In the opinion of the writer of these lines Herr Lilienthal has attacked the most difficult, and perhaps the most important, of the many problems which must be solved before success can be hoped for in navigating the air with flying machines. He has engaged in the effort to work out the maintenance of equilibrium in flight, and to learn the science of the bird. He has made a good beginning and seems to be in a fair way to accomplish some success in riding on the wind.
We have already seen that this has been tried before, and that (to say nothing of ancient myths) F. B. Dante, Paul Guidotti, Francisco Orujo, and Captain Le Bris, all met with partial success in soaring. Singularly enough all four met also with the same accident--i.e., a broken leg, in consequence of the loss of equipoise. Herr Lilienthal has greater chances of success, not only because he seems to have set about his experiments only after thorough investigation and consideration, but also because mechanical knowledge as well as constructive methods and workmanship have greatly improved since even Le Bris's time. Besides this, we have the gliding exploit of M. Mouillard, whose experiment has already been related, and that of M. Ader, which is yet to be mentioned.
Most of the capable inventors who have undertaken to solve the problem of flight have first concerned themselves with the question of motive power, and we shall see hereafter that very great progress has been achieved in this direction since 1890 but no amount of motive power will avail unless the apparatus to which it is applied is stable in the air--unless it can rise, sail, and come down again without danger of losing its equipoise. As has already been said, safety is the first requisite, and until this is assured, all the other elements of success will be unavailable.
Herr l Lilienthal has eliminated for the present the question of motive power, by undertaking to utilize ascending trends of wind, like a sailing bird, and if he succeeds in gliding up as well as down, and to the right or left, and in maintaining at all times the coincidence of the center of gravity with the center of pressure at all angles of incidence, he may not only apply an artificial power hereafter, for use when great speed is required or when there is no wind, but he will also probably have evolved a method of gratuitous transportation through the air when the wind blows under proper conditions; for there seems to be no good reason why a soaring apparatus for one man should cost more than twice as much as a first-class bicycle, or half as much as a city carriage; and when the wind is in the right direction, a good many miles could be sailed over in a day with no expenditure of force save for the evolutions necessary to maintain the equilibrium, although this can only be done under peculiar circumstances, and the commercial use must be very much less than that of bicycles.
That this expectation is not altogether absurd will appear from a brief consideration of the power of the wind; and to make the matter plain we will suppose it to have an upward trend of 15 or 26 per cent. or a very moderate inclination, which must be frequently exceeded. Under that circumstance a horizontal aeroplane will, as previously explained, have the horizontal component of the normal pressure directed to the front and acting as a forward propelling force. We may now calculate what the effect of this would be upon Herr Lilienthal's aeroplane.
This was proportioned in the ratio of 0.75 sq. ft. of surface to the pound of weight; but as the surfaces were concavo-convex, we may assume that the coefficient of efficiency would be about the same as that which we have assumed heretofore for the pigeon, or 1.3 per cent. of the actual surface, and we may further simplify the calculations by assuming the equivalent plane surface as equal to 1 sq. ft. per pound to be sustained. Now if this be exposed to a wind blowing at the rate of 25 miles per hour, at which the rectangular pressure, as given by Smeaton's table, is 3.125 lbs. per square foot, and if we suppose the plane to be inclined forward, so as to point 5 below the horizon, then the wind will make an angle of 10 with the plane, at which the normal pressure, by our tables, will be 0.337 of the rectangular pressure. As the effect upon the plane is in the ratio of the angle which the latter makes with the direction in which we desire to calculate it ie., the horizon, and this angle is 5 , the sine of which is 0.087, then we have for the propelling force for each square foot of sustaining surface:
Drift = 1. X 3.125 X 0.337 X 0.087 = 0.0916 lbs per square foot.
But as the speed is 2200 ft. per minute, we have for the power:
Power = 0.0916 X 2200 . 33000 = 0.00611 horse power per square foot,
which for an apparatus with 172 sq. ft. of sustaining surface furnishes a motive power of 0.00611 X 172 = 1.05 horse power, which is the power at the disposal of Herr Lilienthal when the wind blows 25 miles per hour, with an upward trend of 15.
