Why don't wings have dimples?

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

"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.

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.a...e=source&hl=en

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.

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.

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.

"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" 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.

"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

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 a
-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