Mr. Chanute stated in beginning that when, in 1891, Professor Langley, the eminent astronomer, and the Secretary of the Smithsonian Institution, published his important work, "Experiments in Aerodynamics," the closing paragraph of the summary was as follows: "I wish, however, to put on record my belief, that the time has come for these questions (i. e., those of aerodynamics and aerial navigation) to engage the serious attention not only of engineers, but of all interested in the possibly near practical solution of a problem, one of the most important in its consequences of any which has ever presented itself in mechanics; for this solution, it is here shown, cannot longer be considered beyond our capacity to reach."

Mr. Chanute continued that it did not seem to the general public then, and it possibly might not seem now, as if a commercial and practical flying machine was an achievement to be expected in the near future; yet it did seem opportune for an engineer approaching the end of his professional career to devote some of his leisure to the investigation of the laws which must be here after observed by other engineers in compassing the navigation of the air. He therefore took up the question; and believing that the surest method is first to study past failures in a novel undertaking, he made an investigation of the records of all the experiments, which had been tried during the last two or three hundred years, in the endeavor to imitate the birds. This resulted in a number of technical articles which swelled into a book, in which the attempt was made to eliminate the causes of each failure; for up to that time there had been nothing but failures.

He said he had hitherto abstained from addressing his fellow engineers on the subject, as some might deem it premature, but he had become gradually convinced, not only through investigation but through practical experiment, that it was not only possible but almost certain that man will eventually be enabled to make his way through and on the air by dynamic means, although it might require a considerable and long process of evolution to do so. This evolution was now in progress, and very great advance has recently been accomplished. It chanced that about the year 1888, a number of able men, in various parts of the world, simultaneously took up the question, and the progress which they have made is already greater than that previously achieved during the past two or three centuries. Those men were Mr. Maxim, an American in England, Professor Langley in this country, Mr. Hargrave in New South Wales, and Mr. Lilienthal in Germany. They investigated afresh the laws which underlie the possible solution of the problem of flight, and the results of their labors will probably best appear from a discussion of the various elements of that problem.

These elements number ten at least, and may be considered as so many subsidiary problems, each to be solved separately, perhaps in more ways than one, and those solutions then to be combined into a harmonious whole. They may be stated as follows:

1st. THE SUPPORTING POWER AND RESISTANCE OF AIR

This first problem is the foundation of the whole subject, and, singularly enough, it is only within the last six years that it has been settled beyond question what is the true measure of those properties of air when meeting a surface at an oblique angle of incidence. Sir Isaac Newton gave by implication from his proposition XXXIV, Book 2 of the Principia, a law which has variously been interpreted as meaning that normal fluid pressures vary as the sine, or the square of the sine of oblique incidence. These formulae are today still taught in the schools, and found in text books, although experiments have shown that at very acute angles they give from one-tenth to one-twentieth of the true results. Engineers make current use of them in calculating pressures upon roofs, and upon parts of bridges struck obliquely by the wind, while with later knowledge it can be shown that a wind gust deflected upward under the floor of a bridge, even so little as 5 or 10 degrees, produces such a lifting effect as to account for the blowing off of superstructures hitherto accounted as inexplicable. In point of fact, Professor Langley's experiments showed that oblique air pressures varied not as the sine, or the square of the sine of incidence, but, approximately as indicated in the empirical formula proposed by Col. Duchemin about 1828, in which the relation between the rectangular normal pressure and the oblique normal pressure is represented by:

               2 Sine a
 P = P' x -------------
               1+Sine2 a

In which P = the oblique pressure,
P' = The rectangular pressure,
a = The angle of incidence.

This applies exclusively to planes or flat surfaces, while Lilienthal has shown by experiment that curved surfaces presented with their concave side to the wind afford still greater pressures, these being from twelve times to four times the normal pressures obtaining upon planes at angles between 1 and 5 degrees, which are those most favorable for flight. Thus it is that we are now enabled to calculate with some confidence the support which may be obtained by gliding at any given speed upon the air, and the power required to overcome the resistance. An eminent French mathematician, at the beginning of this century, calculated that a swallow, weighing six-tenths ounces, expended in full flight no less than one-thirteenth of a horse-power. This calculation was evidently erroneous. It would have implied that the weight of a man, say 150 pounds, would require the expenditure of something like 300 horse-power to sustain it in the air, but calculations of the power really required could not be made with confidence until the recent labors of Professor Langley, confirmed as they have been by those of Mr. Maxim, and the still more encouraging coefficients for concave surfaces obtained by Lilienthal and in the experiments which were to be presently described.

2d. THE MOTOR, ITS CHARACTER AND ITS ENERGY.

