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. "

"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

Hi Eunometic and guys.

On Nov 7, 2:59 am, Eunometic wrote:
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. "

I did read the link you posted previously thanks.
I thought about tennis balls (hairy balls :-) too.
Regards
Ken

On Nov 7, 3:59*am, Eunometic wrote:
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. "

None of this is new. When I was into waterskiing way back in
the '80s the best slalom skis had varied textures along the bottom.
Toward the rear the surface was just a little rough, like 1000 grit
sandpaper, which reduced drag on the water. Nearer the front, the
surface was much smoother so that the skier, just by flattening the
ski on the water, could slow down quickly.
I've noticed that when we paint an airplane with the really
shiny smooth urethane paints, it seems to lose a little cruise speed.

Dan

wrote in message
...
On Nov 7, 3:59 am, Eunometic wrote:
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. "

| None of this is new. When I was into waterskiing way back in
| the '80s the best slalom skis had varied textures along the bottom.
| Toward the rear the surface was just a little rough, like 1000 grit
| sandpaper, which reduced drag on the water. Nearer the front, the
| surface was much smoother so that the skier, just by flattening the
| ski on the water, could slow down quickly.
| I've noticed that when we paint an airplane with the really
| shiny smooth urethane paints, it seems to lose a little cruise speed.


Depending upon the size of the aircraft paint can add a considerable weight
burden. However, when the paint is really smooth it can drag along with it
an increasingly thicker layer of turbulent air building toward the aft end
of the aircraft. Dragging this thick turbulent boundary layer causes
increased drag which seems counter-intuitive to smoothness. This is why
various small surface patterns (seems to me somebody should try fractals)
often decrease drag - they decrease the extent of the turbulent boundary
layer thus the drag caused by it.

--
Gregory Hall

Dear Gregor Hall:

"Gregory Hall" wrote in message
...
Depending upon the size of the aircraft paint can add
a considerable weight burden.

The external tank of the space shuttle used to be painted. They
stopped for exaclty this reason.

However, when the paint is really smooth it can

.... [increase] ...

drag along with it an increasingly thicker layer of turbulent
air building toward the aft end of the aircraft.

.... better to say that it allows for earlier boundary layer
separation, essentially increasing the cross sectional area of
the shape.

Dragging this thick turbulent boundary layer causes increased
drag which seems counter-intuitive to
smoothness.

It sure does.

This is why various small surface patterns (seems to
me somebody should try fractals) often decrease
drag - they decrease the extent of the turbulent boundary layer
thus the drag caused by it.

NASA had an aircraft where they sucked air into the upper surface
of the wing, to try and create a "laminar" boundary layer. I
think it took more power than they got extra-lift / reduced-drag.

David A. Smith

"N:dlzc D:aol T:com (dlzc)" wrote in message
...
Dear Gregor Hall:

"Gregory Hall" wrote in message
...
Depending upon the size of the aircraft paint can add
a considerable weight burden.

The external tank of the space shuttle used to be painted. They stopped
for exaclty this reason.

However, when the paint is really smooth it can

... [increase] ...

drag along with it an increasingly thicker layer of turbulent
air building toward the aft end of the aircraft.

... better to say that it allows for earlier boundary layer separation,
essentially increasing the cross sectional area of the shape.

Dragging this thick turbulent boundary layer causes increased drag which
seems counter-intuitive to
smoothness.

It sure does.

This is why various small surface patterns (seems to
me somebody should try fractals) often decrease
drag - they decrease the extent of the turbulent boundary layer thus the
drag caused by it.

NASA had an aircraft where they sucked air into the upper surface of the
wing, to try and create a "laminar" boundary layer. I think it took more
power than they got extra-lift / reduced-drag.

David A. Smith


Probably reduced lift as well. Seems to me sucking air into the upper
surface of the wing would degrade the low pressure caused by the Bernoulli
effect because it would tend to slow down the sped-up air traveling across
the top surface of the wing.

http://www.av8n.com/how/htm/airfoils.html

--
Gregory Hall

"N:dlzc D:aol T:com (dlzc)" wrote

NASA had an aircraft where they sucked air into the upper surface of the
wing, to try and create a "laminar" boundary layer. I think it took more
power than they got extra-lift / reduced-drag.

I was reading about that one, just a few days ago.

It said one of the largest problems was keeping the vent holes open, from
bugs and stuff, and rain changing the laminar flow.
--
Jim in NC

"Gregory Hall" wrote in message
...

snip

| I've noticed that when we paint an airplane with the really
| shiny smooth urethane paints, it seems to lose a little cruise speed.


Depending upon the size of the aircraft paint can add a considerable
weight burden. However, when the paint is really smooth it can drag along
with it an increasingly thicker layer of turbulent air building toward the
aft end of the aircraft. Dragging this thick turbulent boundary layer
causes increased drag which seems counter-intuitive to smoothness. This is
why various small surface patterns (seems to me somebody should try
fractals) often decrease drag - they decrease the extent of the turbulent
boundary layer thus the drag caused by it.

--
Gregory Hall


During WWII they decided to repaint the Spitfire with a flat matt finish
paint so it would be harder to see at night.
It worked, they were harder to see at night. They lost 20mph because of the
increased drag of the matt finish paint.
If you noticed a loss in cruise speed with a slick paint job, I would
suspect your data collection procedures.

Paint can add considerable weight to the aircraft. What in the world makes
you think a smooth surface causes the
thickness of the boundary layer to increase? Have you been mislead by the
installation of Vortex Generators to stir
up the boundary layer?

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

"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.