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      Abbreviated rules   07/28/2017

      Underdawg did an excellent job of explaining the rules.  Here's the simplified version: Don't insinuate Pedo.  Warning and or timeout for a first offense.  PermaFlick for any subsequent offenses Don't out members.  See above for penalties.  Caveat:  if you have ever used your own real name or personal information here on the forums since, like, ever - it doesn't count and you are fair game. If you see spam posts, report it to the mods.  We do not hang out in every thread 24/7 If you see any of the above, report it to the mods by hitting the Report button in the offending post.   We do not take action for foul language, off-subject content, or abusive behavior unless it escalates to persistent stalking.  There may be times that we might warn someone or flick someone for something particularly egregious.  There is no standard, we will know it when we see it.  If you continually report things that do not fall into rules #1 or 2 above, you may very well get a timeout yourself for annoying the Mods with repeated whining.  Use your best judgement. Warnings, timeouts, suspensions and flicks are arbitrary and capricious.  Deal with it.  Welcome to anarchy.   If you are a newbie, there are unwritten rules to adhere to.  They will be explained to you soon enough.  

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^ Why not just take the output from the accelerometer and let the system take care of things (+ one 'push here now') whenever you reach pre-set limits - digital bungee ;)

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The near future has always engaged the imagination of the geek. What will be the next practical use of high tech polymer products?

 

I remember upgrading to an alloy spar on the dingy when I was 10 years old. I could lift the mast by myself!

 

Imagine a carbon/polymer mix that reverted to a basic shape at rest and when underway changed and tuned itself for stable ride height and performance.

 

The not too distant future.

 

Proper geeks with zits and chronic self-pleasure issues are working on this stuff right now!

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Gust response in rigs is a very common falacy. The loads on rigs come form the available righting moment, basic Newtonian Physics, equal and opposite forces. Any variation in wind can not change the righting moment available from boat and crew, at least not in unballasted boats sailed upright like cats and dinghies. In fact if we allow the cat or dinghy to heal even slightly, the righting moments from crew is reduced, the loads on the rig are also reduced, and the mast or what ever other elastometric device you have will relax, in the opposite direction that you want it to.

 

We respond to gusts by feeling the boat start to heal and easing the sails, or as someone said earlier we anticipate the gust approching and adjust the boat to accommodate it by tightenning the cunningham, easing the sail, or luffing, all good boat handling, but the mast can not do this for you.

 

If we think ETNZ has some automated system its more likely to be linked to some accellerometers in the top of the mast, sensing very slight healing movements, and adjusting the flap accordingly. This could potentially feel movements not perceived by the crew and the hydraulics could certainly respond more accurately and more often than someone with a rope or even a keyboard, considering the size of this rig.

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@ Phil S

 

I can now make the jump from my Laser in gusts to this AC wing, thanks.

 

Does not mean I don't enjoy sailing my Laser on a day like to day (sitting inside doing Tax)!

 

But dreams are free and I imagine my self driving a rally car in some of these good apps.

 

I hope one day we can sail a winged cat at 50+ knots through a course against JS.

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Gust response in rigs is a very common falacy. The loads on rigs come form the available righting moment, basic Newtonian Physics, equal and opposite forces. Any variation in wind can not change the righting moment available from boat and crew, at least not in unballasted boats sailed upright like cats and dinghies. In fact if we allow the cat or dinghy to heal even slightly, the righting moments from crew is reduced, the loads on the rig are also reduced, and the mast or what ever other elastometric device you have will relax, in the opposite direction that you want it to.

 

We respond to gusts by feeling the boat start to heal and easing the sails, or as someone said earlier we anticipate the gust approching and adjust the boat to accommodate it by tightenning the cunningham, easing the sail, or luffing, all good boat handling, but the mast can not do this for you.

 

If we think ETNZ has some automated system its more likely to be linked to some accellerometers in the top of the mast, sensing very slight healing movements, and adjusting the flap accordingly. This could potentially feel movements not perceived by the crew and the hydraulics could certainly respond more accurately and more often than someone with a rope or even a keyboard, considering the size of this rig.

 

A couple of wand based cats and several wand(or feeler based) tris do exactly that-the wand responds instantly to the gust causing downforce on the windward foil(or center foil) and additional lift on the lee foil for the duration of the gust......

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While I am dubious about the benefits of windward downforce on small cats, due to the relaitve narrow beam and added lift (and associated drag) necessary on the leeward side to balance the downforce created, I do understand that the AC50s are trimmig the windward rudder foil to provide some downforce.

 

But of course having the computer change that angle in response to gusts would be against the rules.

 

Tacking and Gybing is another thing all together where they seem to be changing the AoA of both main foils and rudders during the turns as well as raising and lowering the board. And since all the foil adjustments now seem to be via buttons or touch pad controls, who knows what degree of combination or sequencing is happenning. This barely seems to be "Manual Control", certainly a lot more functionality than a wand does.

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Phil and I have had this debate before, I believe the missing piece is roll inertia. That is to say I agree that when the crew is fully kicked out and the boat sailing level, there is no magic "extra" righting moment that permits the rig to somehow blade away. It could be imitated by a kinetic motion, but experience shows that isn't necessary.

The best way to think about roll inertia is to think of the long poles that tightrope walkers use to stabilize themselves. The Cg is on center but but the length of of the pole increases the rotationa moment of inertia, slowing speed with which the walker could rotate around the wire. On a high performance boat, which almost by definition will have long righting lever arm, you can see the same phenomenon. It takes "extra energy" to initiate the rotation that is heeling. This is why gust response is a big deal on boats with racks and trapezes or extreme beam like catamarans, but isn't discussed much on heavier narrower boats. I coach the kids to actually be flattening the boat as the puff hits so that the puff has to reverse the downward movement of the crew and reaccelerate them upward.

 

So the phenomenon is real, it just is described incorrectly, and thus misunderstood.