This second problem, now nearly solved, was thought until five years ago to be still more difficult than the obtaining of supporting power from the air. It was known that the motor muscles of birds, though possessing but little more tensile strength than those of land animals, gave out energy at a much more rapid rate, so that it was variously estimated that bird machinery (muscles) weighed from 5 to 20 pounds for one horse-power exerted. Upon investigation in 1890, it was found that the lightest steam engines then in use were those in launches and weighed 60 pounds per horse-power, that the lightest petroleum engines weighed 88 pounds per horse-power, while the lightest electric motor weighed 130 pounds, and the lightest storage battery and dynamo weighed some 200 pounds per horse-power hour. Since then the advance has been very great. Mr. Maxim has produced a steamplant of 360 horse-power which weighs about 8 pounds per horse-power. Professor Langley has built an engine and boiler which weighs 7 pounds and exerts one horse-power, while Mr. Hargrave has constructed a steam engine weighing about 10 pounds to the horse-power. Almost as great advances have been accomplished with petroleum motors, which possess the great merit of dispensing with a boiler, so that for the first time the realization of a sufficiently light motor for a dynamic flying machine seems to be within sight. It now seems probable that this will be accomplished with a petroleum engine when the eccentricities now inherent to that class of unperfected motors have been over come in practice.

3d. THE INSTRUMENT FOR OBTAINING PROPULSION.

The third question relates to the device through which adequate thrust shall be obtained by action upon the air. All sorts of contrivances have been proposed; reaction jets of steam or of compressed air, the explosion of gunpowder or even nitro-glycerine, feathering paddle wheels of varied design, oscillating fins acting like the tails of fishes, flapping elastic wings like the pinions of birds, and the rotating screw. Mr. Maxim and Professor Langley have made many experiments to determine the best form, speed and pitch of the screw to obtain thrust from the air, and have materially improved that instrument, which, to reason from analogy in land and water transportation, seems likely to prove the best device, but both Mr. Hargrave and Mr. Lilienthal have obtained very favorable results with the flapping pinion, which requires no intervening machinery to change the reciprocating action of a piston into a rotary motion, and it seems perhaps possible that success in artificial flight may be obtained with either or both devices.

4th. THE FORM AND KIND OF THE APPARATUS.

This fourth question has elicited great divergence of views among the designers of flying machines. Almost numberless projects have been advanced, but they can all be classified under three heads. 1st. Wings to sustain and propel. 2d. Rotating screws to lift and propel, and 3d, aeroplanes or aerocurves, to consist of fixed surfaces driven by some kind of propelling instrument. The first two have been the first to be proposed and experimented with. They have many warm advocates at the present time, but the practical experiments made within the last five years seem to indicate that success will first be achieved with aeroplanes, or to state it more accurately, by coining a new word, with aerocurves, which have been shown by Lilienthal to furnish much greater lifting reactions. The following table, in which the weight of the operator of a one-man machine is included with the weight of the apparatus, approximately indicates the comparative merit which our present knowledge enables us to assign theoretically to these three varieties of flying machines.

Comparative efficiency of various forms.

Kind of Apparatus	Pounds probably sustained per Horse-power	Proportion probably available for motor.	Resulting possible weight of motor per Horse-power
Screws...	25	17 per cent	4 lbs
Wings....	80	10 per cent	8 lbs
Aerocurves	80	17 per cent	14 lbs

It will be noticed that this involves motors which shall be very light in proportion to their output of energy, and that the fuel and other supplies must also be included in the weights above given, but yet that the desired results for aerocurves at least are now almost in sight.

5th THE EXTENT OF THE SUSTAINING SURFACES.

The fifth problem, relating to the extent of surface required to support the weight of a man, has caused in the past active controversy and gathering of data. It was perceived that in consequence of the law inherent to solids, the surfaces will increase as the squares, and the weights as the cubes of the homologous dimensions; it might well be that the additional relative weight due to the greater leverage should make it impossible to compass any larger flying machine than existing birds. Indeed, it is not so long ago that a distinguished scientist published an article in which he flatly took the ground that an artificial flying machine was impossible for three reasons: 1. That Nature, with her utmost effort, had failed to produce a flying animal of more than fifty pounds in weight. 2. That the animal machine was far more effective than any that man may hope to make. 3. That the weight of any artificial flying machine could not be less, including fuel and engineer, than 300 or 400 pounds. These assertions have since been modified, but the author still holds that the possible limit of weight cannot be pushed much, if at all, beyond 100 pounds of machine and operator together.

In point of fact, flying creatures vary in extent of supporting surface from about 40 square feet to the pound in the butterfly, to an area of 44-100 square feet to the pound in the duck. The amount required depends upon the speed of the creature's flight, the larger soaring birds generally spreading about one square foot or less to the pound, while the experiments of Lilienthal, as well as those to be hereafter described, have demonstrated that a man's weight can be well sustained, at 22 to 25 miles an hour, by an apparatus spreading three-quarters of a square foot to the pound, and that this apparatus need not weigh more than from 23 to 36 pounds, without motor or propeller, so that if the latter weigh some 60 pounds more, we may fairly expect to compass a dynamic machine with a weight of about 100 pounds, carrying a man of about 150 pounds, upon sustaining surfaces of rather less than 200 square feet in area.

6th. THE MATERIAL AND TEXTURE OF THE APPARATUS.

