Fig. 72b.—When an aeroplane is driven through the air, it encounters stationary air and leaves it with a downward trend. With a thick curved aeroplane, as shown, the air follows both the top and the bottom surfaces, and the direction that the air takes is the resultant of these two streams of air. It will be seen that the air takes the same direction that it would take if the plane were flat, and raised fromatoc, which would be substantially the same as shown atf,h,g. It has, however, been found by actual experiment that the curved plane is preferable, because the lifting effect is more evenly distributed, and the drift is less in proportion to the lift.
Fig. 72b.—When an aeroplane is driven through the air, it encounters stationary air and leaves it with a downward trend. With a thick curved aeroplane, as shown, the air follows both the top and the bottom surfaces, and the direction that the air takes is the resultant of these two streams of air. It will be seen that the air takes the same direction that it would take if the plane were flat, and raised fromatoc, which would be substantially the same as shown atf,h,g. It has, however, been found by actual experiment that the curved plane is preferable, because the lifting effect is more evenly distributed, and the drift is less in proportion to the lift.
Fig. 72b.—When an aeroplane is driven through the air, it encounters stationary air and leaves it with a downward trend. With a thick curved aeroplane, as shown, the air follows both the top and the bottom surfaces, and the direction that the air takes is the resultant of these two streams of air. It will be seen that the air takes the same direction that it would take if the plane were flat, and raised fromatoc, which would be substantially the same as shown atf,h,g. It has, however, been found by actual experiment that the curved plane is preferable, because the lifting effect is more evenly distributed, and the drift is less in proportion to the lift.
Fig. 72c.—Aeroplanes experimented with by Mr. Horatio Philipps. In the published account which is before me, the angles at which these planes were placed are not given, but, by comparing the lift with the drift, we may assume that it was about 1 in 10.Fig. 5 seems to have been the best shape, and I find that this plane would have given a lifting effect of 2·2 lbs. per square foot at a velocity of 40 miles per hour.
Fig. 72c.—Aeroplanes experimented with by Mr. Horatio Philipps. In the published account which is before me, the angles at which these planes were placed are not given, but, by comparing the lift with the drift, we may assume that it was about 1 in 10.Fig. 5 seems to have been the best shape, and I find that this plane would have given a lifting effect of 2·2 lbs. per square foot at a velocity of 40 miles per hour.
Fig. 72c.—Aeroplanes experimented with by Mr. Horatio Philipps. In the published account which is before me, the angles at which these planes were placed are not given, but, by comparing the lift with the drift, we may assume that it was about 1 in 10.Fig. 5 seems to have been the best shape, and I find that this plane would have given a lifting effect of 2·2 lbs. per square foot at a velocity of 40 miles per hour.
Philipps’ Experiments.
As far as the actual navigation of the air is concerned, balloonists have had everything to themselves until quite recently, but we find that at the present moment, experimenters are dividing their attention about equally between balloons or machines lighter than the air, and true flying machines or machines heavier than the air. In all Nature, we do not find any bird or insect that does not fly by dynamic energy alone, and I do not believe that the time is far distant when those now advocating machines lighter than the air, will join the party advocating machines heavier than the air, and, eventually, balloons will be abandoned altogether. No matter from what standpoint we examine the subject, the balloon is unsuitable for the service, and it is not susceptible of much improvement. On the other hand, the flying machine is susceptible of a good deal of improvement; there is plenty of scope for the employment of a great deal of skill, both mechanical and scientific, for a good many years to come.
I do not know that I can express myself better now than I did when I wrote an article for the Engineering Supplement of theTimes, from which I quote the following:—
“The result of recent experiments must have convinced every thinking man that the day of the balloon is past. A balloon, from the very nature of things, must be extremely bulky and fragile.
