistant with my thinking and inconsistant with the top of the
> ball moving towards the golfer as described earlier on the page...
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>
>

Somebody (NASA/University?) built a "tube wing" thing once.

The wing was a large dia tube mounted - well - like a wing.

The tube rotated - "leading edge" up to create a circulation effect.
(as the aircraft moved forward - no hovering allowed this area)

It worked, but drag was a real drag...


Just a suspicion that the lift vector of a golf ball changes in flight.

Any flight path deviation due to rotational lift vectors would be strongest
early in the flight, but decrease as velocity decays below Re(crit)(combined
forward motion plus rotational effects) and the path becomes more ballistic.

Also didja catch the "Happy Non-Hooker" ball?


Richard

[Dancing Fingers]

I vaguely remember reading that the optimal dimple shape was hexagonal,
rather than round, like the standard golf ball. But the PGA tends to
be conservative in adopting such a radical change. I think spin is
more related to hooking or slicing because golf balls will always
travel further than a comparable spherical ball, without dimples, even
when struck by a machine. The question, for me, is do dimples create
eddy currents of air that reduces drag at slow airspeed? Second, what
is the optimal dimple size relative to the shape of the main body.
Chris

Peter Dohm wrote:
> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
> ...
> > "Peter Dohm" > wrote in message
> > ...
> > >>
> > > I've seen a video of that, but don't recall where. However, I believe
> > > that
> > > you have it backward--the flow detaches earlier (from the non-spinning
> > > golf
> > > ball) and reduces the drag.
> > >
> > > I am not quite sure how that might relate to wings and propellers; but I
> > > suspect that they (wings and props) are two radically different, and
> > > possibly opposite, phenomena.
> > >
> > > Peter
> >
> > Ok, now you've done it. You are going to make me look this up...
> >
> >
> http://www.fi.edu/wright/again/wings.avkids.com/wings.avkids.com/Book/Sports/instructor/golf-01.html
> > description and a drawing...
> >
> > http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml
> > with a little math and some graphs
> >
> > http://turb.seas.ucla.edu/~jkim/sciam/0197moinbox3.html
> > plots drag as a function of Reynolds number for a golf ball and a smooth
> > sphere - a good starting pont if you want to dimple your nosegear strut to
> > reduce drag - just figure you your own Reynolds number...
> >
> > That's enough. Didn't find the picture I was looking for. But I see
> > references to both the reduction in wake and Magnus effect that converts
> the
> > spin into lift. Apparently both contribute to the increase in range. (and
> > the drawings I've seen show the boundry layer staying attached longer as I
> > thought.)
> >
> > --
> > Geoff
> > The Sea Hawk at Wow Way d0t Com
> > remove spaces and make the obvious substitutions to reply by mail
> > When immigration is outlawed, only outlaws will immigrate.
> >
> >
> It looks like I misremembered as well, since all of them show the flow
> remaining attached further around the dimpled ball. However, the
> explanation of top spin under "How a Golf Ball Produces Lift" in the first
> link does introduce a problem, since the result of Magnus Effect seems
> (intuitively) reversed from the separation issue. The author's description
> of the direction of lift is consistent with the description under "Hook and
> Slice" which I know (regrettably) to be absolutely true.
>
> So all of the articles agree on a couple of points, and appear to have
> obtained the same photo for publication. However the Magnus Effect, while
> well known to be true to every golfer (usually in a detrimental way) appears
> to be backward in some sense.
>
> For the moment, this appears to have moved from my Solved Problems List to
> my Unsolved Problems List.
>
> Peter

[Peter Dohm]