The sixth question relates to the material to be selected for the framing of the machine, for the motor, and to the texture of the sustaining surfaces. Nature accomplishes her purposes with bone, flesh and feathers, but man has at his command metals, fuel and textile fabrics. Many hopes were expressed some years ago, when aluminum first became a commercial metal, that it was about to solve the problem of aerial navigation. Later investigations have developed the fact that aluminum is as yet inferior to steel per unit of weight. It is lighter, but it is also weaker. For a beginning wood will do very well. It is a fact, realized by few engineers, that the best woods, so long as they remain undecayed, are actually stronger in proportion to their weight than the ordinary grades of steel. Wood is easily and cheaply procured and shaped, and whatever success has hitherto been had in gliding flight has been accomplished with wooden frames covered with textile fabrics. The latter are probably inferior in efficiency to the ribbed surface of feathers, as quite recent experiments tend to show, but they will answer for a beginning.

Thus we see that six out of the ten subsidiary problems involved in the general question have been approximately solved. Not all, but most of this has been accomplished within the last few years. The remaining four problems are more difficult of solution, but even towards this, gratifying advance has been made.

7th. THE MAINTENANCE OF THE EQUILIBRIUM.

The seventh problem relates to the stability of the apparatus in the air, and especially in a wind. This equilibrium must be maintained at all angles of incidence and under all conditions of flight and of wind, in rising, in sailing and in coming down. The first requisite for this is that the center of gravity shall constantly be in a vertical line with the center of pressure, and unfortunately the latter is almost constantly varying with the relative wind, with the speed and with the angle of incidence. It is a peculiarity of air pressures, ascertained by experiment, that as the angle of incidence changes, the position of the resultant center of pressure also changes. When air meets a surface at right angles, the center of pressure coincides with the center of that surface, but when the angle becomes more acute, the center of pressure moves forward until it approaches a position about one-fifth of the distance back of the front edge on a plane. This movement is approximately expressed by what is known as Joessel's formula for square planes:

In Which
	C = (0.2 +0.3 Sin a) L.
	C= The distance from the front edge.
	L= The whole length fore and aft.
	a = The angle of incidence.

This formula is found not to be accurate for oblong planes, and even not strictly true for square planes, but it is understood that recent experiments are likely to produce a more accurate formula for planes. The great need, however, is for a formula which shall accurately express the movements of the center of pressure on concavo-convex surfaces. They are known to present some curious anomalies, but no physicist, so far as is known, has yet reduced them to the reign of law. The problem of stability may be said to have been very considerably advanced. The experiments hereinafter to be described were undertaken with the sole view of evolving the solution of this question, for it is held to be of the very first importance. Far more so than seems to be realized by experimenters; for until automatic equilibrium is secured, and safety is ensured thereby, under all circumstances, it will be exceedingly dangerous to proceed to apply a motor and a propeller. Birds preserve their balance by instinct, by skill acquired through long evolution and tentative practice. Man will have to work out this problem thoroughly, even to the temporary disregard of the others, if he is ever to make his way safely upon the air.

8th. THE GUIDANCE IN ANY DESIRED DIRECTION.

The eighth problem relates to the steering. It has been generally supposed that this would be best effected by horizontal and vertical rudders, but the experiments of Lilienthal, and those to be here described, have shown that slight changes in the position of the center of gravity are more immediate and effective. This problem cannot be said to be fully worked out, but it is not that a good deal of experimenting will be required, and that such experiments will be fraught with danger. He had nevertheless advised in his writings, and in an article in the Engineering Magazine for April, 1896, that experiments be carried on preferably with full sized machines, carrying a man, as the more fruitful and instructive method. This was good advice, but it might prove dangerous for others to follow. He therefore deemed it desirable that he should ascertain himself how much of risk this involved, if made with due care and precaution.

It was not the intention, in these experiments, to seek to invent a flying machine, although that impression may have been conveyed by some of the newspaper notices of them. The intention was mainly to study the seventh problem-the maintenance of the equilibrium-which it was hoped to gain automatically. This it was expected to do by reversing the method of Lilienthal, who moved his bodily weight to bring back the center of gravity under the center of pressure, as fast as the latter shifted from any cause. It had occurred to Mr. Chanute that it might be preferable to provide moving mechanism within the apparatus itself, to shift the surfaces so as to bring back the varying center of pressure over a fixed center of gravity, and that in such care the operator need not move at all, except for the purpose of steering. The results have been exceedingly gratifying. Two forms of apparatus have been evolved, each equipped with a different device, which are now believed to be materially safer than any heretofore produced. With them several hundred flights have been made, extending over two seasons, without the slightest personal accident.

In December, 1895, Mr. Chanute secured the services of Mr. A. M. Herring, a civil and mechanical engineer, who had for some years been making experiments in Aviation, this being the recent name given to attempts to imitate the birds. The first thing done, after some groping with 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 admit of grouping its surfaces in various ways. This kite proved exceedingly stable, flying in gusty winds without the eccentricities common to that class of apparatus. 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. With these two machines Mr. Chanute and Mr. Herring, and two assistants (Mr. Avery and Mr. Butusov), went in June, 1896, to the desert sand dunes at the south end of Lake Michigan, north of Miller Station, about thirty miles from Chicago. The Lilienthal-like machine was the first tested.

