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Angles of lean

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Old 07-09-2004, 02:40 PM
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discoboy
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Default Angles of lean

Firstly, I'm new to all this sailing stuff so I might be running before I walk but I'm building a wing sail catamaran, with a past in aircraft I thought it easier then all that sewing. I've been looking around the internet and found that most rigid wing sails are used on speed sailing boats, I've also noticed that a lot of them have the wing (sail) leant over to one side.

I was wonding if anyone knew why this was, is it so that the lift created by the wing also lifts the hull out of the water?

Also, what would be a good poisition for my wing pivot, I've read some pages saying that 10% rear of the leading edge will keep the wing self adjusting itself to the right angle of attack. I might have missread this though...
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Old 07-16-2004, 04:20 PM
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Default RE: Angles of lean

Anyone???
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Old 07-19-2004, 11:17 AM
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Default RE: Angles of lean

Ok, so I don't know if it's directly applicable, but I found this ([link=http://www.rclandsailing.com/design.html#mast]rclandsailing.com[/link]) a while ago. Seems to discuss what you were asking about. Hope it helps some.

Jonathan

PS - You could also try doing a search for "Wing Mast" on Google. It'll probably come back with tons of information.
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Old 07-30-2004, 03:45 PM
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Default RE: Angles of lean

A sailboat leaning is said to be heeling or heeled. The amount is called a heel angle.

With conventional sails and hulls, the optimum is usually about 15 degrees -- at that angle the loss of driving power is still pretty low from the air spilling out of the sail and the sail appearing smaller to the wind, but there's a significant reduction in wetted area under the water.

I'm not too sure how much wing sails benefit or suffer from heeling. I do know that the drag reduction on a multi-hulled baot is better that on a monohull if you can get that windward hull out of the water.

I'm assuming that you've looked at the Burt Rutan/Dennis Conner Stars and Stripes catamaran of the mid '80s? Very attractive boat and outrageously fast, even with the conventional sails that it used in its best-known outing. Of course its best known outing was something of a joke that did no good for peoples' respect of yacht racing, BUT IT WAS THEIR FAULT!! Anyway, I'd look for info on that one of you haven't already.
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Old 08-12-2004, 08:56 PM
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Default RE: Angles of lean

Hi Disco,

The rigid sail, or wing for sailing has many technology issues that really apply to boats only. On an airplane, a non-symmetrical foil is used in most aircraft, with a symmetrical foil used for hi-performance aerobatics.

Problem with sailing is, you just about have to go with a symmetrical, as the sail does not have a constant angle of attack that can be controlled through the vertical plane(elevator-elevon). The angle of attack is never consistent for a vertical foil that moves horizontally through a variable direction and velocity (Wind). Wind provides your thrust in sailing, and is not overcome as in flying by the use of a prop. Wind provides your 'thrust', and you must be much more aware of it's effects than in flying. In flying wind is a consideration to take into effect, in sailing, it is your source of power, and everything else is a consideration.

This is why sailors constantly need to sheet and trim the sails to the 'apparent wind' and why 'flexible' sail material is still used.

On a rigid vertical wing, as the "sail" cannot form to the apparent wind, but must be tilted to it. (i.e. rotating Mast, adjusting foil, etc) This creates a weight and complexity problem that the racer making a course would just as soon not deal with.

Wing sails work great in one direction and at limited apparent wind angles, but their perfomance envolope is relatively narrow, and the controls cumbersome. This is why they are not used for course or match racing, but primarly for speed trials in one direction, and perhaps the reverse course. They have the potential to be much faster in a straight line over a "sailed" boat, but they give up almost all their manuevering ability to do so. Kind of like racing a rail dragster against a BMW. The dragster will win if the race is 1/4 mile long and straight, but the BMW will eat it for lunch once a turn or two is introduced, especially over a distance. with multiple turns.

As to your specific question why wings are canted leewards (away from wind) this is due to the wings inherint stability. In a 'puff', the loading force on a rigid wing can increase more rapidly than any sail trimmer could adjust for. This is a saftey issue. By canting the wing, the loading is delayed, and less force driven to the hull. This improves the stability of the boat. Without the delay, the chance of being dunked and turning turtle becomes extreme.

Just a word or caution. You are a novice to sailing, and you are about to undertake the two most challenging sailing issues there are. First, control of a multi-hull(catarmaran) which is much harder to sail, especially in R/C, and then adding a rigid wing sail that quadruples the complexity.

This is not beginning sailing!!!!.

I'm not trying to squash you here, but, this is like going from a 40 size trainer with an instuctor, to going to a twin turbine powered R/C F-15 on your second outing to the airfield. You are bound to pitch-pole, or capsize this boat, find it un-controllable, and decide that R/C sailing sucks.

I would suggest you learn sailing from a keel boat type, I.E. Victoria, Seawind, Victor, Northwind, or what ever else they happen to sail in your area. Learn the rules, and learn to race and control a boat.

Then move to a multi-hull; then decide about rigid sail wings.

This will save you a lot of money, let alone heartache.

Chris
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Old 08-16-2004, 03:49 AM
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Default RE: Angles of lean

Cheers for that,

With the Cat I'm considering building the radio gear into the boat permanently with just a small hatch for charging the battery and turining it on and off. Because of this I wanted to be sure the boat had some chance of working so I've cobbled together a sailing dingy to try a few sails on. I've decided not to build a rigid wing.

>>First, control of a multi-hull(catarmaran) which is much harder to sail, especially in R/C,

In what ways are a multi-hull harder to sail?
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Old 08-16-2004, 07:17 AM
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Default RE: Angles of lean

Disco,

Here is the the major difference, Speed. A properly designed multi hull on a beam reach will have one hull out of the water. Now boats generally like to head up into the wind during a puff. On a cat, that puff wants to increases the heel, and if your not paying close attention and controlling your sheeting, the boat wants to capsize to leeward.
Second problem especially in r/c is the width of the boat and it's performance around a mark. A cat needs more manuevering room to tack. Third, and the most scary of all is running downwind. Lets say your heading on a run in a good breeze, and a strong puff hits you. A cat will want to bury the bow. This leads to a pitch-pole. The the boat capsizes stern over bow. It can be avoided, but because a cat gernerally is sailing faster, your reactions have to be faster as well.

Multi-hull sailing is just more difficult. While there are multi-hull classes, especially in Europe, they are not near as prevalent as monohulls for these reasons.
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Old 08-16-2004, 12:07 PM
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Default RE: Angles of lean

Typical, my main reasoning behind beuilding a Cat was that I wanted a boat that wouldn't capsize so easily. With only a motorbike for getting me to my local pond I wanted a boat that would pack away easily so thought keels and tall masts were out of the question. The boat I've half built is 12" long and uses micro radio control.
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Old 08-16-2004, 12:40 PM
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Default RE: Angles of lean

This is my trial boat

Lengh:8"
Width:6.5"
Mast Height:10"
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Old 08-17-2004, 03:40 PM
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Default RE: Angles of lean

Doh! didn't upload the images...
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