SHC

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Phil and I have had this debate before, I believe the missing piece is roll inertia. That is to say I agree that when the crew is fully kicked out and the boat sailing level, there is no magic "extra" righting moment that permits the rig to somehow blade away. It could be imitated by a kinetic motion, but experience shows that isn't necessary.

The best way to think about roll inertia is to think of the long poles that tightrope walkers use to stabilize themselves. The Cg is on center but but the length of of the pole increases the rotationa moment of inertia, slowing speed with which the walker could rotate around the wire. On a high performance boat, which almost by definition will have long righting lever arm, you can see the same phenomenon. It takes "extra energy" to initiate the rotation that is heeling. This is why gust response is a big deal on boats with racks and trapezes or extreme beam like catamarans, but isn't discussed much on heavier narrower boats. I coach the kids to actually be flattening the boat as the puff hits so that the puff has to reverse the downward movement of the crew and reaccelerate them upward.

 

So the phenomenon is real, it just is described incorrectly, and thus misunderstood.

SHC

 

That's a great tip, coach.

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Two very good points Steve. Inertia, and anticipation.

 

On small boats we can see the gust approaching by the look of the water. But on big boats most of the gust is way above the water and will not necessarilly show on the surface, in fact at the height of the AC50 rig and in the enclosed sound, the gusts at the top may be completly separate from those on the surface, not just wind sheer but simple turbulance from being downwind of land and buildings.

 

So having something on top of the mast sensing either wind strength and direction, and/or lateral movement would sound like a very good idea. Having it coupled automatically to the trim controls seems like an even better one. Still think this is more likely what we are observing than some elasticity solution.

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Gust response in rigs is a very common falacy. The loads on rigs come form the available righting moment, basic Newtonian Physics, equal and opposite forces. Any variation in wind can not change the righting moment available from boat and crew, at least not in unballasted boats sailed upright like cats and dinghies. In fact if we allow the cat or dinghy to heal even slightly, the righting moments from crew is reduced, the loads on the rig are also reduced, and the mast or what ever other elastometric device you have will relax, in the opposite direction that you want it to.

 

We respond to gusts by feeling the boat start to heal and easing the sails, or as someone said earlier we anticipate the gust approching and adjust the boat to accommodate it by tightenning the cunningham, easing the sail, or luffing, all good boat handling, but the mast can not do this for you.

 

If we think ETNZ has some automated system its more likely to be linked to some accellerometers in the top of the mast, sensing very slight healing movements, and adjusting the flap accordingly. This could potentially feel movements not perceived by the crew and the hydraulics could certainly respond more accurately and more often than someone with a rope or even a keyboard, considering the size of this rig.

Passive gust response has been the reality in windsurfer rigs since the late 80s, and similar passive wingtip control systems have existed in bird wings for millions of years - guess where we stole the idea from? It's no coincidence that one of the other designers I worked with in the 90s had an owl's wing on his desk.

 

I think the speed regime is hugely important in these discussions - we are talking about boats going 30-50kts, and many of the lessons from small dinghies and slower cats simply don't apply at that speed. The reality of extreme speed is the necessity for both constant power, and absolute control of the hull's direction and trim. Anything - chop, sudden gust or shift etc - that knocks you off kilter slows you down. Going to foils largely eliminates the impact factor of chop, thanks to their surface piercing nature, but makes the angle of attack of the entire system far more critical, since at any given time the foils are indexed to the hull and the rig. This means that - if the boat pitches slightly forward, for example - the foils lose lift and down you go.

 

As I've noted, impact with chop etc is largely negated by the use of foils, but what is NOT negated is pitching etc induced by changes in pressure at the tip of the 77' rigid wing. Adding a passively responsive upper flap would both allow you to drive the wing harder without destabilizing flight (more power), and reduce tip vortices (less drag).

 

PS: Steve Clark's point about roll inertia also applies to the pitching axis (longitudinal inertia), and there is also a good deal of momentum associated with going 40 plus knots which also adds some stability to the system.

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The other thing to consider with regards to effective righting moment, is that the majority of crews on skiffs and dinghies are operating just outside the 'optimum max righting moment->power ratio' at any given point of time - be this related to waves, gusts, fitness or mechanical elasticity, or judgement of boat trim/setup.

 

The better guys are closer to that maximum for more of the time, but the human interface is a weak link. The observations of rig/sail response to gusts is often exactly this situation of optimum vs real-time.

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Sorry I am not much of a drawer.

 

Looking from on top of the wing.

 

 

post-66708-0-87097600-1493778883_thumb.jpg

 

Is it possible to have the top of the wing on the other side of the apparent wind,

 

providing both righting moment and a small force forward?

 

As shown

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Whilst not qualified to comment on this topic I appreciate the discussion on this thread. One question I did have is whether in manoeuvres there is the ability to take advantage of a slingshot or catapult effect in pushing the boat through the a tight tack or gybe and use the flicking motion so as not to loose any speed or, the holy grail perhaps, gain it say with a higher entry speed upwind than in the downwind leg just completed? I must say that I am biased and loved the tacking duels of the old AC and have seen very little of that close action with cats...

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Sorry I am not much of a drawer.

 

Looking from on top of the wing.

 

 

attachicon.gifWing forces.jpg

 

Is it possible to have the top of the wing on the other side of the apparent wind,

 

providing both righting moment and a small force forward?

 

As shown

short answer I think is no..

the apparent wind angle increases with height as well which complicates it

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I guess mixing high and low pressure on the same side is it's failure?

there is an issue there, but in general, the force vectors for real aerofoils don't work like that unfortunately!

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Passive gust response was not invented or perfected by windsurfers. It existed and was understood in other sailing classes long before the windsurfer was invented. The sailboard guys discovered it on their own, but they are wrong to believe that they discovered it first.

SHC

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Sorry I am not much of a drawer.

 

Looking from on top of the wing.

