Tim,
Here are three links that describe a rig that's remotely similar to
what you propose. Okay, very remotely.
Instead of chamfered blocks that can flip in either direction, it uses
rigid snowshoe-type frames to create the 25% of the sail as a
double-skinned airfoil that surrounds the mast. It then transitions to
a single skin sail for the other 75%. You don't get the benefit of a
flat windward side, but you do get the benefit of a simpler system that
should reef easily.
http://www.dunnanddunnrealtors.com/Catamaran.html
(see top-view drawings 1/4 of the way down the page)
http://www.woodenboat.com/forum/showthread.php?t=54225
(see a bottom-view photo 1/3 of the way down the page)
http://www.themultihull.com/wharram2/jp1.htm
(see the side-view photo on the far right)
The junk-rig crowd has christened this a "swing-wing junk rig", and
claims it is better to windward than a normal sloop. I can see why one
might call it a swing-wing, but I'm not sure the word "junk" belongs in
the name. You could just as easily call it a swing wing una, or just a
swing wing; junk doesn't appear to describe how it works. Those who use
it sing its praises, but I haven't seen any actual tests or comparisons
with other rigs.
In any case, it's a decent compromise. You can get many of the
benefits of a wing sail, particularly a nice leading edge that can
develop lift without mast-induced turbulence, but also don't have to
worry about how to control sail shape.
The Omer wing sail ( http://www.omerwingsail.com/ ), originally
mentioned in this group by proadude, is a great design, but
unfortunately it requires hydraulics to shape the sail on each tack.
Not only is that more work than I'd like to do, it's also more expense
and complexity. I can't get enthusiastic about a sailboat with a sail
that only works properly when the hydraulics are functioning.
The designs at Wingsails.com ( http://www.wingsails.com/ ) are similar
to the swing wing, but don't seem as if they can be reefed easily. The
last thing I'd want to do during each reef is to inflate/deflate a
bladder, or insert/remove foam padding.
Thus, the swing wing looks like it will function well, and reef,
without much input or effort from the crew. It would need soft
sailcloth, like a Wharram soft wing sail, and therefore wouldn't have
the shape-holding characteristics of reinforced mylar, but would more
than make up for shape issues with the benefits of the wing.
---
You could say it's a more complex equivalent of an extra-large wing
mast with a normal mainsail, and you'd probably be right. If the wing
were situated properly around the center of rotation, you could probably
get a good angle and sail shape without using a mechanical mast
rotator. That wing mast would also provide a lot of flotation in the
event of a possible capsize.
Which leads to two questions:
- What costs less? An 800 cm deep wing mast with sail track and a
normal mainsail, or a round mast with a swing wing sail?
- What's safer to have up as bare poles in a big blow or on a
mooring? The wing mast might create noticeably less drag than the round
mast due to its shape, but I have heard about boats with bare wing masts
starting to sail while moored in crowded harbors.
Any thoughts?
Of course, this isn't meant to stop discussion on the dyna-rig. It's
nice to see Todd continuing his work, as well as Rob planning a test of
his own.
But regardless of the benefits of the dynarig, there's also something
to be said about sails that aren't symmetrical fore-and-aft.
- Mike
Tim Barker wrote:
--- Hi Todd ,JT
Dont know much about various rigs or design but it looks like the dyna
rig shares many of the characteristics of the AYRS or Bolger rig
theres some good stuff on the proa file about various strengths and
weakness' which seem to mirror what Jt is talking about.
Jt your right i think, about a symetrical rig not having a feathered
position but i do think that you can have a soft wing sail that can be
formed to a predetermined camber exactly and repeatably without
resorting to "forcing" battens or using hydraulics as in the Omer wing
sail.
Regardless of wether the sail is double or single skinned couldnt you
use "hinged" segments instead of battens to give the shape ?
Cant draw it so hope i can describe it well enough for you to visualize.
Imagine "cubes " threaded on some spectra line, if the line is tight
the cubes would form a long "solid bar", slacken the line a bit and
hold the end cube and the cubes would form a linear curve. Now imagine
each cube had a raised "D" across one end and a recessed "D" across
the other end, kind of like a jigsaw puzzle piece except they wouldnt
lock, thread them on the line and keep the line tight you have your
solid bar again, only this time because the "d" section in one block
perfectly sits in the recess of the next block you now cant twist the
blocks on the line . Add a little slack in the line and you have a
nice linear curve again but because of the slack it will still be in
both plaines.
