ASIDE: The following is never complete, progress usually achieved by people mailing me, which gets me back into thinking about tetras, and thus adding even more information to these pages. So the more people mail me with questions, information, or their experiences, the better the page gets.
Tetrahedrals being an unusual kite and has as a result unusual problems. 2 of the biggest is weight, and transport. Another is stability in the air.
The solutions to this either involve taking the kite almost completely apart, to store in a long bundle, OR somehow folding them up into a flat package, which is itself not great for transport.
Alternatively, if each cell is built completely separately, the cells can be stacked into each other for transport, This produces a very large bulky stack, but means that on the field you can construct virtually ANY type of tetrahedral variation you like. (See the Ring and Rod Construction method below).
From personal experience I have found that the wider tetrahedrals tend to fly much more stable. These "wide" shapes allow for multiple bridle lines which by its nature seem to stabilise the kite. If the kite swings badly, the extra bridle lines quickly returns the kite to stability.
As such the wide tetra shown at the top of the page, flies extremely stable and high! Even the 10 cell irregular "keystone" tetra (top left) I have found to me much more stable than a regular 10 cell "solid" tetrahedral structure. The main difference, is that three bridle lines are used in the "keystone" shape, instead of just two for the same sized "solid" shape.
However I have found that if a tetra is light enough and large enough, they continue to fly stable even when some cells have collapsed and half the tetra has "pancaked", like a building after an earthquake!.
This allows you to use lighter weight spars such as straws, skewers, or very light dowel. Anything else is just getting too heavy. See the Building techniques below for more information.
The joints a fully braced cell is where the action realy is. and can consist of "tinker toy" sockets, to string, to plastic tubing and so on. Just how the joint is constructed also equates to how easily a fully braced tetra can be transported.
For example if each cell is build completely separate to each other, and only joined together on the field, then the individual cells can be stacked into each other. It is still bulky and three dimensional, but a very large kite will stack into a much smaller volume.
If the joint can fold, then one spar from each cell can be removed (or folded out of the way, and the kite can fold up accordian like, into a flat package.
If all the spars are removeable, then you spend a lot of time during setup and take down on the field, but the kite stored into a not very long linear bundle, like most other kites. A further advantage is that individual spars are also then very easy to replace.
One problem with this is that the center of the leading edge of the cell tends to get pushed in ward, unless a very light weight spar is provided to stop this, or the edges has a slight inward curve built into them (as in cody box kite construction).
The spars however, must be very rigid. as such it is only really suitable for modern carbon fiber, or epoxy tubing. Also a string or other light spar is also needed accross the back of the cell as part of the tensioning process.
Transport however is straight forward. either the trailing edge tenson is released, or the center tensoning is released, and each cell will collapse into a easily transportable bundle of loose sticks and fabric.
Some of the largest (and prettiest) ripstop tetras in the world are built using this method.
Again to cut down the number of spars only 3 sticks are used. One along the leading edage and the other along the trailing edge. These are then pushed apart by a "mast" stick bewteen them.
This has a number of distinct advantages. First the leading edge is suported, and second both the cross and leading edge spars can extend across multiple cells! This means that connections between cells can be extremely rigid, and produce a very strong structure, with only 3 spars per cell instead of 6.
However strong spars are required to prevent them from breaking from the side on stressed imposed by the mast. Also 2 of the spars have to be removed for transport, increasing the setup and take down time involved.
A great web site for viewing this technique is Bell Tetra Info, and Plan, particularly toward the bottom of the page.
However straws do not compress very well, tending to foldup under stress. As such straw tetrahedrals tend to be one time affairs. Due to this, construction is usally limited to a full cell bracing. That is every edge of the cell is braced by a straw.
W McClure <firstname.lastname@example.org>, recomends that to strengthen a very large straw tetras with some long thin dowel along the outside edges of the tetra. Of course this adds to the weight of the tetra, but can make the kite last a lot longer than it otherwise normally would.
The straw cells are then covered with either tissue, plastic, or cellophane (warning: cellophane shrinks!), and then individual cells from teams of students, or a whole class, are then tied together to form larger tetrahedrals.
For examples see Glenda Woodburg's Straw Tetrahedral plan is especially good. It dissappeared from the web for two years but has re-appeared. Also quite good is the Ford Middle School, Straw Tetrahedral. Another is the Kansas City Tetrahedron plan by Dave Ellis.
If you want to fold a straw tetra flat for transport, I have had success with using hat elastic. in the trailing edges of four cell units. For more information on this method see... my own straw plan.
The major problem with this technique, is that string such as a nylon thread, or cotton, which is plenty strong enough, is that it tended to cut into the drinking straw. Some people recomment superglueing a small segment of slit straw onto the ends of the bracing straws, to prevent this.
Steve Swindell suggests just touching each straw end to a frying pan, or other metal plate heats on a stove set to medium or medium-low heat. Touch the straw to the blade, BARELY pressing down (not much more than the weight of the straw is needed) for about 1 second.
Wether either method is worth the effort is another matter, and depends on how much effort you want to put into your straw tetra.
How he actually used them he did not say. But they could be hot glued into spiked balls for the straws to slot into, or just superglued glued into the straw ends to stop the string cutting into the straw.
Essentually you use cheap bamboo skewers sold in your local supermarket for satay sticks. These are joined together using a very thin walled plastic tubing from the electonics industry, and cable ties to form the corner joints. The cells are then covered with mylar plastic commonly sold as a silver gift wrapping foil for christmas presents or for flowers sellers.
The result is a very strong but ultra light weight kite using very modern materials. The kites fly at a very high angle, and very stable. For transport the trailing stick on every cell has one end "unpluged" and the whole kite folded up like an accordian into a flat package. Both kites photoed at the top of this page are of this constriuction technique.
The bamboo skewers I have found to get brittle with age, and thus most prone to fracture during landings, or other disasters. I have seen my tetra completely demolised when a rope from a large Peter Lynn Octopus whip across a tetrahedral I had sitting on the ground in just the wrong spot. Only the bridle ring from from that kite was worth the salvage.
Also if the kite does fly then the inherent strength of the spars will ensure that very little damage will result due to crashes, landings, or collisions with other kites and kite lines.
Vinal plastic tubing from the local hardware, or if you can get them, specialised hard plastic joints are typically used for construction.
The individual cells are then pre-built (any of three different ways) and stacked into each other for transport. On the flying field the complete kite is put together in any variation you desire for that days flying using cable ties to join it all together.
A Fantastic solutaion and extremely versitile.