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will the wing take off? |
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Dougal
Really should get out more Joined: 23 Sep 09 Location: England Online Status: Offline Posts: 556 |
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Topic: will the wing take off? Posted: 24 Oct 11 at 11:42am |
Very good point - modular or, as you say, 'some other cleverness' is obviously the way forward. Two piece masts are the norm in many classes, so why not two (or more) piece wings as well? |
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getafix
Really should get out more Joined: 28 Mar 06 Location: United Kingdom Online Status: Offline Posts: 2143 |
Post Options Quote Reply Posted: 24 Oct 11 at 11:46am |
or perhaps some kind of two or three piece solid structure with a zip-fastened covering?
although I don't much like the idea of a stretchy cloth/fabric getting back involved again as it opens the door back up to the sail-making "community" .... |
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rogue
Really should get out more Joined: 04 Dec 08 Location: United Kingdom Online Status: Offline Posts: 978 |
Post Options Quote Reply Posted: 24 Oct 11 at 1:52pm |
A lego tower of wing sections with some clever connecting controls up the internal luff tube... stack them up in light winds, lose a section or two in heavy winds.
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ham4sand
Far too distracted from work Joined: 27 Jul 09 Location: United Kingdom Online Status: Offline Posts: 452 |
Post Options Quote Reply Posted: 24 Oct 11 at 3:02pm |
i have to say that the controls bit mentioned above seems like its going to be the trickiest
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John Hamilton
cherub 2645 - cheese before bedtime cherub 3209 - anatidaephobia laser 176847 - kiss this |
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17mika
Groupie Joined: 03 Nov 06 Location: Italy Online Status: Offline Posts: 53 |
Post Options Quote Reply Posted: 24 Oct 11 at 3:40pm |
I have always wondered.. What about gust response?
I mean most hi performance dinghies have some flexing of the mast which authomatically flattens the main and opens the leech, keeping it all manageable (and fast) in the gusty stuff.
I believe C-class wings have some sort of flexibility in the wing elements, which make them flex a bit dynamically, but the structure is not exactly bulletproof.
How can you make it responsive without making it fragile?
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Medway Maniac
Really should get out more Joined: 13 May 05 Location: United Kingdom Online Status: Offline Posts: 2788 |
Post Options Quote Reply Posted: 25 Oct 11 at 12:14am |
imho, wings will never become the dominant rigs in conventional dinghies.
They make sense in cats (and maybe foiling Moths) because they sail at such high speeds that the apparent wind is so far forward on average that a high lift to drag ratio such as can be delivered by a wing is very desirable. Dinghies require high max thrust but do not require such a high L/D, especially considering the downsides of wings, namely the cost and complexity to make something adjustably-cambered that can deliver a high thrust as well. Then there are the rigging, launch and storage problems. I just don't think the limited advantages will ever outweigh the downsides. That said, I'd be delighted to be proved wrong, and will watch developments with interest...
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Chris 249
Really should get out more Joined: 10 May 04 Online Status: Offline Posts: 2041 |
Post Options Quote Reply Posted: 25 Oct 11 at 5:33am |
Well said, MM.
Over on Boat Design Forum, two of the designers of the AC winning wing (Boeing aero Tom Speer and MIT professor Mark Drela) have pointed out that thin flexible foils such as fabric sails actually have aerodynamic advantages over fatter foils like wings. Thin foils are actually more powerful and can be adjusted easily; there used to be a Drela post where he said that glider pilots would envy the way yachties can easily and quickly adjust their foil's aerodynamics in use. As Drela notes; "Thin airfoils are capable of the highest CL and CL/CD values, but only within a narrow CL range (or alpha range).... a soft sail allows the possibility of changing the camber of a thin airfoil, which can greatly extend the low-drag range if done appropriately. So a thin airfoil which always has the appropriate camber shape dialed in at any given operating point will in general be superior to a thick airfoil." He went on to look at a thin foil that had a max lift coefficient of 3, compared to the 2.3 of a thick foil. As Speer says; "the notion that because aircraft wings are very efficient and have thick sections, while sails have thin sections and generally lower lift/drag ratios, and therefore a thick sectioned sail will aerodynamically superior to a sail rig with a thin section simply because it is thick, is a mistaken idea. Airplanes have thick sections because they are structurally stronger and because they have to operate efficiently at low lift coefficients in cruise. This is generally not the case for most sailing craft, except for very high-speed craft like landyachts and iceboats. A sail rig can operate at comparatively high lift coefficients even in high winds because it has the luxury of being able to reduce area. This makes the narrower operating range of the thin section acceptable." As far as I can see (I'm in no way an expert, of course) all this ties in with the real world, not surprisingly. Wingsails in slower craft have been around for decades and have never seemed to show any performance increase. Wingsails in fast boats do work. It seems that the factors that make a boat slow (high resistance, lower stability etc) mean that soft sails work best on it, while the factors that make a boat fast (low resistance, high stability, and often a restricted wind and sea range) mean that a wingsail works best on it. We see this very clearly in windsurfers, where you can easily swap between various types of board and sail. The lift/drag characteristics of the sail and hull have to match (which is what Mark points out elsewhere). A low drag/low lift rig is a dog on a high drag hull and a high drag/high lift rig is a dog on a low-drag hull. It's not just a matter of adding a wingsail to a conventional dinghy and watching it take off - or like changing a Mirror kite to an assy and expecting it to tack downwind. Wingsails are likely to only work on boats that are already inherently quick; a bit like adding foils to a GP14 is unlikely to significantly improve their performance.
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getafix
Really should get out more Joined: 28 Mar 06 Location: United Kingdom Online Status: Offline Posts: 2143 |
Post Options Quote Reply Posted: 25 Oct 11 at 1:48pm |
with you some of the way there, but then you said " a bit like adding foils to a GP14 is unlikely to significantly improve their performance." got to dissagree. OK, the wind-band would be very narrow, but supposing you could create enough momentum to get the GP up onto the foils (and they will go, just needs to be blowing big) then you'd see a vast improvement in performance |
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ham4sand
Far too distracted from work Joined: 27 Jul 09 Location: United Kingdom Online Status: Offline Posts: 452 |
Post Options Quote Reply Posted: 25 Oct 11 at 2:04pm |
Kevin Ellway did some foiling analysis for a cherub, and found it wouldn't have a positive effect on vmg upwind and down, apart from in a band of wind that was approx 5 knots across-ish. This wind band also happened to be the average wind in Wellington, New Zealand, hence why the R-class, which mainly sail in that area, have adopted foils with such success. Anyway my point is that you would (probably) never get a gp14 to have a better vmg with foils, and too be honest, i can hardly believe they would even lift off the water, they're so heavy!!!!! A foil big enough to lift them would be super draggy I'd expect in non-foiling situations. Plus, the sheer power from the centre foil would probably rip the centreboard case apart before the hull lifted.
There, I'v just answered a completely hypothetical question, got bored i guess!
Edited by ham4sand - 25 Oct 11 at 5:10pm |
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John Hamilton
cherub 2645 - cheese before bedtime cherub 3209 - anatidaephobia laser 176847 - kiss this |
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tgruitt
Really should get out more Joined: 02 Dec 04 Online Status: Offline Posts: 2479 |
Post Options Quote Reply Posted: 25 Oct 11 at 4:07pm |
Next time you get bored maybe you could learn how to use apostrophes and capital letters properly (and the use of their, there and they're). I'm not the spelling police but forums shouldn't be an excuse for sloppy grammar.
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Needs to sail more...
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