Featured Archive Item: Bell Tetrahedral Cells & the Bell Tetra Challenge

After his description of Bell’s Sable Island kite in the last newsletter, DF Board President Scott Skinner discusses Bell’s tetrahedral cells and announces Drachen’s Bell Tetra Challenge.

After describing Alexander Graham Bell’s Sable Island kite (a version of Hargrave’s box kite) in DF’s last Archive feature, I will focus now on the tetrahedrals themselves. The DF Archive holds four early cells, without coverings, from Bell’s laboratory at Beinn Bhreagh, made before he had switched to aluminum tubing for the frames in October 1903. The slender 10-inch spars are black spruce, held together with deftly designed connectors (now rusted) made from tin cans. Hector McNeil, Bell’s foreman, fabricated the connectors for Bell, and the two obtained a joint patent on them in 1907. J.H. Parkin has said, "It will be evident to those familiar with shopwork that McNeil was a wizard with tools." The cells DF holds support this judgment, as they do Bell’s own opinion of his tetra principle-"It is astonishing how solid such a framework appears even when composed of very light and fragile material."

What path had Bell taken to tetrahedral construction? Curiosity had led his exploration in many directions. He had always been fascinated with flight, but witnessing Samuel Langley’s flying machine in 1891 had sparked that interest into activity. He began his flight experiments by trying to understand thrust; he constructed rocket and steam powered propellers and rotors of various designs to determine how to generate maximum thrust. Then his attention turned to the lifting properties of different airfoils or wing designs, and he had begun his kite experiments in 1896 not only to come to some understanding of lift but to study the properties of wind currents in his pursuit of manned flight.

Bell had worked chiefly with kites based upon Australian Lawrence Hargrave’s box kite, a design that had proven its worth in meteorological flights. But by 1902, Bell was incorporating the tetrahedral cell into his kites’ designs. (A tetrahedral figure is one in which three equilateral triangles are joined to form a four sided shape.) This configuration had many inherent advantages. The kites were structurally stronger, and by combining the cells of smaller kites into one large kite, the surface area-to-weight ratio was retained. Bell’s tetrahedrals reached their apex with 1907’s Cygnet, his kite made from 3393 cells, which flew to a height of 51 meters and stayed aloft for over 7 minutes. 

The tetrahedrals also proved to be very stable in flight. One of the most significant design characteristics of kite stability is dihedral: the bow, or angle of wings to one another. As is quickly seen on a tetrahedral cell, if one side of the cell is exposed to more wind than the other, it creates more lift, causing the cell to align itself to an equilibrium position in the wind. 

Bell became convinced that stability was the key to manned flight: tetrahedral kites could provide that stability and permit experimentation without risk to human life. The Wrights, however, knew that a certain amount of instability was necessary and important to manned flight. As they had seen with countless beginning bicyclists, a certain amount of muscle memory and repetition would lead to stability, just as it would for the first pilots in their airplanes. 

To honor the creative mind of Bell and to celebrate the 100th anniversary of the flight of the Cygnet kite, the Drachen Foundation invites all to participate in building a Bell four-cell tetrahedral kite and make it their own. The Foundation has an easy-to-assemble kit with the necessary connectors and dowels, so that your four cells will be compatible with everyone else’s.

Once constructed and flown, send us two photos of your creation, one of the kite and one which proves its flyability. A distinguished panel of judges will choose the most interesting applications of Bell’s tetra principles and award these individuals a $250. gift certificate toward purchase of kite merchandise from Goodwind’s Kites. Go here for information.

– Scott Skinner 


Young Explorer Field Research

DF awarded its 2006 Young Explorer grant, co-sponsored by the Pacific Northwest Chapter of The Explorers Club, to Oregon high school senior Aron Curzon.


News for Educators: Wind Art Curriculum Development 

DF continues the kite curriculum development project it began during the 2005-06 school year at Lockwood Elementary. New lessons are being created with support from the Washington State Arts Commission.


Kite Sailing Symposium a Success 

Scott Skinner describes the first KSS as a "fast and furious weekend of events highlighted by lectures, discussions, and more than a little fun." Read more.


DF Visitor: Patrick de Koning

Dutch kite maker Patrick de Koning stopped by the DF Study Center and talked with Renea Nielsen about his past experiences and future plans for manlifting with kites. 

Patrick de Koning, kite maker from the Netherlands specializing in using kites for manlifting, stopped by the Drachen Foundation study center for a visit while vacationing in the area and gave Drachen staff the opportunity to learn about his endeavors.

"Aviation started with more than the plane, " de Koning says. " I wanted to lift because it wasn’t difficult and dangerous." De Koning became interested in kites around the age of twenty, beginning with building stunt kites. Because he didn’t like the roaring noise they made, he moved on to making deltas, then the Conynes that he now uses for manlifting, following the French model.

Soon becoming interested in manlifting, de Koning commissioned friend Cocky Eek to be lifted. Dangling beneath the kites, Eek seems to fly herself in the ephemeral Tyvek dress that she created for this purpose, moving her arms to make its train bend and flow far beneath her. Their first attempt in 2001 was a wild success, the kites lifting Eek over 140 meters. Here, the wind was too great, pulling those holding the tether along the beach and leaving de Koning hanging in the air. He now tethers his kites to a large commercial truck. 

The manlifting is usually done with six kites, though de Koning himself has built a total of seven for this purpose. Each attempt requires at least thirty-five people to set up and guide the tether. "I don’t have to have a steady crew," says de Koning. "It’s not complicated to get people to participate in this experience; they can touch it.they are a part of it." 

Though he hasn’t been yet lifted himself, needing to supervise from the ground, he has more ambitious plans for the future that he prefers to keep a secret. What drives de Koning to pursue the adventure? "The place, the performance of just flying, the excitement, the collaboration."