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      A Few Simple Rules   05/22/2017

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ProaSailor

AC62 Wing

57 posts in this topic

Using only the model I had, I made a little GH (Grasshopper) script to compare the length of the flap trailing edges (the red lines) when they are flat vs. "twisted" - using the same angles mentioned in the rules discussion thread (-26 degrees at bottom to +18 degrees at top). Twisted, they stretch between 0.4" (top) to 1.1" (bottom), or about 2% to 3% longer.

flap_stretch.png

To make the old model better, I used only two GH components to divide each flap axis by ten and create a "plane" at each point, perpendicular to the axes. One more GH component ('SubSet') sifted out the planes at the end of each axis:

gh_flap_sections.pngflaps_divided.png

A bit more effort to intersect those planes with the original flap surfaces to produce nine intermediate foil sections per flap, then rotate them "appropriately":

flaps_divided_sections.pngflaps_divided_sections_twist.png

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Then more effort to loft them with the end curves - most precise yet:

 

AC62_wing_reverse_Jun25c.png

AC62_wing_reverse_Jun25b.png

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At forty-four degrees difference between top and bottom ends, that's an average of eleven degrees "twist" per flap (~25'), or about one degree of rotation per intermediate section drawn above, every ~0.77 meters (~30").

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Awesome stuff - I have no idea how it works, but impressive, none the less.

 

PS: Lots of people complained about "línea amarilla" - but nobody is complaining now!

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Totally awesome. Googling grasshopper now.

 

Grasshopper is a fantastic programming tool for Rhino CAD. Incredible power, yet simple and fun to learn. All Rhino CAD operations appear as GUI widgets that you connect with "wires", passing "geometry" through a long series of steps. Each step copies the geometry from the previous step so part of the basics are disabling preview mode for all widgets but the ones you want to see.

 

When you get what you like, you "bake" the GH widget(s) representing the geometry you want to see as "real" Rhino curves and surfaces.

 

Grasshopper has many other operations (as widgets) you expect in a programming language, like list management, sorting, logic, etc.

 

Can get weird and mysterious working with parallel data paths between GUI widgets. It eventually helps to get into the weeds and understand 'Path Mapper' for selection and mapping of indices to get a subset of the "data tree".

 

I love it!

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^

I'll take your word for it :D Me, I merely enjoy your end results

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Very, very cool thing to be into. And +1 to Xlot.

 

Would love to see an animation of the wing twisting, if you're up to that effort.

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flat_twist_Jun26.png

 

I fixed a slight misalignment in the flap trailing edges, then realized that they are slightly longer as an arc than the straight lines I measured previously.

 

So I updated the GH compare script to measure both length of trailing edge and surface area of flaps. Slightly more "stretch", still not much - I was off by a factor of ten in percentage stretch yesterday - it's only 0.3% to 0.4% stretch in twisted vs. flat!

 

flap_stretch_gh.png

 

Flap surface areas shown are for one side only ("Area"/2).

 

 

AC62_wing_reverse_Jun26a.png

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Would love to see an animation of the wing twisting, if you're up to that effort.

There are manual steps to the process... And many ways to trim the flaps... So skipping the surface lofting, here are animations showing plus/minus 25 degrees at five degree increments, for three "graph mapper" conditions:

  • zero twist
  • conventional twist
  • reverse twist

wing_anim1.gifwing_anim2.gifwing_anim3.gif

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Wow!! Thank you, that is very very cool.

 

Any chance of a wind-trail animation? Bet that would take a fancy widget in the GH workflow..

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Next question: how would you like to control one of these wings yourself - and what do you think the controls might look like?

 

We could see Langford working the sheet - but how and who is controlling the twist?

 

Amazing imagery btw.

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Pretty sure Kyle and Glenn had buttons for the other controls.

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Buttons labeled what?

 

From looking at these pretty pictures one could imagine controls for flap offset port and starboard. But if it's a button, then one push represents n degree offset - like foil control?

 

So you might end up with two buttons for the top flap and two buttons for the bottom.

 

But what about maneuvers - where you want to mirror image the whole thing - nice and smooth?