 

 

attachicon.gifWing forces.jpg

 

Is it possible to have the top of the wing on the other side of the apparent wind,

 

providing both righting moment and a small force forward?

 

As shown

I had a masthead rigged 1-tonner that had full top 2 battens. In breeze and flat water, the main trimmer could get the top battens popped to weather with the lower portion trimmed normally. It was very fast. Pointed high with reduced heel.

 

Can't get my current frac rig to do the same. Just blade out the main and use the leach.

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Passive gust response was not invented or perfected by windsurfers. It existed and was understood in other sailing classes long before the windsurfer was invented. The sailboard guys discovered it on their own, but they are wrong to believe that they discovered it first.

SHC

I'm not for a moment suggesting that windsurfers invented passive gust response, and I don't know of any designer in the industry that believes they did. In my comment, I noted that such systems have existed in nature for millions of years. But what I will say is that - thanks to relatively deep pockets in the industry throughout the 80s and 90s, and incredibly low prototyping costs - windsurfers have a tremendous amount of experience with such systems, operating in speed regimes (reaching at least, where such systems have the greatest benefit) not that far off what is currently happening in the AC.

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So having something on top of the mast sensing either wind strength and direction, and/or lateral movement would sound like a very good idea. Having it coupled automatically to the trim controls seems like an even better one. Still think this is more likely what we are observing than some elasticity solution.

 

Yeah, but my understanding is that it would be illegal. If that's correct and you can't feed the sensor data back into the algorithm, then the best choice seems to be to have a passive elastic solution for buffering quick fluctuations, and manual input controlling the characteristics of that buffering system.

 

I get the idea that's suggested by some here, that the sensors could place a dot on the wing trimming slider on the tablet and the trimmer would just tap on that dot every second to initiate the human input, but that would take away the most important advantage of a fully automated system, the immediate responsiveness. So with the human delay introduced, I can't see how that would work better than manual control by a top sailor with many years of experience capable of anticipating things that the sensors cannot see. Also, that top sailor could be much more useful having his eyes on the water and the competition and not staring at a red dot on the screen.

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^ Different strokes. I think you will find different degrees of automation being used (ATM) - because some will question some of the same things you have, others simply do not have the capacity

 

An accelerometer is not illegal - also no point in sticking it up the mast - it can do precisely the same job from the most advantageous point in terms of weight and connectability.

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Perhaps there is a little camera at the top of the mast for some cylor to look for hot patches ahead?

 

And of course a cylor could just hold the yes button down ?

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OR's wing rake

 

post-66708-0-50300900-1493842395_thumb.jpg post-66708-0-51114400-1493842414.jpg

AC34 AC35 bow down (Thanks Hobie 16 for picture).

 

Poor design last time? Learning all the time?

 

Cs have wing rake like AC34?

 

They also have a new wing, Can we spot the improvements?

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Is it just me or do we have really good photos from ACEA of the ART and TNZ boats, but not many of OR?

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@ Barnyb

 

You know the referee and the measurers are on OR's team, surely?

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post-66708-0-25644900-1493843624_thumb.jpg

 

The sealing strip is tapered to the back

 

post-66708-0-93981700-1493843667.jpg

 

The sealing strip is parallel.

 

So there are different rakes (between OR and SB others?)

 

And before some one corrects me and ETNZ

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^ Don't think that's ^ all down to rake is it - looks more like different takes on where to put the break between 'wing' and the 'removable panels' - which will both have been included in the o/all OD shape one would expect, otherwise some wings would be bigger than others right?

 

edit - I take it all back, that's a freebe area, as below......

 

 

Nicely done by GTF...

 

8 Mar 2017

AC Class Articles TECH FOCUS #1 - The AC Class rules

Exit the leggy 22-metre spiders, which dominated the race zone in San Francisco in 2013. Farewell to the AC62, which had been hinted at for a while. Make way for the AC Class… On 1 April 2015, it was decided that the 35th edition of the America’s Cup would be held on catamarans with a fixed wing, measuring some fifteen metres or so in length, which is a lot smaller than those from the 2013 edition, as well as being quicker thanks to the use of foils that transform the multihulls into fighter planes. Given the progress made in the design of the appendages, the speeds are virtually identical.

Certain elements of the boat are common to all the competitors, while others can be developed.

 

The framework provided by the official America’s Cup Class (AC Class) measurement

  • The AC Class must measure 15 metres.
  • The maximum permitted beam equates to 8.48 metres.
  • The maximum water draught is 2.40 metres.
  • The wing must measure 23.60 metres high from the mast foot.
  • The shape of the hull below the waterline, the sail width and surface area, the cockpits and the Pod on which the wing sits, are all one-design.
  • The structure of the wing, the appendages (rudders and foils), the electronic and hydraulic control systems and the fairings are free of regulations.

 

m2259_crop169014_1300x765_proportional_1m2260_crop169014_1300x765_proportional_1

Caption:
- white : one-design parts
- red : one-design in shape but free of regulations in structure
- blue : free of regulations parts

Using this framework, Groupama Team France’s engineers, split into different sectors, each worked on optimising the boat’s performance within the limits of the regulations.

The next TECH FOCUS will be on: the wing. See you tomorrow!

 

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@ Nav

 

Thanks.

 

I still think it comes from wing rake then bow down platform at some times (upwind or down wind I've forgotten?)

 

SB's would make it hard to seal to the platform in all positions ?

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In part 4 of Jason Smith's excellent videos of Artemis: @ 1:55 there is a shot of Artemis sailing away from the camera on starboard tack. By luck, Jason is lined up almost perfectly with the centerline. You can see the twist in the flap, evidenced by seeing the Swedish flag on the starboard ( windward) side if the wing. It is easy to project that the top of the wing is cambered in the opposite direction than the bottom of the wing.

This is more profound than wash out, and implies that the Artemis design team has at least decided to give inverting the wing a look, or have embraced the idea. Weather they are pushing the minimum tip wash, or deriving righting moment is hard to tell without looking at the woolies in the wing.

