Why don't wings have dimples?

"cavelamb" wrote in message
ink.net...
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...

You're right. Then we could prove a lot one way or the other--especially if
a little smoke was part of the system. There would still be the effects of
scale and Reynolds number, which are supposed to be quite significant, but a
lot could still be learned. At least it should be possible to either verify
or deny the assertion that grooved or dimpled props produce a virtual
"switch pitch" effect.

Maybe next year.

Regards,
Peter

"Peter Dohm" wrote

You're right. Then we could prove a lot one way or the other--especially
if
a little smoke was part of the system. There would still be the effects
of
scale and Reynolds number, which are supposed to be quite significant, but
a
lot could still be learned. At least it should be possible to either
verify
or deny the assertion that grooved or dimpled props produce a virtual
"switch pitch" effect.

Maybe next year.

I would be willing to bet a month's salary that at *least* one of the big
prop makers have done all of this kind of research.

After all, these companies strive to eek out hundredths of a percent
improval of propeller efficiency.

Any takers?

April Fools! (so I'm a little late, sue me! g) I'm too poor (and not
enough of a gambler) to risk any of my salary, even if it is a "sure thing"
bet! g

Still my point stands. Me thinks that if these tricks have not shown up on
your manufactured props, the gain is not significant enough to be worth the
effort of incorporating them into the props.
--
Jim in NC

"Morgans" wrote in message
...

"Peter Dohm" wrote

You're right. Then we could prove a lot one way or the
other--especially
if
a little smoke was part of the system. There would still be the effects
of
scale and Reynolds number, which are supposed to be quite significant,
but
a
lot could still be learned. At least it should be possible to either
verify
or deny the assertion that grooved or dimpled props produce a virtual
"switch pitch" effect.

Maybe next year.

I would be willing to bet a month's salary that at *least* one of the big
prop makers have done all of this kind of research.

After all, these companies strive to eek out hundredths of a percent
improval of propeller efficiency.

Any takers?

April Fools! (so I'm a little late, sue me! g) I'm too poor (and not
enough of a gambler) to risk any of my salary, even if it is a "sure
thing"
bet! g

Still my point stands. Me thinks that if these tricks have not shown up on
your manufactured props, the gain is not significant enough to be worth
the
effort of incorporating them into the props.
--
Jim in NC


The issue is certainly not in first place on my priority list. But I am not
ready to suppose that it can't be done, nor that it hasn't been done.

There seem to me to be good and sufficient reasons to suppose that the big
porp makers might *not* give much effort to certifying and announcing higher
performance props for the low end of the performance spectrum. For example,
if the effect is sufficient to be really usefull on a 100 to 115 Kt
airplane, it might also make the performance of the prop more sensitive to
surface condition. In addition, if applied to SLSA, it could become more
tedious to certify within the limitation on maximum speed--and there are
already some which require aerodynamic faults introduced for the US market
with their existing props.

That leaves the Cessna 172 as the only obvious candidate for which anyone
might certify and announce such a prop. Remember that the major prop
manufacturers are primarily in the business of certified props for certified
engines which qualify for single engine night and IFR flight. It has been
done before; the Cessna 150 received a Clark-Y prop, which was regarded as a
fairly new improvement, shortly before it was replaced by the Cessna 152.

I am curious, but not holding my breath.
Peter

"Peter Dohm" wrote

That leaves the Cessna 172 as the only obvious candidate for which anyone
might certify and announce such a prop. Remember that the major prop
manufacturers are primarily in the business of certified props for
certified
engines which qualify for single engine night and IFR flight. It has been
done before; the Cessna 150 received a Clark-Y prop, which was regarded as
a
fairly new improvement, shortly before it was replaced by the Cessna 152.

I am curious, but not holding my breath.

Fair enough. Go for it, then let us know!
--
Jim in NC

On Fri, 16 Jun 2006 00:40:30 -0400, "Morgans"
wrote:


"Peter Dohm" wrote

You're right. Then we could prove a lot one way or the other--especially
if
a little smoke was part of the system. There would still be the effects
of
scale and Reynolds number, which are supposed to be quite significant, but
a
lot could still be learned. At least it should be possible to either
verify
or deny the assertion that grooved or dimpled props produce a virtual
"switch pitch" effect.

Maybe next year.

I would be willing to bet a month's salary that at *least* one of the big
prop makers have done all of this kind of research.

After all, these companies strive to eek out hundredths of a percent
improval of propeller efficiency.

Any takers?

April Fools! (so I'm a little late, sue me! g) I'm too poor (and not
enough of a gambler) to risk any of my salary, even if it is a "sure thing"
bet! g

Still my point stands. Me thinks that if these tricks have not shown up on
your manufactured props, the gain is not significant enough to be worth the
effort of incorporating them into the props.
--
Jim in NC


I'm sure dimples would work on propellers my plane definatly flies
slower after I clean the bugs off the prop and bugs are just dimples
in reverse.

Drew Dalgleish wrote:

On Fri, 16 Jun 2006 00:40:30 -0400, "Morgans"
wrote:


"Peter Dohm" wrote


You're right. Then we could prove a lot one way or the other--especially
if
a little smoke was part of the system. There would still be the effects
of
scale and Reynolds number, which are supposed to be quite significant, but
a
lot could still be learned. At least it should be possible to either
verify
or deny the assertion that grooved or dimpled props produce a virtual
"switch pitch" effect.

Maybe next year.

I would be willing to bet a month's salary that at *least* one of the big
prop makers have done all of this kind of research.

After all, these companies strive to eek out hundredths of a percent
improval of propeller efficiency.

Any takers?

April Fools! (so I'm a little late, sue me! g) I'm too poor (and not
enough of a gambler) to risk any of my salary, even if it is a "sure thing"
bet! g

Still my point stands. Me thinks that if these tricks have not shown up on
your manufactured props, the gain is not significant enough to be worth the
effort of incorporating them into the props.
--
Jim in NC



I'm sure dimples would work on propellers my plane definatly flies
slower after I clean the bugs off the prop and bugs are just dimples
in reverse.


Well, let's postulate something ...

A LONG, slow turnng propeller,
pretty wide chord.

Tips are turning about the same sped a golf ball flies (get it?)

Dimpling the prop might produce amazing results.

But the prop on a 172?
Probably not a lot of help because the velocity is way above RN(crit).


Richard

karel wrote:

because dimples don't have wings either?



Mary sez it's all the work of Lift Demons,
That's her story, and she's sticking to it.