“It has always appeared to the writer that it would be absolutely impossible to make a dirigible balloon that would be of any use, even in a comparatively light wind. Experiments have shown that only a few hundred feet above the surface of the earth, the air is nearly always moving at a velocity of at least 15 miles an hour, and more than two-thirds of the time at a velocity considerably greater than this. In order to give a balloon sufficient lifting power to carry two men and a powerful engine, it is necessary thatit should be of enormous bulk. Considered as a whole, including men and engine, it must have a mean density less than the surrounding air, otherwise it will not rise. Therefore, not only is a very large surface exposed to the wind, but the whole thing is so extremely light and fragile as to be completely at the mercy of wind and weather. Take that triumph of engineering skill, the ‘Nulli Secundus,’ for example. The gas-bag, which was sausage-shaped and 30 feet in diameter, was a beautiful piece of workmanship, the whole thing being built up of goldbeater’s skin. The cost of this wonderful gas-bag must have been enormous. The whole construction, including the car, the system of suspension, the engine and propellers, had been well thought out and the work beautifully executed; still, under these most favourable conditions, only a slight shower of rain was sufficient to neutralise its lifting effect completely—that is, the gas-bag and the cordage about this so-called airship absorbed about 400 lbs. of water, and this was found to be more than sufficient to neutralise completely the lifting effect. A slight squall which followed entirely wrecked the whole thing, and it was ignominiously carted back to the point of departure.
“We now learn that the War Office is soon to produce another airship similar to the ‘Nulli Secundus,’ but with a much greater capacity and a stronger engine. In the newspaper accounts it is said that the gas-bag of this new balloon would be sausage-shaped and 42 feet in diameter, that it is to be provided with an engine of 100 horse-power, which it is claimed will give to this new production a speed of 40 miles an hour through the air, so that, with a wind of 20 miles an hour, it will still be able to travel by land 20 miles an hour against the wind. Probably the writer of the article did not consider the subject from a mathematical point of view. As the mathematical equation is an extremely simple one, it is easily presented so as to be understood by any one having the least smattering of mathematical or engineering knowledge. The cylindrical portion of the gas-bag is to be 42 feet in diameter; the area of the cross-section would therefore be 1,385 feet. If we take a disc 42 feet in diameter and erect it high in the air above a level plain, and allow a wind of 40 miles an hour, which is the proposed speed of the balloon, to blow against it, we should find that the air pressure would be 11,083 lbs.—that is, a wind blowing at a velocity of 40 miles an hour would produce a pressureof 8 lbs. to every square foot of the disc.[3]Conversely, if the air were stationary, it would require a push of 11,083 lbs. to drive this disc through the air at the rate of 40 miles an hour.
[3]Haswell gives the pressure of the wind at 40 miles an hour as 8 lbs. per square foot, and this is said to have been verified by the United States Coast Survey. Molesworth makes it slightly less; but the new formula, according to most recent experiments (Dr. Stanton’s experiments at the National Physical Laboratory and M. Eiffel’s at Eiffel Tower), is P = 0·003 V², which would make the pressure only 4·8 lbs. per square foot, and which would reduce the total H.P. required from 472 to 283, where P represents pounds per square foot and V miles per hour.
[3]Haswell gives the pressure of the wind at 40 miles an hour as 8 lbs. per square foot, and this is said to have been verified by the United States Coast Survey. Molesworth makes it slightly less; but the new formula, according to most recent experiments (Dr. Stanton’s experiments at the National Physical Laboratory and M. Eiffel’s at Eiffel Tower), is P = 0·003 V², which would make the pressure only 4·8 lbs. per square foot, and which would reduce the total H.P. required from 472 to 283, where P represents pounds per square foot and V miles per hour.
“A speed of 40 miles an hour is at the rate of 3,520 feet in a minute of time. We therefore have two factors—the pounds of resistance encountered, and the distance through which the disc travels in one minute of time. By multiplying the total pounds of pressure on the complete disc by the number of feet it has to travel in one minute of time, we have the total number of foot-pounds required in a minute of time to drive a disc 42 feet in diameter through the air at a speed of 40 miles an hour. Dividing the product by the conventional horse-power 33,000, we shall have 1,181 horse-power as the energy required to propel the disc through the air. However, the end of the gas-bag is not a flat disc, but a hemisphere, and the resistance to drive a hemisphere through the air is much less than it would be with a normal plane or flat disc. In the ‘Nulli Secundus’ we may take the coefficient of resistance of the machine, considered as a whole, as 0·20—that is, that the resistance will be one-fifth as much as that of a flat disc. This, of course, includes not only the resistance of the balloon itself, but also that of the cordage, the car, the engine, and the men.