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flap_stretch_gh.png

Fixed two copy/paste unit conversion errors related to area, and updated the graphic. The sq. meters and percentage were correct, the sq. centimeters and sq. inches were wrong.

 

Still, 48 square inches on a flap that is ~25' tall by ~10' fore/aft isn't much stretch at all. 48 sq.inches divided by ten feet is a gap of less than ~1/2" average? One inch at the trailing edge, zero at the axis? Intriguing... "easy" to fill that gap.

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Any chance of a wind-trail animation? Bet that would take a fancy widget in the GH workflow..

Yes sir. At a range of wind speeds and trim configurations, of course. My Virtual Wind Tunnel plugin is right here... oh, sorry, don't have one. Glad to work with anyone who does,.

 

Seriously, any fancy rendering, including all the basic Rhino view modes (Shaded, Render, Technical, X-Ray, etc.) don't work on GH previews like I used in these animations, only on "baked" surfaces. So any of that requires baking the whole wing in a series of separate layers - every five degrees of rotation, for example - before even starting any kind of serious "rendering" for animation.

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Next question: how would you like to control one of these wings yourself - and what do you think the controls might look like?

 

We could see Langford working the sheet - but how and who is controlling the twist?

 

Amazing imagery btw.

 

These are great questions. I designed my GH "circuit" for controlling twist to be proportional and symmetrical, providing the "mirror image" effect; the twist gradient is applied to either side, it has zero effect in the middle, more effect as rotation angle increases.

 

At first, one might think a separate control for each of the five "end curves" would be handy. The curves in yellow, top and bottom of each flap:

 

flat_twist_Jun26.png

 

What I've noticed though is that even in the extreme "reverse twist" case on the right, these control curves always form a smooth spiral arc connecting their trailing edges. A simple arc can be determined using only the difference between the top and bottom curves - one control. The intermediate three end curves (flap joints) would be slaved to follow the spiral. The spiral could be more complex, if necessary, by adding a single control point in the middle to shape the slope by moving it up or down.

 

One more control is needed to set the angle of the bottom end curve relative to the wing spar. The top four flap end curves are all set relative to the bottom one so moving the bottom one affects them all.

 

And there is wing spar rotation, of course. So at a minimum, three controls would be enough - four to get more complex twist.

 

In theory... B) Easy with software and hydraulics. There have been some clever mechanical wing control systems around for awhile. I'd like to know more about how they work?

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Next question: how would you like to control one of these wings yourself - and what do you think the controls might look like?

 

We could see Langford working the sheet - but how and who is controlling the twist?

 

Amazing imagery btw.

 

These are great questions. I designed my GH "circuit" for controlling twist to be proportional and symmetrical, providing the "mirror image" effect; the twist gradient is applied to either side, it has zero effect in the middle, more effect as rotation angle increases.

 

At first, one might think a separate control for each of the five "end curves" would be handy. The curves in yellow, top and bottom of each flap:

 

flat_twist_Jun26.png

 

What I've noticed though is that even in the extreme "reverse twist" case on the right, these control curves always form a smooth spiral arc connecting their trailing edges. A simple arc can be determined using only the difference between the top and bottom curves - one control. The intermediate three end curves (flap joints) would be slaved to follow the spiral. The spiral could be more complex, if necessary, by adding a single control point in the middle to shape the slope by moving it up or down.

 

One more control is needed to set the angle of the bottom end curve relative to the wing spar. The top four flap end curves are all set relative to the bottom one so moving the bottom one affects them all.

 

And there is wing spar rotation, of course. So at a minimum, three controls would be enough - four to get more complex twist.

 

In theory... B) Easy with software and hydraulics. There have been some clever mechanical wing control systems around for awhile. I'd like to know more about how they work?

 

Lots of photos and some schematics of the AC45 mechanical (string-drive) controls in the 'News from the Viaduct thread' IIRC - although there was no revolution, just a fully engineered serial production of what had been done by hand in 'C's etc before.

