Dimples On Model Aircraft Could Greatly Extend Range

On Nov 7, 9:35*am, "Ken S. Tucker" wrote:
On Nov 6, 1:44 pm, wrote:



On Thu, 6 Nov 2008 01:54:20 -0800 (PST), in sci.engr.mech "Ken S. Tucker"

wrote:
On Nov 5, 2:40 pm, wrote:
On Wed, 5 Nov 2008 13:59:27 -0800 (PST), in sci.engr.mech "Ken S. Tucker"

Not quite. *As far as riblets go, it is my understanding that the height
and spacing of the riblets is specified according to the boundary thickness
such as to prevent the growth of turbulent bursts which causes an exchange
of low momentum fluid near the surface with higher momentum fluid from
above. This momentum exchange being a loss/drag mechanism. The other point
of importance is the orientation of the riblets along streamlines.

Yes, that's seems clear...but NOT simple :-).

That's a lot different that your original point that it was not well
understood.

Well I think we're nit-picking sematics, my quote,

"My understanding is the theory is NOT _well_ understood,
but is evolving, along with applications, by experimental
feed-back, aka trial & error, (I'm using SM board). "

Note the word "theory"

Also after the original riblet research was performed
similarities to shark scales/skin were observed.
http://ntrs.larc.nasa.gov/search.jsp...de%20matchall&...

Yes! Thanks for those links.
Those papers are experimental results and testing,
AFAIK, there is NO generally accepted theory of the
"riblets effect", though it appears to be evolving.
(If you have a ref to a General Theory of Riblets, I'd
would appreciate a link).

I'm guessing: At a molecular level the riblets control
the turbulent interfacing between fluid and surface
and inhibit the integrated formation of macroscopic
turbulence, such as Eddy's. That micro control is
certainly a quantum relation between molecules in
the fluid and the interacting solid surface, whereby
the micro turbulences are quantized.

Setting aside sharks skin, we may want to have a
look at penguin swimming, that also has very low
resistance.
Regards
Ken

Riblets aren't the only way; hair and feathers have a similar effect.

"With Robert Brodkey, professor of chemical engineering, Koeltzsch has
now turned his attention away from sharks, to penguins and seals. He
hopes to determine whether hair makes these aquatic mammals more
hydrodynamic. Initial studies by other scientists have shown that
natural and artificial fibers can reduce drag by amounts that vary
from 1.5 to 50 percent.

Continued research could show whether hair would improve the design of
boat hulls and even airplanes, Koeltzsch said.

"Wouldn’t it be something if, in the future, airplanes had hairy
surfaces?" he asked. "

Hi m

On Nov 9, 2:26 pm, wrote:
On Thu, 6 Nov 2008 14:35:21 -0800 (PST), in sci.engr.mech "Ken S. Tucker"

wrote:

Well I think we're nit-picking sematics, my quote,

"My understanding is the theory is NOT _well_ understood,
but is evolving, along with applications, by experimental
feed-back, aka trial & error, (I'm using SM board). "

Note the word "theory"

What theory do you mean? It seems it's well understood how to design the
riblets to minimize drag. If you mean the theory of the underlying fluid
dynamics then I wouldn't hold your breath. We still don't have adequate
turbulence models to begin with.

Yes, well turbulence is a problem.

Also after the original riblet research was performed
similarities to shark scales/skin were observed.
http://ntrs.larc.nasa.gov/search.jsp...de%20matchall&...

Yes! Thanks for those links.
Those papers are experimental results and testing,
AFAIK, there is NO generally accepted theory of the
"riblets effect", though it appears to be evolving.
(If you have a ref to a General Theory of Riblets, I'd
would appreciate a link).

Not sure by what you mean by this. The requirements to design the riblets
are known. What more do you want?

We build and fly models (wingspan ~ 24", speed 20 mph)
what riblet would you recommend? We could glue a
sandpaper to the surface of one wing, balance, and
test fly to observe yaw anomally.

I'm guessing: At a molecular level the riblets control
the turbulent interfacing between fluid and surface
and inhibit the integrated formation of macroscopic
turbulence, such as Eddy's. That micro control is
certainly a quantum relation between molecules in
the fluid and the interacting solid surface, whereby
the micro turbulences are quantized.

Fluids as it effects most every situation we deal with, including this one,
deal with the macroscopic properties and not the microscopic or molecular
properties of the media. There is no quantum relationship between the fluid
and the surface in continuum flow which we are addressing here. That only
becomes important in rarefied gas dynamics.

That is where turbulence begins, a vacuum like back
suction.
Pardon the poopy ascii, of a circulation,

Good Air === (going above wing)
/\----------
| |
| |
o--------\/
Surface

"o" is pulled up and cycles around.
Regards
Ken

On Nov 6, 9:40*am, wrote:
On Wed, 5 Nov 2008 13:59:27 -0800 (PST), in sci.engr.mech "Ken S. Tucker"



wrote:
On Nov 5, 1:08 pm, wrote:
On Wed, 5 Nov 2008 12:52:12 -0800 (PST), in sci.engr.mech "Ken S. Tucker"

wrote:


The fundamental studies were done at NASA Langley Research Center *in the
late 70s/early 80s. The first open use of riblets was on *the boat Dennis
Connor (sp?) used to win back the America's Cup, being applied via a
special 3M tape. The wind tunnel test articles from that study reside in
the basement of the building next door to the one the branch I work
resides. I my be wrong but It's possible the same the facility used in the
study was also used for the work leading to the Speedo LZR Racer suit.

German researchers concurrently came up with the same conclusions from
studying
shark skin, they've continued with considerable efforts in 'printing'
them into
UV cured paints and other techniques. In any case the riblet effect
has been
known for over 50 years. http://researchnews.osu.edu/archive/riblets.htm

"Bret Cahill" wrote in message
...
Have they tried dimples on radio controlled aircraft? The size and
speed could designed around the magic Reynolds number = 100,000 where
the coefficient of drag drops precipitously.

Dimpling could vastly extent the range of large and slow as well as
small and fast radio controlled aircraft.

A competitive cyclist is the right size and speed for Nre = 100,000 so
dimple suits can work. Same for golf balls.

Nre = 100,000 for widebodies going 0.5 knots so dimples won't work
except on the runway.

From fluid mechanics the Reynolds number is the ratio of inertial
forces/viscous forces.

N re = Diameter X velocity X density of fluid/viscosity of fluid.


Bret Cahill



Do her dimples make her faster?

http://underscorebleach.net/content/.../p2/arched.jpg

--
Gregory Hall

"Gregory Hall" wrote in message
...
|
| "Bret Cahill" wrote in message
| ...
| Have they tried dimples on radio controlled aircraft? The size and
| speed could designed around the magic Reynolds number = 100,000 where
| the coefficient of drag drops precipitously.
|
| Dimpling could vastly extent the range of large and slow as well as
| small and fast radio controlled aircraft.
|
| A competitive cyclist is the right size and speed for Nre = 100,000 so
| dimple suits can work. Same for golf balls.
|
| Nre = 100,000 for widebodies going 0.5 knots so dimples won't work
| except on the runway.
|
| From fluid mechanics the Reynolds number is the ratio of inertial
| forces/viscous forces.
|
| N re = Diameter X velocity X density of fluid/viscosity of fluid.
|
|
| Bret Cahill
|
|
|
| Do her dimples make her faster?
|
| http://underscorebleach.net/content/.../p2/arched.jpg
|

No, I think it is more likely her dimples would make you faster.