PL. 36. PATHS OF FLIGHT OF AERODROME NO. 5, JULY 29, 1899◊
PL. 36. PATHS OF FLIGHT OF AERODROME NO. 5, JULY 29, 1899◊
A trial run in the house-boat was also made on Aerodrome No. 6, while waiting for the weather to become more suitable, but, unfortunately, the result of this test was disastrous. The aerodrome had been placed on trestles and[p149]held down to the floor by wires fastened to the cross-frame. In the midst of the test one of the wires slipped, allowing the aerodrome to push forward and thus permitting the propellers to come in contact with the wires which held it to the floor. Both propellers were entirely demolished and the cross-frame was broken off short just at the right-hand engine. The disaster was entirely due to the carelessness of one of the workmen in tightening one of these wires, a further example of the extreme heedlessness of workmen, even in the most important details, which concern the very existence of the machine.
After the very satisfactory trial of Aerodrome No. 5 in the shop two days previous, it was hoped, now that the weather had become suitable, that a good flight with the superposed wings would be obtained. The aerodrome, equipped with these wings, was accordingly placed on the launching apparatus and the burners were lighted, but they refused to work properly, a steam pressure of only 80 pounds being obtained. After much delay the burners were finally got to work properly, but the wind had increased in velocity to such an extent that it was necessary to remove the aerodrome to the interior of the house-boat. As the wind continued to increase in velocity it was decided to make another trial of the aerodrome inside of the house-boat. Upon doing this it was very soon found that there was a small leak in the front turn of one of the coils of the boiler, and the steam from this played directly against the burner, causing it to work intermittently. A new coil was substituted, and after some adjustment a very excellent run was obtained, the steam pressure reaching 130 pounds and the propellers making 654 R. P. M.
In the afternoon the wind quieted down and the aerodrome, equipped with superposed wings, was again placed on the launching apparatus. The burners were lighted but again refused to work properly, the vaporizing tip being stopped up with soot. This caused the burner to “flood,” which sent a sheet of flame through the stack and burned the rear right wing.
A new wing was substituted, the burner tip was cleaned out and everything was again put in readiness for a flight. Upon lighting the burners, 1 minute and 58 seconds were required to raise 120 pounds steam pressure. The underneath launching apparatus, with the disappearing track, worked perfectly, the aerodrome dropping slightly, but going straight ahead. It, however, continued to descend for a distance of about 100 feet, the bow being elevated about 5 degrees. The bow then became horizontal, the aerodrome rising slightly at the same time, but going only about 50 feet farther, when it again started to descend slightly, and finally settled gently on the water between 300 and 500 feet from the house-boat, with its bow elevated about 3 degrees. There was a hiss as the hull touched the water, showing that the fire was still burning and making it[p150]improbable that the failure of the flight was due to lack of power. The data on settings of wings, tail, etc., are given on Data Sheet No. 11.
The speed of the launching car, one foot in front of the point at which the aerodrome was released, was twenty feet a second, as shown by the carbon record sheet carried by the launching car and moved in front of a tuning fork which had been set in vibration.
The aerodrome, being uninjured in the previous flight, was again placed on the “underneath” launching apparatus, and before attaching the wings a short run was made in order to see that everything was in proper working condition. As everything seemed to be all right, the wings and tail were immediately adjusted for another trial. As the bow was slightly elevated in the previous trial, it was thought best to bring theCGa little farther forward, and this was accordingly done. As the aerodrome also seemed to drop slightly in leaving the launching car in the above trial, the tension of the launching springs was slightly increased so as to increase the velocity at the moment of release.
Just as the sun was setting the aerodrome was again launched, 1 minute and 30 seconds having been required to raise 120 pounds steam pressure, but the pressure was rising very rapidly at the moment of launching. There was an absolutely dead calm prevailing, the river being as smooth as glass. The launching apparatus, with the disappearing track, worked perfectly. Immediately upon being released the aerodrome went straight ahead, with its midrod horizontal, but gradually glided downward as though the wings had very little lifting power, and settled in the water about 200 feet from the house-boat. The velocity of the launching car, 1 foot before the aerodrome was released, was 22 feet a second, as shown by the carbon record sheet.
In the above trials of the superposed wings, the conditions of the wind and of the aerodrome were certainly as favorable as could be expected. There was as much power being furnished by the engine as had been furnished in the previous flights with the “single-tier” wings, and the balancing of the aerodrome was exceedingly good. The superposed wings, unquestionably, had a fair trial and proved inferior to the “single-tier” ones, for they had a supporting surface of 2.75 square feet to the pound, whereas with the “single-tier” wings there was approximately 2 square feet to the pound. The decreased lifting power of the superposed wings seems to be another confirmation of the results of the Allegheny experiments with the “plane-dropper.”40
As more time had already been given to these tests than it seemed well to[p151]spend on them at that time, owing to the pressure of the work of construction for the large machine, it was deemed best to discontinue them for the time being, and as soon as time could be found for it, to construct a set of wings with superposed surfaces, using only two surfaces and making their distance apart at least equal to or greater than their width.