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^

Apart from scale, I believe the original Hubbard (self-tacking) design could not manage reverse camber

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I would look for some way to induce twist that is independent of camber angle, effectively twisting the top without moving the bottom. Then you can independently change camber (the angle relative to the wing spar of the bottom edge of the bottom flap), making reverse twist possible.

 

This pic gives some clues - found here:

 

DSC00102a.jpg

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I revised my GH wing control script, scrapped the mysterious graph mapper (which had controls of its own) to implement three "simple" controls as described earlier. It is a "beginner's mind" approach, maybe naive and impractical. I left out some important internal details for now; they seem relatively straightforward, given the control lines available.

These diagrams show two tillers mounted apart from the wing, probably controlled by lines attached to winches (not shown). They don't need to be tillers, they could be a pair of traveler tracks or any convenient arrangement to act as quadrants, pulling a pair of lines back and forth, up and down through the mast pivot point, as shown.

ctrls_Jun28a.png


The blue one (bottom with ball) controls camber - literally the "camber boom" at the bottom of the wing, the bottom edge of the bottom flap.

The green one (top) controls the angle of the top edge of the top flap, relative to the "camber boom" at the bottom. It is the twist control. Three flap joint angles in between top and bottom are split evenly. It can be confusing because unlike the top edge it controls, the angle of the green tiller is always relative to the boat in this scenario. It means that when the green tiller is in the middle, there is no twist, the camber angle will be used all the way to the top.

The third control, wing rotation, is not shown in these diagrams. Any conventional wing tiller arrangement will do.

The three controls work independently of each other.

wing_anim_Jun28a.gif

Controls at bottom of wing, top of wing is at bottom left of image.

P.S. The pulleys at the base of the mast obviously can't be attached to it; they remain fixed relative to the tillers. The control lines are allowed to twist above...

P.P.S. The animation shows only negative angles on camber and mast rotation and only positive on the top flap (green tiller). All three can be either positive or negative angles. Things don't make sense when the difference between camber and top flap exceed ninety degrees.

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It occurs to me that maybe, in practice, it is preferred to control camber by having lines directly attached to the aft end of the "camber boom", the trailing edge of the bottom flap. That still works for this plan, leaving only one control not attached to the wing - the green tiller for the top end of the flaps, the twist control.

 

I left out a part because it was a little confusing - it is a copy of (and directly controlled by) the green twist tiller. Located at the bottom of the wing, adjacent to and below the camber boom; it rotates with the wing at a fixed angle relative to camber, parallel to the top end. The difference between it and the camber boom is mechanically and evenly split for the angles of the three intermediate flap joints (somehow...).

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really cool! thanks for the drawings. this is the stuff worth reading. sorry, i have no other input.

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Apart from the well known self-tacking advantage, I think you should consider force balance more. That is, one shouldn't have to supply (much) manual power to camber upper flaps. In the Hubbard system, the force on the boom countering the wing sheet is "brought upstairs" by cables to do that. Plus, I'm convinced the flaps trailing edges are connected, and that should transmit a portion of the cambering effort.

 

Indeed, on AC72s little power was taken by wing inner workings, I believe for OR a single cylinder actualed a rather interesting (if still unexplained*) sloping beam.

 

* Not that anybody has yet explained ETNZ's/LR's system, either

 

4d006083f3af7b868b722dcaaef2ba40_zpsc8da

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I suspect that what I have in mind isn't much different from how it's done now. The two external tillers I drew are a distraction. One might be handy for twist control but apparently, on the AC45, they just use a line hanging on the wing. The effect is the same. Twist is simply an adjustment of control line positions between the "camber boom" and the four upper pivot points.

 

Wing-AC45-camber-control-jjga-.jpg

 

from this 2012 article by Jack Griffin.

 

 

At 3:37 in the video, he explains that the small quadrant is the twist control system:

 

ac45_twist_ctrl.jpg

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Another pic. From what I can tell, it's as simple as this - pulling the line/blocks marked in green above returns the small quadrant (purple) to the middle, removing twist because it makes the attached control lines equal length. Easing the line allows the top to twist off because the control lines become longer on one side than the other. The lines attached closest to the quadrant pivot point will be least affected so are for the lowest flap; the control lines attached further aft move more so they go to the top of the wing. There is no way to force it to twist off - easing does that - the only force possible is to trim in.