“Multiplying 1,181 by the coefficient ·20, we shall have 236; therefore, if the new balloon were attached to a long steel wire and drawn by a locomotive through the air, the amount of work or energy required would be 236 horse-power—that is, if the gas-bag would stand being driven through the air at the rate of 40 miles an hour, which is extremely doubtful. Under these conditions, the driving wheels of the locomotive would not slip, and therefore no waste of power would result, but in the dirigible balloon we have a totally different state of affairs. The propelling screws are very small in proportion to the airship, and their slip is fully 50 per cent.—that is, in order to drive the ship at the rate of 40 miles an hour, the screws would have totravel at least 80 miles an hour. Therefore, while 236 horse-power was imparted to the ship in driving it forward, an equal amount would have to be lost in slip, or, in other words, in driving the air rearwards. It would, therefore, require 472 horse-power instead of 100 to drive the proposed new balloon through the air at the rate of 40 miles an hour.
“It will be seen from this calculation that the new airship will still be at the mercy of the wind and weather. Those who pin their faith on the balloon as the only means of navigating the air may dispute my figures. However, all the factors in the equation are extremely simple and well known, and no one can dispute any of them except the assumed coefficient of resistance, which is given here as ·20. The writer feels quite sure that, after careful experiments are made, it will be found that this coefficient is nearer ·40 than ·20, especially so at high speeds when the air pressure deforms the gas-bag. Only a slight bagging in the front end of the balloon would run the coefficient up to fully ·50, and perhaps even more.”—Times, Feb. 26, 1908.
Fig. 73.—The enormous balloon, “Ville de Paris,” of the French Government. This balloon is a beautiful piece of workmanship, and is said to be the most practical balloon ever invented, not excepting the balloon of Count Zeppelin. Some idea of its size may be obtained by comparing it with the size of the men who are standing immediately underneath.
Fig. 73.—The enormous balloon, “Ville de Paris,” of the French Government. This balloon is a beautiful piece of workmanship, and is said to be the most practical balloon ever invented, not excepting the balloon of Count Zeppelin. Some idea of its size may be obtained by comparing it with the size of the men who are standing immediately underneath.
Fig. 73.—The enormous balloon, “Ville de Paris,” of the French Government. This balloon is a beautiful piece of workmanship, and is said to be the most practical balloon ever invented, not excepting the balloon of Count Zeppelin. Some idea of its size may be obtained by comparing it with the size of the men who are standing immediately underneath.
Since writing theTimesarticle, a considerable degree of success has been attained by Count Zeppelin. Accordingto newspaper accounts, his machine has a diameter of about 40 feet, and a length of no less than 400 feet. It appears that this balloon consists of a very light aluminium envelope, which is used in order to produce a smooth and even surface, give rigidity, and take the place of the network employed in ordinary balloons. It seems that the gas is carried in a large number of bags fitted in the interior of this aluminium envelope. However, by getting a firm and smooth exterior and by making his apparatus of very great length as relates to its diameter, he has obtained a lower coefficient of resistance than has ever been obtained before, and as his balloon is of great volume, he is able to carry powerful motors and use screw propellers of large diameter. It appears that he has made a circuit of considerable distance, and returned to the point of departure without any accident. A great deal of credit is, therefore, due to him. His two first balloons came to grief very quickly; he was not discouraged, but stuck to the job with true Teutonic grit, and has perhaps attained a higher degree of success than has ever been attained with a balloon. However, some claim that the French Government balloon, “La Patrie” is superior to the Zeppelin balloon at all points. When we take into consideration the fact that the Zeppelin machine is 400 feet long and lighter than the same volume of air, it becomes only too obvious that such a bulky and extremely delicate and fragile affair will easily be destroyed. Of course ascensions will only be made in very favourable weather, but squalls and sudden gusts of wind are liable to occur. It is always possible to start out in fine weather if one waits long enough, but if a flight of 24 hours or even 12 hours is to be attempted, the wind may be blowing very briskly when we return, and an ordinary wind will not only prevent the housing of Count Zeppelin’s balloon, but will be extremely liable to reduce it to a complete wreck in a few minutes.[4]
[4]Shortly after this was written, the Zeppelin machine was completely demolished by a gust of wind.
[4]Shortly after this was written, the Zeppelin machine was completely demolished by a gust of wind.
I am still strongly of the opinion that the ultimate mastery of the air must be accomplished by machines heavier than the air.
(From our own Correspondent.)
Berlin, Friday.
Germany’s fleet of “air cruisers,” or dirigible airships, will, it is proudly announced to-day, presently number six:—
The first announcement of the last-named airship was given inThe Daily Mailseveral months ago. The company has engaged a celebrated military aeronaut, Captain von Krogh, as commander of the vessel. The Study Society’s new non-rigid ship will be sold to the War Office as soon as she has completed her trial trips.
