Why don't wings have dimples 2

"Jim Logajan" wrote in message
.. .
Dancing Fingers wrote:
The thing of it is that the car they used, as I remember, also had a
very aerodynamic shape and it still helped.

Disagree - it was not "aerodynamic" on the downstream side.

Do you recall when they showed the wind tunnel and water tank tests?
Do you
recall seeing that there was an area behind the car with turbulent
air?
Well if the car had been elongated so that the body tapered off such
that
it filled that area of turbulence, then I suspect they would have
gotten
different results.

Check out the following site:

http://www.grc.nasa.gov/WWW/K-12/rocket/shaped.html

Notice that the prism has a slightly lower drag coefficient than the
flat
plate. As that web site states "Comparing the flat plate and the
prism, and
the sphere and the bullet, we see that the downstream shape can be
modified
to reduce drag."

I wonder if they would have gotten the same results by attaching a foil
to direct some of the air down from the trunk to make the turbulent area
smaller. Back in the '70s an uncle of mine attached one to the rear of
his station wagon to keep the rear window cleaner. He swore it helped
his gas mileage as well.

--
We have met the enemy and he is us-- Pogo

Anyolmouse

I'm just wondering if any aero student, for their senior or masters
project, ever built a model with dimples and put it in a wind tunnel.
Remember the Mythbusters didn't expect this results based on the dirty
car which got worst mileage. This would suggest that a deliberately
designed airfoil, with certain embedded geometric shapes, could effect
drag under certain conditions.


Chris

"bildan" wrote in message
...
Aerodynamisists have been trying to create "surface treatments" to
improve laminar flow for a century. So far, the mirror smooth
surfaces of sailplanes are best.

There is a guy, a Dr. Sinha, (http://sinhatech.com/) claiming to have
something called a "deturbulator" which is a sort of flexible tape
stuck on wing surfaces. If it works, and survives the rigors of
actual flight operations, it might be a big deal. I wouldn't hold my
breath.

Actually turbulator tape is fairly common stuff on sailplanes In comes in a
zig-zag pattern or with dimples. Scroll halfway down this page to see the
stuff: http://www.wingsandwheels.com/page29.htm
Google "sailplane turbulator tape" for more info.

Vaughn

"vaughn" wrote in message ...

"bildan" wrote in message
...
Aerodynamisists have been trying to create "surface treatments" to
improve laminar flow for a century. So far, the mirror smooth
surfaces of sailplanes are best.

There is a guy, a Dr. Sinha, (http://sinhatech.com/) claiming to have
something called a "deturbulator" which is a sort of flexible tape
stuck on wing surfaces. If it works, and survives the rigors of
actual flight operations, it might be a big deal. I wouldn't hold my
breath.

Actually turbulator tape is fairly common stuff on sailplanes In comes in a
zig-zag pattern or with dimples. Scroll halfway down this page to see the
stuff: http://www.wingsandwheels.com/page29.htm
Google "sailplane turbulator tape" for more info.

Vaughn


It should be noted the exact placement location of "sailplane turbulator tape" varies dependent on the airfoil. The first turbulator tape I place of my HP-14 ruddervators was the "dimpled" variety. (It is less expensive then the zig-zag.) I couldn't see much improvement. That wasn't the case when I upgraded to zig-zag. I only have turbulator tape on the ruddervators. Adding turbulators to the wing airfoil has shown only marginal performance improvement, so I haven't bothered.

Wayne
http://tinyurl.com/N990-6F

On Oct 23, 5:22*am, "Anyolmouse" wrote:
"Jim Logajan" wrote in message

.. .





Dancing Fingers wrote:
The thing of it is that the car they used, as I remember, also had a
very aerodynamic shape and it still helped.

Disagree - it was not "aerodynamic" on the downstream side.

Do you recall when they showed the wind tunnel and water tank tests?
Do you
recall seeing that there was an area behind the car with turbulent
air?
Well if the car had been elongated so that the body tapered off such
that
it filled that area of turbulence, then I suspect they would have
gotten
different results.