However if we take a chamfer off the face of a bloch either side of
the raised "D" of say 3 degrees and do that to each block and thread
them on the line and tension the line we would have a solid bar in one
direction and a linear curve of 3 degrees for each block in line in
the other plane. It would be simple light and incredibly strong as the
loads on the blocks are compression loads not in tension as in
traditionally hinged systems.
>From there you could "program" almost any curve by varying the angle
of the chamfers and the number of blocks.For single skin aerofoils the
chamfers would be the same both sides of the "D". For double skin
"thick" foils you could have chamfers one side of the d and have the
other side unchamfered , this way whichever way you pulled the
trailing edge the top side skin of the wing would form the curved
upper surface and the bottom side skin of wing would form the straight
bottom surface ,or in fact any curve you "programmed" in.
Blocks could be carbon ,plastic or ally extrusion cut into segments.
Or the idea might be compleat and utter crap!
Cheers Tim
In harryproa@yahoogroups.com.au
<mailto:harryproa%40yahoogroups.com.au>, "jjtctaylor" <jtaylor412@>
wrote:
Todd,
Then your your scale testing has confirmed much of what Marchaj
explains
mathematically.
a) You get better lift, Cl, than a una rig. Something on the order
of maximum 1.6 to 1.7.
Versus a typical mainsail without jib which maxes out at 1.2.
b) properly trimmed the rig creates less drag, Cd. which is usually
the biggest culprit for
heeling. Alhough lift vector is perpendicular or slightly forward
of foil centerline thus
close reach we always get some heel.
c) A wing with fixed camber has NO feathered position. Lift and
drag is always acting on
the rig. Messy business in tight situations.
d) There is a sweet spot for lift and it is really small !!!!
Usually a thin film foil tops out at
15 degrees angle of attack, after which the foil stalls and lift
drops to below 1.0 while drag
rises quickly. OK for broad reach, really bad for close reach. So
you have confirmed the
need for active wing tracking. But wing tracking via rudders always
follow the wind, thus
are always suboptimized. You will find rudder size and torque
distance greatly affects the
tracking performance. The rudder size increases drag while smaller
rudders dampen he
response by the square of the distance away from pivot point.
e) Maltese Falcon takes advantage of an array wing which uses the
slot effect between
wings to help reduce the onset of stall.
You can take advantage of Marchaj teachings. Jibs have a huge
affect on lift and
forgiveness for angle of attack. Jibs do NOT have be large. 13% of
the wing chord I think
he explains. Need to address the stall or forever be hassled by
lesser performance. "C"
class boats are VERY actively managed in attempt to keep the wing in
the groove.
So next steps for performance is try some rudders, and some wing
slats at the leading
edge(s) to soften the stall issue. Keep looking for a way to
release the wing camber when
needed. Shoot more videos.
Then scale up you might be appalled at the cost to make a rig
successful. The bearings
alone required for 600 square feet of sail are typically about
$10,000 US. Less won't
work, they bind due to mast deflection or cheaper home-made
materials deform under
the loads.
As usual if it was easy someone would have already done it ! But
the challenge makes it
fun. I'll have a true biplane rig to try and get some slot effect,
but symmetric foils for
feathering. YES BIG BUCKS for bearings !
JT
--- In harryproa@yahoogroups.com.au
<mailto:harryproa%40yahoogroups.com.au>, "tsstproa" <bitme1234@> wrote:
Funny really, They still needed real world testing before crunching
numbers into a computer for a base on what can and can't be done!
Then what publish to all telling what is possible and what is not!
Based only, on their real world experiment.
How much experience do they have in real world testing?
I agree there is a common all around camber for best all around
performance. But even that is somewhat slack. I agree about
controling up wind heeling moment for maximum forward drive. I
believe in turning that heeling force into drive force.
Numbers make it easy to see false truths because its so easy to see
difference + or -.
But real world is where you see the truth which is harder to
calculate by a control number.
Who's controling those who control.
Todd
TSSTPROA
--- In harryproa@yahoogroups.com.au
<mailto:harryproa%40yahoogroups.com.au>, "captian_rapscallion"
<captian_rapscallion@> wrote:
This looks like what I have....
http://syr.stanford.edu/HISWA_Tyler_2002.pdf
<http://syr.stanford.edu/HISWA_Tyler_2002.pdf>
--- End forwarded message ---