Alexander Graham Bell’s Tetrahedral Kites | Hacker News Reader

Alexander Graham Bell’s Tetrahedral Kites

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161 pointsflannery31 comments

The kites were part of his exhaustive investigations into aerodynamics. There is an amazing display of his experimental propellers at the Bell Museum in Baddeck, Nova Scotia. They show how he methodically varied attributes to derive optimal pull. Well worth the visit.

I once built a simple box kite. It was remarkable for me how easy it was and how it could somehow perform even when there seem to be no wind. It was easier to built than a diamond kite.

It was years ago and sometimes I'm thinking about building one again and placing some action camera up there. To make a few drone-like shots, but for much less money. But also because it's fun.

I built mine with a few wood slats, two shopping bags, some string and glue.

I built a diamond kite with my dad and it is one of my favortie childhood memories. For some reason I have never done it with my kids yet (Finding that awesome kite paper has been elusive) but I have built dozens with kids I worked with. Such a great learning experience.

http://www.my-best-kite.com/kite-paper.html

This one looks like a Sierpinsky Triangle :)

https://c1.staticflickr.com/5/4226/35286566316_65bcda7d3f_b....

That'd be a Sierpinski tetrahedron, but it's the same idea. I think it's pretty interesting that these were made about ten years before Sierpinski described the fractals, but then again the design appeared in mosaics from much earlier:

https://s-media-cache-ak0.pinimg.com/originals/52/98/75/5298...

https://s-media-cache-ak0.pinimg.com/600x315/7b/7c/06/7b7c06...

Where were those pictures taken?

Reverse google image sleuthing leads to a pinterest board[0] that alleges they are of the Cosmatesque style[1], which means they maybe originate from somewhere in medieval Italy?

[0] https://www.pinterest.com/paulettecadic/pavements-des-cosmat...

[1] https://en.wikipedia.org/wiki/Cosmatesque

Thanks for the sleuthing. I found them myself by searching for Cosmati mosaics, since Wikipedia mentions them in the article about the Sierpinski triangle.

Captions for the two images:

Francesco De Comité took this photograph in the Church Santa Maria in Trastevere, Rome,

Civita Castellana - Santa Maria Maggiore - Motivo detto "setaccio di Sierpinski"

'The Sierpinsky gasket makes me wanna cry.'

I can't hear the name Sierpinsky without thinking of 'Mandelbrot Set' by Jonathan Coulton.

I hate that the part about Mandelbrot still being alive is no longer true :(

I just thought they should be called Sierpinskites.

It's really inspiring and impressive the stability of these kites. The weight to lift ratios are also fantastic. The linked National Geographic articles are very informative and interesting.

Methinks this would make an excellent platform for a kite-antenna.

I'm sure that kite design will be very stable in the air. But I guess the triangular wings are not very efficient and disturb each others airflow.

I wonder how the tetrahedral design compares with the Cody kite design, from the same era. That design looks more efficient to me, and has been proven to scale big enough to lift people in the air.

As a kid I built several small Cody kites and they fly amazingly well. We combined several and flew with up to 1km of line, hundreds of meters high.

https://en.wikipedia.org/wiki/Samuel_Franklin_Cody

"tetrahedral beings were flown both unmanned and manned during a five year period from 1907 until 1912" So, according to the article they did carry people.

An important consideration is these kites where lighter per lifting area so they needed less wind and would also fall slower without wind making them somewhat safer. The added redundancy is also an important consideration.

PS: It's actually fairly easy to build a kite that can lift a person in a strong wind as even a simple parachute will work. see: parasailing which can work at even 15mph. The problem is finding a design that fails safely.

Do SpaceX's grid fins operate on similar principles?

https://i.stack.imgur.com/rnHbB.jpg

(edit: and these: http://www.aerospaceweb.org/question/weapons/q0261.shtml )

I'm sure that those are designed such to eliminate as much drag as possible while also providing steering capabilities on descent?

On descent, one might think that increased drag is something of a useful feature.

True, except if it has an uncontrollable effect on the overall steering of the system.

Drag will vary greatly based on weather and wind, so it is likely not something one would want to count on.

I believe that variability would be the domain of the control system and launch/recovery parameters to handle no matter what the fin design. The shorthand way to think about it is that the fin should not add any variability that the control system does not have the authority to overcome (and by some margin above that) - else one would not choose that combination of design elements; apoligies if im retreading something you already know...

Yes, true - I just wasn't articulating that as clearly as you have.

I was thinking of "we don't want to rely on drag as a function of descent" rather than "drag doesn't matter, because the control system is fully advanced and capable enough to deal with any variance brought on by drag"

AFAIK, grid fins are made the way they are to circumvent the problems of supersonic shockwaves rendering conventional fins useless. So it's a different situation.

We built one in my company's lobby a few months back! https://c2.staticflickr.com/6/5332/30663005756_793b436f73_k....

Inspired apparently by (the under-appreciated) Lawrence Hargrave's box kites:

https://en.wikipedia.org/wiki/Lawrence_Hargrave

I had a tetrahedral kite growing up. That thing was amazing. It would lift off in a light breeze. And boy did it pull when the wind picked up. Great fun.

Is that a Sierpinski's triangle kite almost ten years before Sierpinski wrote about it!? Regardless truly awesome.

Yup. But (at least according to Wikipedia's article about the ST) the pattern was around -- in art -- centuries before Sierpiński!

Maybe, but it's not like "Sierpinski's" triangle was unknown before him. It appears far, far back in human history.

Let us not forget Samuel Franklin Cowdery: http://www.atlasobscura.com/articles/man-lifting-kites-cody (not tetrahedral, but impressive)

What's with that last picture?

The one of them kissing? I thought that was really cute and somewhat challenges my prejudices about people of that era being repressed, cold, unemotional and reluctant to exhibit public displays of affection.

Its amazing anyone thought it feasible to risk life and limb at the vagaries of the wind. Unpowered flight is fundamentally dangerous.

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