This, of course, varies with the trend and the strength of the wind; but it will be noticed that with the data assumed it will amount to some 6 horse power for an aeroplane with 1000 sq. ft. of sustaining surface--an amount which will probably be surprisingly great to those who have not considered the subject.
It will doubtless be objected that these calculations are all based upon the assumption that the wind has an ascending trend, and that this condition does not uniformly obtain, particularly at sailing heights above the earth, where the wind may be horizontal at the very time that experiment shows an ascending trend near the surface. This is granted; it is acknowledged that the calculations of power to be obtained from the wind are predicated upon an assumption which may be untrue part of the time; but the answer to the main objection is that the birds soar at all times when there is wind enough (not too much), and that while we cannot yet explain how they do it, man ought to be able to avail himself of the same circumstances as the birds, if only he can maintain his equilibrium.
This is what Herr Lilienthal has undertaken; he has done so with great prudence and good sense, and so far as the results of his experiments have been published they teach several valuable lessons, which may be summed up as follows:
Of course, even if this be worked out, the practical usefulness of a soaring machine would be very limited. It could only be availed of when the wind blew with about the favorable velocity (neither too slow nor too fast), and its field of daily use would probably be limited to the trade wind latitudes, or, in other words, to those regions inhabited by the sailing birds; but if the equipoise be worked out, if man succeeds in devising an adequate soaring apparatus and in learning how to use it, unhampered by the necessity for looking after a motor at the same time, it will not probably be long before some motor is added to confer upon him command of space at all times.
In June, 1891, the quidnuncs in Paris were interested in the rumored success of some experiments with a flying machine carried on near Paris, in the private park of Mr. E. Pereire, the banker, by M. Clement Ader, who was said to have succeeded in rising to a height of about 60 ft., and in flying a distance variously estimated at 100 to 400 yds.
M. Ader is a well-known French electrician, the inventor of a telephone, and has long been interested in the flying-machine problem. In 1872 he constructed an artificial bird 26 ft. across and weighing some 53 lbs., with beating wings actuated by the muscular force of the operator's legs, aided by elastic auxiliary pectorals. In high winds, and restrained by ropes in order to guard against accidents, it would lift up a man, but it was found, as many times before, that man has not the requisite energy to sustain his weight in calm air. Subsequently the same apparatus, or a modification of it (for the accounts are not quite clear), was set up under a shed at Passy and visited by M. de la Landelle,37 who states that the operator was stretched horizontally (a bad position) between the wings, and worked with his feet and hands the organism of transmission to the parts that acted upon the air. A certain lifting effect was produced, but not enough to sustain the whole weight. I his apparatus was never photographed, but its inventor now contemplates unboxing it and setting it up again as a curiosity.
In 1891 as already mentioned, M. Ader built another artificial bird 54 ft. across, with which he experimented in the open air with such close privacy as he could secure; but the details are being kept secret, as the inventor states that he believes that it is destined to play an important part in the national defense of his country. He merely mentions the fact that the motor and the man who works it are placed in the interior of the machine, which is shaped like a huge bat; that the motor is actuated by a "mixture of a combination of vapors," and that the instrument of propulsion is a screw (of which he tried some eight patterns) placed at the head; that the whole apparatus rests upon skates or upon wheels, and that he needs a long smooth, flat space to gather headway by sliding or rolling some 20 or 30 yds. or more. He stated that he had already expended some $120,000 in his aerial experiments during the 15 years that he had been working at the problem, and that he contemplated exhibiting his machine in the air, if he could secure the use of the great machinery hall built for the Paris Exposition of 1889.
The above data are extracted from an account of an interview with M. Ader, published in the Paris Temps of July 9, 1891, in which he gave an interesting account of the preliminary studies that led to his last conception, the result, as he says, of a private theory of the resistances of air, which he proposes to publish some day.