ETNZ on the basis of one video, seems to have the greatest capacity to make fast adjustments of their upper flap, which would be expected with the leg driven hydraulic pumps.

SHC

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Except forestay length is basically fixed - so rake is defined.

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Surf sailer,

 

Are you Barry S by any chance? Or someone else from the Neil pride windsurf program?

Nils R - I worked with Barry for years, we spent hours contemplating his owl wing and 'flying' it around the design loft.

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Except forestay length is basically fixed - so rake is defined.

 

A minute difference between the forestay fastening on the deck or relative height of the mast step would see to that.

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@ Steve,

 

As with all your posts it will take me a long time to digest all the meaning.

 

So slowness of response does not reflect my gratitude for your imput.

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Except forestay length is basically fixed - so rake is defined.

 

A minute difference between the forestay fastening on the deck or relative height of the mast step would see to that.

 

 

The wing deck fitting could surely slide forward or back without altering the forestay length?

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Except forestay length is basically fixed - so rake is defined.

 

A minute difference between the forestay fastening on the deck or relative height of the mast step would see to that.

The wing deck fitting could surely slide forward or back without altering the forestay length?

All these bits are one-design, you can find the numbers in the rules - we won't be seeing massive rake differences in the boats. Yes, small variances available, but nothing that make you look at a side by side photo and say 'wow, look how much rake XYZ are running'.

 

What you are seeing in the skirts on SB and ETNZ are just the result of choices made to the framing in the wing. Look at the next frame up the wing and you can see an angle difference to the bottom.

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@ Rohanoz

 

Look at the diagram above I think you will find the fore deck is free for all?

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In part 4 of Jason Smith's excellent videos of Artemis: @ 1:55 there is a shot of Artemis sailing away from the camera on starboard tack. By luck, Jason is lined up almost perfectly with the centerline. You can see the twist in the flap, evidenced by seeing the Swedish flag on the starboard ( windward) side if the wing. It is easy to project that the top of the wing is cambered in the opposite direction than the bottom of the wing.

This is more profound than wash out, and implies that the Artemis design team has at least decided to give inverting the wing a look, or have embraced the idea. Weather they are pushing the minimum tip wash, or deriving righting moment is hard to tell without looking at the woolies in the wing.

ETNZ on the basis of one video, seems to have the greatest capacity to make fast adjustments of their upper flap, which would be expected with the leg driven hydraulic pumps.

SHC

I think you are spot on with this, but would go further and suggest that Artemis and ETNZ are doing rather different things with the wings. I do believe that Artemis are reversing the top of the wing and making gains because of this, although I am not sure whether it really can be gaining righting moment. With ETNZ, it looks more like they are using the top flap as a power control instead of moving the mainsheet. For me, intuitively, I think the Artemis idea has the most potential and would be a big step forward.

 

The question I would have is how on earth they manage to keep flow hooked up correctly in the lower section and upper section at the same time. All I have read says that starting or keeping flow over a wing is the hardest part. Is it possible to have sensors that tell you when flow is attached or not? Is it simply trial and error, because it seems to me that there are moments when Artemis hits a "turbo" button. Could it be they are constantly adjusting and that they have found it's not slower if they don't have it working perfectly but when it does hook up, wow.

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@kiwing - here's an example how those force vectors are decomposed with standard and inverted trims. Not totally right as you'd be able to trim the lower bits of your wing differently if you have more righting moment to play with but it gives you an idea of where the forces are pointing..

 

You definitely pay a drag penalty but the righting moment from a small force with a long lever might be worth while

 

wing%20vectors_zpsujkfyigr.png

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post-66708-0-07193700-1493856691_thumb.jpgpost-66708-0-36898800-1493856702_thumb.jpgpost-66708-0-78580600-1493856713_thumb.jpgpost-66708-0-26920900-1493856725_thumb.jpg

1.53,1.54.1.55,1.56 sec in Jason excellent video.

 

Can't see what Steve is talking about.

 

But in many places coming or going there is an "S" in the trailing edge of their wing which suggests 3 elements working !

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Rusto,

Great drawings showing the real forces but I think we are talking about much bigger lift/drag ratios, and much finer apparent wind angles. Also at the ratio of boat speed to wind speed of these boats the impact of wind sheer is much reduced so the difference in apparent wind agles between deck and mast top are much less.

So if you adjust your drawings with Lift more like 25 times drag (my guess, Stev might have a better number), reduce deck apparent to maybe 10 deg and mast top apparent to 12 degress, I think the picture becomes much more conventional. I think the impact of reflex will become a huge vector slowing the boat.

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@ Rusto

 

This is going to take some serious time getting my 1968 Physics 2 mind around. (oh the dust and cobwebs !!)

 

But I will, and thank you for stooping to my level to give me a hand.

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@ Phil S

 

Some of that is what my intuitive self was saying but the rational self was saying where are the drawings wrong ? No answer ....

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@ Rusto

 

This is going to take some serious time getting my 1968 Physics 2 mind around. (oh the dust and cobwebs !!)

 

do keep us informed

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@ Rusto

 

This is going to take some serious time getting my 1968 Physics 2 mind around. (oh the dust and cobwebs !!)

do keep us informed

The ghost busters are here !!

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@ Rusto

 

This is going to take some serious time getting my 1968 Physics 2 mind around. (oh the dust and cobwebs !!)

 

But I will, and thank you for stooping to my level to give me a hand.

Haha, there is a fair bit to get your head around...

The way I see it is that your foil produces lift and drag forces (in green and red) which are defined perpendicular and parallel to the onset flow respectively. The resultant in black is the vector sum of those two. Then you can extract the drive and side force components (blue and yellow) from that resultant. Hope that helps!

 

Gets even more interesting when you have to integrate all these force in the height dimension too to get pitch and roll moments :wacko:

One day I'll write some code to do it for a whole wing.. might be able to run a bit of optimisation on it to see how well the inverted trim works.

