Why don't wings have dimples?

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?

"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...r/golf-01.html
description and a drawing...

http://www.aerospaceweb.org/question...cs/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.

In article ,
"Peter Dohm" wrote:

"Alan Baker" wrote in message
...
In article . com,
"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

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

"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...r/golf-01.html
description and a drawing...

http://www.aerospaceweb.org/question...cs/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

"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

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...r/golf-01.html

description and a drawing...

http://www.aerospaceweb.org/question...cs/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?

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...

"Peter Dohm" wrote in message
news

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message
...
http://www.fi.edu/wright/again/wings...r/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" The Sea Hawk at wow way d0t com wrote in message
news:HvednScQQ67J5A3ZnZ2dnUVZ_oGdnZ2d@wideopenwest .com...


"Peter Dohm" wrote in message
news

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in
message
...
http://www.fi.edu/wright/again/wings...r/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.