How keel winglets really work
 

DSK wrote:
A model
airplane designer would not be concerned with that, though ;)


Now Doug, don't go making fun of model plane designers, remember
"The Flight of the Phoenix", (Shute, IIRC). ;-) One case where
the movie was just as good or better than the book, a rare event.

Cheers
Marty

How keel winglets really work
 

One case where
the movie was just as good or better than the book, a rare event.


ALL James Bond movies were better than ANY James Bond book.

How keel winglets really work
 

Martin Baxter wrote:
Now Doug, don't go making fun of model plane designers,

Sorry, I was not meaning to belittle any model airplane designers. Just
pointing out that a wing keel for a sailboat fulfills a rather different
function... several, actually!

... remember
"The Flight of the Phoenix", (Shute, IIRC). ;-) One case where
the movie was just as good or better than the book, a rare event.

Never read the book, the movie was pretty good. We'll have to ask Peter
W about which is better...

Fresh Breezes- Doug King

How keel winglets really work
 

DSK wrote:
Nav wrote:

If set up with dihedral or when heeled, yes they can -but its small as
their area is small.


I'm not saying you're wrong, but the wing keel designers I've talked
with have never mentioned it. First of all the winglet is mostly
horizontal. Here is where Jax's favorite, the 'sine function' comes
in... if the winglets produce a net lift, then it is going to be mostly
up or down unless the dihedral and/or heel angle gets very large, like
greater than 45 degrees.

Yes, that was my point. Did you see the dihedral on current IACC
winglets? It's up to about 30 degrees (by eye). That neans when the heel
is 30 degrees (a typical 'powered up' design heel angle) one winglet is
horizontal the other within 30 degrees of vertical. The latter winglet
adds some useful keel area. The question I ask you to think about is
which one is controlling the keel tip vortex by a plate effect... The
answer is, of course, that they are too small to do that well and they
are really workin in conjunction with the bulb (that provides an
endplate effect). I don't think I'm giving TNZ design secrets away but,
what these long thin winglets are doing "flying" in the keel vortex
which is why they are at the back of the bulb. They extract lift and
energy from the vortes and increase overall keel efficiency. If they
actually generate a lift (or a torque) in a direction oppostite to that
of the votex then they rob it of energy and return energy to the keel
system (or reduce parasitic drag if you prefer). Second they are not
symmetrical in section. The winglet with the negative angle of attack
generates less negative lift in the vortex than that with the postive
angle. The net effect is postive lift and again vortex energy robbing.

OK?

Cheers MC

How keel winglets really work
 

Sorry, the discussion is getting confused. There are two issues, the
plate effects and winglets that fly. I mentioned AC yachts as examples
of flying winglets -most other boats just have simple plates. See my
discussion of winglets elsewhere in this thread.

Cheers

Matt Colie wrote:

Sorry,

But the wings are an AC keel are not intended to function of an aircraft
winglet. The function of the aircraft application has been effectively
described here, the the wings on a keel have a primary function that is
different. The tip vortices are pretty much confounded buy the huge
bulb (much like an aircraft tip tank will do).

The wings are actually designed to provide additional lift to windward
that is not dependent on the keel blade attack angle.

That is why they pay so much attention to the attack angle of the wings
during the set up and trials. They have to play out a dual between more
angle for more lift to weather when heeled and less angle for less drag
with the boat upright going to leeward.

As the current IACC rules have not allowed this to be trimed underway,
they only get to set it once per race, and if you listen to the
discussions going on the background, you will here them talk about the
adjustment as three-quarters or one-half degree.

Matt Colie (certifications available on request)

Nav wrote:



Oz wrote:

On Mon, 02 Feb 2004 11:27:49 +1300, Nav
scribbled thusly:



DSK wrote:


Navvie wrote:



From: http://www.djaerotech.com/dj_askjd/d.../wingfin1.html




This is from a model airplane web site, and some of the terminology
for
hydrodynamics is rather different. For one thing, we don't talk
about the
"helix angle" of underwater foils. For another, attempting to get a
net
forward (or windward) lift component from keel winglets isn't going
to work
because they have to sail on both tacks.



Yep, that's why they are on both sides.

Cheers




Which chucks you whole spiel out the window.
Ever see a jet with winglets that extend to the lower side of the
wing?



