Why don't wings have dimples?

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

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...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

"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
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.


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

Hopefully these links will help you somehow.

http://www.lessonexchange.net/Mech_E...rodynamics.pdf

http://library.thinkquest.org/10556/.../topics/22.htm

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

http://www.interactiveinstruments.co...CH%20PAPER.htm

http://mercury.pr.erau.edu/~hayasd87.../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" 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

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_E...rodynamics.pdf

http://library.thinkquest.org/10556/.../topics/22.htm

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

http://www.interactiveinstruments.co...CH%20PAPER.htm

http://mercury.pr.erau.edu/~hayasd87.../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

"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

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

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.

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