About the year 1875 paragraphs were floating in the American newspapers concerning the "California flying machine," which was said to be under construction in San Francisco. This was the design of Mr. Marriott, of. the San Francisco Newsletter formerly a fellow-worker with Mr. Stringfellow in aeronautical pursuits, and also a resident of Chard.
Mr. Marriott had already experimented in 1867-69 with an elongated-balloon, provided with attached aeroplanes, from which he expected to obtain additional sustaining power when at speed--a system which has been many times proposed, and which is often brought forward again by inventors who are not aware of the prior experiments.
Mr. Marriott's balloon model was 28 ft. long, 9 1/2 ft. in diameter, with aeroplanes extending for half its length, and was to be driven by a light steam-engine, rotating a propeller 4 ft. in diameter 120 times a minute. The utmost speed that could be obtained was five miles per hour, and as this was not sufficient to stem the winds that constantly prevail in San Francisco, the inventor turned his attention to a design for an aeroplane.
This is said, in the report of the Aeronautical Society of Great Britain for 1875 to have consisted of three planes, superposed longitudinally, with an interval between them of about 10 ft. In transverse length the whole structure was to be 120 ft. fixed upon a foundation of trussed bamboo, the planes being unequal in size, the largest on the top being of the above dimensions and about 40 ft. wide, the three planes being rigidly supported by two masts about 40 ft. high and stayed by wire rigging.
To the lower end of each mast were to be affixed small wheels, to run down an inclined rail, in order to impart the necessary initial velocity to the apparatus, and this impulse was then to be continued by means of a steam-engine enclosed in a square compartment capable of holding the engineers. This compartment was to be located in the center of the trussed bamboo keel. The engine was to work four screw propellers' two of them vertical and two horizontal, their place of working breaking up the continuity of the longitudinal planes. The weight of the whole machine was estimated at 1500 lbs., including the motive power and the engineer.
No drawings or detailed description of this aeroplane were ever published, the inventor's idea being to keep his plans secret until he had made a success of the machine. It was never completed, for Mr. Marriott sickened and died before the apparatus was ready for trial, and his associates did not care to risk the great outlay which would have been necessary to test so large and expensive an apparatus. The weight of the motor and the equilibrium would have been the stumbling-blocks.
At the meeting of the Aeronautical Society of Great Britain for 1876 M. Senecal gave some noses on the stability of aeroplanes of different forms, which he illustrated with paper models, and these experiments are so easily reproduced that the following account of them, quoted from the report, will probably prove interesting:
He said that while planes of even width and thickness (load uniformly distributed) revolve upon their own axes, and their path of translation is rectilinear, the motions of triangular planes are much more complicated. These planes are obtained by dividing the circumference into blades of different widths. These blades, besides revolving upon their axis, rotate also round a vertical conic axis, whose base is upward, the vertex of the plane describing a spiral round the conical axis.
He found that the rate of revolution and rotation increases in direct proportion as the base and the length of the blade decreases and the length traveled over in a unit of time decreases also in the same proportion. The shifting of the center of gravity. (pressure ?) of these blades is most interesting. It was found that the center of gravity of narrow planes was near the vertex and on The edge of the plane, but recedes toward the base and axis as it widens; it also travels from the axis toward the edge and vertex as the rate of revolution increases, and possibly that, at high velocities of rotation, the center of gravity will be beyond the edge. The size of blade that revolves and rotates most steadily represents the eighteenth to the twenty-fourth part of the circumference. He also proved that by cutting a small plane out of the base it had the same effect as applying a weight at that point before cutting it. The plane will then revolve and rotate round with its base turned toward the vertical axis.
He also liberated several narrow strips of paper, showing, while revolving, nodal and ventral sections similar to musical strings in vibration, the number of aliquot parts increasing with the length of the ribbons and disappearing as the width increases.
