Björn:
I don't think flogging of the leading edge is likely a problem.... Battens break the sail down into small enough sections that this should not be a big problem. An analogy would be the flex wing as used on trikes. Basically a wing based on hang glider technology, flown on a motorized three wheel undercarriage, mounted to that you can control the aircraft by weight shift. Extremely strong and rugged, and very forgiving. Among the aircraft I've flown, these are far and away the most stable and forgiving. They either are completely single surface, or double surface part way back, much like a soft wing sail. The battens do not wrap around the leading edge tube, they just slide into pockets in the wing. Some have been built that have 100% double surface, a couple of which are capable of speeds exceeding 100 mph.... very small high performance hotrod wings. I've never seen flogging. They often have mylar inserts to help shape the leading edge.
Sails on boats see very low wind speeds compared to aircraft. The aircraft of this type that are designed to fly in lower speed ranges all have single surface wings.... Those speed ranges are still above anything boats other than Americas Cup racers see.
Frankly I think this is a case of racing technology that really is probably of little benefit to the likes of me.... I can't speak for you. It reminds me of a conversation I had with a friend who was working on his pride and joy (pickup). A 1964 Ford F100 that he put a 300 cubic inch 6 cylinder in. It's his daily driver. He excitedly told me about an article he read about all the hop up things you can do to get more horsepower out of that engine. Special intake manifold for a 4 barrel carburetor, special exhaust, special camshaft, etc............ I burst his bubble when I explained that none of that would give him the slightest gain at under about 6000 RPM, and some of it would cost him performance in this daily driving range. I've watched people fall into this sort of thinking again and again. They always end up with something that really isn't useful in the real world. Now I have no doubt that there are members here who are passionate about racing and love to push things to the limit.... not really happy unless they are flying the windward hull. I've been "round the block" a few times so to speak, and while I still have that hot rod streak, when it comes to the boat I want to build it will be oriented toward "practical". I need it to get me anywhere on the watery face of the planet in comfort and safety......... I don't need to be the first one there.... but I don't want to be the last either ;-) There is a perverse pleasure in overtaking someone and then watching them slip over the horizon behind you... I don't think I'll ever get over that
I suspect that Pete let himself be seduced by the promise of higher performance, discovered that it was fairly minimal for his kind of sailing, that the soft wing sails were a pain to handle for reefing, etc, not justifying the small incremental gain that probably only manifested itself under limited conditions and points of sail. Unfortunately, Carly's blog, while it mentions unpicking and redesigning the sails, does not even remotely hint at the source of dissatisfaction..... It may be that Pete just is an incessant experimenter and tinkerer???
H.W.
On 06/11/2018 03:21 PM, Björn bjornmail@gmail.com [harryproa] wrote:
I don't think flogging of the leading edge is likely a problem.... Battens break the sail down into small enough sections that this should not be a big problem. An analogy would be the flex wing as used on trikes. Basically a wing based on hang glider technology, flown on a motorized three wheel undercarriage, mounted to that you can control the aircraft by weight shift. Extremely strong and rugged, and very forgiving. Among the aircraft I've flown, these are far and away the most stable and forgiving. They either are completely single surface, or double surface part way back, much like a soft wing sail. The battens do not wrap around the leading edge tube, they just slide into pockets in the wing. Some have been built that have 100% double surface, a couple of which are capable of speeds exceeding 100 mph.... very small high performance hotrod wings. I've never seen flogging. They often have mylar inserts to help shape the leading edge.
Sails on boats see very low wind speeds compared to aircraft. The aircraft of this type that are designed to fly in lower speed ranges all have single surface wings.... Those speed ranges are still above anything boats other than Americas Cup racers see.
Frankly I think this is a case of racing technology that really is probably of little benefit to the likes of me.... I can't speak for you. It reminds me of a conversation I had with a friend who was working on his pride and joy (pickup). A 1964 Ford F100 that he put a 300 cubic inch 6 cylinder in. It's his daily driver. He excitedly told me about an article he read about all the hop up things you can do to get more horsepower out of that engine. Special intake manifold for a 4 barrel carburetor, special exhaust, special camshaft, etc............ I burst his bubble when I explained that none of that would give him the slightest gain at under about 6000 RPM, and some of it would cost him performance in this daily driving range. I've watched people fall into this sort of thinking again and again. They always end up with something that really isn't useful in the real world. Now I have no doubt that there are members here who are passionate about racing and love to push things to the limit.... not really happy unless they are flying the windward hull. I've been "round the block" a few times so to speak, and while I still have that hot rod streak, when it comes to the boat I want to build it will be oriented toward "practical". I need it to get me anywhere on the watery face of the planet in comfort and safety......... I don't need to be the first one there.... but I don't want to be the last either ;-) There is a perverse pleasure in overtaking someone and then watching them slip over the horizon behind you... I don't think I'll ever get over that
I suspect that Pete let himself be seduced by the promise of higher performance, discovered that it was fairly minimal for his kind of sailing, that the soft wing sails were a pain to handle for reefing, etc, not justifying the small incremental gain that probably only manifested itself under limited conditions and points of sail. Unfortunately, Carly's blog, while it mentions unpicking and redesigning the sails, does not even remotely hint at the source of dissatisfaction..... It may be that Pete just is an incessant experimenter and tinkerer???
H.W.
On 06/11/2018 03:21 PM, Björn bjornmail@gmail.com [harryproa] wrote:
Peak L/D is about the same on a thin cambered airfoil as on a cambered airfoil of normal thickness (4-7% camber, 9-14% thickness or so).
But the normal thickness foil has a good L/D over a wider range of angle of attack. At low angles of attack the thick foil has low drag. The thin has high drag, because flow separates on the windward side. To get rid of the drag, the camber has to be reduced.
The nice thing about a soft sail is that you can change the shape of it. Both camber and twist. But it takes a lot of knowledge and experience from the sailor and sailmaker to set, and be able to set, a good shape.
A rigid wingsail is probably easier to sail due to the wide operating range of angle of attack. But I'm not sure if it is faster, because it will not twist, so the whole sail will never work at the optimum angle if attack.
Glenn Ashby actively used twist to trim the wingsail on the winning americas cup boat, so I think this is important for performance. The boat had a "semi rigid" wingsail, which is probably optimal for performance, but seem fragile to me.
I've never seen a video of a soft wingsail sailing fast, so my guess is that it will start flogging/collapse on the leading edge at speed. What do you think?
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Posted by: StoneTool <owly@ttc-cmc.net>
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