It will be remembered that the prime object in making these tests was to obtain data for use in the balancing of the large aerodrome and in constructing a launching apparatus for it. The chief deductions drawn from them were: First: That it would be best to construct the first set of wings for the large machine on the “single-tier” plan, and later to make a set of superposed ones, should further experiments with new designs develop a type of superposed surfaces which gave as good lifting power as the “single-tier” ones. Second: That the proportioning of the coefficient of elasticity of the Pénaud tail should be given as careful attention as the setting of the wings. Third: That the “underneath” launching apparatus was equally as good as the “overhead” one, and that both worked as well as could be desired; and, fourth, that while short periods of calm weather might be expected during some part of the day on a portion of the days of each month, yet the most favorable conditions were more apt to be met with between the first break of day and the actual rising of the sun, or from an hour preceding sunset until darkness actually came.
It will be noted that while considerable delay was experienced in making these tests, nearly all of it was due to the very delicate adjustments required in the power-generating apparatus of the aerodrome, but it should also be noted that when these adjustments were accurately made the models operated exceedingly well, and could be depended upon to give good flights of sufficient duration to permit a careful study of their action while in the air.
In the experiments of June 27 and July 7, above described, the aerodrome immediately after leaving the launching apparatus began to rise with its midrod pointed upward at an angle of about 15 degrees. From Data Sheet No. 6, which gives in detail the important data as to the settings of the wings, the elasticity of the Pénaud tail,41etc., we note that the tail had a negative angle of712degrees, and that the spring which held it at this angle was of such a stiffness that it required 1240 grammes placed at its center of figure to depress it to the horizontal. It will also be noticed that the position of the front and rear[p152]wings relative to the center of gravity of the machine was not the same as that which existed at the time of the very successful flights of 1896, as shown by Data Sheet No. 1 of No. 5, May 6, 1896. When the elasticity of the tail was adjusted before making this test it was thought that it was made the same as in the experiments of 1896, though accurate data as to the exact amount of this elasticity had, unfortunately, not been kept.
A slight change had also been made in the method employed of attaching the Pénaud tail to the machine. In 1896 the tail was attached to the machine by means of a flat piece of wood (hickory) which had been steamed and bent to the proper extent to cause the rudder to have a negative angle of about 5 degrees, but no accurate note was made of its angle or stiffness, so that in 1899 no data were available as to exactly what the angle had been or how stiff the spring was. Owing to the fact that wood not only warps and twists, but also that any piece which has been steamed and bent gradually loses a certain amount of its curvature, it was decided in 1898 to change this method of attaching the tail, the wooden spring being replaced by a coiled steel spring attached to an upper guy-post and connected to the tail by a bridle wire fastened to the center of figure of the tail.
After the experiment of July 7, 1899, a lower spring, consisting of small rubber bands, was connected by a wire to the lower part of the rudder and fastened to the guy-post, thereby more nearly reproducing the conditions obtained when using a wooden spring, which, of course, tends to return the rudder to its normal position when it is displaced in either direction. After attaching this lower spring to the rudder, the experiment of July 14 was made, and it was found that the aerodrome still flew with its midrod pointed upward at a very steep angle. It was, therefore, felt certain that the upper spring on the rudder was too stiff, and that it should not require so much as 1240 grammes to bring it to the horizontal. This spring was, therefore, replaced by a weaker one, and the angle of the rudder was also decreased until it had a negative angle of only 5 degrees and required only 200 grammes placed at its center of figure to bring it to the horizontal. From the description of the flight of July 19, it will be seen that these changes immediately corrected the tendency of the aerodrome to point its nose upward at such a sharp angle, and it will be later seen that after a further slight adjustment the flight of July 29 was made, in which the proper balancing was obtained and the aerodrome made a good horizontal flight.
After these preliminary tests with the “overhead” launching apparatus, it was dismounted and the “underneath” one substituted and the experiments of July 28, 29 and August 3 were made. Everything connected with this “underneath” launching apparatus worked perfectly from the start and four flights of the aerodromes were made using it.
