Of the categories, changing the structural order of the cells is generally easier, while modifying construction requires forethought as the spar lengths change. Combining the two methods can also lead to some very interesting results.
I myself had trouble stabilising this regular tetrahedral. However, Spence Wikel's 16 cell Sierpinski Tetrahedral (expand the photo, right to see), shows one recommended solution. The addition of extra side bridles ensures that regular tetra's, can't just suddenly swerve to either side due to wind changes or sail flap. The bridles in that case become unbalanced and forces the tetra back on course real fast.
The later "wide" tetra's below do not have this problem as they have more side-by-side bridle lines due to their width. "Long" tetras also are more stable due to the extra length.
The reason for this instability is two-fold. First the kite is small in size relative to amount of frame work needed in the kite. Tetras with more cells (NOT larger cells) provide more lift for their weight, and thus fly better, especially in lighter winds. Still the weight tends to make the kite swerve from side to side in large figure 8's. Having said this an ultra light straw and plastic tetras of this type, seems to have no trouble flying well, and rock steady.
The second reason for its failure to fly well is that the kites centre of gravity is very high with regard to the kite sail structure. Larger tetras has more sail above the centre of gravity which ensures that kite know which way is up. The high dihedral angle of the wings then makes other larger tetras rock steady when flying.
Make four of the above 4 cell kites, and then tie or clip them together (corner to corner) using fishing clips, split rings, curtain rings, normal string, ribbon, wherever, to create a larger 16 cell tetrahedral kite.
The variation is called a "Sierpinski Tetrahedral Structure" after a 'fractal' geometric pattern of the same name for 2 dimensional triangles. For more information of that fractal see Fractals, and Fractal Dimension, for a more mathematical overview, of the Sierpinski Triangle from which the Sierpinski Tetrahedron was an 3D extension. You may be also interested in The Sierpinski Tetrahedron, and from the same author, Building paper Sierpinski Tetrahedral.
This is an interesting structure as while it is solid looking it also has a sort of 'swiss cheese' holey effect, which makes it fascinating to look at. Especially when flying in the air. Even graham Alexander Bell experimented with this tetrahedral variation, (see below).
It is also the easiest compound regular tetrahedral structure to build, as the connectors only have to deal with either 3 spars at the corners or 6 spars elsewhere in the kite (same as for a 4 cell tetrahedral above). All the other variations have joint involving 9 or ever 12 spars all jointing together at the same point, which can get difficult to build.
|Other examples are...|
|One commercial model flown by Al Hargus III, from an article in Kite Life EZine (May98) -- now offline.|
|Spence Wikel also has built one. His web site contains lots of photos of this and another tetra he has built.|
|Here is a lovely tie-died straw tetra, by Ernie|
The photo to the right shows Mr Bell himself flying such a third generation
Sierpinski Tetrahedral, and was taken in 1903 at Bell's home on the island of
Cape Breton, Nova Scotia, Canada. An amazing sight indeed.
Shown left is a colourful 64 cell Sierpinski tetra made by Volere Volare of
And again to the left is a 64 cell drinking straw tetra made for a UK
Children's Science TV Series Big
Bang. The view is from directly below the kite, looking upward.
And here is a tetra-lite design (Bamboo BBQ skewers and thin plastic tubing), from K÷vessi Zsolt in Budapest. This design allows it to fold up flat for transport.
Ross Leighton <firstname.lastname@example.org> has built the pictured 10 cell tetrahedral from 6mm dowel. You can find his email in the responses to my own tetrahedral kite plan page. He has also provided me with photo showing how he created the '9 spar joint', required for this kite.
This is also equivalent to the 16 cell structure where the 'hole' in the middle of the kite has been filled in with 4 more cells. This of course makes the kite less 'holey' and much more solid looking, than the 16 cell Sierpinski structure.
This structure is very large, and very very strong. However I would not continue this process further to 5 cells per edge. Why? Because, while the tetra gets larger, and stronger, the wind would start having problems penetrating to the cells at the rear of the kite. This in turn reduces the gain in lift and increases the drag of the kite making it less efficient.
A a class of fourth grade students in Bakersfield, California, made such a
tetrahedral using straws and brightly coloured tissue paper. You can see more
photos of their effort on the page 100 Cell Straw Tetra,
final construction and results. Congratulations a job well done.
The photo to the left shows Diane Hislop, a school teacher with one such kite made by his primary school class after the success of their 100 cell tetrahedral.
Mr Bell's early experiments with tetrahedral kites did just that, and one of the more famous tetrahedral kites is his boat tetra.
Bell's Tetra 'Boat' is created using 20 cells in total. A standard 4 four cell tetrahedral is continually added to, to extend the front and rear faces, until it is 7 cells long (1 wide, 7 long, 2 height), forming the boats 'hull'. On to the top of this two regular 4 cell tetras were then added, forming the boats 'sail' or 'bow', depending on exactly where they were placed.
The above diagrams show some 2 cell long ''wide'' tetrahedrals of increasing width. while the next diagram if of 3 cell long ''wide'' tetrahedrals.