"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
news:LbydnT9K86ux5w3ZnZ2dnUVZ_tOdnZ2d@wideopenwest .com...
> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
> news:HvednScQQ67J5A3ZnZ2dnUVZ_oGdnZ2d@wideopenwest .com...
> >
> >
> > "Peter Dohm" > wrote in message
> > . ..
> >>
> >> "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in
> >> message
> > <...>>
> >>
http://www.fi.edu/wright/again/wings.avkids.com/wings.avkids.com/Book/Sports/instructor/golf-01.html
> >>> description and a drawing...
> >>>
> > <...>
> >> So all of the articles agree on a couple of points, and appear to have
> >> obtained the same photo for publication. However the Magnus Effect,
> >> while
> >> well known to be true to every golfer (usually in a detrimental way)
> >> appears
> >> to be backward in some sense.
> >>
> >> For the moment, this appears to have moved from my Solved Problems List
> >> to
> >> my Unsolved Problems List.
> >>
> >> Peter
> >
> > Dunno, looked OK to me. If the ball is flying across your screen from
> > right to left think of an airfoil moving from right to left, low
pressure
> > on top, circulation has to be clockwise in this view to accelrate the
flow
> > across the top and decelerate it around the bottom -
> >
> > "1877, British scientist P.G. Tait learned that a ball, driven with a
spin
> > about a horizontal axis with the top of the ball coming toward the
golfer
> > produces a lifting force. This type of spin is know as a backspin."
> >
> > That would be clockwise in a view where the ball is moving from right to
> > left...
> >
> > Note: Have you ever seen a drawing or wind tunnel picture where the
object
> > was traveling from left to right or the air was moving from right to
left?
> > How did we become so consistant?
> >
>
>
> oops, didn't read far enough:
>
> "The dimples also help in the generation of lift. By keeping the flow
> attached, the dimples help promote an asymmetry of the flow in the wake.
> This asymmetry can be seen in Figure 5. In this figure, the smoke shows
the
> flow pattern about a spinning golf ball. The flow is moving from left to
> right and the ball is spinning in the counter-clockwise direction. The
wake
> is being deflected downwards. This downward deflection of the wake implies
> that a lifting force is being applied to the golf ball."
>
> This is inconsistant with my thinking and inconsistant with the top of the
> ball moving towards the golfer as described earlier on the page...
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>
>
I thought that I would be able to find a web site with the wind tunnel video
that I'm sure I've seen of this; however, for this evening at least, I must
admit that I have indeed struck out.

This is a subject that I would really like to understand; although I would
settle for a couple of good practical rules of thumb. If I happen to find
anything, I'll be sure to post it--or a link as appropriate.

Peter

[JP]

Hopefully these links will help you somehow.

http://www.lessonexchange.net/Mech_Eng_Golf%20Ball%20Aerodynamics.pdf

http://library.thinkquest.org/10556/cgi-bin/data/topics/22.htm

http://www.geocities.com/k_achutarao/MAGNUS/magnus.html

http://www.interactiveinstruments.com/RESERCH%20PAPER.htm

http://mercury.pr.erau.edu/~hayasd87/2004UBMSRCHome/2004-06-23-W/

JP

"Peter Dohm" > wrote in
t...

> I thought that I would be able to find a web site with the wind tunnel
> video
> that I'm sure I've seen of this; however, for this evening at least, I
> must
> admit that I have indeed struck out.
>
> This is a subject that I would really like to understand; although I would
> settle for a couple of good practical rules of thumb. If I happen to find
> anything, I'll be sure to post it--or a link as appropriate.
>
> Peter
>
>

[Morgans]

"Peter Dohm" > wrote

> I thought that I would be able to find a web site with the wind tunnel
> video
> that I'm sure I've seen of this; however, for this evening at least, I
> must
> admit that I have indeed struck out.
>
> This is a subject that I would really like to understand; although I would
> settle for a couple of good practical rules of thumb. If I happen to find
> anything, I'll be sure to post it--or a link as appropriate.

I'll try one time to help you understand.

Think of your observation from aboard the golf ball. Ignore the fact that
the ball is spinning, as you are taking your observations.

The ball is moving through the air. If there is no spin, the airspeed across
the mass of the ball is the same on the top or the bottom; that is a given.

Now spin the ball as it is moving, with the bottom of the ball going towards
the destination of the ball. Now think of the airspeed 2 millimeters off the
surface of the ball, and what the airspeed is, at that point. Is the air
moving slower on the bottom? Sure it is, because the rough surface (the
dimples) of the ball is rubbing on the air, and slowing the air's movement,
as compared to the mass of the ball; faster than if the ball was smooth.
What is the air doing on the top surface? Two millimeters above the
surface, the air is being accelerated, as the roughness of the ball tries to
grab the air an throw it past the ball.