PL. 37. EXPERIMENTAL FORMS OF SUPERPOSED SURFACES, 1898, 1899 (SEE ALSO PLATES 64 AND 65)◊
PL. 37. EXPERIMENTAL FORMS OF SUPERPOSED SURFACES, 1898, 1899 (SEE ALSO PLATES 64 AND 65)◊
[p153]
It will be recalled that in “Experiments in Aerodynamics” Mr. Langley made tests of the soaring speed, etc., of surfaces when superposed. In many of his experiments with rubber-driven models, he also employed superposed surfaces. During the summer of 1898 several forms of superposed surfaces, of a proper size for use on the steam-driven models Nos. 5 and 6, were constructed and were tested under as nearly as possible the same conditions as would exist when used on the aerodrome, by mounting the surfaces on the whirling-table and measuring their soaring speed, lift, drift, etc., to determine just what arrangement of surfaces gave the greatest lifting effect with the least resistance. Two of the forms which were tested are shown in Plate37, Figs. 1 and 2, and Plates64and65. At the conclusion of these tests, it was decided to construct a set of surfaces on the plan shown in Plates64and65, and to have them ready for use on either of the models Nos. 5 and 6. These surfaces were taken to Chopawamsic Island in April, 1899, when all of the other aerodromic material was first carried there. It was planned to make some tests with them to determine whether or not it would be best to use superposed surfaces on the large aerodrome or to follow the plan of “single-tier” ones, which had the great advantage of having already proved their worth in the successful flights of the models. On August 3, Aerodrome No. 5, equipped with these superposed surfaces, was launched. It will be noted from Data Sheet No. 11 that the superficial area of the superposed surfaces was considerably greater than that provided by the “single-tier” ones, and on the assumption of the same efficiency per unit of surface in both cases, the aerodrome should have soared at a less speed and required less power when using the superposed surfaces. The results obtained, however, were just the reverse, the aerodrome being unable to sustain itself when using the superposed surfaces, whereas with the “single-tier” ones it was evident that a slight excess weight might easily have been carried without preventing the aerodrome from soaring properly. While it was felt that these tests were not entirely conclusive as to the superior lifting power of the “single-tier” surfaces, yet as the engine builder was constantly promising, each time with increased emphasis, that he would within less than a fortnight deliver the engine for the large aerodrome, and that it would develop even more power than the specifications called for, it was deemed best to cease the experiments with the models and concentrate all effort on the completion of the large aerodrome frame and the construction of a set of “single-tier” supporting surfaces for it. It was recognized from the first that the “single-tier” supporting surfaces lacked the rigidity which could be secured by the truss construction afforded by the superposed plan, yet these models, which were the only machines in the history of the world that had ever flown successfully, had been equipped with “single-tier” surfaces; and the experience so dearly bought during the long[p154]years of development of these models had taught the very valuable lesson that in work of this kind where we have no margin on anything, but everything has to be calculated on the “knife-edge” basis, it is an exceedingly unwise thing to introduce any modification from what has been proved to be satisfactory, unless such modification is absolutely necessary.
The principal object in building the one-eighth size model of the large aerodrome, as mentioned in the first part of this chapter, was to determine by actual experiment whether the new form of “underneath” launching apparatus, which had just been designed, was likely to prove as satisfactory as the original “overhead” type, which had been used in the successful flights of the models in 1896. Yet after it was completed this aerodrome was found so very strong and stiff, even though roughly constructed by merely tying the joints of the tubing together with wires and soldering over the joints, that it was decided to equip it with power, if a suitable form of power could be found which could be easily applied. Just at this time liquid air as a motive power was attracting considerable attention all over the country, and attempts were made to procure a small power plant for operation by liquid air. After devoting considerable time to the matter it was found impossible to do anything with it just at that time, as the liquified air could not be obtained in Washington, and one of the chief experimenters in New York, who had been given a commission to make certain experiments at his plant, so continuously delayed beginning them that it was found necessary to give up the idea.
However, after the completion of the tests of the launching apparatus some experiments were made in flying the model as a kite. For this purpose a mast twenty feet high was constructed and so arranged that it could be mounted at the center of a small power launch. The model aerodrome was flown by a cord connected to it by a bridle, the cord passing over a swivel pulley on top of the mast and down into the boat, whence it could be played out or hauled in as occasion required. By heading the launch into the wind it was possible to secure sufficient relative velocity to cause the model to support itself and a number of tests were made in this way. It was found that when the bridle was attached at the point at which the propellers would deliver their thrust, had they been in use and driven by power, the model flew exceedingly well, maintaining its equilibrium even during very strong gusts. Owing to the rolling produced by waves from the large boats which were continually passing in the part of the river where these tests were made, the power launch was often in danger of being upset by its tall mast; and finally, when the tests were just reaching the point where accurate information was being obtained on the balancing of the model, a sudden rolling of the boat caused the mast to snap off while the model was in the air. Before it could be picked up from the water a passing boat had swamped it and it was lost in the river.[p155]
Although the model was, as has been said, rudely constructed and, therefore, did not represent a serious loss, yet the pressure of the more important construction work for the large machine prohibited the construction of another rough model for continuing these kite experiments, which it was felt could not at best be more than approximate indications of the general stability of the machine under practical conditions.