Interesting / Cheap Rigs....

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ChrisClarke
ChrisClarke
51 posts
51 posts
30 Oct 2012 11:29pm
I just found this post on the excellent outrigger canoe blog by Gary Dierking:

outriggersailingcanoes.blogspot.com/2012/10/ulua-rig-on-wheels.html

The sails on these rigs are typically cut totally flat but can generate high lift coefficients when the sheet is slackened off and they assume a conical shape with lots of camber. They might provide a good combination of 'starting grunt' and then flatten off nicely to allow reasonably high speed? I guess the low aspect ratio is the ultimate limitation on performance?





These look to be mounted on a Libre Micro Race
cisco
cisco
QLD
12365 posts
QLD, 12365 posts
1 Nov 2012 11:29am
For a trike of this size and type it would be fair to assume a top speed of around 100 kmh in ideal conditions.

The idea of the sail's draught being adjusted with sheeting alone is so simple and logical.

Flat cut and no battens really makes for an inexpensive sail.

The windreamers that the guys in Spain sail have very simple sails which at first look seem to be low performance but they really get them going.

I would really like to see one of these rigs competing against a "conventional rig".

If we are not talking about speed records but more a club racing situation I suspect these rigs would go quite well.
Nikrum
Nikrum
TAS
1972 posts
TAS, 1972 posts
1 Nov 2012 3:03pm
OK! So the next thing to consider is that in using a sail of that nature one has raised the center of effort so that on a smaller Kart like that you would think that it would be unstable in Higher Winds?? No??
Ron
landyacht
landyacht
WA
5921 posts
WA, 5921 posts
1 Nov 2012 8:05pm
it would certainly be worth a trial .it couldnt take too long to make one
ChrisClarke
ChrisClarke
51 posts
51 posts
1 Nov 2012 8:10pm
Yes, you have a good point but there are compromises with all rigs. After all, high aspect ratio conventional rigs have a higher centre of effort than low aspect ratio ones, but the pros generally outweigh the cons.

Maybe you can get away with a smaller area overall and shorter mast with this rig? (area up in higher wind strength, deep camber for starting from rest/accelerating) Maybe you can't - but they certainly look cheap to try out!

There was wind tunnel work done some years ago by C.A. Marchaj on various rigs for a paper "Planform Effect of a Number of Rigs on Sail Power" and this 'crab claw' rig seemed to stand out from the crowd:



I think the graph shows that the bermudan rig edges ahead to windward (which I imagine will provide a higher ultimate top speed for a land yacht) but does not provide nearly as much 'grunt' at higher angles of attack (where a landyacht would be when accelerating from low speed).

To be fair it is probably the case that the bermuda rig tested was a pretty dated and water based type - I would expect a modern land yacht rig to be considerably better, especially to windward.
Nikrum
Nikrum
TAS
1972 posts
TAS, 1972 posts
2 Nov 2012 9:06am
Chris,
I would imagine it has all been done before as in this game there are a lot of us who will experiment down to a Paper Napkin on a full sized rig just to see what happens (Normally a Blowout). Sail configuration depends a lot on Rolling Resistance/Running Surface Hardness, Areas as "Hard as a dogs forehead" offer little resistance and then it gets down to tires width and tire pressure. Then if you have really excellent sideways resistance you can get the very best of speeds with a flatter shaped sail. I use a sail that is as flat as a tablecloth and derive shape from a large Luff Pocket and shaped CF Battens. When starting off the acceleration
is quite surprising. There are the odd one or two people that have been driving down the beach watching the waves only to have a Land Yacht sail by, the reaction is generally to accelerate and "Clock" my speed. It also appears that the Higher thew Speed the higher up the sail power is generated, to a point where it becomes down right scary (Especially with ones butt just a couple of inches/CM above the Sand.
Ron

Once again I could be wrong but I should think that set up would be good in lighter conditions where a Standard Rig would have problems getting moving. Like a lot of us for me "The Faster the Better".
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