The ball does not care if it is spinning. Don't measure the speed of the
air as compared to the spinning surface, but compare it to the mass of the
ball moving through the air, OK? So review what we have said. The air is
being slowed on the bottom, and speeded up across the top. That will cause
lower pressure on the top than the bottom, which will cause lift. That will
keep the ball in the air longer, and fly further, which is what golfers
want.

I hope that helped. :-)
--
Jim in NC

[Peter Dohm]

The Embry-Riddle link leads to someespecially fascinating discussion,
including that some efects of the dimples are related to Reynolds Number.
However, I clearly have a distance to go before understanding this
subject--even enough to safely apply any rules of thumb.

Thanks,
Peter

"JP" > wrote in message
...
> Hopefully these links will help you somehow.
>
> http://www.lessonexchange.net/Mech_Eng_Golf%20Ball%20Aerodynamics.pdf
>
> http://library.thinkquest.org/10556/cgi-bin/data/topics/22.htm
>
> http://www.geocities.com/k_achutarao/MAGNUS/magnus.html
>
> http://www.interactiveinstruments.com/RESERCH%20PAPER.htm
>
> http://mercury.pr.erau.edu/~hayasd87/2004UBMSRCHome/2004-06-23-W/
>
> JP
>
> "Peter Dohm" > wrote in
> t...
>
> > I thought that I would be able to find a web site with the wind tunnel
> > video
> > that I'm sure I've seen of this; however, for this evening at least, I
> > must
> > admit that I have indeed struck out.
> >
> > This is a subject that I would really like to understand; although I
would
> > settle for a couple of good practical rules of thumb. If I happen to
find
> > anything, I'll be sure to post it--or a link as appropriate.
> >
> > Peter
> >
> >
>
>

[Peter Dohm]

"T o d d P a t t i s t" > wrote in message
...
> "Peter Dohm" > wrote:
>
> >The Embry-Riddle link leads to someespecially fascinating discussion,
> >including that some efects of the dimples are related to Reynolds Number.
> >However, I clearly have a distance to go before understanding this
> >subject--even enough to safely apply any rules of thumb.
>
> If you are interested in the aerodynamics of spinning balls,
> or want to try to extend the state of our knowledge of
> aerodynamics as applied to aircraft design, then by all
> means, keep on looking at dimples.
>
> However, if your real interest is in reducing the drag of an
> aircraft, you'd be better off studying up on laminar flow
> and interference drag. There is enough information out
> there in the glider community on fairings, control seals,
> inexpensive laminar flow testing techniques (old motor oil,
> pieces of yarn, microphones or stethoscopes) to keep you
> busy for a long time and which will really produce drag
> reduction.
> --
> T o d d P a t t i s t
> (Remove DONTSPAMME from address to email reply.)
>
> Make a commitment to learn something from every flight.
> Share what you learn.

Well, I already know a lot of the rules of thumb for drag reduction,
especially with laminar flow, and that is my first choice for choosing or
building an airplane.

I am also interested in general aerodynamics, and am somewhat intrigued by
the issue of dimples. Particularly, grooves and dimples could be quite
interesting as related to propellers. Regrettably, there is a /very/ finite
limit to the percentage of time I can devote to that, so my progress may be
gradual.

Regards,
Peter

[[email protected]]

cavelamb wrote:
>
> ...
>
> Somebody (NASA/University?) built a "tube wing" thing once.
>
> The wing was a large dia tube mounted - well - like a wing.
>
> The tube rotated - "leading edge" up to create a circulation effect.
> (as the aircraft moved forward - no hovering allowed this area)
>
> It worked, but drag was a real drag...

Obviously they needed dimples on it...

>

A few years back I saw a TV show about a sailboat using he same
effect. It had big rotating column on the bow. I think the rotation
rate was adjusted to the windspeed and direction to keep the
thrust aligned astern.