FIG. 222. Modified Lilienthal

The Figure 222 represents Mr. Herring in the Lilienthal type of apparatus, poised in a wind at the top of a sand hill about thirty feet high, preparatory to making a glide. The machine spread 168 square feet of sustaining surface, was equipped with a double rudder, and weighed thirty-six pounds. With this about 100 glides were made, the longest being 116 feet. It proved from the outset an awkward machine to handle. Lilienthal, whose skill had been developed by four or five years of practice, obtained valuable and safe results with it, but it was otherwise with novices. Its operation involved a struggle with the wind before it could be brought under control, and this continued after the flight had begun.

In Fig. 223 this machine is shown gliding a short height over the ground. This was practiced to avoid untoward accidents, for the winds experimented in, of 12 to 17 miles per hour, constantly varied the position of the center of pressure so far and so rapidly through their fluctuations, that the operator had to shift his position as actively as a tight-rope dancer, but to greater distances, to avoid being overturned. The body had to be moved at times some 15 or 18 inches, and not infrequently in landing the apparatus was broken. This involved less personal risk than might be supposed because the radiating ribs curve downward, as shown,

FIG. 223. Lilienthal Type Under Way.

so that they first come into contact with the ground when an awkward landing is made, and save the operator from harm. Similar experience seems to have obtained with an acrobat in a public garden in Vienna, with Professor Fitzgerald in Dublin, with Mr. Lamson in Maine, and with the Journal newspaper in New York, although Mr. Pilcher, in England, has succeeded well with a modified Lilienthal apparatus of his own building. At last, the machine shown on Figs. 222 and 223, after having been broken and mended a number of times, was finally discarded altogether, and within six weeks thereafter Lilienthal's sad death occurred while experimenting with his double-decked apparatus.

After abandoning this first 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.

Fig. 224 exhibits a front view of this arrangement. 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,

FIG. 224. First Form Multiple-Wing Machine.

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.

Fig. 225 shows 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.

FIG. 225. Sixth Form Multiple-Wing Machine.

Fig. 226 shows a front view of the same machine in flight. About two hundred glides were made, in winds of 13 to 22 miles an hour, on a descending course of about 1 in 4 (14^o), the longest flight being 82 feet from a height of about 20 feet. There was, however, undue friction in the wing pivots, thus retarding their

FIG. 226. Front View Multiple-Wing Machine in Flight.

automatic 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 towards the end of August they were taken out to the wilderness of sand dunes, north of Dune Park, about five miles from Miller.

FIG. 227. Seventh Form Multiple-Wing Machine.

Fig. 227 shows the multiple-wing machine as reconstructed. This 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 10^o to 11^o, and of diminishing the required movements of the operator to one or two inches in preserving the equilibrium.

FIG. 228. Multiple-Wing Machine in Flight.-(From a drawing.)

Fig. 228, reproduced from a drawing, shows this apparatus as it appeared in flight. 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 to those to be hereafter described. Yet the principles deemed to be sound, and it is believed that the apparatus can be further improved.

FIG. 229. Two-Surfaced Machine with Side Keels.

Fig. 229 exhibits the next full-sized machine which was built. It is seen to be very simple in construction, and to consist in 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.

With this apparatus as shown in Fig. 230, several hundred glides were made, varying in length from 150 to 360 feet, at angles of descent of 7 1/2 to 10 degrees, and during the six weeks occupied with the experiments, not the slightest accident occurred either to the operators or to the machines.

FIG. 230. Two-Surfaced Machine Just Starting.

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.

Fig 231 shows a side view of this apparatus in flight. On this occasion a glide was made of about 300 feet 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 to pass over the heads of the spectators. 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. A piece of trestle work will be observed in the background. This was used to launch the machine which is next to be described.

Fig. 232 exhibits the fifth full-sized apparatus which was experimented with in 1896. It was the invention of a Russian, who claimed that he had already attained success in soaring flight with it, and as this closely resembled the machine of Captain Le Bris, who was said to have sailed with such a machine in France, in 1867, it was determined to give the design a trial.

FIG. 231. Under Way and Level with the Starting Point.

FIG. 232. The Albatross Machine.

It was a somewhat complicated apparatus. Over the top was an aeroplane, below which two great wings extended, 40 feet across, and beneath which again there was a boat-like frame which could be transformed into a skiff by enclosing it with oiled canvas. The whole spread of supporting surface was 266 square feet and it weighed 190 pounds. As this could not, like the other machines, be carried about on a man's shoulders, special appliances were required to launch it.

FIG. 233. The Albatross on the Ways.

This appliance is exhibited by Fig. 233, and consisted of trestle work built down the slope of the hill. It involved the great disadvantage that it could only be used when the wind blew straight up the trestle, a rare occurrence. Nevertheless two launches were made, but in ballast, as there was no absolute certainty about the equilibrium. On the first occasion, with 130 pounds of ballast, it went off very well indeed, but did not sail very far. In alighting, some of the ribs of the boat-frame were cracked but were replaced in an hour. On the second trial, with 90 pounds of ballast, but in a quartering, unfavorable wind, the latter swung the machine around, after it left the ways, and upon one of the wings striking a tree, the apparatus fell and was broken. On neither occasion would the operator have been hurt had he been in the machine, but it was evidently much too heavy and too cumbrous to be successfully used in experiments designed solely to work out the problem of equilibrium.