M. Senecal then enunciated the following law: that planes, of whatever form, but of even thickness and rigid margin, in order to translate steadily must carry their maximum load on a line representing the first third part from the anterior margins of the plane; but one can, with impunity, apply graduated weights from that line right on to the edge, and, in some instances, a good distance beyond the edge, and high rate of speed is the result. The rate of translation increases directly with the load placed on the different points of the graduations from that line of the center of gravity.
While the account of the action of these paper planes is not very clear, it is sufficiently so to permit the curious in such matters to repeat the experiments, and these will be found more instructive than any description of the results, however accurately expressed. The action will be found to be greatly modified by slightly folding the back edges as already described.
In 1877 Mr. Barnett, of Keokuk, Ia., patented in the United States a flying machine somewhat similar in arrangement and principle with that of Pénaud and Gauchot. It consisted in an aeroplane something like a boy's triangular kite, but with the two longitudinal halves set at a diedral angle from the central spine or spar, in order to obtain lateral stability. Just under this kite a boat-shaped car was to be affixed, carrying the motor, which was to rotate two propellers mounted upon shafts at the front of the apparatus, and turning in opposite directions. An adjustable tail was to carry part of the weight and to regulate the angle of incidence, the car being provided with wheels so as to run over the ground until the speed was great enough to give a sustaining reaction.
This design is not without merit, but it leaves unsolved the two principal problems concerning aeroplanes--i.e., the providing a light motive power, which shall cot weigh more in proportion than that of the birds in ordinary flight say 20 lbs per horse power, and the providing for automatic stability, which, as already explained, should be greater for an inanimate machine than for a live bird. The form of the triangular kite is not stable, as many a boy has found out to his sorrow by providing an insufficient tail, and if the kite form is to be used, it will probably be best to experiment with shapes that fly without a tail, some of which will be noticed hereafter.
Mr. Barnett is understood to have tried many experiments, extending over a period of 30 years. He first constructed a plain flat kite some 12 ft. long and 10 ft. wide, under which was hung a frame so as to attach and ad just the mechanism for turning two propellers rotating in opposite directions. This machine was not placed on wheels, but he was much pleased with the clutch that the propellers took on the air. Next he constructed an apparatus to carry the weight of a man. This consisted of a kite or aeroplane of canvas 27 ft. square, from which hung a propelling arrangement somewhat similar to that shown by Mr. Maxim in the Century Magazine for October, 1891 as the manner of connecting the aeroplanes and attaching the screws in his experimental apparatus. This machine was placed on wheels, being the running gear of a light spring wagon, and as Mr. Barnett knew of no motor sufficiently light for actual flight, he determined first to experiment with his own muscular power.
The propellers were two bladed, each blade being of oil-cloth and a sector of a circle, or like a piece from the ordinary round pie. The operator was beneath and rotated them through appropriate gearing. He ran the machine along smooth country roads, but as soon as speed was gained, the increasing air pressure, acting forward of the center of figure, in accordance with the law of JoOEssel, already given, would tip up the front of the aeroplane and disturb the equilibrium. This led the inventor to believe that the propellers were too far below the aeroplane, and he altered their position. but without any better result; the machine would still tip backward, presenting a greater angle of incidence, and increasing the resistance. Moreover, it would not keep to the line of the road, but, as it was propelled, would run off to either side into the grass, weeds or uneven ground, swerving in a way which would have involved great danger if it had been able to rise into the air.
Picking out a quiet evening, near dusk, the inventor determined to give it an extra good test over smooth ground, and while apprehensive that if it left the earth It might lurch and come to grief, he managed by "main strength and awkwardness" to get under considerable headway, when the front end tipped up so much as to break and splinter the main support, and the inventor came very near getting hurt.
This terminated the experiments with that machine. Subsequently the inventor entered it for exhibition at the State fair as an "automatic kite," and he says quaintly that he entered, at the same time, some samples of tomatoes, cabbage and grapes of his own growing; received a premium on the tomatoes and cabbage, and favorable mention on the grapes, but concluded at the last moment not to take the "kite" to the fair ground, as it did not perform as he desired.
