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Why don't wings have dimples?



 
 
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  #1  
Old June 12th 06, 12:52 AM posted to rec.aviation.homebuilt
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Default 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

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  #2  
Old June 12th 06, 01:06 AM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?

"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.


  #3  
Old June 12th 06, 01:18 AM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?


"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


  #4  
Old June 12th 06, 01:42 AM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?


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


  #5  
Old June 12th 06, 02:32 AM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?


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".

  #6  
Old June 12th 06, 04:28 AM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?

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/19...-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



  #7  
Old June 12th 06, 06:57 AM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?

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

  #8  
Old June 12th 06, 08:08 AM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?

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.

Wings produce that downward flow with their shape.
  #9  
Old June 12th 06, 02:07 PM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?

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

  #10  
Old June 12th 06, 03:10 PM posted to rec.aviation.homebuilt
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Default Why don't wings have dimples?


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

 




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