 

Pull-wing-China-Team-09.jpg

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Another pic. From what I can tell, it's as simple as this - pulling the line/blocks marked in green above returns the small quadrant (purple) to the middle, removing twist because it makes the attached control lines equal length. Easing the line allows the top to twist off because the control lines become longer on one side than the other. The lines attached closest to the quadrant pivot point will be least affected so are for the lowest flap; the control lines attached further aft move more so they go to the top of the wing. There is no way to force it to twist off - easing does that - the only force possible is to trim in.

 

Pull-wing-China-Team-09.jpg

 

Yes, that's how it works - both camber and twist were "limited" on the AC45 wing - you could ease either control to increase camber or twist (assuming enough wind "to blow" in the camber / twist). Trimming the lines returned the respective quadrant to the center line reducing camber / twist to 0°

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Another pic. From what I can tell, it's as simple as this - pulling the line/blocks marked in green above returns the small quadrant (purple) to the middle, removing twist because it makes the attached control lines equal length. Easing the line allows the top to twist off because the control lines become longer on one side than the other. The lines attached closest to the quadrant pivot point will be least affected so are for the lowest flap; the control lines attached further aft move more so they go to the top of the wing. There is no way to force it to twist off - easing does that - the only force possible is to trim in.

 

Pull-wing-China-Team-09.jpg

Yes, that's how it works - both camber and twist were "limited" on the AC45 wing - you could ease either control to increase camber or twist (assuming enough wind "to blow" in the camber / twist). Trimming the lines returned the respective quadrant to the center line reducing camber / twist to 0°

 

Thanks Jack. What got me interested in this, besides the IGES file of the wing, was this comment by Gino Morrelli:

 

"One thing that was possible under the AC72 rule, but now is mandated, is a wing design that can be over-rotated to a negative angle of attack," he said.

It seem to me that the AC45 twist system is clearly not up to that task? And that being able to induce twist without relying on easing alone will be a major change to the control system. Well, maybe not so major - just two lines on that smaller quadrant instead of one, allowing it to be pulled to either side instead of only to the middle.

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The AC45 wing not up to the task? Maybe. They certainly had to add a wing extension after the fact, to broaden the usable wind range/usable locations.

But it seems to me mandating a negative angle of attack in the AC62 is trying for a de-facto reef - trying to get the most from the wing and avoid cancelled races. Something they have learned from experience and which may not apply in other classes of winged boats - who are not trying to sail to a TV schedule!?

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^

The AC45 wing not up to the task? Maybe. They certainly had to add a wing extension after the fact, to broaden the usable wind range/usable locations.

 

My sources said the wing extension did nothing but decrease the righting moment when used.

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^ Yep. it had a bit of the 'agricultural' look to it.

 

What's your take on the need for a reverse camber wing now.. and was the AC45 wing deficient for not having this designed in?

 

They can always chuck that requirement into the AC45 class rule - at the same time they add the full foiling clause! :)

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Before further discussion of controlling "reverse twist" on the AC62, I'd like to summarize what I've learned about how the AC45 wing control system works.

 

My text and arrows on the image found here:

 

AC45_DSC00102a.jpg


And again on an image from a post by nav in this January 2011 thread, Driving Lessons for an AC45:

 

AC45NZ1D8_4411.jpg

 

When the "twist quadrant" is centered, the 3 flap control lines are equal length, port and starboard, so all flap control arms rotate at the same angle as the "camber boom" at the bottom - no twist.

 

It's still not clear to me where the tail end of the camber control line goes, but like the twist control line on the bottom of flap #1 that centers the twist quadrant (removing twist), the effect of trimming is to center the camber boom (removing camber).

 

Easing either control line allows wind pressure alone to increase camber or twist, respectively.

 

On the twist quadrant, note the "1:2" ratio on flap control lines #2 and #3 caused by using a block (an inverse 2:1 because the tail is the load). So in addition to differences in lengths caused by being attached to the quadrant at different radius points, #2 and #3 will change faster than #1. These changes in lengths of control lines are tuned further by the design of each control arm (levers/tillers of arbitrary length). Note how control arm #2 is smaller than the others.