Never flown inverted on a 747-400 no. Come to that I've never flown on
any inverted jet, but if they were flying both sides up with equal
frequency you can bet there would be winglets on top and bottom... It
really isn't all about the end plate effect you know. Look at AC
winglets -its all about controlling the parasitic drag from the keel tip.

OK?

Cheers

How keel winglets really work
 

Peter Wiley and Donal don't read such books Jax.

Cheers

JAXAshby wrote:

One case where
the movie was just as good or better than the book, a rare event.



ALL James Bond movies were better than ANY James Bond book.

How keel winglets really work
 

Nav wrote:
... Did you see the dihedral on current IACC
winglets? It's up to about 30 degrees (by eye). That neans when the heel
is 30 degrees (a typical 'powered up' design heel angle)

what? You need a new protractor. I din't see any IACC boats sailing at
heel angles of over 20 steadily, much less 30. And IMHO 12 ~ 15 is much
more common.

Anyway, I don't remember the details of the keel winglets this time
around, other than one whale tail design that looked cool but I don't
remember which boat it was on.


......The question I ask you to think about is
which one is controlling the keel tip vortex by a plate effect... The
answer is, of course, that they are too small to do that well and they
are really workin in conjunction with the bulb (that provides an
endplate effect). I don't think I'm giving TNZ design secrets away but,
what these long thin winglets are doing "flying" in the keel vortex
which is why they are at the back of the bulb. They extract lift and
energy from the vortes and increase overall keel efficiency. If they
actually generate a lift (or a torque) in a direction oppostite to that
of the votex then they rob it of energy and return energy to the keel
system (or reduce parasitic drag if you prefer).

Does the winglet no produce a tip vortex of it's own? And wouldn't that
counter the one from the main section of keel foil?

Anyway, this is a lot closer to what happens (as I understand it) than
what you were saying the first time around.

... Second they are not
symmetrical in section. The winglet with the negative angle of attack
generates less negative lift in the vortex than that with the postive
angle. The net effect is postive lift and again vortex energy robbing.

OK?

Dude, check your geometry. Each winglet may not be symmetrical, but they
are paired. The overall design *is* symmetrical. Any beneficial effect
they have on keel efficieny is in the area of reduced drag and increased
lift on the main keel section.

If the winglets prodcued net lift themselves, then it would be pulling
the boat down in the water, which would not help speed.

DSK

Cheers MC

How keel winglets really work
 

DSK wrote:
Nav wrote:

... Did you see the dihedral on current IACC winglets? It's up to
about 30 degrees (by eye). That neans when the heel is 30 degrees (a
typical 'powered up' design heel angle)


what? You need a new protractor. I din't see any IACC boats sailing at
heel angles of over 20 steadily, much less 30. And IMHO 12 ~ 15 is much
more common.

Lord, why don't you think about what I write. I said powered up! Next
you will be saying powered up is not where the boat is at max power.

Cheers

How keel winglets really work
 

DSK wrote:

Nav wrote:


... Second they are not symmetrical in section. The winglet with the
negative angle of attack generates less negative lift in the vortex
than that with the postive angle. The net effect is postive lift and
again vortex energy robbing.

OK?


Dude, check your geometry. Each winglet may not be symmetrical, but they
are paired. The overall design *is* symmetrical. Any beneficial effect
they have on keel efficieny is in the area of reduced drag and increased
lift on the main keel section.

Yes, I said the lift was coupling energy back into the keel. Why do you
have to say the same thing and yet not agree?

Now please try to think about it a bit more. Look at the vortex down
it's axis and imagine an (e.g.) Clarke y type section across the vortex.
Does it produce more lift on one side than the other? The key is that
the vortex gives one side of the wing a negative angle of attack and the
other an equally postitive angle of attack. Now couple that to an
assymetric type section (e.g. Clarke Y) and what have you got? Do you
get it now?


Cheers

How keel winglets really work
 

Few realize that the lift resulting from a fart puts undue pressure upon the
sphincter.
One must not forget the extra energy garnered from the convergent/divergent
airflow across the sphincter. Is mass conserved in this case?



"Nav" wrote in message
...


The Professor wrote:


What happens when , at low airspeed, one injects air into the airflow?


Depends on injection flow rate and position doesn't it? If it's a fart
people may complain.

Cheers