--

FF

[Jim Carriere]

wrote:
> A few years back I saw a TV show about a sailboat using he same
> effect. It had big rotating column on the bow. I think the rotation
> rate was adjusted to the windspeed and direction to keep the
> thrust aligned astern.

I think a similar or perhaps the same boat was featured in Popular
Science magazine in the mid 1980s.

[[email protected]]

Peter Dohm wrote:
>
> ...
>
> Well, I already know a lot of the rules of thumb for drag reduction,
> especially with laminar flow, and that is my first choice for choosing or
> building an airplane.
>
> I am also interested in general aerodynamics, and am somewhat intrigued by
> the issue of dimples. Particularly, grooves and dimples could be quite
> interesting as related to propellers. Regrettably, there is a /very/ finite
> limit to the percentage of time I can devote to that, so my progress may be
> gradual.
>

Check with the powered paraglider people. I've been told that
some of their props have a groove running along the crowned
face of the blade.

A prop is just a wing rotating rapidly around the wing root. But the
effective airspeed of a prop appproaches Mach 1, where compressibility
becomes important.

A supersonic prop would be interesting....

--

FF

[JP]

This supersonic prop project produced some strange results...

http://www.aerospaceweb.org/question/aerodynamics/q0031b.shtml

http://www.wpafb.af.mil/museum/annex/an48.htm

http://www.1000aircraftphotos.com/Postcards/818.htm

JP


> kirjoitti
glegroups.com...
>
> Peter Dohm wrote:
>>
>> ...
>>
>> Well, I already know a lot of the rules of thumb for drag reduction,
>> especially with laminar flow, and that is my first choice for choosing or
>> building an airplane.
>>
>> I am also interested in general aerodynamics, and am somewhat intrigued
>> by
>> the issue of dimples. Particularly, grooves and dimples could be quite
>> interesting as related to propellers. Regrettably, there is a /very/
>> finite
>> limit to the percentage of time I can devote to that, so my progress may
>> be
>> gradual.
>>
>
> Check with the powered paraglider people. I've been told that
> some of their props have a groove running along the crowned
> face of the blade.
>
> A prop is just a wing rotating rapidly around the wing root. But the
> effective airspeed of a prop appproaches Mach 1, where compressibility
> becomes important.
>
> A supersonic prop would be interesting....
>
> --
>
> FF
>

[Montblack]

("JP" sent links)


Interesting links.

11 of 12 ...hmm?

http://www.wpafb.af.mil/museum/annex/an48.htm
"Between 22 July 1955 and 9 October 1956, two XF-84H prototypes (S/N
51-17059 and 51-17060) made twelve test flights. Eleven of the twelve
flights ended in emergency landings. Sounds produced by the aircraft's
turboprop engine caused nausea and headaches among ground crews, earning the
XF-84H the unofficial nickname "Thunderscreech." Though the XF-84H was the
fastest single-engine propeller driven aircraft ever built, it never
approached supersonic speed. Due to poor performance and high maintenance
requirements, the XF-84H never became operational."

http://www.1000aircraftphotos.com/MilitaryJets/RepublicF84.htm


Montblack
Ted Striker: Because of my mistake, six men didn't return from that raid.
Elaine Dickinson: Seven. Lieutenant Zip died this morning.

[Peter Dohm]

"T o d d P a t t i s t" > wrote in message
...
> "Peter Dohm" > wrote:
>
> >I am also interested in general aerodynamics, and am somewhat intrigued
by
> >the issue of dimples. Particularly, grooves and dimples could be quite
> >interesting as related to propellers.
>
> I wasn't trying to discourage you from looking into it, just
> pointing out that despite a great deal of work that has been
> done on golf balls and dimples, it has found little
> application in aviation. You'd be going down a path that I
> know has been trod before. Perhaps you'd find something new,
> but I'd expect it to take a lot of effort. If it were easy
> or obvious, it would have been developed before.
>
I believe that you are right.

> BTW, my glider wing *does* have dimples, for reasons
> discussed elsewhere in this thread (trips the laminar flow
> into turbulent flow).


> --
> T o d d P a t t i s t
> (Remove DONTSPAMME from address to email reply.)
>
> Make a commitment to learn something from every flight.
> Share what you learn.