Moved, probably, by the accounts of the sailing of large birds published by M. Mouillard as witnessed by him in Africa, M. Ader first obtained from the zoological gardens some eagles and some large bats, and observed their flight in his workshop. Judging this to be insufficient, he next went to Algeria, but could find none of the large vultures near Constantine; so, disguising himself as an Arab, he went into the interior with two Arab guides, and by enticing the birds with pieces of meat left in secluded places, he succeeded in obtaining ample observations.
M. Ader states that he became fully convinced that these vultures, some of them measuring 10 ft. across, do not beat their wings when rising on the air; that they flap them at most two or three times when first rising from the ground, and then hold them rigidly spread out to the current of wind upon which they ride, and upon which they rise in great circling sweeps by merely adjusting their aeroplane to the varying conditions of incidence and force of wind.
Starting from his theory and observations, M. Ader next built the machine which he has been experimenting with near Paris, in the presence, it is said, of only three or four persons, and with many precautions to avoid divulging his secret. He has even announced that he intends, from patriotic motives, to take no patents in foreign countries, so as not to divulge the design of his apparatus, and that all he can say at present is that the problem is an exceedingly difficult one, involving enormous mechanical difficulties, which increase rapidly with the size of the apparatus.
Naturally this reticence excited curiosity, and the French paper L'Illustration, in its issue of June 20, 1891, published a picture from which fig. 75 is reproduced, and it also made the following comments:
Nobody has seen anything, nobody knows anything, but L'Illustration has its friends everywhere. One of them was hunting rarely in the environs of Paris, when he caught a glimpse through the leaves of a strange object resembling an enormous bird of bluish hue. It was impossible to approach close to it; an enclosure surrounded the private park shut in by the forest in which the aforesaid machine was situated. Assuredly it could only be a flying machine. Our friend is something of a limner as well as an engineer, and he communicates to us the sketch which he made from a distance, and which is as correct as it was practicable to make it. Upon making due inquiry it turns out to be the invention of M. Ader the electrician, well known for his telephone apparatus, and it seems that the machine has really flown several hundred yards, rising some so to 65 ft., and holding a course through space.
The name of the inventor of this machine should be a guarantee of its possible success; still we have our doubts. It is said to have glided a certain distance in the air--100 or 200 or, say, 400 yds. But can it continue to do so for several hours, without having recourse to some fixed supply of power to recharge the motor actuating it ? For this is the vital point: what is the motor? As the inventor is an eminent electrician, thoroughly understanding this new science, he must have selected his favorite motor, the dynamo.
But electric accumulators are impracticable on account of their weight, while primary batteries act for only a short time, and they, too, are heavy.
Therefore, for the present, and until we have witnessed a convincing experiment, at which we shall have seen with our own eyes the generator of the power employed, we shall remain skeptics, and we shall believe (and this only because of the high scientific standing of the inventor) that it the machine sketched by our friend can really fly, it is only for a very brief period of time.
In point of fact, it is surmised by the writer of these lines that M. Ader has really been experimenting with a soaring machine, using a motor only to get under way, and (if the sketch of the apparatus is correct) that the principal difficulty he has met with has been to maintain the equilibrium. He may have had a few good flights under favorable circumstances, but he must have had many mishaps.
It is probable that one of his errors lies in adopting too large a sustaining surface, under the mistaken belief that this would promote safety. It would probably do just the reverse, by enabling little wind gusts and ground currents to upset the equipoise. The machine is 54 ft. across, and must spread to the breeze twice the surface employed by Herr Lilienthal, which we have already seen is found by the latter to be dangerous in winds of more than 23 miles per hour.
In August, 1891 M. Trouvé, whose mechanical bird with flapping wings actuated by explosions within a Bourdon tube, and whose hovering screw machine, worked by a dynamo connected by a wire to a source of electrical energy remaining on the ground, have already been noticed, deposited with the French Academy of Sciences a sealed letter, containing descriptions and drawings of an aeroplane, which he believes to be destined to solve successfully the problem of aerial navigation.
