As early as 1894, inspired by the work of the German glider experimenter Otto Lilienthal, Chanute began to design gliders capable of carrying human beings into the air. Anxious to provide employment for younger engineers and flying machine enthusiasts, he began contracting for the construction of several gliders.
The first thing done, after some models, was to build a kite, in order to test the stability of the proposed gliding machine. This was called the "ladder kite," from its resemblance to a step-ladder in one of its postures, for it was so constructed as to allow grouping its surfaces in various ways. This kite proved exceedingly stable, flying in gusty winds. Then the construction of a similar machine was begun. which was capable of carrying a man, but first Mr. Herring rebuilt a machine, previously tested by him in New York, somewhat similar to that of Lilienthal, so that the known should be tested before passing to the unknown.
Chanute selected the sand dunes along the southern shore of Lake Michigan as the perfect place to test his creations. The area was close to Chicago. The little train station at Miller, Indiana served as an entry point into Dune country. The area offered a number of other important advantages, including steady winds, dunes from which a glider could be launched in any direction, an abundance of sand for soft landings, and, Chanute hoped, relative isolation.
Chanute and his four assistants pitched their tents on a spot within the present city limits of Gary, Indiana, on June 22, 1896. Augustus Herring, the most experienced member of the group, had brought a glider based on the standard Lilienthal monoplane design. William Avery, a Chicago carpenter, had constructed a multi-wing glider designed by Chanute, while William Butusov would attempt to launch his own glider, the Albatross, down a wooden ramp. Dr. James Ricketts, a Chicago physician with "a slack practice and a taste for aeronautics," would cook for the group and provide emergency medical service as required. Chanute's dogs, Rags and Tatters, rounded out the party.
Herring and Avery did most of the flying. The Lilienthal glider proved to be a disappointment. After abandoning this Lilienthal form of machine, the experimenters in the sand dunes next tested the machine built after the fashion of the ladder kite which had proven so steady in the air.
It consisted of six pairs of wings, superimposed and trussed together, pivoted at their roots upon a central frame, the lower chord of which was spread open to receive the man at the center. Here he was expected only to move for the purpose of steering, the stability to be maintained by the movements of the wings above him, which swung on their pivots back and forth, restrained by rubber springs, when the wind struck one side more than the other, or changed the center of pressure fore and aft. It will be seen that this is just the reverse of the first method tested, in which the man moved and the wings remained fixed. This wing movement took place as expected, but it was very soon found that there was an essential difference between the support from the wind derived from the same arrangement when flown as a kite, at an angle of incidence of 30 to 40 degrees, and when flown as a gliding machine, at an angle with the wind of three or four degrees, which is the most favorable for reducing the total resistance to a minimum. It was found that at very acute angles the moving air was deflected downward by the front wings, so that the support under all the following wings was greatly diminished, and that the apparatus was inefficient when its surface was considered. This had been expected, from prior experiments, and the frame had been designed so that the grouping of the wings could be readily changed. Then began an interesting and instructive evolution. The grouping of the wings was gradually changed, through six permutations, each being guided by gliding flights and by releasing bits of featherdown in front of the machine, and watching the paths of the air currents which swept past the wings. The result of this evolution was to change greatly the outward appearance of the apparatus while retaining the same general principle.
Chanute's glider, featuring multiple sets of wings that could be arranged in various configurations, was more interesting, covering distances of from 50-116 feet through the air. The group returned to Chicago on July 4. They would spend the next month repairing their various craft and building a new glider featuring three wings set one on top of the other, all linked together with a truss of the sort that Chanute had employed in constructing railroad bridges. Herring was apparently responsible for the cruciform tail.
Sixth Form Multiple-Wing Machine
The improved arrangement as seen from one side in flight. It will be noticed that no less than five of the six pairs of wings have been superimposed at the front, and trussed together. That the operator is within and under them, and that a single pair of wings remains at the rear to serve as a tail. This tail was flexible and vibrated up all down in flight when the angle of incidence varied in consequence of the back and forth movements of the pivoted front wings.
About two hundred glides were made, in winds of 13 to 22 miles an hour, on a descending course of about 1 in 4 (14o), the longest flight being 82 feet from a height of about 20 feet. There was, however, undue friction in the wing pivots, thus retarding theirautomatic action, so that the operator had to move two or three inches, as against some 15 or 18 inches on the previous machine, and there being some further defects in the spacing of the wings, both vertically and horizontally, it was determined to rebuild the machine with the practical information thus obtained.