[cavelamb]

wrote:

> cavelamb wrote:
>
>>...
>>
>>Somebody (NASA/University?) built a "tube wing" thing once.
>>
>>The wing was a large dia tube mounted - well - like a wing.
>>
>>The tube rotated - "leading edge" up to create a circulation effect.
>>(as the aircraft moved forward - no hovering allowed this area)
>>
>>It worked, but drag was a real drag...
>
>
> Obviously they needed dimples on it...




I wonder if that was ever investigated....


>
>
> A few years back I saw a TV show about a sailboat using he same
> effect. It had big rotating column on the bow. I think the rotation
> rate was adjusted to the windspeed and direction to keep the
> thrust aligned astern.
>

[cavelamb]

Peter Dohm wrote:

> The Embry-Riddle link leads to someespecially fascinating discussion,
> including that some efects of the dimples are related to Reynolds Number.
> However, I clearly have a distance to go before understanding this
> subject--even enough to safely apply any rules of thumb.
>
> Thanks,
> Peter
>
> "JP" > wrote in message
> ...
>
>>Hopefully these links will help you somehow.
>>
>>http://www.lessonexchange.net/Mech_Eng_Golf%20Ball%20Aerodynamics.pdf
>>
>>http://library.thinkquest.org/10556/cgi-bin/data/topics/22.htm
>>
>>http://www.geocities.com/k_achutarao/MAGNUS/magnus.html
>>
>>http://www.interactiveinstruments.com/RESERCH%20PAPER.htm
>>
>>http://mercury.pr.erau.edu/~hayasd87/2004UBMSRCHome/2004-06-23-W/
>>
>>JP
>>
>>"Peter Dohm" > wrote in
t...
>>
>>
>>>I thought that I would be able to find a web site with the wind tunnel
>>>video
>>>that I'm sure I've seen of this; however, for this evening at least, I
>>>must
>>>admit that I have indeed struck out.
>>>
>>>This is a subject that I would really like to understand; although I
>
> would
>
>>>settle for a couple of good practical rules of thumb. If I happen to
>
> find
>
>>>anything, I'll be sure to post it--or a link as appropriate.
>>>
>>>Peter
>>>
>>>
>>
>>
>
>


It's a "stickyness" thing, Peter.

Air is sticky.

It sticks to surfaces.
That's what the boundry layer does.

With the tube rotating leading edge up, the air stuck to the surface of the tube
takes a free ride over the top! (maybe not really, but get the picture?)

Moving, the air attached to the surface exhibits a reduced pressure
(ohnoherewegoagain!)
Sucking the boundry layer down tighter in the process.

Note where the incomming air stream separates.

No rotation would be about centered.
But rotating UP pulls the separation point Down.

Circulation rules apply, and the trailing wake also has a downward vector.
(a result of the Lift Drag Vector)(which is probably not square with anything
but itself, and changes throughout the Lift phase of the flight).

The "Happy Non_Hooker" ball only had dimples in a band around the ball.
Line the band up vertically and smack it square - that's where it goes!
No Hook no slice, because the lift vector is only vertical.

The rules committie outlawed the Non-Hooker because (as they said) it took
the skill out of the game.




Having considered all the ramifications of this over the last few days, I'm
releived that I never took up the "sport"...

[cavelamb]

Peter Dohm wrote:

> "T o d d P a t t i s t" > wrote in message
> ...
>
>>"Peter Dohm" > wrote:
>>
>>
>>>The Embry-Riddle link leads to someespecially fascinating discussion,
>>>including that some efects of the dimples are related to Reynolds Number.
>>>However, I clearly have a distance to go before understanding this
>>>subject--even enough to safely apply any rules of thumb.
>>
>>If you are interested in the aerodynamics of spinning balls,
>>or want to try to extend the state of our knowledge of
>>aerodynamics as applied to aircraft design, then by all
>>means, keep on looking at dimples.
>>
>>However, if your real interest is in reducing the drag of an
>>aircraft, you'd be better off studying up on laminar flow
>>and interference drag. There is enough information out
>>there in the glider community on fairings, control seals,
>>inexpensive laminar flow testing techniques (old motor oil,
>>pieces of yarn, microphones or stethoscopes) to keep you
>>busy for a long time and which will really produce drag
>>reduction.
>>--
>>T o d d P a t t i s t
>>(Remove DONTSPAMME from address to email reply.)
>>
>>Make a commitment to learn something from every flight.
>>Share what you learn.
>
>
> Well, I already know a lot of the rules of thumb for drag reduction,
> especially with laminar flow, and that is my first choice for choosing or
> building an airplane.
>
> I am also interested in general aerodynamics, and am somewhat intrigued by
> the issue of dimples. Particularly, grooves and dimples could be quite
> interesting as related to propellers. Regrettably, there is a /very/ finite
> limit to the percentage of time I can devote to that, so my progress may be
> gradual.
>
> Regards,
> Peter
>
>

All we need is a wind tunnel...

[karel]

because dimples don't have wings either?

[cavelamb]

Peter Dohm wrote:

> "T o d d P a t t i s t" > wrote in message
> ...
>
>>"Peter Dohm" > wrote:
>>
>>
>>>I am also interested in general aerodynamics, and am somewhat intrigued
>
> by
>
>>>the issue of dimples. Particularly, grooves and dimples could be quite
>>>interesting as related to propellers.
>>
>>I wasn't trying to discourage you from looking into it, just
>>pointing out that despite a great deal of work that has been
>>done on golf balls and dimples, it has found little
>>application in aviation. You'd be going down a path that I
>>know has been trod before. Perhaps you'd find something new,
>>but I'd expect it to take a lot of effort. If it were easy
>>or obvious, it would have been developed before.
>>
>
> I believe that you are right.
>
>
>>BTW, my glider wing *does* have dimples, for reasons
>>discussed elsewhere in this thread (trips the laminar flow
>>into turbulent flow).
>
>
>
>>--
>>T o d d P a t t i s t


Which, if I'm not mistaken, is exactly what the dimples on the ball do...

:)

[cavelamb]

Dancing Fingers wrote:

> I vaguely remember reading that the optimal dimple shape was hexagonal,
> rather than round, like the standard golf ball. But the PGA tends to
> be conservative in adopting such a radical change. I think spin is
> more related to hooking or slicing because golf balls will always
> travel further than a comparable spherical ball, without dimples, even
> when struck by a machine. The question, for me, is do dimples create
> eddy currents of air that reduces drag at slow airspeed? Second, what
> is the optimal dimple size relative to the shape of the main body.
> Chris
>

Get a golf ball and measure it.
That's right about optimal dimensions for a golf ball. :)

The dimples trip the boundry layer at a lower Reynolds Number than
RN(crit) where the boundry layer would separate naturally on a
round (undimpled) ball.

Better?

[Morgans]

"cavelamb" > wrote

> Having considered all the ramifications of this over the last few days,
> I'm
> releived that I never took up the "sport"...

I never took it up because...

The days my dad came home from work after playing golf, he was always ****ed
off. (for you Brits, that does not mean drunk <g>)

Why take up a form of recreation, whose primary result is to make you more
uptight? Not me!
--
Jim in NC

[Peter Dohm]

