Why don't wings have dimples?

This supersonic prop project produced some strange results...

http://www.aerospaceweb.org/question...s/q0031b.shtml

http://www.wpafb.af.mil/museum/annex/an48.htm

http://www.1000aircraftphotos.com/Postcards/818.htm

JP


kirjoitti
glegroups.com...

Peter Dohm wrote:

...

Well, I already know a lot of the rules of thumb for drag reduction,
especially with laminar flow, and that is my first choice for choosing or
building an airplane.

I am also interested in general aerodynamics, and am somewhat intrigued
by
the issue of dimples. Particularly, grooves and dimples could be quite
interesting as related to propellers. Regrettably, there is a /very/
finite
limit to the percentage of time I can devote to that, so my progress may
be
gradual.


Check with the powered paraglider people. I've been told that
some of their props have a groove running along the crowned
face of the blade.

A prop is just a wing rotating rapidly around the wing root. But the
effective airspeed of a prop appproaches Mach 1, where compressibility
becomes important.

A supersonic prop would be interesting....

--

FF

("JP" sent links)


Interesting links.

11 of 12 ...hmm?

http://www.wpafb.af.mil/museum/annex/an48.htm
"Between 22 July 1955 and 9 October 1956, two XF-84H prototypes (S/N
51-17059 and 51-17060) made twelve test flights. Eleven of the twelve
flights ended in emergency landings. Sounds produced by the aircraft's
turboprop engine caused nausea and headaches among ground crews, earning the
XF-84H the unofficial nickname "Thunderscreech." Though the XF-84H was the
fastest single-engine propeller driven aircraft ever built, it never
approached supersonic speed. Due to poor performance and high maintenance
requirements, the XF-84H never became operational."

http://www.1000aircraftphotos.com/Mi...epublicF84.htm


Montblack
Ted Striker: Because of my mistake, six men didn't return from that raid.
Elaine Dickinson: Seven. Lieutenant Zip died this morning.

"T o d d P a t t i s t" wrote in message
...
"Peter Dohm" wrote:

I am also interested in general aerodynamics, and am somewhat intrigued
by
the issue of dimples. Particularly, grooves and dimples could be quite
interesting as related to propellers.

I wasn't trying to discourage you from looking into it, just
pointing out that despite a great deal of work that has been
done on golf balls and dimples, it has found little
application in aviation. You'd be going down a path that I
know has been trod before. Perhaps you'd find something new,
but I'd expect it to take a lot of effort. If it were easy
or obvious, it would have been developed before.

I believe that you are right.

BTW, my glider wing *does* have dimples, for reasons
discussed elsewhere in this thread (trips the laminar flow
into turbulent flow).


--
T o d d P a t t i s t
(Remove DONTSPAMME from address to email reply.)

Make a commitment to learn something from every flight.
Share what you learn.

wrote:

cavelamb wrote:

...

Somebody (NASA/University?) built a "tube wing" thing once.

The wing was a large dia tube mounted - well - like a wing.

The tube rotated - "leading edge" up to create a circulation effect.
(as the aircraft moved forward - no hovering allowed this area)

It worked, but drag was a real drag...


Obviously they needed dimples on it...




I wonder if that was ever investigated....




A few years back I saw a TV show about a sailboat using he same
effect. It had big rotating column on the bow. I think the rotation
rate was adjusted to the windspeed and direction to keep the
thrust aligned astern.

Peter Dohm wrote:

The Embry-Riddle link leads to someespecially fascinating discussion,
including that some efects of the dimples are related to Reynolds Number.
However, I clearly have a distance to go before understanding this
subject--even enough to safely apply any rules of thumb.

Thanks,
Peter

"JP" wrote in message
...

Hopefully these links will help you somehow.

http://www.lessonexchange.net/Mech_E...rodynamics.pdf

http://library.thinkquest.org/10556/.../topics/22.htm

http://www.geocities.com/k_achutarao/MAGNUS/magnus.html

http://www.interactiveinstruments.co...CH%20PAPER.htm

http://mercury.pr.erau.edu/~hayasd87.../2004-06-23-W/

JP

"Peter Dohm" wrote in
. net...


I thought that I would be able to find a web site with the wind tunnel
video
that I'm sure I've seen of this; however, for this evening at least, I
must
admit that I have indeed struck out.

This is a subject that I would really like to understand; although I

would

settle for a couple of good practical rules of thumb. If I happen to

find

anything, I'll be sure to post it--or a link as appropriate.