Camp was accordingly broken up early in July, with the conviction that more had been learned during this two weeks of experiment with full-sized machines than had previously been acquired during about seven years of theoretical study and experiments with models. The equipment was returned to Chicago, where three machines were constructed, and the five men returned to the Dunes on August 21, 1896, establishing a new camp some five miles down the beach from their original site.
Seventh Form Multiple-Wing Machine
The multiple-wing machine as reconstructed consisted of the same wings and of a new frame, and instead of ordinary pivots, there were ball bearings at the ends of vertical wooden posts to which the roots of the wings were attached, the latter being all trussed together, with vertical posts and diagonal wire ties, this being probably the first application which has been made of the Pratt truss to flying machine design. The frame was all made of spruce, the surfaces were of Japanese silk varnished with pyroxelene; the complete machine weighed 33 1/2 pounds, the supporting surface at the front was 143 1/2 square feet, including a concave aerocurve over the top, added when the front wings were cut down to four pairs, and the rear wings or tail measured 29 1/2 square feet in area. With this arrangement a great many glides were made, with the result of more than doubling the lengths previously attained, of reducing the angle of flight to 1 in 5, or 10o to 11o, and of diminishing the required movements of the operator to one or two inches in preserving the equilibrium.
It might have been preferable to omit the aerocurve over the top, and to have placed all the supporting surface in the pivoted wings at the front. This aerocurve was added to save the expense of rebuilding the old wings, and this saving proved to be a mistake. The wings were so far racked and distorted by their prior service that they did not support alike and did not balance the weight properly, and thus the results obtained with that machine were inferior.
After some disappointing test flights, Chanute ordered the bottom wing removed from the new glider, producing a biplane design.
With that modification complete, Herring and Avery were soon making repeated flights of over 200 feet in length, occasionally traveling as far as 350 feet through the air. By the time the group broke camp for good on September 25, 1896, they had completed several hundred flights with the biplane. For the moment, the little craft was the most successful heavier-than-air flying machine in the world.
Two-Surfaced Machine with Side Keels
The next full-sized machine which was built consisted of a single intersection Pratt truss carrying the surfaces, to which was applied a regulating mechanism designed by Mr. Herring. This truss will safely support 300 or 400 pounds applied to the arm bars at the center. In calculating its proportions a basis has to be adopted which is the reverse of that which obtains in the calculation of bridges, for the support, or air pressure, has to be considered as uniformly distributed, and the load has to be figured out as concentrated at the center. It may be mentioned in this connection that one practical difficulty found has been in devising some method of adjustable connection between the vertical posts and the diagonal ties. The latter are from two to five hundredths of an inch in diameter, and it is not practicable either to cut a screw upon them for a nut, nor to apply a sleeve nut or a turn buckle. Perhaps some engineer will suggest a better device than the loop heretofore used, which is made by twisting the wire back upon itself, and which is not adjustable.
The regulating mechanism took care of the equilibrium fore and aft and diminished the effect of the side wind gusts which were then easily overcome by slight side movements of the operator. Towards the last amateurs were permitted to try it under instructions. They made fair glides in safety. One or two cruises by newspaper reporters, and another by a novice, who was picked up by the wind and raised some forty feet into the air, but who landed almost in his tracks as gently as if he had only fallen from the height of a chair.
With this apparatus several hundred glides were made, varying in length from 150 to 360 feet, at angles of descent of 7 1/2 to 10 degrees, at a height of ten to twenty feet above the ground, but it was not uncommon for the machine to sail forty or fifty feet above the ground, and during the six weeks occupied with the experiments, not the slightest accident occurred either to the operators or to the machines. The whole apparatus spread 134 square feet of supporting surface, weighed 23 pounds, and thoroughly supported the weight of a man at speeds of about 23 miles an hour.
The 1896 biplane tested on the Indiana Dunes proved to be a key step on the road to the invention of the airplane. Herring continued to experiment with the design on his own over the next five years. Chanute's publication of the plans and specifications for the glider helped to spark a renewed interest in flight both in America and Europe. In May 1900, Octave Chanute received a letter from Wilbur Wright. "Afflicted with the belief that flight is possible to man," the Wrights had designed a glider of their own. "In appearance, Wilbur noted, "it is very similar to the 'double-decker machine with which the experiments of yourself and Mr. Herring were conducted in 1896-97."
The operator (Mr. Herring in this instance) is seen creeping
under the machine in order to rise with it, when lifted up by
the two assistants, and to place himself within the arm bars