 

Phil S is right too, some of the angles are a bit exaggerated and the lift to drag ratios are conservative.

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@ Rohanoz

 

Look at the diagram above I think you will find the fore deck is free for all?

Foredeck aero fairing is almost 'free for all' - but the forestay position and jib tack are very tightly defined as it mast base position and height - 20mm tolerance in my reading.

 

But I will put a caveat on my reading of this, in that some of the appendix drawings are still missing from the public files (Appendix E), and rule 13-Rigging appears to have undergone quite a few amendments.

 

I wish it was more open (totally open), so that we could see variations and not just state that of the art as defined by a rule book.

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@ Rohanoz

 

How much rake does 20mm difference in step allow? fixing the forestay deck fitting and rotating the top to calc the rake change?

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Surf sailer,

 

Are you Barry S by any chance? Or someone else from the Neil pride windsurf program?

Nils R - I worked with Barry for years, we spent hours contemplating his owl wing and 'flying' it around the design loft.

Haha! We meta few times years back through Naish importer meetings

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On ‎5‎/‎3‎/‎2017 at 5:13 PM, rusto said:

@kiwing - here's an example how those force vectors are decomposed with standard and inverted trims. Not totally right as you'd be able to trim the lower bits of your wing differently if you have more righting moment to play with but it gives you an idea of where the forces are pointing..

 

You definitely pay a drag penalty but the righting moment from a small force with a long lever might be worth while

 

wing%20vectors_zpsujkfyigr.png

I doubt if these diagrams are the results of any calculations. They show the magnitudes of the forces to be the same for the upper and lower wing sections, giving an exaggerated picture of the importance of the tip. In reality, the upper forces should be smaller, by an amount that depends strongly on the wing's planform & twist distribution (as well as other details of the shape).

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On 4.5.2017 at 4:48 AM, Rohanoz said:

Foredeck aero fairing is almost 'free for all' - but the forestay position and jib tack are very tightly defined as it mast base position and height - 20mm tolerance in my reading.

 

But I will put a caveat on my reading of this, in that some of the appendix drawings are still missing from the public files (Appendix E), and rule 13-Rigging appears to have undergone quite a few amendments.

 

I wish it was more open (totally open), so that we could see variations and not just state that of the art as defined by a rule book.

This might shed some light too... just 1° of rake variation allowed, across the fleet

 

Request for Interpretation No. 78

of

AC Class Rule Version 1.8: November 18th 2016

Rule References:

• There is a note in the top right corner of Drawing ACC-W-1001-REVC RIG AND

SAILPLAN.pdf which reads,

o 2) 'BOTTOM STROP LENGTHS TO BE BUILT TO ACHIEVE A RAKE OF BETWEEN

4o AND 5o, WITH A FORESTAY LOAD OF BETWEEN 3.2t AND 3.4t.

Background:

The note appears to provide a method of determining the length of the strops securing the

upper and lower shrouds.

We are unable to find any specific reference to maximum or minimum allowable rig tensions.

Questions:

1. Is there a maximum limit on permissible rig-tension?

2. If there is a maximum permissible rig tension, how is this determined?

3. Is there a minimum limit on permissible rig-tension?

4. If there is a minimum permissible rig tension, how is this determined?

Background:

The notes in drawing ACC-W-1001-REVC RIG AND SAILPLAN.pdf provide the method to be

followed for stepping the wing with a forestay load of between 3.2 and 3.4 tons and a rake

between 4 and 5 degrees.

Interpretation:

“Rig tension” is not a defined term within the AC Class Rule and although generally understood,

any interpretation referencing it may generate confusion.

1. Forestay tension shall be between 3.2t and 3.4t and wing rake shall be between 4

degrees and 5 degrees, per Drawing ACC-W-1001 REVC. There is no other specified

limit on wing rigging tension. Strops on wing rigging shall be built and lashings shall be

adjusted to attain the specified wing rake and forestay tension, and the lengths of those

strops and lashings shall be measured and recorded by the Measurement Committee.

2. Forestay tension and wing rake will be verified by the Measurement Committee using

methodology agreed between the Measurement Committee and the Competitor, and

may be further specified via a published Measurement Methodology, including methods

for verifying ongoing compliance. No change to the AC Class Yacht that could affect

measured wing rake or the allowed forestay tension shall be made without invalidating

the AC Class Yacht’s current measurement certificate.

3. See answer 1, above.

4. See answer 2, above.

END

Issued by the America’s Cup Measurement Committee on March 9, 2017

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14 hours ago, Doug Halsey said:

I doubt if these diagrams are the results of any calculations. They show the magnitudes of the forces to be the same for the upper and lower wing sections, giving an exaggerated picture of the importance of the tip. In reality, the upper forces should be smaller, by an amount that depends strongly on the wing's planform & twist distribution (as well as other details of the shape).

Haha definitely no calculations involved, just an example to help visualise where the forces on your wing might be pointing for different trims.. plenty of unknowns, uncertainties and assumptions. Definitely keen to hear if you have any thoughts

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@ Rusto

Any chance of a redraw of that wing forces diagram with the suggested (or your own suggestions) as to the likely real forces and angles?

It is hard for me to get all the possibilities sorted into what is likely going on, to get a grip on it, and there are a few of us in the same boat.

Indio just posted some fascinating hydro stuff over in the TNZ thread, getting our imaginations back on track ...

What fun this is, thanks.

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^ Atefooterz

The wing is the engine, this all applies to it too?

ETNZ's wing seems to have relative movement up  the wing, sections moving relative to other sections, particularly the top.

Does this hydro talk of indio's apply to the wing too and is there more advantage applying it to the wing?

Your Video gif would be good if I could do it and find the right bit of ETNZ video.

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Wow some one just stated as if there were no doubt that OR's wing is the best.

Is that an accepted fact and why?