 

A couple of photos found here (thedailysail.com) showing how the control lines emerge above and connect to the flap control arms (aka "yokes").

 

AC45_AC45NZ1D5_1800_800.jpg

AC45_AC45NZ1D5_1796_800.jpg

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You have some great tools there Proa and it's great that you are sussing the control systems, that bodes well for the AC62 graphics to come - but it is a bit like reinventing the wheel.

 

Here are a few bits and pieces you might enjoy...

 

Wing 1:

 

 

First sail:

 

 

Tools:

 

 

A basic animation:

 

 

The circus hits town:

 

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Launch, Oracle:

 

 

Time lapse, Artemis:

 

 

Crew roles, JP Morgan BAR(Oracle 3):

 

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Best thread since the Cup ended.

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To review:

  1. When the twist quadrant is centered (trimmed), there is no twist - the angle at the top matches the camber angle at the bottom.
  2. The twist quadrant is eased to allow twist at the top - the angle at the top reaches zero relative to the the leading edge, resulting in zero lift.
  3. Reverse lift at the top is achieved by continuing to rotate the top in the same direction as easing, twice the angle of easing to zero angle/lift, using force as needed.

wing_anim_Jul4b.gif

 

 

Two consequences of the reverse twist capability are:

  1. need a bigger twist quadrant with at least twice the arc angle.
  2. need two control lines to control the twist quadrant instead of just one.

I can think of a few ways to use two control lines to rotate the quadrant. (A single hydraulic piston could do the job too!)

 

The easiest might be to lead two lines to the same place as the one is now, under the bottom flap, but rigged like traveler car controls.

 

Another would be to lead two lines through the mast pivot to fixed controls (tiller/traveler) that don't rotate with the wing.

 

Or the twist quadrant (bright green below) could be extended with an attached tiller, controlled by a pair of sheets, similar to mainsheet leads, The camber spar is bright blue.

 

reverse_twist_Jul4b.jpg

reverse_twist_Jul4a.jpg

 

I see no value in being able to trim the twist quadrant beyond center. For reverse lift at the top, It needs to be "eased" twice as far, with muscle.

 

I don't think I'm inventing anything or solving engineering issues. Just playing.

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P.S. The twist quadrant I drew has an arc of 100 degrees and the attached tiller is parallel to the top of the trailing element (+-50 degrees relative to the camber boom). But the 1:2 block rigging system for control lines on the AC45 amplifies the rotational effect so the quadrant can be smaller (50 degrees?) and only swing half as far (+-25 degrees?). The AC45 quadrant appears to be roughly a ~36 degree arc?

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The easiest might be to lead two lines to the same place as the one is now, under the bottom flap, but rigged like traveler car controls.

 

Like this - two lines that bring the ends of the quadrant to the center, rotating either direction, a full fifty degrees (+-25):

 

two_ctrl_lines.png

 

two_ctrl_lines_b.png

 

P.S. The blue camber boom is way too thick! 0.1 meter. I'll fix that next time.

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I wonder if the GC32 foil trim control might be adapted to rotate the twist quadrant? (from

)

 

gc32_foil_ctrl.jpg

 

On second thought, the worm gear would not respond to easing as we would like the flaps to do. It must be rotated for movement in either direction. Forget about it.

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Like this - two lines that bring the ends of the quadrant to the center, rotating either direction, a full fifty degrees (+-25):

 

two_ctrl_lines.png

 

two_ctrl_lines_b.png

 

So looking from the top on this animation again, on starboard tack, leading element rotation and camber both locked at twenty degrees:

  • Twist quadrant is centered by pulling yellow line.
  • Easing yellow line allows top of trailing element to rotate off twenty degrees, in direct line with leading element - zero lift.
  • Red line is then pulled to rotate top another twenty degrees, giving negative twenty degrees relative to the leading element, causing reverse lift at top.

wing_anim_Jul4b.gif

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It will help understand better this interesting conversation: definition for plane wings

post-43482-0-09477800-1404613856_thumb.jpg

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In case anyone's interested, the fifty degree twist quadrant depicted above has a radius of 0.644 meter, it's arc length is 0.562 m (22"). Half of that is the distance that the red and yellow lines must trim and ease, +-0.281 meter (+-11"). Allowing 22" total for trim and ease takes only ~21% of the distance between the turning blocks and the end of the camber boom (2.7 meters, 8.9 feet), leaving the remainder (~79%, 2+ meters, ~7 feet) for the action of multi-part blocks attached to the tail ends of the red and yellow twist control lines.