He has built two more machines of such dimensions as to support a man within the last six or seven years, and has tested them upon a smooth pasture, but found this, after many weeks of trial, too rough and uneven for his purpose. The tracks of animals a bunch of grass, or a corncob would check the speed, so that with all his strength he could not arrive at sufficient velocity to leave the ground. This is not surprising, for Professor Langley has since shown that the best that can be done with a plane is to sustain 209 lbs. by the exertion of one horse power, and this without any hull resistance whatever, so that, as man cannot steadily exert much more than one-tenth of this power, a total weight of about 20 lbs. is the maximum that he can hope to support and drive through the air by the exertion of his own unaided strength.
Mr. Barnett has of course experimented with a considerable number of small models. He first tried clock springs, but found them too heavy; and all would-be inventors had better avoid wasting effort with them; next he tried twisted indict-rubber, and while he found great irregularity in its action, he succeeded in obtaining a number of fair flights among many failures. He experimented with superposed planes, but the result was not satisfactory. His last model, produced in 1892 resembles his original design, and, driven by rubber bands, succeeded in getting a preliminary start by running over a platform 12 ft. long, slightly inclined, and flying through the air "above the hollyhocks and other flowers" until it struck the side of a house 30 ft. away, and 4 ft. higher than the platform.
India-rubber is a good reservoir of power to experiment with. The flights are brief, as the power is soon spent, but they give an opportunity of testing the equilibrium, the proportions, and the adjustment of the parts, which may suggest themselves to an experimenter as possibly efficient.
An apparatus patented in France by M. Pomøs in 1878 is represented in fig. 57. It consisted in two supporting planes in front, together with a keel plane, and a large vane behind, to maintain the course. Two propelling screws on the same horizontal shaft were to impart motion, and although they are shown as actuated by hand on the figure, the same inventor had already patented, in 1871 in connection with M. de la Pauze a gunpowder motor, in which a series of charges, exploded by electricity, were made to pass through a tube and to impinge against the buckets of a revolving wheel, from which the motion was to be communicated to the propellers. Neither this motor nor the aeroplane possess merit, and indeed the latter is about as badly arranged as it can be, for as the air pressures which are to sustain the weight act with a leverage increasing toward the tips of the wings, or sustaining planes, the latter should taper in plan from the center of the apparatus outward, instead of tapering inward as shown in the figure, in order to obtain a light and strong construction. it is not known whether M. Pom¿s experimented at all, but if he did, it must have been with very small models, for his design is quite unsuitable for a large one, and has been here included in order to point out the deficiencies of such a design.
FIG. 57. -- POMÈS -- 1878
In 1878 Mr. Linfield constructed an apparatus to test his conception of an aeroplane. It consisted of plane surfaces extended on a framework 40 ft. X 18 ft. at its greatest width, and measuring about 300 sq. ft. in surface, the weight of the apparatus being 189 lbs. It was mounted upon wheels, and driven over a macadamized road by the action of a screw propeller placed in front of the machine, rotated at about 75 revolutions per minute by the aviator, working a treadle and levers with cross handles. Upon the highway, on an incline of about one in a hundred, a speed of 12 miles an hour was attained without any indication of a rise from the ground. Then by going down hill, a speed of 20 miles per hour was obtained, but still without perceptible effect, which is not be wondered at, for at this speed, with an angle of incidence presumed to have been 6°, the "lift" would be 300 X 2 X 0.206 or, say, 123 lbs., while the weight including the aviator was over 300 lbs. It would have required an angle of 17 at a speed of 20 miles per hour, to have produced sufficient "lift," while at that angle the "drift" alone would have required the exertion of 5 horse power, which the operator was clearly unable to furnish, it being "most dreadful exertion" to work the treadles at the flatter angle of incidence above presumed to have been experimented.
