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Are your eyes better than mine? Answered

I've been watching and re-watching this video of a kite flying (I can't make Vimeo embed).

It's based on the tetrahedral kite, a tried and tested design.  In my experience, kites like this have amazing stability and huge amounts of lift.  This thing should have needed a serious effort to restrain.

But it only gets a few feet off the ground, and then only just.

The huge banner will have something to do with it, but not a lot.

I've squinted at the video of it in flight, and I may be imagining it, but are a lot of the triangular cells the wrong way round, contributing no lift at all, just a lot of drag?

Can you have a look, and see if you can work it out?

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canucksgirl (author)2012-01-12

It looks like there are wires holding the structure together. I wonder how much weight that would add to the design? If it wasn't that windy it may contribute to their lack of lift.

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lemonie (author)2011-12-22

I look at that and I see black; how the hell are you going to get air through it if it's blocking light?
The unit-concept hasn't been scaled-up right.
(Or alternatively "what the hell kind of "wing" is that eh?")

L

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Kiteman (author)lemonie2011-12-23

Cellular tetrahedral kites are opaque from the side, but not from the front (or back).

(I haven't made one for ages - I'll add it to my to-do list for the spring.)

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lemonie (author)Kiteman2011-12-23

There's too much drag & interference, or tendency for air to go around the cube.

L

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PKM (author)2011-12-22

It would help if the video was at all interested in showing you how the kite is made, rather than lots of deliberately shaky-cam out-of-focus overexposed arty buggering about.

That's my problem with most of the stuff I see on NOTCOT, actually- all style and very little substance.

</crotchety>

I'd imagine that they have problems with self-occlusion, whereby the faces inside the cube don't contribute any lift because they are in the wind shadow of the front faces, so the overall lift is proportional to size² whereas the mass is size³. 

A quick Google around shows me that most multi-cell tetrahedron kites are constructed like Sierpinski gaskets with large internal voids, which I'd guess eliminates this problem.

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Kiteman (author)PKM2011-12-22

I've just exchanged emails with the kite's designer (Sash Reading) - you're right, it's the dead-weight of the inner cells.

He said:

The lack of lift was due to the sheer mass of the structure - it was fully celled all the way through, with every edge of each wing containing a carbon spar. this added to the aesthetic but greatly hindered its flying ability. ultimately its an installation rather than a kite, so just the mere fact that it lifted into the sky (albeit rather clumsily) was enough to jsutify it as a kite and a sculpture

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rimar2000 (author)2011-12-22

Sure that my eyes are worse than yours, KITEM. I only see a triangle out of alignment (center of my image). In my humble opinion, the reason is very simple: the structure is too heavy for that surface. Each triangle would be a square, in which case the lift force would be doubled.

I agree with you in that banner can't influence too.

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