Intro: Bell Tetrahedral Kite
Alexander Graham Bell used tetrahedral kites in the early 1900s to disprove the theory that size detrimentally effected a flying machine's ability to get off the ground. This Instructable will show you how to make your own tetrahedral kite using bendable drinking straws and Tyvek. It's similar in its design to other kites shown here, but this kite uses less material and is guaranteed to get off the ground in very little wind.
The kite shown in this Instructable was awarded 2nd place in the 2009 Fly NY kite competition in NYC. Not too shabby for a first attempt at kite design! Visit Haptic Lab for more information about the project.
Step 1: Ingredients
You will need the following items:
1. bendable drinking straws (a pack of 200 works great)
2. craft or floral wire cut into 3" lengths
3. small pliers for bending and cutting ties
4. transparent tape
5. sail material: about 2 yards of tyvek, tissue paper, or mylar
6. craft glue
7. thin wood dowels (4 or 5 total)
This project shouldn't cost you more than $10.
Step 2: Straw Triangles
A tetrahedron is the simplest Platonic solid: a triangle with 4 faces. To build the individual tetrahedral cells that make up the kite, start with three straws. Flatten the long end of each straw and insert it into the short end of another straw. Make a triangle.
Step 3: Making Wings
Unlike other drinking straw "tetras", this kite only needs two straw-triangles per cell. By using less material, your kite will fly better and at lower wind speeds. To make a cell, simply tape two straw-triangles together. Angle the wings slightly as shown, but don't worry about making an exact 105-degree angle: the bend in the corners will flex for you.
Step 4: Making Connections
Make the bottom of the kite first. Connect several tetra cells together by twisting 3" bits of wire. Clip the twisted ends off; you'll get poked later on if you don't. Keep connecting, making a larger triangle out of the small cells. I recommend using 3 or 4 rows as shown.
Step 5: Kite Skeleton
Now that you've made several larger cell groups of 6 or 9 cells each, start making connections 3-dimensionally. The joints at the bottom will have 4- and 8- point connections; keep using the wire to secure the cells together. A wide kite built of at least 4 rows will fly best; if the kite is too narrow, it tends to get a little crazy in the air...
Step 6: Making Sails
Use Tyvek (mailing envelopes work great), tissue paper, mylar, or any lightweight sheet material to make the sails. Start with a sheet roughly 20" x 30" in size. Fold in half four times. Make a template out of poster board or a cereal box, and position it on the folded sail material at the closed outer corner, matching a perfect right angle. Cut the material on the 3 angled sides. Unfolded, you will have 8 individual sails. Make as many sails as you need- Tyvek is dirt-cheap.
Step 7: Attaching Sails
Using a tiny bit of craft glue (Sobo, Elmer's, etc) secure the sails to each cell, folding the material around the bottom taped edge. Though a bit counter-intuitive, the kite flies with the sails oriented like a flock of "V"s. Trim any access sail material for a good, tight fit.
Step 8: Tying the Bridle
Basically, tie your nylon line at points 1/3 the way down on the "bottom" edge or widest section of the kite ("bottom" is the taped edge of the tetrahedral cells). You'll have a bundle of lines- tie them off at a point roughly 1.5 times the width of your kite, making sure there is no slack in the lines. From this tie-off or bridle point, attach the main flying line. Use a figure-8 knot for tying: it's easy and much stronger than a square knot.
Step 9: Flight Test
Your kite should take off in about 10mph winds. It's helpful to have a friend for getting it off the ground- stand about 30-50 feet away from one another, with the kite facing the wind. Once the sails catch the wind, the kite should soar straight up in the air very quickly. It will level off depending on the angle of how you attached the lines.
The kite is collapsible, which makes it a great urban traveler. Right before flying however, attach a few thin wood dowels across the top-most cells with wire- being careful to keep the sails spread into equal widths. The rigidity of the wood along the top is critical: without cross-bracing, your kite will fold up like an accordion and crash to the ground as fast as it went up into the air.