Subsequently Mr. Linfield built another machine upon a different principle. It was 20 ft. 9 in. in length, 15 ft. in width, and 8 ft. 3 in. high; the sustaining surfaces being in two frames, each 5 ft. square. Each frame contained 25 superposed planes of strained and varnished linen 18 in. wide and spaced 2 in. apart, thus somewhat resembling a cupboard without front or back, and with shelves very close together. These frames were slung on either side of a cigar-shaped car at its maximum section, being set at a diedral angle to each other, so that the apparatus, could it have been seen in the air, would have resembled a huge cigar with a pair of saddle bags attached thereto. There was a nine-bladed screw at the front, and a guiding vane, like the tail of a dart, behind; the entire sustaining surfaces in the two frames being estimated to aggregate 438 sq. ft., and the whole machine, which was mounted on four wheels, weighing 240 lbs., to which 180 lbs. must be added for the operator, thus providing a little over one square foot of sustaining surface per pound.
Mr. Linfield was to stand between the two front wheels and actuate two treadles to rotate the screw, which was 7 ft. in diameter but when the time arrived for testing the machine upon an ordinary macadamized road, it was stated that this could not be done on account of the impossibility of blocking the road during the trial. This was in a measure fortunate, for it led Mr. Linfield then to arrange with a railway to mount the machine on a flat car and to tow it behind a locomotive. When a speed of 40 miles per hour was attained the machine rose entirely free from the car, but was not allowed to swerve very far, as there was a side wind blowing, and it swung very close to the telegraph poles as it was. The tow line was some 15 ft. long, and the pull thereon was 24 lbs., which for a 240-lb machine (without the aviator) indicates an angle of incidence of 1 in 10 or 6°. At this angle, and at a speed of 40 miles per hour, at which the air pressure would be 8 lbs. to the square foot, the total lift for a single plane ought to be 438 X 8 X 0 .206 = 722 lbs., so that, if the 240 lbs. of machine was just sustained, it indicates that the very narrow spacing (2 in.) between the superposed aeroplanes greatly interfered with their efficiency.
Mr. Linfield also tested the efficiency of superposed screws. He placed nine of them some 6 in. apart upon a vertical shaft. These were all with two narrow blades and 3 ft. in diameter, but in whatever relative position they were placed radially, he could get no greater lift from the nine screws than he could from the top and bottom screws only, 4 ft. apart, the seven intermediate screws being removed.
The idea of testing the apparatus by towing it on a railway car was evidently a good one, but this disclosed such inefficiency of lifting power and of stability as to put an end to the experiments.
We next come to a series of very careful experiments, tried by an able mechanician, which almost demonstrate that artificial flight is accessible to man, with motors that have been developed within the last two years. These experiments were carried on by M. V. Tatin, who was then Professor Marey's mechanical assistant. He first began with beating wings, and produced, in 1876, the artificial bird which has already been briefly noticed under the head of "Wings and Parachutes." This was driven by twisted rubber; not only did M. Tatin find that the power required was unduly great, but he also found that this power could not be accurately measured, the torsion of indict-rubber being erratic and stretching unequally. He constructed a large number of mechanical birds of all sizes and various weights; he tried many modifications and entire or partial reconstructions, and finally concluded, after spending a good deal of time and money, to take up the aeroplane type, to be driven by a reservoir of compressed air. With this his efforts were successful almost from the first, and he produced in 1879 the apparatus shown in fig. 58, which is practically the first that has risen into the air by a preliminary run over the ground. This machine consisted in a silk aeroplane, measuring 7.53 sq. ft. in surface, being 6.23 ft. across and 1.31 ft. wide, mounted in two halves at a very slight diedral angle, on top of a steel tube with conical ends which contained the compressed air. This reservoir was 4 3/4 in. in diameter and 33 1/2 in. long, was tested to a pressure of 20 atmospheres, and worked generally at 7 atmospheres; its weight was only 1.54 lbs., and its cubical capacity 0.28 cub. ft. From this (the vital feature of the machine) the stored energy was utilized by a small engine, with oscillating cylinder, placed on a thin board on top of the tube, and connected by shafts and gearing to two propellers with four vanes each, located at the front of the aeroplane. These propellers were 1.31 ft. in diameter, and rotated in opposite directions some 25 turns per second, their velocity at the outer end being about 100 ft. per second. The vanes were of thin bent horn set at a pitch of about 1.50 ft., and they towed the apparatus forward instead of pushing it.