This ended the experiments of 1896. A fuller account will be found in the "Aeronautical Annual" .for 1897, edited by Mr. James Means, of Boston, whose publications during the last three years have done very much towards advancing the study and solution of the problem of Aviation. Detailed plans of the multiple-wing machine will be found in the 1897 issue.

The results of these experiments in 1896 were to develop two machines which are believed to be safer than any others previously tried. To advance materially the solution of the problem of equilibrium. To learn much about the management of flying apparatus in the wind, and to determine with some accuracy the power required. For this purpose the lengths and heights of some of the flights were measured. They were also timed, and it was found that the power expended was from 619 to 789 foot-pounds per second, or 1.13 to 1.43 horse-power to sustain 178 pounds in the air. This, however, was in a rising trend of wind. In nearly calm air, the power expended was found to be 2 horse-power, or at the rate of 89 pounds sustained per horse-power.

FIG .234. Getting Ready.

This represented the actual thrust required to be exerted by a propeller. If we assume the latter to possess only an efficiency of 70 per cent, then we should require 2.85 actual horse-power on the shaft, and if the internal friction of the engine diminished its efficiency to 70 per cent of its indicated horse-power, then a motor of about five indicated horse-power might be expected to maintain an apparatus of the above type, carrying a man, in horizontal flight through the air. A result which is surely encouraging.

Mr. Chanute continued by saying that in 1897 he had inaugurated experiments with models for the purpose of testing still a third method of obtaining automatic equilibrium, but that these had not proceeded very far. That Mr. Herring, having been requested by an amateur to supply him with a gliding machine, had built a new one with his regulating mechanism, and that the pictures next to be shown had all been taken from flights made with that apparatus, it having been tested at Dune Park in September, 1897.

Fig. 234 exhibits the machine at the top of the hill, preparatory to making a glide. lt is a common saying that a child must creep before he learns to walk, and something of the same required training obtains with a flying machine. 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.

FIG. 235. Poised for Flight.

Fig. 235 shows the apparatus poised in the wind. This involves generally a struggle with the breeze, which buffets the surfaces either from one side or the other, or fore and aft. A skillful operator resists this by bracing the machine against his back and keeping the front edge depressed, facing the wind accurately. As soon as this poise has been obtained, two or three running steps are taken, the front edge is slightly raised, and a leap is taken forward.

FIG. 236. The Flight Begun.

Fig. 236 shows the result, which is that the man is lifted up and supported by the air, and then sails forward at a slightly descending angle, the motive power being furnished by gravity, and the supporting power, which is due to the speed, being assisted by the adverse wind.

Fig. 237 exhibits the machine as thoroughly under way, the regulating mechanism providing for the fore and aft equilibrium, which is the most precarious and productive of accidents. If the wind be steady, and the operator has placed himself at just the right point within the arm bars, the glide might continue without any movement on the man's part, but there are incidents which are apt to occur in consequence of the irregularity of the wind, such as that shown in the next picture.

In Fig. 238, the apparatus is shown as struck by a side gust. The illustration in this particular picture was somewhat exaggerated by the fact that the camera was not held quite level, but it is clear that the left wing has been raised by the gust,

FIG. 237. Well Up.

FIG.FIG. 238. Struck by a Side Gust

and that the operator has thrown his feet towards that side, in order to bring the wing down. It may be well here to remark that when in flight the bodily movements should be just the reverse of those which are instinctively made if standing on the ground. In the latter case, if one finds himself going over in one direction, the foot on that side is instinctively thrown out to that side; on a flying machine, if one willing is found to be depressed, the weight should be thrown to the opposite side in order to bring the wing down. This requires some practice to become second nature, but after awhile it is done semi-automatically, and without stopping to think.

FIG. 239. Righted Again.

In Fig. 239 the machine has been righted up and is gliding forward on an even keel at a flatter angle of descent than the slope of the hill, so that the next picture shows increased height.

In Fig. 240 it is seen directly overhead of the camera and thoroughly under control, the legs having been raised up ready to be thrown in any direction to do the steering.

In Fig. 241 the trees have been passed for some distance, the apparatus is sailing steadily, and the ground is being gradually approached.

FIG. 240. Passing Overhead.

FIG. 241. Sailing Along

In Fig. 242, the foot of the hill has been nearly reached, and it is time to think of alighting. This is very easily accomplished by pushing the weight of the body backward on the supporting bars, through a movement of the fore arms. The effect of this is to raise the front edge of the machine, thus increasing the angle of incidence and the consequent air pressure. This stops the speed, and as the diminished velocity also diminishes the pressure, the apparatus oscillates gently to a level keel, and the operator alights on the ground with almost no jar.