This method of depositing sealed descriptions of inchoate inventions with the Academy of Sciences is a favorite one in France, and answers generally much as the filing of a caveat does in the United States.
Nothing is known, of course, concerning the designs for this aeroplane, but M. Trouvé says that he has made great strides toward developing his aerial apparatus since 1870, and especially since 1884 that his laboratory experiments have convinced him that while his explosion motor is satisfactory as to the power exerted in proportion to weight, wings are less efficient than screws as instruments of propulsion. He has therefore designed an aeroplane propelled by two screws, rotating in contrary directions, which he believes to be superior to the former arrangement of beating wings.
The arrangement of this aeroplane is said to be such that the surface may always be proportioned to the weight to be carried, no matter what that weight may be.
The method of obtaining initial velocity is ingenious and effective. The apparatus is to be placed upon a railway car, and this is to be towed by a locomotive upon an ordinary railway, until the speed is sufficient to furnish the required reactive support from the air; when, the machine rises, and is thenceforth supported by its sustaining surfaces, driven by the two screws moved by the explosion motor.
M. Trouve believes that success is now a simple question of money expenditure, and that the daring man, favored by fortune, who first navigates the air will reap the glory of that success with less title thereto than his predecessors, who have pointed out the way.
In 1891 Gustav Koch, an aeronaut of Munich, published a pamphlet entitled "Free Human Flying, as the Preliminary Condition of Dynamic Aeronautics,"38 which contains the plan and description of an apparatus designed by him, in order to endeavor to imitate the soaring of the birds, and which also gives an account of the experiments which he had tried with models. This design has been thought worthy of trial, and the Bavarian Ministers of the Interior and of Education in May, I893, granted 1,600 marks ($400) to Herr Koch to enable him to make experiments. This he is about to do (with an assistant) over the lake of Constance near Lindau, and while the results may not prove satisfactory, they cannot but prove interesting.
The aeroplane designed by Herr Koch consists in a pair of rigid wings, approximately shaped like those of the dragon fly each about 27 ft. long and 6 ft. broad, back of which there is a triangular tail, some 7 ft. long and about 8 ft. wide at the rear end. The wings are to be constructed of bamboo, covered with unbleached silk slightly oiled, and pivoted to the back of the operator. The latter is to lie horizontally, face downward, in a sort of hammock suspended from a frame which attaches to the wings, and the latter can thus be swung forward or back within small limits, so as to change their position with respect to the center of gravity, but they have no flapping action whatever. The operator is to swing the wings and to elevate or depress the tail by means of pedals on which his feet rest, and of lines leading to his hands.
It will thus be seen that the action of the apparatus, which is some 57 ft. across, consists in altering the position of the center of pressure, with respect to the center of gravity, by swinging the wings forward or back, and thus changing the angle of incidence which the apparatus makes with the course, while still further changes can be produced by the action of the tail.
The weight of the aeroplane. including the mechanism which works it, is estimated at 99 lbs., and that of the operator at 176 lbs., making a total of 275 lbs., to be sustained by about 325 sq. ft. of surface.
Herr Koch proposes to test the apparatus by taking it up beneath a balloon and cutting it loose when about 3,000 ft. in the air. The first experiments, of course, are to be tried with a dummy instead of a man, and if these indicate sufficient strength and stability, the operator is to take the place of the dummy. He expects the machine to descend like a stone for the first second or two, and then, when air pressure has gathered under the wings, to gradually right itself, and to glide downward upon an easy slope, which would bring it down to the water in about 8 minutes and a distance of some 2 1/2 miles, thus being a dirigible parachute. Meanwhile, however, the operator is expected to bring the apparatus under control; by swinging the wings forward he expects to tilt the planes so as to glide upward again, by virtue of the acquired momentum, and by movements of the tail and of his own
body, which has a certain latitude of motion in the hammock, he expects to tack and to sail upon the wind like a soaring bird, sweeping in circles or making a series of zigzag glances, during which elevation might be gained by utilizing the force of the wind.