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On 5/3/2017 at 6:32 PM, Phil S said:

Rusto,

Great drawings showing the real forces but I think we are talking about much bigger lift/drag ratios, and much finer apparent wind angles. Also at the ratio of boat speed to wind speed of these boats the impact of wind sheer is much reduced so the difference in apparent wind agles between deck and mast top are much less.

So if you adjust your drawings with Lift more like 25 times drag (my guess, Stev might have a better number), reduce deck apparent to maybe 10 deg and mast top apparent to 12 degress, I think the picture becomes much more conventional. I think the impact of reflex will become a huge vector slowing the boat.

I have studied apparent wind using a formula based off a windsurfer theory on my winged dirtboat. Keep in mind my wings are only 20 to 24' tall. So less wind gradient. The vectors Ive come up with are about 3 to 4 degrees in max wind limit conditions for racing. Around 30mph going down wind around 85 mph. The windier it gets the more difference in angle. Diminished gains in speed as it gets windier due to drag or lateral resistance. Upwind the angle is about 2/3rds of the down wind angle. Over the years I've used almost all my different dirtboats as iceboats too. When Ive had a gps on the top speeds are almost identical. Its hard for some iceboaters to digest that. 

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3 hours ago, Kiwing said:

Wow some one just stated as if there were no doubt that OR's wing is the best.

Is that an accepted fact and why?

Well it's certainly the most bouyant we've seen so far.

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3 hours ago, Kiwing said:

Wow some one just stated as if there were no doubt that OR's wing is the best.

Is that an accepted fact and why?

Given how many different design choices contribute to the overall performance of the boat, it is hard to imagine that we will ever know which wing is better than the other. Same can be said for most of the components IMO. 

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7 minutes ago, Woolfy said:

^ Glad you did. I think it went over jayspers head.:rolleyes:

Nah. Was just trying to answer Kiwing's question. 

Besides being funny I thought it was obvious to most.

I'm still waiting for them to develop wave piercing hulls like Australia did in 95.

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1 minute ago, Woolfy said:

^^ Wave or hull?

 

No no no! THEY want to develop hull piercing hulls!

I want them to develop wave piercing hulls! 

Don't give the picks any more ideas

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1 hour ago, jaysper said:

Nah. Was just trying to answer Kiwing's question. 

Besides being funny I thought it was obvious to most.

I'm still waiting for them to develop wave piercing hulls like Australia did in 95.

I'm sure its not far off. They need to break B1 so they can launch B2 complete with cycles. The recent capcises are getting us used to them doing this so no one crys foul when they go banana for real.

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6 hours ago, Happie Jack said:

Without knowing anything about ice or dirt boats, i would have imagined the same set up being faster on ice with less friction, i guess good wheels & bearings are efficient. So a wing design may top out for max speed but in both modes is there any difference for acceleration (ice to dirt)?

Apart from the relative height lever effect the other main thing about ice/dirt V water is being able to speed up, as a gust hits, not have the lag than can catch out a water sailing platform, especially during manouvers when below true wind speed.

On good smooth hard ice it easier to sail in less wind than on a drylake bed. Less friction and air density may play into that. 

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I was wondering how the AC wings keep from having flutter or oscillation issues with the wings since they don't have positive control systems. Do they have a dampening system to prevent it? Think of wing oscillation as a luffing sail. It is driven side to side by the wind. Usually to self destruction. This can happen to us even parked. I learned this the hard way on my first wing attempt in the 80's. 3 month s to build and 3 seconds to destroy. Here is an extreme example of wing oscillation. This isn't a solid wing just a deep wing mast without the sail on in high winds. He was radared at 78 mph as it unfolded. The spar was controlled by a 3/16'' ss cable connected to a mast rotation limiter. It snapped after he lifted a wheel and  sheeted out allowing the spar to oscillate. 

 

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10 hours ago, Nutta said:

I'm sure its not far off. They need to break B1 so they can launch B2 complete with cycles. The recent capcises are getting us used to them doing this so no one crys foul when they go banana for real.

So, Oracle are a bunch of pricks but I don't understand this conspiracy theory.

It sounds more like you are mocking the theory rather than anything else, but others here seem to think its the real deal.

If they want to switch to cycling, they have plenty of time to modify the existing boat legally rather than turtling it so they can use boat #2.

Besides, which one of those sailors would really want to be on the boat when it folded like a deck of cards, especially after what happened to Bart last time around?

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There are so many Protocol restrictions on what a boat 2 could be, that they didn't even go there. It would for example have to be a carbon copy of (then-current) boat 1 anyway.

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I have a hard time believing the points in the upper left corner, with Cl>2 and Cd<0.04.  The flow is separated on half the flap, and the drag is less than for the small points where the flow is fully attached - really?

I think this video is a good illustration of the role of the slotted flap.  It's job is to decelerate the flow from the main element's trailing edge dumping velocity to the apparent wind velocity, without separating.  At 0:12, the flap tab (#4 element in C-class parlance) is deflected +10 deg, and the pressure increase that would result from attached flow separates the flow.  At 0:15, the flap is deflected more, but the flap tab has a-10 deg deflection, which flattens the pressure distribution and doesn't stress the tired boundary layer so much.  This keeps the flow attached.  At 0:22, the flap has straightened out so it is similar to the existing flaps, and this is about as good as the section can do.  From there, the lift doesn't necessarily get any higher, and the drag goes up as separation sets in.

This is consistent with what I've found using the MSES code to design wingsail sections.  I couldn't make a flap tab (#4 piece) increase the performance, either.  A comparatively thin flap with flat contours for most of the flap worked as well as anything.  

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13 hours ago, jaysper said:

So, Oracle are a bunch of pricks but I don't understand this conspiracy theory.

It sounds more like you are mocking the theory rather than anything else, but others here seem to think its the real deal.

If they want to switch to cycling, they have plenty of time to modify the existing boat legally rather than turtling it so they can use boat #2.

Besides, which one of those sailors would really want to be on the boat when it folded like a deck of cards, especially after what happened to Bart last time around?