FIG. 242. Time to Think of Alighting

The curious in such matters will see this manoeuvre performed thousands of times a day by the sparrows in the street. Mr. Herring and Mr. Avery, who were the experts who operated this machine at Dune Park, seldom or never struck the ground with greater force than would have been produced by jumping down one or two feet, and even when racing no sprained ankles occurred.

Fig. 243 shows the apparatus being carried back preparatory to making another glide. These were generally 200 or 300 feet long, and occupied 8 to 14 seconds, although it takes nearly 20 minutes to describe one of them. The sport is so exciting, the sensation of flying through the air is so delightful, that the operators immediately desire to make another glide, and they generally alternate in taking such flights. Each of the pictures shown has been taken from a different glide, but the effort has been made to have each represent a different phase, so that the sequence of aerial transit might be followed.

Mr. Chanute further said that the first requisite towards devising an artificial flying machine was to learn how such machines behaved in the air, and that he therefore advised constant practice to acquire the science of the birds. That the present auditors would doubtless like to know in greater detail just how it felt to be riding on the air, and he therefore begged to introduce Mr. Herring, who would describe the remainder of the pictures.

Mr. Herring stated that the slides previously described by Mr. Chanute were views of flights taken toward what was known as the valley or southwest side of the hill. But those from view 23 onward were from the lake side or northern slope.

FIG. 243. Going Back Again.

Fig. 243, he said, represented very well the method of carrying. the machine in mild or moderate winds, for in toiling up the slope the operator's feet sank so deeply in the fine yellow sand that outside aid was sometimes sought from the wind pressure on the surfaces. This pressure, which was a lifting one, amounted in some cases to more than 100 pounds, but that there were drawbacks to its use which required considerable practice of the carrier to overcome. These drawbacks, he said, were first, those due to the varying direction at which the wind arrived - each variation producing very wide range of travel of the center of lifting effort, and, consequently, considerable leverages to contend with - leverages so great that the 25 pounds weight of machine often became almost a negligible factor beside the forces which had to be occasionally contended with unless great care and quickness of action were exercised to always point the front of the apparatus into the momentary direction of the wind; the accurate judging of the extent of these momentary changes was a matter in itself which required considerable practice.

FIG. 244. Near the Starting Point.

Another difficulty of handling the machine on the steep slope was, he said, due to a property peculiar to arched surfaces, namely, to a strong propelling component which they possessed at small positive, as well as negative, angles of inclination (to the horizontal), when held in a strongly ascending current of air, such as always existed in winds at the hillside. This propelling component,which tended to force the carrier back down the hill against the wind, would frequently be brought about by gusts, or disturbances in the wind which affected the vertical trend and produced these propelling components so suddenly and with such force, in winds of 20 miles an hour or over, that it was generally safer to employ two men to carry what in a calm would be a comparatively light load for one.

After arriving at the starting point, which, he said, was not at top of the hill but just a few feet beyond the position shown in the Figure 244, the apparatus was held with the chord of the surfaces pointed downward at a considerable negative angle in order that the machine should sustain only its own weight, and at the same time the apparatus was directed squarely into the momentary wind so that both sides lifted equally, and, while the machine was thus poised, the operator (in front of the apparatus), released his hold and slipped quickly underneath, passing his arms over the longitudinal bars (called arm bars), beneath the lower surface, at the same time grasping the front pair of diagonal struts which joined these bars to the framing. This done, the whole machine was lowered until the small cross-piece in the rear of the operator rested on his hips or the small of his back. In this position a considerable leverage could be exerted, and with practice even a novice could soon hold the machine under perfect control until the actual start was made down the hill.