Check out the following site:

http://www.grc.nasa.gov/WWW/K-12/rocket/shaped.html

Notice that the prism has a slightly lower drag coefficient than the
flat
plate. As that web site states "Comparing the flat plate and the
prism, and
the sphere and the bullet, we see that the downstream shape can be
modified
to reduce drag."

I wonder if they would have gotten the same results by attaching a foil
to direct some of the air down from the trunk to make the turbulent area
smaller. Back in the '70s an uncle of mine attached one to the rear of
his station wagon to keep the rear window cleaner. He swore it helped
his gas mileage as well.

--
We have met the enemy and he is us-- Pogo

Anyolmouse- Hide quoted text -

- Show quoted text -

Yeah, in the ?50s? the 'Kamm back' was tried on several makes. Hope
that "kamm" is the correct spelling.

Harry K

On Oct 23, 5:22*am, "Anyolmouse" wrote:
"Jim Logajan" wrote in message

.. .





Dancing Fingers wrote:
The thing of it is that the car they used, as I remember, also had a
very aerodynamic shape and it still helped.

Disagree - it was not "aerodynamic" on the downstream side.

Do you recall when they showed the wind tunnel and water tank tests?
Do you
recall seeing that there was an area behind the car with turbulent
air?
Well if the car had been elongated so that the body tapered off such
that
it filled that area of turbulence, then I suspect they would have
gotten
different results.

Check out the following site:

http://www.grc.nasa.gov/WWW/K-12/rocket/shaped.html

Notice that the prism has a slightly lower drag coefficient than the
flat
plate. As that web site states "Comparing the flat plate and the
prism, and
the sphere and the bullet, we see that the downstream shape can be
modified
to reduce drag."

I wonder if they would have gotten the same results by attaching a foil
to direct some of the air down from the trunk to make the turbulent area
smaller. Back in the '70s an uncle of mine attached one to the rear of
his station wagon to keep the rear window cleaner. He swore it helped
his gas mileage as well.

--
We have met the enemy and he is us-- Pogo

Anyolmouse- Hide quoted text -

- Show quoted text -

Ooops that was not a foil, it was a 'chopped' off back. And I think
it was in the 60s.

Harry K

Dancing Fingers wrote:
I'm just wondering if any aero student, for their senior or masters
project, ever built a model with dimples and put it in a wind tunnel.
Remember the Mythbusters didn't expect this results based on the dirty
car which got worst mileage. This would suggest that a deliberately
designed airfoil, with certain embedded geometric shapes, could effect
drag under certain conditions.


Chris

It's not that simple and straight forward.

What SIZE dimples?
Diameter?
Depth?
Located WHERE?

It's not that simple and straight forward.

What SIZE dimples?
Diameter?
Depth?
Located WHERE?

I thought that was the point of research project? Why do golf balls
have dimples in the size and geometry that they do and go from there.
Didn't the the old German Stork have a very rough surface in the nose
area? May thy knew something that we overlook?

On Oct 24, 3:28*am, Dancing Fingers wrote:

I thought that was the point of research project? *Why do golf balls
have dimples in the size and geometry that they do and go from there.
Didn't the the old German Stork have a very rough surface in the nose
area? *May thy knew something that we overlook?

Your general thesis that there is some ancient mystery to aerodynamics
that is not well understood by modern aero engineers and not well
modeled by modern CFD software is humorous but not enlightening.
TANSTAAFL and all that.

"Capt. Geoffrey Thorpe" covered it pretty well when he wrote:

The dimples in a golf ball help reduce drag by making
the boundry layer turbulant which helps it flow just a
little further around the back side and reduce the area
behind the ball where the air flow is seperated (compared
to a laminar boundry layer). Also, the dimples work only
across a limited range of Reynolds numbers (less than
3*10^5).

That's pretty much all there is to it. Where you can get laminar flow,
you hang onto it as long as you can because it offers the lowest drag.
Where the laminar flow starts to stagnate and threatens to form a
separation bubble, you trip it over into turbulent with a feature such
as a vortex generator, a turbulator, a dimple, or whatever, because
turbulent flow has less drag than separated flow.

Thanks, Bob K.