 

The two tail ends of the of the multi-part blocks could still be lead through the front element pivot point, where they would be under less tension than if they had not passed through the blocks first...

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P.S. I re-constructed this animation today using the 50 degree twist quadrant but forgot that it's now designed to turn only half the angle at the top of the trailing edge. So animation is wrong is that respect, quadrant is turning twice as far as intended.

 

wing_anim_Jul4b.gif

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P.S. I re-constructed this animation today using the 50 degree twist quadrant but forgot that it's now designed to turn only half the angle at the top of the trailing edge. So animation is wrong is that respect, quadrant is turning twice as far as intended.

Here is a new one that gets it right, matching the new drawings today. The 50 degree twist quadrant relies on the 1:2 blocks like the AC45 to turn only half as far as the top of the trailing element. It is being used to 80% of its capacity (20 degrees of 25 max.) on one side only.

 

wing_anim_Jul5a.gif

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Brilliant.

 

The 72's used hydraulics to control aspects of the wing, it wasn't all as per the 45's right?

The AC62 rule seems to leaves flap angle unrestricted as far as I can see.

What use do you see negative flap angle being put to Proa?

Have we got any closer to understanding IM's comments re: variation in wing area to suit different venues?

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Depends on how quick and responsive the twist controls are. Reverse twist clearly has potential to keep the boat from tipping over. But it might also increase maneuverability by enabling "snap rolls", a quicker transition during tacking?

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Another large animation - 1.0 Mbyte - but pretty cool:

http://islandcad.com/grasshopper/ac/ac62wing/reverse_twist_tack_Jul6a.gif

Shows a full tack using reverse twist. Note that from the reverse position ("top flap" dial at 40 degrees), all three controls are then changed at exactly the same rate to keep the top of the trailing element at a fixed angle relative to the lead element during the tack. Because reverse twist effectively tacks the top first, so the lead element and camber boom are just catching up.

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Another large animation - 1.0 Mbyte - but pretty cool:

 

http://islandcad.com/grasshopper/ac/ac62wing/reverse_twist_tack_Jul6a.gif

 

Shows a full tack using reverse twist. Note that from the reverse position ("top flap" dial at 40 degrees), all three controls are then changed at exactly the same rate to keep the top of the trailing element at a fixed angle relative to the lead element during the tack. Because reverse twist effectively tacks the top first, so the lead element and camber boom are just catching up.

 

Updated that animation for reverse twist on both tacks.

 

Here is an interactive version of the same thing. Use "Position" slider to choose one of 32 frames or "Delay" slider to change speed of animation (slide full left to zero delay for highest speed).

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As before, twist tacking the top of the wing first, followed by the bottom - viewed from the top:

 

wing_anim_Jul20c.gif

  • flaps rotate +-40 degrees relative to camber
  • camber rotates +-20 degrees relative to forward element
  • forward element rotates +-20 degrees relative to boat

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As before, twist tacking the top of the wing first, followed by the bottom - viewed from the top:

 

wing_anim_Jul20c.gif

  • flaps rotate +-40 degrees relative to camber
  • camber rotates +-20 degrees relative to forward element
  • forward element rotates +-20 degrees relative to boat

 

This texture makes it a lot more simple to see how the top element rotates past the center line (backwinds?).

 

I love the idea you had a couple posts up where a super nimble control system would allow the sailors to really roll tack on the foils.

 

Your next mission, if you choose to accept it, is to model how the boat rotates under the wing and how the foils act in the water; all while going through a tack or gybe.

 

Koukel

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