Continuing, Mr. Herring said that in view of the small size of the machine, exposing in the present instance but 131 square feet of surface, one in first handling it would be surprised at the very great lifting effect, as well as the extent of the disturbing forces which come into play in comparatively light winds. He explained that this increased lifting effect was due to the very great superiority of arched surfaces over plane ones. This superiority had been first discovered and explained by the late Otto Lilienthal, a German engineer, who pointed out that the lifting forces which come into play were those due to a considerable thickness of air strata swinging around the arched profile of the surfaces - producing by their centrifugal moment (a partial vacuum on the upper or convex side of the surfaces and an added pressure on the lower or concave side - these together), giving lifting effects at small angles of inclination, such as from three to four degrees, (the same as used in flight on the present apparatus) equal to from eight to twelve times as much as could be produced by perfectly plane surfaces at the same angles and speed. It was common practice, Mr. Herring said, to designate all these machines as aeroplanes, although it was probable that if the inventor were limited to flat surfaces man flight would not be possible with them, and, in view of the wide differences between the properties of plane and arched surfaces, Mr. Chanute and he used the word aerocurve, to designate the latter form. Continuing, the speaker said that on account of the internal irregularities which all winds possessed, it was a great deal more difficult to control any gliding machine on the ground than when the operator was in the air, and that this was especially true of the machines, that had been provided with the automatic regulating devices; on these, he said, the effect of the operator to keep the balance proper, while in flight, was, except in extreme cases, almost nil; but that when automatic regulation was absent or momentarily shut off, the flights, in winds of upwards of fifteen miles an hour, were marked by numerous movements of the operator requiring great quickness and considerable bodily strength which tired one almost as much as carrying the machine single handed up the hill. He said, to gather an idea of what those difficulties were which had to be contended with by either the operator or the mechanism, one might recall the actions of smoke issuing from a chimney which, if watched for any two succeeding fractions of a second, would show that its course was rarely the same, that in moderate or high winds it consisted of thousands of irregular curves and twists which came with a suddenness and irregularity greater than any man could intelligently follow, even mentally. He stated that their experiments had convinced them that similar disturbances existed throughout all winds, even the most steady, and that as each of these changes or "gusts" had its disturbing effects any apparatus depending for dynamic support on the air, it was plain to be seen why Mr. Chanute had placed so much importance on the problem of securing automatic equilibrium, as the latter was, undoubtedly by far the most important of all the many difficulties connected with the whole subject. Consequently, nearly all of their recent experimental work had been directed to a study of these "gusts," or wind changes, and especially to the counteraction of their disturbing effects by automatic machinery. For both felt convinced that without ample provision for automatically overcoming at least the more dangerous of these gusts a practical aerocurve, or aeroplane flying machine would be out of question. Mr. Herring said he felt himself to be too much of an enthusiast to express his own opinion of what had been accomplished by these experiments, but would leave it to others to form their opinions of the results, which, he said, were substantially as follows: That, whereas the maximum (natural) wind velocity in which an unregulated machine was ever controlled by an operator (Lilienthal) was in the neighborhood of 22 miles an hour, they had been able to experiment on the: machine here shown in winds of 31 1/2 miles an hour, corresponding to wind energy of about three times as great, with entire safety, and with another apparatus and more complex regulator this limit had been raised very much higher. Also, notwithstanding the fact that neither Mr. Avery nor the speaker, who operated the machines, possessed anywhere near the skill exhibited by Lilienthal, the latter's best flights had, nevertheless, been equaled if not exceeded.

He said that before describing the succeeding views, he wished to explain that, though he had stated that the exertion required in keeping the balance proper of the present machines was almost nil, he did not wish to convey the impression that movements of the operator's weight were therefore not resorted to. On the contrary, they were very necessary in directing both the course and the angle of descent, and that extreme sensitiveness of the machine to these movements of the operator was an essential feature to secure success with this type of apparatus, and that the ability to gauge these movements, as well as the speed and angle of the machine on the other hand, were the main points of skill required of the operator. Returning again to the views, he stated that after the machine was poised, as previously explained, the front edges were brought down until the chord of these surfaces pointed downward nearly parallel with the slope of the hill. In this position a running start was made towards the wind; the operator meantime advanced himself on the arm bars until he reached the proper position for flight, and as the speed in creased, the apparatus gradually carried more and more of the operator's weight until he was entirely sustained. From this point the machine carried him the balance of the flight through the air, at a speed, and an angle of descent, dependent almost wholly upon his position on the apparatus. This speed varied all the way from 10 to 40 miles an hour in reference to the ground or from 18 to 57 miles per hour in reference to the air, at the will of the aviator. A perfect guide, the speaker said, to the speed of the machine in reference to the air was furnished the operator, as well as to the spectators below, by the pitch of the note which the wires and framing made in passing through the air, a note similar to the shrieking of the shrouds of a ship in a storm.

The running start in a calm consisted of about half a dozen steps; in moderate winds, from two to three; and in high winds (those above 25 miles an hour), it was only necessary to give a slight positive inclination to the surfaces, when the machine and operator were raised high in the air, and then commenced their forward journey against the wind. The advance at a positive angle of inclination was due to the fact that arched surfaces possessed a strong propelling component, even at .small positive inclinations (to the horizontal) in strongly ascending currents such as always existed on the windward slope of the hill. After reaching a certain point over the hillside (approximately one-third the way down the hill), a sudden decrease in support was generally experienced, due, in all probability, to a mass of slower moving air between the base and top of the hill, as measurement with the anemometer showed very much higher wind at the starting point and at the foot of the hill (or over the level stretch below) than between the two. The relationship in a 23-mile wind having been found to be as follows: Velocity at the lake, 20 miles per hour; at the foot of the hill (distant 300 feet), 16 miles; from first third to middle of the hill 9 miles per hour; starting point (one third from top), 23 miles; and top, 231/2 miles per hour. From which it would be seen that from starting in a wind of somewhat higher velocity than that necessary for support ( 211/2 to 22 miles per hour), the machine (in the space of from one to one and a half seconds) passed into a wind capable of exerting but little more than one-sixth of that effect;

FIG. 245. Two Seconds After Start.

the equilibrium, however, remained practically undisturbed; but to prevent losing headway, he said the operator should, in such a case, move his weight slightly to bring the surfaces at a greater negative angle than would be produced automatically by the regulating mechanism, as shown in Fig. 245, so that gravity might add to the speed during the descent and thus store a large part of the energy of the fall. After reaching the lowest point of this descent, which he said in some cases seemed to be attributable to a current of air curling backward against the mean wind, the operator again shifted his weight (or if he remained quiet the freshening wind would perform the same function through the regulating mechanism, but less quickly) and give the surfaces a slight positive angle as shown in Fig. 246,