More suggesting the unbelievable shouldn't be completely unexpected in this whole Mongolian Clusterfuck...

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Tom: I don't believe it either.

I have been consulting with FlexSys exploring whether their morphing wing technology would benefit our wing design. To do a first level analysis of the benefit, we coerced Ian Hogg and Red Cedar Technology to use their HEEDS optimization software and to give us a sense of whether it was worth the trouble using STAR-CCM+ CFD.  The pay off was a demonstration and presentation at their user conference last fall.  That animation was part of the presentation.  So we demonstrated what could be done with this process and admitted that we didn't believe some of the results. We had some difficulty communicating the operating conditions,  The exercise did  demonstrate that the problem was more complex than "just making the flap assymetrical."

From the Red Cedar web site:

Within HEEDS®, you can easily define design parameters and multidisciplinary design goals, and choose analysis tools to judge a design’s performance. Then, HEEDS performs design iterations automatically while searching for design parameter values that simultaneously meet all targets and criteria. Using advanced, proprietary optimization algorithms and intelligent strategies, HEEDS effectively searches even the most complicated design spaces, helping you to discover better designs, faster.

From what I was able to understand of the process and what I say at the conference, this is very cool stuff. Unfortunately all well beyond my computer literacy but a powerful tool.  I recommend HEEDS to all the Design Bros.

SHC

 

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@ SHC

How I'd love to have met you and watched a C class regatta, I did sail a paper tiger in the late 70s and dreamed of a tornado but Kids and mortgages took over.  A friend has a newish 30foot cat which I go out on and love doing 18 knots with little noticeable sense of speed (wind over the deck compared to water under the net.)

But I have watched that video and video of Cs and they send a tingle up my spine as do these cats.

And dabbling in this information and US772's glimpses into his word gives me a real lift for the day.  I am late for work because I read your stuff, thank you.

 

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2 hours ago, Steve Clark said:

Tom: I don't believe it either....

SHC

 

Steve, any reason why STAR-CCM+ and HEEDS? Was it just availability or something particular that you or Flexsys wanted? Other vendors have similar tools, not sure if you were able to compare.

Regarding results, you mentioned difficulty capturing operating conditions (I interpret that as boundary and flow conditions). Was your group happy with choices of turbulence model, mesh quality, boundary layer mesh, etc, or was that thought to also contribute to possible errors? Maybe that was left to Red Cedar Technology?

Also interested, if you can say, what the range of permissible flexed shapes were for the Flexsys technology, and how they are found (FEA simulation based on structure, and actuator input loads?).

Finally, if you were to integrate such a thing into your wings, would it be actuator agnostic - i.e. one could achieve the same shapes with strings, hydraulics, or piezos, or for example, is something like an actuator integral to the skin necessary?

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On 4/29/2017 at 10:32 AM, Steve Clark said:

The jibs kind of freak me out. I don't know what they are doing there except holding telltales.

Looks like ETNZ agree - they tried jibless sailing. Interesting they did it in very light winds. Would it be because the apparent wind is more forward in light winds?

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It seems Jibs aren't necessary but time might bring out a rule ......

But that makes the wing more like an A or a C which might make something you A and C class sailors know more relevant.

Will I go off searching or will I just ask?

C class cat's wing is 3 bits (2 elements and a flap) which makes it different but ...

How many elements does an A class wing have ? and what rake do they usually have? and Glen knows a bit about A class so what might we look for ??

There is so much smoke and so many mirrors, all the watching of Jason's vids leaves these untrained eyes with not much to chew on.

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All successful C Class wings have been slotted wings. That is to say with the "flap" a distinct airfoil separated from the trailing edge of the "Main" wing.  The majority of the CClass wings have had an attached flap on the trailing edge of the main wing which is deflected in concert with the flap.  The weight and complexity of this intermediate flap can be eliminated with different configuration of the flap pivots to maintain the correct slot geometry.  

The AC wings and jibs were the subject of an exhaustive study by JB Braun using the North Sails suite of CFD tools, and the conclusion was that the wings were faster with jibs in front of them. This is counter to my intuition, but I did not do the study, and indeed my only knowledge is second hand.  However, it seems to me that the AC50's are overpowered and starved for righting moment. In the classic practice, this means that the boats will go faster with less sail area, which would suggest that the jibs are undesirable, and should not be set as soon as the boats can foil.

ETNZ seems to be the team most agessively addressing the de powering aspect of the design, as evidenced by their aggressive use of flap twist and dynamic adjustment of the upper flap.  While the section shape and profile of the wings are controled, tht teams have very diffferent ideas of the optimal trim a settings. So it is more interesting than it appears .

SHC

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Thank you Steve,

A few impressions of "weird" things at the top of ETNHZ's wing have suggested to me they might be using their wing for more than just forward power, more low end torque (in an engine analogy) and stability in manoeuvres.  We have also seen some weird photos of ETNZ's foils that suggest they have a great low speed foil.  In Auckland there was a vid of them lifting off for a few seconds, in what looked like flat conditions. Never to be repeated to my knowledge.

Once again thank you for your insightful ideas, that stimulate imaginings, which enlivens the left field.

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do you think that this depowering would best benefit straight line speed and hinder manoeuvres where a more powered profile may be advantageous for getting up out of the water?

I think I have noticed a more subtly trimmed wing on ETNZ in the last couple of videos, but they were light air sails.

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18 hours ago, Steve Clark said:

All successful C Class wings have been slotted wings. That is to say with the "flap" a distinct airfoil separated from the trailing edge of the "Main" wing.  The majority of the CClass wings have had an attached flap on the trailing edge of the main wing which is deflected in concert with the flap.  The weight and complexity of this intermediate flap can be eliminated with different configuration of the flap pivots to maintain the correct slot geometry.  