A tail of silk fabric 1.97 ft. across at the rear, by a length of 1.97 ft., was set at a slight upward angle and braced by wire stays, in order to provide for the longitudinal stability upon the principle advanced by Pénaud and the whole apparatus was placed on a light running gear consisting first of four wheels, and subsequently of three wheels. The total weight was 3.85 lbs., so that the sustaining surface of the aeroplane (omitting the tail) was at the rate of 1.95 sq. ft. to the pound.
FIG. 58 -- TATIN -- 1879.
After a vast deal of preliminary testing and adjustment, the apparatus was taken to the French military establishment at Chalais-Meudon, where it was experimented with in 1879 upon a round board platform 46 it. in diameter. Upon this the machine would be set upon its wheels, the front and rear ends being fastened to two light cords carried to a ring around a central stake, and the compressed air would be turned on to the engine. The propellers would put the apparatus in motion and it would run from 65 to 165 ft. over the boards, until it attained a velocity of 18 miles per hour, when it would rise into the air, still confined radially by the two cords, and make a flight of about 50 ft., when, the power being exhausted, it would fall to the ground, almost invariably injuring the running gear in doing so.
The flights were not very high, but on one occasion the apparatus passed over the head of a spectator. The angle of incidence was 70 or 8 o, and the power developed by the engine was at the rate of 72 33 foot-pounds per second, gross; but as its efficiency was only 25 to 30 per cent, of the gross power, the effective force was at the rate of 18.08 to 21.70 foot-pounds per second, or, say, at the rate of 5 footpounds per second (300 foot-pounds per minute) per pound of apparatus.
This power was measured with great care, the machine being provided with a tiny gauge and tested repeatedly with a dynamometer. M. Tatin calls attention to the fact that the minuteness of the engine greatly diminished its efficiency, and that with large machines it would be comparatively easy to obtain 85 per cent. of the gross power developed. He draws the conclusion that his apparatus demonstrates that 110 lbs. can be sustained and driven through the air by the exertion of 1 horse power--a most important conclusion, which will be further discussed hereafter.
To return, however, to the experiments: they are described as follows by M. Tatin27
I will pass without description a series of preliminary experiments which led me to modify certain details, until all conditions were favorable. I then had the satisfaction of seeing the apparatus start at increasing speed, and in a few seconds the carriage barely touches the ground; then it leaves it entirely at a speed of about 18 miles per hour, which agrees closely with the calculations. It describes over the ground a curve similar to those described by small models gliding freely, and when it comes down after its orbit, the shock as so violent as to injure the running gear. This accident recurred upon each experiment carried out under the same conditions; the carriage was soon destroyed, and even the propellers were injured, although they could be repaired. l then tried another experiment, which I had already attempted several times without success, in consequence of inadequate preparation. The apparatus, the running gear being removed, was suspended by two grooved wheels running freely over an iron telegraph wire 260 ft. long, stretched as rigidly as practicable. When the speed became sufficient, the apparatus rose, and then one of the propellers struck the iron wire; the front grooved wheel overtook the machine, and the propeller was destroyed. These accidents caused no repining, for they demonstrated that in all cases the apparatus had completely overcome the force of gravity.