"cavelamb" > wrote in message
ink.net...
> Peter Dohm wrote:
>
> > "T o d d P a t t i s t" > wrote in message
> > ...
> >
> >>"Peter Dohm" > wrote:
> >>
> >>
> >>>The Embry-Riddle link leads to someespecially fascinating discussion,
> >>>including that some efects of the dimples are related to Reynolds
Number.
> >>>However, I clearly have a distance to go before understanding this
> >>>subject--even enough to safely apply any rules of thumb.
> >>
> >>If you are interested in the aerodynamics of spinning balls,
> >>or want to try to extend the state of our knowledge of
> >>aerodynamics as applied to aircraft design, then by all
> >>means, keep on looking at dimples.
> >>
> >>However, if your real interest is in reducing the drag of an
> >>aircraft, you'd be better off studying up on laminar flow
> >>and interference drag. There is enough information out
> >>there in the glider community on fairings, control seals,
> >>inexpensive laminar flow testing techniques (old motor oil,
> >>pieces of yarn, microphones or stethoscopes) to keep you
> >>busy for a long time and which will really produce drag
> >>reduction.
> >>--
> >>T o d d P a t t i s t
> >>(Remove DONTSPAMME from address to email reply.)
> >>
> >>Make a commitment to learn something from every flight.
> >>Share what you learn.
> >
> >
> > Well, I already know a lot of the rules of thumb for drag reduction,
> > especially with laminar flow, and that is my first choice for choosing
or
> > building an airplane.
> >
> > I am also interested in general aerodynamics, and am somewhat intrigued
by
> > the issue of dimples. Particularly, grooves and dimples could be quite
> > interesting as related to propellers. Regrettably, there is a /very/
finite
> > limit to the percentage of time I can devote to that, so my progress may
be
> > gradual.
> >
> > Regards,
> > Peter
> >
> >
>
> All we need is a wind tunnel...
>
You're right. Then we could prove a lot one way or the other--especially if
a little smoke was part of the system. There would still be the effects of
scale and Reynolds number, which are supposed to be quite significant, but a
lot could still be learned. At least it should be possible to either verify
or deny the assertion that grooved or dimpled props produce a virtual
"switch pitch" effect.

Maybe next year.

Regards,
Peter

[Morgans]

"Peter Dohm" > wrote

> You're right. Then we could prove a lot one way or the other--especially
> if
> a little smoke was part of the system. There would still be the effects
> of
> scale and Reynolds number, which are supposed to be quite significant, but
> a
> lot could still be learned. At least it should be possible to either
> verify
> or deny the assertion that grooved or dimpled props produce a virtual
> "switch pitch" effect.
>
> Maybe next year.

I would be willing to bet a month's salary that at *least* one of the big
prop makers have done all of this kind of research.

After all, these companies strive to eek out hundredths of a percent
improval of propeller efficiency.

Any takers?

April Fools! (so I'm a little late, sue me! <g>) I'm too poor (and not
enough of a gambler) to risk any of my salary, even if it is a "sure thing"
bet! <g>

Still my point stands. Me thinks that if these tricks have not shown up on
your manufactured props, the gain is not significant enough to be worth the
effort of incorporating them into the props.
--
Jim in NC

[Peter Dohm]

"Morgans" > wrote in message
...
>
> "Peter Dohm" > wrote
>
> > You're right. Then we could prove a lot one way or the
other--especially
> > if
> > a little smoke was part of the system. There would still be the effects
> > of
> > scale and Reynolds number, which are supposed to be quite significant,
but
> > a
> > lot could still be learned. At least it should be possible to either
> > verify
> > or deny the assertion that grooved or dimpled props produce a virtual
> > "switch pitch" effect.
> >
> > Maybe next year.
>
> I would be willing to bet a month's salary that at *least* one of the big
> prop makers have done all of this kind of research.
>
> After all, these companies strive to eek out hundredths of a percent
> improval of propeller efficiency.
>
> Any takers?
>
> April Fools! (so I'm a little late, sue me! <g>) I'm too poor (and not
> enough of a gambler) to risk any of my salary, even if it is a "sure
thing"
> bet! <g>
>
> Still my point stands. Me thinks that if these tricks have not shown up on
> your manufactured props, the gain is not significant enough to be worth
the
> effort of incorporating them into the props.
> --
> Jim in NC
>
>
The issue is certainly not in first place on my priority list. But I am not
ready to suppose that it can't be done, nor that it hasn't been done.

There seem to me to be good and sufficient reasons to suppose that the big
porp makers might *not* give much effort to certifying and announcing higher
performance props for the low end of the performance spectrum. For example,
if the effect is sufficient to be really usefull on a 100 to 115 Kt
airplane, it might also make the performance of the prop more sensitive to
surface condition. In addition, if applied to SLSA, it could become more
tedious to certify within the limitation on maximum speed--and there are
already some which require aerodynamic faults introduced for the US market
with their existing props.