The Army will then possess three dirigibles, each representing one of the three opposed types of construction—rigid, half-rigid, and non-rigid—with a view to arriving at a conclusion on their merits.
..........
“Only a year or so ago, our authorities were talking of aerial navigation in its relation to war as ‘an interestingand instructive study.’ Now we must reckon it as the gravest problem of the moment. The cleverest aeronauts in England should be called upon at once to design an airship, not only as efficient as that of Count Zeppelin’s, but possessed of even greater speed. (His average was said to be about 34 miles an hour.) In speed will lie the supremacy of the air when it comes to actual warfare. Of two opposing airships, the faster will be able to outmanœuvre its adversary and hold it at its mercy.”—Daily Mail, July 11, 1908.
GERMANY AS THE AERIAL POWER.
TEUTONIC VISION.
A LANDING OF 350,000 MEN.
Herr Rudolph Martin, author of books on war in the air and “Is a World-War Imminent?” points out how England is losing her insular character by the development of airships and aeroplanes.
“In a world-war,” he said to me, “Germany would have to spend two hundred millions sterling in motor airships, and a similar amount in aeroplanes, to transport 350,000 men in half an hour during the night from Calais to Dover. Even to-day the landing of a large German army in England is a mere matter of money. I am opposed to a war between Germany and England, but should it break out to-day, it would last at least two years, for we would conclude no peace until a German army had occupied London.
“In my judgment it would take two years for us to build motor airships enough simultaneously to throw 350,000 men into DoverviaCalais. During the same night, of course, a second transport of 350,000 men could follow. The newest Zeppelin airship can comfortably carry fifty persons from Calais to Dover. The ships which the Zeppelin works in Friedrichshafen will build during the next few months are likely to be considerably larger than IV., and will carry one hundred persons. There is no technical reason against the construction of Zeppelin airships of 1,100,000 or even 1,700,000 cubic feet capacity, or twice or three times the capacity of IV. (500,000 cubic feet).
“I am at present organising a German ‘Air Navy League,’ to establish air-traffic routes in Germany. Aluminium airships could carry on regular traffic between Berlin and London, Paris, Cologne, Munich, Vienna, Moscow, Copenhagen, and Stockholm. In war time these ships would be at the disposal of the German Empire.
“The development of motor airship navigation will lead to a perpetual alliance between England and Germany. The British fleet will continue to rule the waves, while Germany’s airships and land armies will represent the mightiest Power on the Continent of Europe.”—Daily Mail, July 11, 1908.
It is needless to say that the above was written before the wreck of Zeppelin’s machine.
For many years scientific mechanicians and mathematicians have told us that the navigation of the air was quite possible. They have said it is only a question of motive power; “Give us a motor that is sufficiently light and strong, and we will very soon give you a practical flying machine.” A domestic goose weighs about 12 lbs., and it has been estimated that it only exerts about one-twelfth part of a horse-power in flying—that is, it is able to exert one man-power with a weight of only 12 lbs., which seems to be a very good showing for the goose. However, at the present moment, we are able to make motors which develop the power of ten men—that is, one horse-power—with less than the weight of a common barnyard fowl. Under these conditions it is quite evident that if a machine can be so designed that it will not be too wasteful in power, it must be a success. It is admitted by scientific men that all animals, such as horses, deer, dogs, and also birds, are able to develop much more dynamic energy for the carbon consumed than is possible with any thermodynamic machine that we are able to make. It may be said that many animals are able to develop the full dynamic energy of the carbon they consume, whereas the best of our motors do not develop more than 10 per cent. of the energy contained in the combustibles that they consume; but, as against this, it must be remembered that birds feed on grass, fruit, fish, etc., heavy and bulky materials containing only a small percentage of carbon, whereas with a motor we are able to use a pure hydrocarbon that has locked up in its atoms more than twenty times as much energy per pound as in theordinary food consumed by birds. I think, in fact I assert, that the time has now arrived, having regard to the advanced state of the art in building motors, when it will be quite a simple and safe affair to erect works and turn out successful flying machines at less cost than motor cars; in fact, there is nothing that stands in the way of success to-day. The value of a successful flying machine, when considered from a purely military standpoint, cannot be over-estimated. The flying machine has come, and come to stay, and whether we like it or not, it is a problem that must be taken into serious consideration. If we are laggards we shall, unquestionably, be left behind, with a strong probability that before many years have passed over our heads, we shall have to change the colouring of our school maps.