In order to continue the experiments I built a new carriage and new propellers, hoping to make them strong enough to stand the shocks during a new set of experiments, from which to deduce accurately the work done, The new running gear had but three wheels, these being larger and lighter than the old. The propellers, on the other hand, were made heavier) but modified so as to rotate more easily. Their vanes were made of a thin sheet of horn bent hot to the proper curvature. The inner two-fifths from the hub consisted of steel wire, this portion of a propeller requiring much force for rotation, and giving out but small effect toward propulsion; but the diameter and the pitch were the same as formerly.
I was, unfortunately, unable to make all the experiments I desired with this repaired apparatus. I intended to study the results with various angles of incidence in the planes and various pitch of the propellers; then to study the important question as to the best proportion between the sustaining surface and the diameter of the propellers; and lastly the speed of translation which will best utilize the force expended.
I was nevertheless enabled to deduce the following figures from my experiments. These figures are not absolutely exact, but sufficiently so to serve as a guide to others who may wish to engage in similar work. Calling A the sustaining surface in square meters (without the tail), and V the speed of translation in meters per second, then we may say:
Lift = 0. kg. .045 A V2.
And the motor will need to develop effective work at the rate of 1.50 kilogrammeters per kilogramme of the weight (4.935 foot-pounds per second per pound), which corresponds to one horse power for each 110 lbs. weight of the apparatus.
These experiments seem to demonstrate that there is no impossibility in the construction of large apparatus for aviation, and that perhaps even now such machines could be practically used in aerial navigation.
Such practical experiments being necessarily very costly, I must, to my great regret, forego their undertaking, and I shall be satisfied if my own labors shall induce others to take up such an enterprise.
The effective work done by this aeroplane having been accurately measured, it affords a good opportunity of testing the method of estimating resistances which has been proposed by the writer in estimating the work done by a pigeon.
The weight of M. Tatin's apparatus was 3.85 lbs. Its aeroplane surface was 7.53 sq. ft., the angle of incidence was 8 o, and the speed was 18 miles per hour, at which the air pressure would be 1.62 lbs. per sq. ft. Hence we have, by the table of "lift and drift":
Lift, 8 o = 7.53 X 1.62 X 0.27 = 3.29 lbs.,
which indicates that a small part of the weight was sustained by the tail.
The hull resistances are stated by M. Tatin to have been almost equal to that of the plane. These hull resistances would consist of that of the tube, of 0.12. sq. ft. midsection, which, having conical ends and parallel sides, will have a coefficient of about one-third of that of its midsection. The resistance of the wheels and running gear will be slightly greater, but must be guessed at, as the wheels would continue to revolve through inertia and thus increase the resistance.
The front edge of the aeroplane, which was of split reed and about one-eighth of an inch thick, was 6.23 ft. long; but as the back edge of the aeroplane and the side borders of the tail would also produce some air resistance, we may call the edge resistance as equal to 6 ft. in length, by a thickness of 0.01 ft., without any coefficient for roundness. We then have the following estimate of resistances:
|Drift 8||7.53 X 1.62 X 0.0381||= 0.4648 lbs.|
|Tube||0.12 X 1.62 / 3||= 0. 0648 lbs.|
|Wheels and gear||estimated||= 0.1000 lbs.|
|Edges of wings||6 X 0.01 X 1.62||= 0.0972|
|Total resistance||= 0.7268 "|
and- as the speed was 18 miles per hour, or 26.40 ft. per second, we have for the effective power required:
Power = 0.7268 X 26.4 = 19 19 foot-pounds per second,
which agrees very closely with the 18.08 to 21.70 foot pounds per second said to have been effectively developed, and is at the rate of 5 foot-pounds per pound of apparatus, or of 110 lbs. of weight per horse power.
This last is the important point. Now that Mr. Maxim has produced a steam-engine which, with its boilers, pumps, generators, condensers, and the weight of water in the complete circulation, weighs less than 10 lbs. to the horse power, aviation seems to be practically possible, if only the stability can be secured, and an adequate method of alighting be devised.
AÈronaute September. 1880.
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