I have found from personal experience that wide tetra's are so much more stable than the regular tetrahedrals. I think that may be because the bridle is forked to two or more points side by side, which has a huge stabilising effect on the whole kite, preventing spins and spirals, due to wind turbulence.
For example a regular 4 cell tetra would be 1 cell wide, 2 cells long and 2 high or 1×2×2 tetrahedral. As another example, the 13 cell, 'wide' tetra (above), can be classed as a 4 wide, 2 long and 2 high, or 4×2×2 tetra.
Note that multiplying these dimensions does NOT give you the number of cells. These kites are not rectangular or cubic in nature, and as such a straight multiplication will fail. Any one out their like to figure a formula?.
Also you will note that the height (or number of layers) of a tetra is usually equal to its length. As such the height may be left off the kites size, when the tetra is completely filled out with cells. This is not always the case as the designer may have decided not to fully fill it out, height wise, especially for 'long' tetrahedral kites. The hull of Bell's Boat (above) is an example of a 1×7×2 tetrahedral.
Here is a photo of a 5×3 'wide' tetrahedral (34 cell) built by TetraLite Kites.
Shown right is a photo of Paul Chapman's 5×4 (60 Cell) wide tetra. This was found in High as a Kite, Gallery 4The record for a multi-cellular tetrahedral is 3,393 cells known as the "Cygnet" and was itself a 'wide' variant. This was set by the inventor of this type of kite, Graham Alexandra Bell (See What is a Tetrahedral Kite?). This kite only had one flight, being towed into the air by a steam boat, and carried a passenger.
Here is a photo of one of Mister Bell's earlier wide tetras. This one is a 13×12 cell tetra. Anyone like to calculate the number of cells?
The 'exotic' kite use 5 normal tetra cells but the 6'th is split in half and used on either side of the kite. Another description of it is to take a 7 cell wide tetra (2 wide, 2 long, and 2 high) and remove half the uppermost corner cells on each side. From head or tail on, the kite looks vaguely hexagonal in shape.
The 10 cell 'keystone', is basically 3, 4 cell tetra's, which all share a single cell in the middle of the kite. When flying it has three 'points' facing forward into the wind. It is called a 'keystone' as its shape when seen front on, looks vaguely like the keystone used in a stone arch.
To the left is a photo of a solid but incomplete (thus irregular) tetra flown at Long Beach in 1998. Also note that the edges of the cells are curved slightly to prevent edge flap. That is because this tetra used a corner bracing method of construction.
Shown right is a distant photo of a 55 cell tetrahedral, in a airplane-like structure. It consists of a 34 cell wide tetra, joined to a 10 cell wide, by a set of 11 extra cells. The kite known as 'Cometa' was created by Erik Delgado.
The tetrahedral thus created will still look like a normal tetrahedral kite but will pull just a little more. The kite however would be a little bit more unstable, and may need to have more cells, to make it larger and more stable, or a tail added to the trailing cell(s).
By increasing the trailing edge to 50% longer, the kite will become closer to a normal dihedral angled kite, but will require a tail to stabilise the kite. Also the way a tetrahedral kite is framed so that it does not allow the leading edge to stretch slightly up and backward would also cause the kite to be unstable. Very tight cell 'skins' are also recommended.
The "Chicago Fire" tetrahedral kite, with its distinctive white and black striped panels on the left side and solid colour panels on the right is one of the more famous, distorted tetrahedral kites. None of the two sides, or the leading or trailing edges are the exact same length! though it seems to contain an angle fairly close to (but not quite) a 90 degree angle.
David Petre <email@example.com> wrote to add the following about
this commercial tetra...
The spine is 62cm total length and the spreader is 79cm total length.
Those two spars are long, and extend beyond the kite itself , with one
end a ferrule and the other an extension to push into the ferrule to
connect the cells. The cell itself has a spine of 55cm, a spreader of
72cm with a leading edge of 45cm and a trailing edge of 61cm. |
I bought the first 4 cell unit and it didn't fly very well, so I had to buy 12 more for a total of 16 to get a good stable kite. The cells are held together with bunji cords.
Making a different change to each individual cell in a tetra can lead to some very interesting a weird designs. Tetras can become very un-tetrahedral in style, though still being based on that cellular design.
For example the photo left is a tetralite 10 cell 'keystone' design in which the side cells have a 50% longer bracing spar.
In fact by some small changes you can also help reduce much of the heavy sparing normally required for a tetrahedral...
The resulting "tetra" is a 'long' 1×4×2 variant, but with one side of each of the 6 top level cells folded down horizontally. In fact it is braced the same way as a Tri-D Box, which greatly reduces overall weight of the kite from a typical tetra of that size. The kite was built from the ripstop cells from my 16 cell tetra (See photo in the regular area above), which due to its weight, was never fully stable. This kite on the other hand was rock steady, flying all day on a light sea breeze in the morning, until the rear two cross spar dowels broke when the wind became near gale force in the late afternoon.
To the left is a photo of Robert Harvey's composite tetra of similar design to my tetra-tri-d. This kite was the winner of the Cellular Kite Category at the Festival of Winds, Bondi, Sydney, Australia, in September 2001.
Skys the limit, build your own unique variation.