The AC wings and jibs were the subject of an exhaustive study by JB Braun using the North Sails suite of CFD tools, and the conclusion was that the wings were faster with jibs in front of them. This is counter to my intuition, but I did not do the study, and indeed my only knowledge is second hand.  However, it seems to me that the AC50's are overpowered and starved for righting moment. In the classic practice, this means that the boats will go faster with less sail area, which would suggest that the jibs are undesirable, and should not be set as soon as the boats can foil.

ETNZ seems to be the team most agessively addressing the de powering aspect of the design, as evidenced by their aggressive use of flap twist and dynamic adjustment of the upper flap.  While the section shape and profile of the wings are controled, tht teams have very diffferent ideas of the optimal trim a settings. So it is more interesting than it appears .

SHC

Steve

Did you write this prior to, or in response to, ETNZ testing without a Jib?

I found it interesting, that the team that is reported to be the richest in terms of potential capacity to generate hydraulic power (thanks to cycle power) is also the first team witnessed testing a mode of greatest efficiency and also least draining of hydraulic reserves (the jib must require draw down of hydraulic reserves) but also frees up the management of this element that is potentially distracting for a relatively overworked crew resource.

So flicking the jib off has multiple benefits. Does the jib ever get used to pull the bow down as seen in M32's in the WMRT? This might be one of the few remaining tricks that keeping the jib hoisted can offer.

But if the team is confident of 100% foil time from pre-start to finish then surely a jib becomes largely redundant.

JB Braun findings and the North supply of OD jibs cannot be seen as anything other than a commercial means to an end.

Remember Race 1 of Oracle vs Alinghi in the DoG match at Valencia - Jib down, higher and faster......

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My experience is in  International Canoes, A and C Class where ther is a sail area limit.  So maximum utilization of every square foot is absolute. The AC 50 is not exactly the same case. I believe you can sail with a jib or without a jib, you lose the sail area represented by the jib when you remove it.  In most cases, area is king, particularly down wind. However we are looking at a case which is unprecedented in soft water sailing, with apparent wind angles and speeds in the realm of iceboats. But nevertheless, teams have to accept sailing with less area when they ditch the jib.  The rules may require that the sail be aboard even if it isn't set, 

It is worthy of note that the IC has remained a sloop. The hull while very slippery by monohull standards, is draggy compared to catamarans, so the extra oomph of the jib seems to pay.

SHC 

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I think the King of "A"s has got some clever ideas to make ETNZ go faster at crucial times.  No jib, weight forward, (is the weight of a jib about the weight of a man?)

The other thing I wonder about is, are AC50 wings so powerful they don't the jib? that is they have enough power in the wing? The Jib would move the CE down surely that is a good thing?

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This is my favourite time waster !!

How I would love my older Grandson who seems to have a knack to get onto one of these.

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1 hour ago, Kiwing said:

This is my favourite time waster !!

How I would love my older Grandson who seems to have a knack to get onto one of these.

Very cool. 

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A jib makes the rig look like a biplane when viewed from the apparent wind direction.

The wider apparent sailplan means the mass/sec of air being bent by the rig is greater.

For the same total sideforce with jib+wing, this greater mass is being bent less. The velocities transverse to the AWA are reduced, which reduces the lift-induced drag.

An alternative way of imagining it. The pressures around the rig are spread out and reduced, so their header effect on the incoming air is less detrimental.

If not hull-flying, probably the greater mass of air can be bent the same amount without stall, so the sideforce will be greater. It's hard to say whether the benefits of a jib are related to extra sail area or biplane-effect drag reduction or some combination.


When the AC45s were launched several teams sailed without jibs initially, but jib+wing quickly became universal.

This comment is about lift-induced drag only, so if jib-only is successful there must be other practical benefits outweighing this.

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Geezus, the terminology from you is almost as hard to understand as it is from Basiliscus. :) A compliment, of course.

In plain English, will you be surprised if teams race jib-free? Is up or down the wind range more likely?

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On 5/6/2017 at 5:21 AM, rusto said:

Haha definitely no calculations involved, just an example to help visualise where the forces on your wing might be pointing for different trims.. plenty of unknowns, uncertainties and assumptions. Definitely keen to hear if you have any thoughts

Rusto take a look here if you want to look in to actual numbers, lit drag ratios in the region of 40-60 ish.

http://www.tspeer.com/RigidRigs/40flap/S902fa20.htm

Interestingly a wing with 20deg flap rotation and -4deg AoA still produces a positive lift force!

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1 hour ago, lous said:

Rusto take a look here if you want to look in to actual numbers, lit drag ratios in the region of 40-60 ish. Sorry that was bollocks I was looking at the coefficients.

 

 

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On 16/05/2017 at 8:57 AM, Happie Jack said:

downwind i would think the quick jib ease with the bow lift result

The boats should be more bowdown without a jib. Because the forestay is raked there is a force upwards, it's small but a long way forward of CoG. It might not be visible because the pitch can be trimmed out with rudders elevators.

As far as the biplane/lift-induced drag argument in favour of using jibs, I think it applies in any windspeed.

 

 

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On 5/15/2017 at 9:37 PM, Happie Jack said:

This post is a great example of "what would you do in various conditions with a soft sail?"

How can a wing be designed to work over a large wind range, when many aspects can not be changed by the elastic shape a single skin sail allows: 

Not only a holy grail but i do believe led to a change in C Class championship rules, that all had to use a wingsail, after a drifter series and a low tech soft sail lightweight combo blitzed the heavy wing tribe. Aquarius?

wow, great discussion by wise old men :)

I learn so much from your participation, thx,

I just pop out observations and wonder, amazing the knowledge here.

 

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23 hours ago, lous said:

Rusto take a look here if you want to look in to actual numbers, lit drag ratios in the region of 40-60 ish.

http://www.tspeer.com/RigidRigs/40flap/S902fa20.htm

Interestingly a wing with 20deg flap rotation and -4deg AoA still produces a positive lift force!

Thanks for the link!

Looks interesting - will have a read

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