FIG. 246. Four Seconds After Start.

when by reason of the increased speed of the machine and the fresher wind over the level stretch of the beach, the apparatus immediately rose, some times with greater rapidity than it fell, to almost the same level from which the descent was started, as shown in Fig. 247, the whole operation between Figs. 245 and 247 rarely occupying as much as three seconds. After passing the position shown in the last named figure, the flight as a whole was steady along a gradually descending line of one in six to one in seven, and occasionally but rarely one in eight. In strong winds, however, he continued, the gusts in the wind made considerable undulations in the flight, on a number of occasions raising the machine and operator as much as forty feet above the starting point, and giving the remainder of the course a number of vertical undulations departing from eight to fifteen feet from the mean line of the flights. The sensations produced by these sudden variations being somewhat similar to that experienced in a quick starting elevator.

FIG. 247. Five Seconds After Start.

One great peculiarity, he said, which distinguished the sensation of riding on the air from all other modes of locomotion was the exceeding smoothness and elasticity of the support, and although ascending or descending motions were occasionally imparted to the machine, which were practically equal to what gravity would produce on a free moving body in the same time, yet, the application of these forces was always so elastic that there was never the slightest shock felt.

FIG. 248. Nearly Down.

Continuing, he said the line of flight eventually approached nearer and nearer to the sand when it became necessary to select a proper landing point, and, at the same time, to head the machine directly into the wind, as was being done in Fig 248, the landing in which case would be effected some sixty or seventy feet nearer the camera than the piece of charred wreckage in the foreground (the length of flight being on an average 268 feet horizontally in a descent of 42 feet in windy weather, or 254 feet in a calm from the same point, thus showing that in flights against the wind the ascending trend of the latter (blowing from the lake over the hill) furnished but little more energy than that necessary to overcome its own horizontal component and that the length of flight measured on the ground, in gliding against the wind, was more dependent upon the height from which the flight started than on the velocity of the wind.

FIG. 249. Quartering.

Continuing, Mr. Herring said that so much had formerly been said relative to the necessity of starting and stopping against the wind that the impression had gone abroad that flight in any other direction with the present machines was impossible. He wished, therefore, to call attention to the Figs. 249, 250 and 251, which represented the machine facing north but advancing west of northwest in a wind coming from the northeast. These flights were known as quartering, in that they were made at an angle or "quartering" with the wind in order to make use of the ascending current over the slope which furnished in these flights both support and propulsion.

FIG. 250. Quartering Flight Overhead.

Such flights, he said, in a sufficiently strong wind, could, in a suitable locality, having a long hillside entirely free of obstructions, be prolonged indefinitely, but that his best attempt in this direction lasted only about 48 seconds. This, he said, was accomplished with a similar machine with three superimposed surfaces in covering a distance of 927 feet. There were, however, he said, few localities among the lakeside sand hills where this length of flight might be made except at the risk of running into trees or other obstructions, so that no matter how much longer than the average the level part of any particular flight might be there was still the same operation (that shown in Fig. 252) to be gone through with at the end, namely, the winding up of gravity's spring by man-power. This, said Mr. Herring, was a part of the operation which made one think more of adding the motor than any other. Whether the time were ripe for this step or not could, perhaps, be best judged by others; his individual opinion was, however in the affirmative, and that, judging from the action of power-driven models of the gliding machine, which he had recently built and tested, it was probable, he said, that the power machinery would add to, rather than diminish the stability of the glider, and if this conclusion proved correct, the

FIG. 251 Turning on Quartering Flight

FIG. 252. Winding Up Gravity Spring

finest mode of travel in the world, he thought, for the few, if not for the many, would not only be a possibility but a reasonable certainty of the near future.

President Johnston: I am sure we have all listened with a great deal of interest to Mr. Chanute's very interesting address and Mr. Herring's remarks, and if there are any others who have anything to say on this subject we will be glad to hear from them.

Mr. L. I.. Summers: I would like to call attention to the fact that Mr.Chanute's modesty has prevented his calling attention to the particular work he has done. It is well known that Mr. Maxim in England, has spent a small fortune in perfecting his machine and his effort has been towards constructing a machine of full size, and I believe some $40,000 or $50,000 has been spent on it. He has never succeeded in actually flying, and he has broken his machine several times in getting away from the tracks. Mr. Chanute has endeavored in every way to avoid dangerous experiments and has confined his experiments to solving the problem of equilibrium. He has devoted a number of years to the subject, and I think all those who have read his book and know the great care he has taken to point out the success and failures of others, feel indebted to him. I think; it is a source of congratulation to the West that we have an engineer and a scientist who is willing to devote himself to the subject in the way he has, and along the line he is working unquestionably must come our ultimate success. Many fail to appreciate that equilibrium must first be obtained before we can hope to accomplish successful flight, and to this problem Mr. Chanute's whole attention has been turned.

Thanks to Ms. Simine Short for providing the images and the text for this page.