As the newspaper accounts that we receive from the Continent give all weights and measures in the metric system, it is convenient to have some simple means at hand to convert their values into English weights and measures. I therefore give the following, which will greatly simplify matters both for French and English measurements:—
Fig. 74.—Photograph of a model of my machine, showing the fore and aft horizontal rudders and the superposed aeroplanes.
Fig. 74.—Photograph of a model of my machine, showing the fore and aft horizontal rudders and the superposed aeroplanes.
Fig. 74.—Photograph of a model of my machine, showing the fore and aft horizontal rudders and the superposed aeroplanes.
In my early “whirling table”[5]experiments, the aeroplanes used were from 6 inches to 4 feet in width. They were for the most part made of thin pine, being slightly concave on the underneath side and convex on the top, both the fore and aft edges being very sharp. I generally mounted them at an angle of 1 in 14[6]—that is, in such a position that in advancing 14 feet they pressed the air down 1 foot. With this arrangement, I found that with a screw thrust of 5 lbs. the aeroplane would lift 5 × 14, or 70 lbs., while if the same plane was mounted at an angle of 1 in 10, the lifting effect was almost 50 lbs. (5 × 10). This demonstrated that the skin friction on these very sharp, smooth and well-made aeroplanes was so small a factor as not to beconsidered. When, however, there was the least irregularity in the shape of the aeroplane, the lifting effect, when considered in terms of screw thrust, was greatly diminished. With a well-made wooden plane placed at an angle of 1 in 14, I was able to carry as much as 113 lbs. to the H.P., whereas with an aeroplane consisting of a wooden frame covered with a cotton fabric (Fig. 75), I was only able to carry 40 lbs. to the H.P.[7]
[5]A name given by Professor Langley to an apparatus consisting of a long rotating arm to which objects to be tested are attached.
[5]A name given by Professor Langley to an apparatus consisting of a long rotating arm to which objects to be tested are attached.
[6]I found it more convenient to express the angle in this manner than in degrees.
[6]I found it more convenient to express the angle in this manner than in degrees.
[7]The actual power consumed by the aeroplane itself was arrived at as follows:—The testing machine was run at the desired speed without the aeroplane, and the screw thrust and the power consumed carefully noted. The aeroplane was then attached and the machine again run at the same speed. The difference between the two readings gave the power consumed by the aeroplane.
[7]The actual power consumed by the aeroplane itself was arrived at as follows:—The testing machine was run at the desired speed without the aeroplane, and the screw thrust and the power consumed carefully noted. The aeroplane was then attached and the machine again run at the same speed. The difference between the two readings gave the power consumed by the aeroplane.
Fig. 75.—The fabric-covered aeroplane experimented with. The efficiency of this aeroplane was only 40 per cent. of that of a well-made wooden aeroplane.
Fig. 75.—The fabric-covered aeroplane experimented with. The efficiency of this aeroplane was only 40 per cent. of that of a well-made wooden aeroplane.
Fig. 75.—The fabric-covered aeroplane experimented with. The efficiency of this aeroplane was only 40 per cent. of that of a well-made wooden aeroplane.
Fig. 76.—The forward rudder of my large machine, showing the fabric attached to the lower side. The top was also covered with fabric. This rudder considered as an aeroplane had a very high efficiency and worked very well indeed.
Fig. 76.—The forward rudder of my large machine, showing the fabric attached to the lower side. The top was also covered with fabric. This rudder considered as an aeroplane had a very high efficiency and worked very well indeed.
Fig. 76.—The forward rudder of my large machine, showing the fabric attached to the lower side. The top was also covered with fabric. This rudder considered as an aeroplane had a very high efficiency and worked very well indeed.
