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Old 9th February 2009, 04:30 PM   #11
sztér
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hi windsomniac,

We are planning at my school (Technical University of Budapest) some windsurf sail measurements in the wind tunnel. It's gonna take place in april-may, and I'm responsible for it, so I think there is no problem of generating a sail lift/drag vs angle diagram And if you have any other ideas to measure, just share it!
I read the comment of steady state wind, and that it's not gonna give good results. I agree, that you almost never find steady states in nature, but you have to start somewhere...
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Old 9th February 2009, 04:36 PM   #12
mim
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yeah, you are right, you must start somewhere...

But the idea with the truck, is very close to nature, this I would consider as a second step, after steady state measuremetns.

Good luck, with the experiment...are you going to publish that, or put on some webpage...would be nice to have to possibility to take a look.

Regards,
Michal.
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Old 10th February 2009, 12:22 AM   #13
windsomniac
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Hi sztér,
Thats great! I'm really excited. Yes I have lots of ideas for you. In order of priority I would test the sails for:
1. Lift and drag of sail at various angles of attack (alpha) from 0 to 90 degrees with some special attention at the lower values for alpha 0,2,5,10,15,20,30,60, & 90
2. Variation in % camber on results of 1. a. 5%, b. 10%, c. 15%
3. Variaration of 1. with sail rake (with wings this is called sweep)
a. upright, b. locked down , c. somewhere in between
locking down the sail greatly reduces induced drag under the sail
4. Variation of 1. with negtive heel of the sail with
a. heel at zero, b. heel at 22 deg, c. heel at 45 deg.
When I think of all the permutations of these variations on the experiment I don't think there would be any time for mim's unsteady analysis.
I will get in touch with you about ideas for taking the measurements. For now take a look at the books from author C. A. Marchaj
Thanks,
Dan
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Old 10th February 2009, 04:10 PM   #14
mim
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Hey guys,
that is gonna be a nice experiement...have fun!

Ciao M.

PS: ok unsteady would definetely be too much, if not impossible!
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Old 10th February 2009, 09:31 PM   #15
sztér
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Hi guys,

I got pretty excited too about the experiment! Dan, we should definitely get in contact, especially because I'm not always sure about what negative heel and these things mean... (I'm Hungarian and we use a mixture of English, German and Hungarian terms to describe different things in windsurfing). I don't know if you can see my e-mail address, so I just write it here: lukacseszter1983@yahoo.com.
To mim: I don't think the results are gonna be published, but who knows... Anyways, if you are interested I can send the results to you after the measurements.
Oh, and another thing I almost forgot. The diameter of the wind tunnel is 4 meters, but we can only use 2 meters to measure. So, we need a small sail or a model. I was looking for some prokid riggs, so that the have more or less the same properties as the adult ones. What do you think about this? Would it be better to make a model?

And finally for the unsteady case: actually that would be a nice phd topic, in fluid-structure interaction!

Bye,
Eszter
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Old 10th February 2009, 11:54 PM   #16
Farlo
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Hi Guys, I had a much smaller wind tunnel and my model was ~40 cm high. It was made of aluminium masts and thick plastic (~1 mm) for the sail. 25 years ago cambers were not that popular. Windsomniac can you give me an email address where I will post the results, not before next weeek end I'm afraid.
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