That leaves the Cessna 172 as the only obvious candidate for which anyone
might certify and announce such a prop. Remember that the major prop
manufacturers are primarily in the business of certified props for certified
engines which qualify for single engine night and IFR flight. It has been
done before; the Cessna 150 received a Clark-Y prop, which was regarded as a
fairly new improvement, shortly before it was replaced by the Cessna 152.

I am curious, but not holding my breath.
Peter

[Morgans]

"Peter Dohm" > wrote

> That leaves the Cessna 172 as the only obvious candidate for which anyone
> might certify and announce such a prop. Remember that the major prop
> manufacturers are primarily in the business of certified props for
> certified
> engines which qualify for single engine night and IFR flight. It has been
> done before; the Cessna 150 received a Clark-Y prop, which was regarded as
> a
> fairly new improvement, shortly before it was replaced by the Cessna 152.
>
> I am curious, but not holding my breath.

Fair enough. Go for it, then let us know!
--
Jim in NC

[Drew Dalgleish]

On Fri, 16 Jun 2006 00:40:30 -0400, "Morgans"
> wrote:

>
>"Peter Dohm" > wrote
>
>> You're right. Then we could prove a lot one way or the other--especially
>> if
>> a little smoke was part of the system. There would still be the effects
>> of
>> scale and Reynolds number, which are supposed to be quite significant, but
>> a
>> lot could still be learned. At least it should be possible to either
>> verify
>> or deny the assertion that grooved or dimpled props produce a virtual
>> "switch pitch" effect.
>>
>> Maybe next year.
>
> I would be willing to bet a month's salary that at *least* one of the big
>prop makers have done all of this kind of research.
>
>After all, these companies strive to eek out hundredths of a percent
>improval of propeller efficiency.
>
>Any takers?
>
>April Fools! (so I'm a little late, sue me! <g>) I'm too poor (and not
>enough of a gambler) to risk any of my salary, even if it is a "sure thing"
>bet! <g>
>
>Still my point stands. Me thinks that if these tricks have not shown up on
>your manufactured props, the gain is not significant enough to be worth the
>effort of incorporating them into the props.
>--
>Jim in NC
>
>
I'm sure dimples would work on propellers my plane definatly flies
slower after I clean the bugs off the prop and bugs are just dimples
in reverse. ;)

[cavelamb]

Drew Dalgleish wrote:

> On Fri, 16 Jun 2006 00:40:30 -0400, "Morgans"
> > wrote:
>
>
>>"Peter Dohm" > wrote
>>
>>
>>>You're right. Then we could prove a lot one way or the other--especially
>>>if
>>>a little smoke was part of the system. There would still be the effects
>>>of
>>>scale and Reynolds number, which are supposed to be quite significant, but
>>>a
>>>lot could still be learned. At least it should be possible to either
>>>verify
>>>or deny the assertion that grooved or dimpled props produce a virtual
>>>"switch pitch" effect.
>>>
>>>Maybe next year.
>>
>>I would be willing to bet a month's salary that at *least* one of the big
>>prop makers have done all of this kind of research.
>>
>>After all, these companies strive to eek out hundredths of a percent
>>improval of propeller efficiency.
>>
>>Any takers?
>>
>>April Fools! (so I'm a little late, sue me! <g>) I'm too poor (and not
>>enough of a gambler) to risk any of my salary, even if it is a "sure thing"
>>bet! <g>
>>
>>Still my point stands. Me thinks that if these tricks have not shown up on
>>your manufactured props, the gain is not significant enough to be worth the
>>effort of incorporating them into the props.
>>--
>>Jim in NC
>>
>>
>
> I'm sure dimples would work on propellers my plane definatly flies
> slower after I clean the bugs off the prop and bugs are just dimples
> in reverse. ;)


Well, let's postulate something ...

A LONG, slow turnng propeller,
pretty wide chord.

Tips are turning about the same sped a golf ball flies (get it?)

Dimpling the prop might produce amazing results.

But the prop on a 172?
Probably not a lot of help because the velocity is way above RN(crit).


Richard

[cavelamb]

karel wrote:

> because dimples don't have wings either?
>
>

Mary sez it's all the work of Lift Demons,
That's her story, and she's sticking to it.