These facts taken into consideration with my other experiments with large aeroplanes, demonstrated to my mind that it would not be a very easy matter to make a large and efficient aeroplane. If I obtained the necessary rigidity by making it of boards, it would be vastly too heavy for the purpose, while if I obtained the necessary lightness by making the framework of steel and covering it with a silk or cotton fabric in the usual way, the distortion would be so great that it would require altogether too much power to propel it through the air. I therefore decided on making a completely new form of aeroplane. I constructed a large steel framework arranged in such a manner that the fore and aft edges consisted of tightly drawn steel wires. This framework was provided with a number of light wooden longitudinal trusses, similar to those shown inFig. 76. The bottom side was then covered with balloon fabric secured at the edges, and also by two longitudinal lines of lacing through the centre. It was stretched very tightly and slightly varnished, but not sufficiently to make it absolutely air-tight. The top of this framework was covered with the same kind of material, but varnished so as to make it absolutely airtight. The top and bottom were then laced together forming very sharp fore and aft edges, and the top side was firmly secured to the light wooden trusses before referred to. Upon running this aeroplane, I found that a certain quantity of air passed through the lower side and set up a pressure between the upper and lower coverings. The imprisoned air pressed the top covering upward, forming longitudinal corrugations which did not offer any perceptible resistance to the air, whereas the bottom fabric, having practically the same pressure on both sides, was not distorted in the least. This aeroplane was found to be nearly as efficient as it would have been had it been carved out of a solid piece of wood. It will be seen by the illustration that this large or main aeroplane is practically octagonal in shape, its greatest width being 50 feet, and the total area 1,500 square feet.
Upon running my large machine over the track (Fig. 77) with only the main aeroplane in position, I found that a lifting effect of 3,000 to 4,000 lbs. could be obtained with a speed of 37 to 42 miles an hour. It was not always an easy matter to ascertain exactly what the lifting effect was at a given speed on account of the wind that was generally blowing. Early in my experiments, I found if I ran my machine fast enough to produce a lifting effect within 1,000 lbs. of the total weight of the machine, that it was almost sure to leave the rails if the least wind was blowing. It was, therefore, necessary for me to devise some means of keeping the machine on the track. The first plan tried was to attach some very heavy cast-iron wheels weighing with their axle-trees and connections about 11⁄2tons. These were constructed in such a manner that the light flanged wheels supporting the machine on the steel rails could be lifted 6 inches above the track, leaving the heavy wheels still on the rails for guiding the machine. This arrangement was tried on several occasions, the machine being run fast enough to lift the forward end off the track. However, I found considerable difficulty in starting and stopping quickly on account of the great weight, and the amount of energy necessary to set such heavy wheels spinning at a high velocity. The last experiment with these wheels was made when a head wind was blowing at the rate of about 10 miles an hour. It was rather unsteady, and when the machine was running at its greatest velocity, a sudden gust lifted not only the front end, but also the heavy front wheels completely off the track, and the machine falling on soft ground was soon blown over by the wind.
I then provided a safety track of 3 × 9 Georgia pine placed about 2 feet above the steel rails, the wooden track being 30 feet gauge and the steel rails 9 feet gauge (Fig. 77). The machine was next furnished with four extra wheels placed on strong outriggers and adjusted in such a manner that when it had been lifted 1 inch clear of the steel rails, these extra wheels would engage the upper wooden track.[8]
[8]Springs were interposed between the machine and the axle-trees. The travel of these springs was about 4 inches; therefore, when the machine was standing still, the wheels on the outriggers were about 5 inches below the upper track.
[8]Springs were interposed between the machine and the axle-trees. The travel of these springs was about 4 inches; therefore, when the machine was standing still, the wheels on the outriggers were about 5 inches below the upper track.
Fig. 77.—View of the track used in my experiments. The machine was run along the steel railway which was 9 feet gauge, and was prevented from rising by the wooden track which was 35 feet gauge.
Fig. 77.—View of the track used in my experiments. The machine was run along the steel railway which was 9 feet gauge, and was prevented from rising by the wooden track which was 35 feet gauge.
Fig. 77.—View of the track used in my experiments. The machine was run along the steel railway which was 9 feet gauge, and was prevented from rising by the wooden track which was 35 feet gauge.
Fig. 78.—The machine on the track tied up to the dynamometer.
Fig. 78.—The machine on the track tied up to the dynamometer.
Fig. 78.—The machine on the track tied up to the dynamometer.
Fig. 79.—Two dynagraphs, one for making a diagram of the lifting effect off the main axle-tree, and the other for making a diagram of the lift off the front axle-tree. By this arrangement, I was able to ascertain the exact lifting effect at all speeds, and to arrange my aeroplanes in such a manner that the center of lifting effect was directly over the center of gravity. The paper-covered cylinders made one rotation in 2,000 feet.
Fig. 79.—Two dynagraphs, one for making a diagram of the lifting effect off the main axle-tree, and the other for making a diagram of the lift off the front axle-tree. By this arrangement, I was able to ascertain the exact lifting effect at all speeds, and to arrange my aeroplanes in such a manner that the center of lifting effect was directly over the center of gravity. The paper-covered cylinders made one rotation in 2,000 feet.