Peter








It's a "stickyness" thing, Peter.

Air is sticky.

It sticks to surfaces.
That's what the boundry layer does.

With the tube rotating leading edge up, the air stuck to the surface of the tube
takes a free ride over the top! (maybe not really, but get the picture?)

Moving, the air attached to the surface exhibits a reduced pressure
(ohnoherewegoagain!)
Sucking the boundry layer down tighter in the process.

Note where the incomming air stream separates.

No rotation would be about centered.
But rotating UP pulls the separation point Down.

Circulation rules apply, and the trailing wake also has a downward vector.
(a result of the Lift Drag Vector)(which is probably not square with anything
but itself, and changes throughout the Lift phase of the flight).

The "Happy Non_Hooker" ball only had dimples in a band around the ball.
Line the band up vertically and smack it square - that's where it goes!
No Hook no slice, because the lift vector is only vertical.

The rules committie outlawed the Non-Hooker because (as they said) it took
the skill out of the game.




Having considered all the ramifications of this over the last few days, I'm
releived that I never took up the "sport"...

Peter Dohm wrote:

"T o d d P a t t i s t" wrote in message
...

"Peter Dohm" wrote:


The Embry-Riddle link leads to someespecially fascinating discussion,
including that some efects of the dimples are related to Reynolds Number.
However, I clearly have a distance to go before understanding this
subject--even enough to safely apply any rules of thumb.

If you are interested in the aerodynamics of spinning balls,
or want to try to extend the state of our knowledge of
aerodynamics as applied to aircraft design, then by all
means, keep on looking at dimples.

However, if your real interest is in reducing the drag of an
aircraft, you'd be better off studying up on laminar flow
and interference drag. There is enough information out
there in the glider community on fairings, control seals,
inexpensive laminar flow testing techniques (old motor oil,
pieces of yarn, microphones or stethoscopes) to keep you
busy for a long time and which will really produce drag
reduction.
--
T o d d P a t t i s t
(Remove DONTSPAMME from address to email reply.)

Make a commitment to learn something from every flight.
Share what you learn.


Well, I already know a lot of the rules of thumb for drag reduction,
especially with laminar flow, and that is my first choice for choosing or
building an airplane.

I am also interested in general aerodynamics, and am somewhat intrigued by
the issue of dimples. Particularly, grooves and dimples could be quite
interesting as related to propellers. Regrettably, there is a /very/ finite
limit to the percentage of time I can devote to that, so my progress may be
gradual.

Regards,
Peter



All we need is a wind tunnel...

because dimples don't have wings either?

Peter Dohm wrote:

"T o d d P a t t i s t" wrote in message
...

"Peter Dohm" wrote:


I am also interested in general aerodynamics, and am somewhat intrigued

by

the issue of dimples. Particularly, grooves and dimples could be quite
interesting as related to propellers.

I wasn't trying to discourage you from looking into it, just
pointing out that despite a great deal of work that has been
done on golf balls and dimples, it has found little
application in aviation. You'd be going down a path that I
know has been trod before. Perhaps you'd find something new,
but I'd expect it to take a lot of effort. If it were easy
or obvious, it would have been developed before.


I believe that you are right.


BTW, my glider wing *does* have dimples, for reasons
discussed elsewhere in this thread (trips the laminar flow
into turbulent flow).



--
T o d d P a t t i s t


Which, if I'm not mistaken, is exactly what the dimples on the ball do...

Dancing Fingers wrote:

I vaguely remember reading that the optimal dimple shape was hexagonal,
rather than round, like the standard golf ball. But the PGA tends to
be conservative in adopting such a radical change. I think spin is
more related to hooking or slicing because golf balls will always
travel further than a comparable spherical ball, without dimples, even
when struck by a machine. The question, for me, is do dimples create
eddy currents of air that reduces drag at slow airspeed? Second, what
is the optimal dimple size relative to the shape of the main body.
Chris


Get a golf ball and measure it.
That's right about optimal dimensions for a golf ball.

The dimples trip the boundry layer at a lower Reynolds Number than
RN(crit) where the boundry layer would separate naturally on a
round (undimpled) ball.

Better?

"cavelamb" wrote

Having considered all the ramifications of this over the last few days,
I'm
releived that I never took up the "sport"...

I never took it up because...

The days my dad came home from work after playing golf, he was always ****ed
off. (for you Brits, that does not mean drunk g)

Why take up a form of recreation, whose primary result is to make you more
uptight? Not me!
--
Jim in NC