Such is the scheme; it is not wholly devoid of merit, because the soaring birds perform those very manoeuvres, and they do it much in the way which Herr Koch has indicated, hut it may be questioned whether his apparatus is properly designed to accomplish the results desired. In the first place, the sustaining surface and the spread across are too great, and will terribly strain the strength of materials. It would be better to shorten the wings and to make them broader in order to reduce the length of leverage. 1 in the second place, the horizontal position selected for the operator, probably to reduce horizontal resistance, is decidedly bad, because it is unnatural to man, and gives him inadequate control over the apparatus. The man should be placed vertically, and instead of manoeuvring, as planned, to cause the back part of the tail to strike the ground first and roll along, while the aeroplane settles forward slowly, the operator should alight on his feet and stop his impetus while running if he alights on land. In the third place, the mode of experimenting proposed is exceedingly dangerous. Herr Koch says, quite properly, that the first step toward success in artificial flight consists in acquiring the skill to manage an apparatus, but until that skill has been acquired it will evidently be little short of suicide to cut himself loose high in air, even if over a bed of water.
Perhaps, however, these various elements of failure have already been eliminated. The design was published in 1891 and may by this time have been so remodelled as to lead, not to an absolute success, for this is not to be expected, but to such partial control over the apparatus as to warrant further experiments.
In the Cosmopolitan Magazine for November, 1892 and in Cassier's Magazine for February, 1893 appeared two analytic articles by M. J. P. Holland, in which he takes the ground that mechanical flight has already been proved to be attainable, that what remains to be done is merely to combine things already tried and proved by other experimenters; and in which articles he advances three proposals or designs for flying machines.
In the Cosmopolitian article M. Holland proposes to place two aerial screws, superposed and rotating in contrary directions, above a spindle-shaped body containing the machinery, with a pair of wings or aeroplanes attached. This may be termed his first design, as indicated by his figs. 2, 3 and 4. In his second design the spindle and the superposed screws are retained, but the supporting surface consists of lo narrow, superposed, concavo-convex aeroplanes, somewhat like a Venetian blind, and they as well as the screws are mounted upon a frame pivoted to the spindle-shaped body, so that the screws may first be used to raise the apparatus from the ground, and then to drive it forward when the frame is raised to the vertical; support being then derived from the aeroplanes. This is indicated in M. Holland s figs. 5, 6 and 7.
In the Cassier's Magazine article the design is further modified by placing the aerial screws side by side in the frame instead of superposing them. The superposed aeroplanes are retained, but the number is increased to 16, and the mode of operation is much the same.
The design is somewhat similar to that which Mr. Phillips experimented in England, which was illustrated in Engineering of May 5, 1893, but is an improvement upon the latter design in the provision for pivoting the Venetian-blind aeroplanes to the body, and in the employment of two screws instead of one for the propelling instrument.
36One theorist expounds his ideas as follows: "One point I have studied, and that is, How can a twenty pound wild goose carry itself so easily? Weigh every feather you can pick off from a wild goose, and they will not weigh one pound. Now if the feathers be picked off from the goose he can come no nearer flying than we can.
"So there we have it clearly demonstrated that one pound of goose feathers can pick up nineteen pounds of goose and carry this nineteen pounds and its one pound of feathers through space at about half a mile a minute, if in a a hurry.
"Now my theory is this, and it applies to all birds. Notice any bird
when he suddenly starts to fly, and you will notice a lightning-like quiver of
his feathers. I believe that this quiver causes the production of a negative
force of magnetism, or some kind of force which pushes the bird from the
earth- just the reverse of the loadstone. He then has only to use his wings to
propel the body, for the magnetic negative earth-force does the lifting, and
that is all produced by the feathers. If it were not, then the bird ought to
fly when divested of his feathers. This is the force which should be looked
for; whoever discovers it will make a fortune."
37 Dans les airs, G. de la Landelle, pp. 236 237
38 Der freie Menschliche Flug als Vorbedingung dynarnischer Luftschiffahrt. Müatnchen, 1891.
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