Fig. 79.—Two dynagraphs, one for making a diagram of the lifting effect off the main axle-tree, and the other for making a diagram of the lift off the front axle-tree. By this arrangement, I was able to ascertain the exact lifting effect at all speeds, and to arrange my aeroplanes in such a manner that the center of lifting effect was directly over the center of gravity. The paper-covered cylinders made one rotation in 2,000 feet.
When fully equipped, my large machine had five long and narrow aeroplanes projecting from each side. Those that are attached to the sides of the main aeroplanes are 27 feet long, thus bringing the total width of the machine up to 104 feet. The machine is also provided with a fore and an aft rudder made on the same general plan as the main aeroplane. When all the aeroplanes are in position, the total lifting surface is brought up to about 6,000 square feet. I have, however, never run the machine with all the planes in position. My late experiments were conducted with the main aeroplane, the fore and aft rudders, and the top and bottom side planes in position, the total area then being 4,000 square feet. With the machine thus equipped, with 600 lbs. of water in the tank and boiler and with the naphtha and three men on board, the total weight was a little less than 8,000 lbs. The first run under these conditions was made with a steam pressure of 150 lbs. to the square inch, in a dead calm, and all fourof the lower wheels remained constantly on the rails, none of the wheels on the outriggers touching the upper track. The second run was made with 240 lbs. steam pressure to the square inch. On this occasion, the machine seemed to vibrate between the upper and lower tracks. About three of the top wheels were engaged at the same time, the weight on the lower steel rails being practically nil. Preparations were then made for a third run with nearly the full power of the engines. The machine was tied up to a dynamometer (Fig. 78), and the engines were started with apressure of about 200 lbs. to the square inch. The gas supply was then gradually turned on with the throttle valves wide open; the pressure soon increased, and when 310 lbs. was reached, the dynamometer showed a screw thrust of 2,100 lbs.,[9]but to this must be added the incline of the track which amounts to about 64 lbs. The actual thrust was therefore 2,164 lbs. In order to keep the thrust of the screws as nearly constant as possible, I had placed a small safety valve—3⁄4-inch—in the steam pipe leading to one of the engines. This valve was adjusted in such a manner that it gave a slight puff of steam at each stroke ofthe engine with a pressure of 310 lbs. to the square inch, and a steady blast at 320 lbs. to the square inch. As the valves and steam passages of these engines were made very large, and as the piston speed was not excessive, I believed if the steam pressure was kept constant that the screw thrust would also remain nearly constant, because as the machine advances and the screws commence to run slightly faster, an additional quantity of steam will be called for and this could be supplied by turning on more gas. When everything was ready, with careful observers stationed on each side of the track, the order was given to let go. The enormous screw thrust started the machine so quickly that it nearly threw the engineers off their feet, and the machine bounded over the track at a great rate. Upon noticing a slight diminution in the steam pressure, I turned on more gas, when almost instantly the steam commenced to blow a steady blast from the small safety valve, showing that the pressure was at least 320 lbs. in the pipes supplyingthe engines with steam. Before starting on this run, the wheels that were to engage the upper track were painted, and it was the duty of one of my assistants to observe these wheels during the run, while another assistant watched the pressure gauges and dynagraphs (Fig. 79). The first part of the track was up a slight incline, but the machine was lifted clear of the lower rails and all of the top wheels were fully engaged on the upper track when about 600 feet had been covered. The speed rapidly increased, and when 900 feet had been covered, one of the rear axle-trees, which were of 2-inch steel tubing, doubled up (Fig. 80), and set the rear end of the machine completely free. The pencils ran completely across the cylinders of the dynagraphs and caught on the underneath end. The rear end of the machine being set free, raised considerably above the track and swayed. At about 1,000 feet, the left forward wheel also got clear of the upper track and shortly afterwards, the right forward wheel tore upabout 100 feet of the upper track. Steam was at once shut off and the machine sank directly to the earth imbedding the wheels in the soft turf (Figs. 81and82) without leaving any other marks, showing most conclusively that the machine was completely suspended in the air before it settled to the earth. In this accident, one of the pine timbers forming the upper track went completely through the lower framework of the machine and broke a number of the tubes, but no damage was done to the machinery except a slight injury to one of the screws (Fig. 83).