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luff vs boom length
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jingebritsen



Joined: 21 Aug 2002
Posts: 2427

PostPosted: Sun Sep 30, 2012 5:50 am    Post subject: Reply with quote

now that's some techy fiddling going on there. for those that like it. lots to play with. those that don't, "OMG, get me away from the insanity!"

was the wind particularly light that day? the sailor's stance looks like planing is a come and go kinda thing. or a defensive, "i have to muscle the crap out of this right now." i'd certainly like to try some of these sails, first hand. looks like fun for my techy side of life.

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DelmarEdward



Joined: 05 Aug 2012
Posts: 23

PostPosted: Sun Sep 30, 2012 8:48 am    Post subject: Reply with quote

The high aspect foil may be more efficient, but i don't think it's more powerful at lower wind speeds. Doesn't being more efficient in a foil mean a longer surface area with undisturbed air flow? Doesn't power come from the depth of the camber?

I would think then that a low aspect sail with a deep draft is more powerful AND less efficient, which would be what you want to plane early.

Isn't this the same thing that happens with an airplane wing during take off and landing with the flaps?
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DelmarEdward



Joined: 05 Aug 2012
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PostPosted: Sun Sep 30, 2012 9:00 am    Post subject: Reply with quote

as an aside for those with not much to do on rainy windless sunday morning there is an interesting thread on wing efficiency on airliners.com.

Note the gliders wing- very high aspect, but it also never has to have the power to take off and climb, only glides down.
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U2U2U2



Joined: 06 Jul 2001
Posts: 3061
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Sun Sep 30, 2012 10:16 am    Post subject: Reply with quote

I think David Ezzys answer on your long/short question, says that their is no definitive answer, too too many variables, except both long is best

comparison to aircraft seems to come up more so in relation to fins, I can see some relation , but to me our forces are different, particularly when turning.

on aircraft their are plenty of designs that look like they would never be able to fly at all.. the Short Brothers sky van being but one, the first time I saw one , I said looks like the box it came in , where is the plane ?




theses were actually quite stable to fly in, for about a hour transit

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jingebritsen



Joined: 21 Aug 2002
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PostPosted: Sun Sep 30, 2012 10:46 am    Post subject: Reply with quote

that plane reminds me of the bumble bee, or the 747. neither of those look ready to fly either.
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isobars



Joined: 12 Dec 1999
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PostPosted: Sun Sep 30, 2012 2:26 pm    Post subject: Reply with quote

U2U2U2 wrote:
longer luff, shorter boom

then U2U2U2 wrote:
a longer boom is always the best for light air.

Which is it?
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swchandler



Joined: 08 Nov 1993
Posts: 5832

PostPosted: Sun Sep 30, 2012 2:27 pm    Post subject: Reply with quote

Remember the "Guppy"?
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zirtaeb



Joined: 03 Jul 2009
Posts: 2396

PostPosted: Sun Sep 30, 2012 2:40 pm    Post subject: Reply with quote

Theory, long booms are better for light air.
Preference...U2 prefers shorter boom, taller luff.
Me, preference, whatever works the better.
We know the newest NP's and Hansen's have super long booms for their biggest
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U2U2U2



Joined: 06 Jul 2001
Posts: 3061
Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Sun Sep 30, 2012 2:47 pm    Post subject: Reply with quote

isobars wrote:
U2U2U2 wrote:
longer luff, shorter boom

then U2U2U2 wrote:
a longer boom is always the best for light air.

Which is it?


you quotes in part are what David Ezzy said, but only those areas that you want to make a point on, (as in prove me wrong or cast my opinion/preference in dubious light) )the entire post by him below again:

It depends on how long and short the luff and boom are.


A longer boom "evens" out the wind so it carries through the lulls better.



A longer luff is usually associated with a bit less leech roach, which is better in lighter wind.


So, the best would be a longer luff and a longer boom.


If the luff is not too short, a longer boom is always the best for light air.

especially read the bit: so best would be a longer luff and longer boom.

From his dissertation, their are too many variables, without knowing the lengths, and then other factors come into play to make a generalization that holds true in all sail specs. as if the luff is not too short, then a LONGER BOOM IS BEST FOR LIGHT AIR, but consider that the luff is too short, then what, back to the drawing board.

his other point is:
A longer luff is usually associated with a bit less leech roach, which is better in lighter wind.

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U2U2U2



Joined: 06 Jul 2001
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Location: Shipsterns Bluff, Tasmania. Colorado

PostPosted: Sun Sep 30, 2012 2:50 pm    Post subject: Reply with quote

swchandler wrote:
Remember the "Guppy"?


yes, the original I think was a KC97 AirForce conversion, but then came variations even a super guppy.

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