"He goes up there on the side of the hill on sunny afternoons and with a lot of thing-ma-jigs fools away the whole blessed day, flying kites, mind you. He sets up a blackboard and puts down figures about these kites and queer machines he keeps bobbing around in the sky. Dozens of them he has, all kinds of queer shapes, and the kites are but poor things God knows! I could make better myself." — Comments of a boatman in Baddeck, Nova Scotia, on the tetrahedral-kite experiments of Alexander Graham Bell
Alexander Graham Bell (right) and his assistants observing the progress of one of his tetrahedral kites (1908)
Since kites were used to test both aerodynamics and flight stability, they played an important role in the development of aviation. Lawrence Hargrave (1850 - 1915) — who was an English engineer, explorer, astronomer, and aeronautical pioneer — first created the high-performance box kite, or cellular kite, in 1892. In turn, his work inspired the Scottish-born inventor Alexander Graham Bell (1847 - 1922), whose aeronautics experiments, beginning in the late 1890s, led to the development of the respectable tetrahedral cell kite that had impressive strength as well as great lift.
Bell was actively attempting to build a kite that was scalable and big enough to carry both a man and an engine while staying in Baddeck, Nova Scotia, where he and his family spent their summers starting in the mid-1880s. As evidenced by the quote above, local observers did not have much confidence in his attempts; still, Bell and his collaborators carried out 1200 carefully documented experiments over a span of 20 years using kites made up of tetrahedrally shaped cells that created a kind of tetrahedral truss, or rigid frames, based on tetrahedral geometry.
For those of us who have been out of school for a while, this may need some clarification. Generally speaking, a tetrahedron is a polyhedron with four sides. A polyhedron, however, has two definitions: "In geometry, a polyhedron is simply a three-dimensional solid which consists of a collection of polygons, usually joined at their edges." And in algebraic topology, a polyhedron is "a space that can be built from such 'building blocks' as line segments, triangles, tetrahedra, and their higher dimensional analogs by 'gluing them together' along their faces."
In a notebook entry made on August 25th, 1902, Bell documented his excitement "as he linked perceptions gleaned from many months of tests. Frustrated that he could not draw the cell well, he described the shape as a 'figure composed of 4 equilateral triangles having 4 triangular faces bounded by 6 equal edges.'" The up side was that the tetrahedral kite was stable and easy to fly, since the large number of structural spars made it relatively heavy; the down side was that it required moderate to strong winds to operate.
Bell celebrated his breakthrough in "The Tetrahedral Principle in Kite Structure" (1903) that was featured in National Geographic — which was published by the National Geographic Society that Bell co-founded with 32 other members. He wrote:
"In the words of an old writer, 'We cannot consider as impossible that which has already been accomplished.' I have had the feeling that a properly constructed flying-machine should be capable of being flown as a kite; and, conversely, that a properly constructed kite should be capable of use as a flying-machine when driven by its own propellers. I am not so sure, however, of the truth of the former proposition as I am of the latter.
"Passing over in silence multitudinous experiments in kite construction carried on in my Nova Scotia laboratory, I come to another conspicuous point of advance — another milestone of progress — the adoption of triangular construction in every direction (longitudinally as well as transversely); and the clear realization of the fundamental importance of the skeleton of a tetrahedron, especially the regular tetrahedron, as an element of the structure or framework of a kite or flying-machine.
"A framework formed upon this model of six equal rods fastened together at the ends constitutes a tetrahedral cell possessing the qualities of strength and lightness in an extraordinary degree. It is not simply braced in two directions in space like a triangle, but in three directions like a solid. If I may coin a word, it possesses 'three-dimensional' strength; not 'two-dimensional' strength like a triangle, or 'one-dimensional' strength like a rod. It is the skeleton of a solid, not of a surface or a line."
Between 1907 and 1909, Bell was the chairman of the Aerial Experiment Association, which he co-founded with his wife and aviation pioneer J.A.D. McCurdy [1886 - 1961], inventor F.W. Baldwin [1882 - 1948] as well as a few other "young engineers, such as Glenn H. Curtiss [1878 - 1930], an American builder of motorcycle engines, and Lieutenant Thomas Selfridge [1882 - 1908], who acted as observer from the American army. The team — which split its time between the United States and the Bell estate at Baddeck — conducted its first successful experimental flight on December 6th, 1907.
From an initial one-cell model, Bell advanced to a "Cygnet" model. The test aircraft — a 40-foot long, 200-pound, 3393-cell tetrahedral kite covered in maroon silk — was placed on pontoons and towed by an offshore steamer near Baddeck. It attained a height of 168 feet above water and stayed in the air for seven minutes while being piloted by Selfridge. Unfortunately, it was difficult to control and when the wind dropped, the Cygnet crashed into the water. Though further attempts at flight were made with Cygnet II and III, all models were ultimately deemed inefficient.
Before disbanded in 1909, the association did achieved a record on July, 4th, in 1908. "Curtiss flew the June Bug to become the first aircraft to fly one kilometer in the western hemisphere, for which the association was awarded the Scientific American Trophy." The awesome series of black and white photographs below depict Bell and his colleagues as they're demonstrating and testing out a range of different tetrahedron kite designs. It's an interesting mix of geometry, design, and aviation history. But, going strictly by the pictures, it also looks like a bunch of adults enjoying pleasant Canadian summers, while flying kites in the name of science.
June 2, 1903 | Selections from "Journal by Alexander Graham Bell, from January 2, 1903 to August 26, 1904"
June 18, 1903 | Selections from "Journal by Alexander Graham Bell, from January 2, 1903 to August 26, 1904"
April 30, 1904 | Selections from "Journal by Alexander Graham Bell, from January 2, 1903 to August 26, 1904"
Note* Alexander Graham Bell had a long history of experimenting with tetrahedron kites. The six consecutive photos featured above are among his earliest attempts. Photos are selections from his Journal by Alexander Graham Bell, from January 2, 1903 to August 26, 1904, via the Library of Congress.