â—Š[p133]CHAPTER IIIEXPERIMENTS WITH MODELS
[p133]
Immediately after the contract for the engine had been placed and the actual work had been begun, attention was given to the problem of providing means for properly launching the aerodrome. On the theory that the plan of launching the small aerodromes, which had finally been adopted after many years of painstaking experiment, would be the best to employ for the large aerodrome, Mr. Langley decided to have constructed a large house-boat with the launching track arranged on it in a way similar to that used for the small machines. While the general plans for this boat had been under consideration for some time, the actual working drawings were completed in January, 1899, and so great seemed the need for expediting its construction, in order to have it ready at the time when the engine was expected, that the contract which was made for its construction specifically provided for its being completed promptly, there being a large forfeit to cover any delay on the part of the contractor.
While the boat itself was being constructed, the working drawings were completed for the house to be built on it, and a contract was made for the construction of this house within a given period, there being also a time forfeit in this contract.
When the end of February arrived, it was found that, although the engine builder had succeeded in constructing an engine which weighed one hundred pounds, and which theoretically should have given something over twelve horse-power, yet he was unable to make it work properly. And then began a protracted period of most exasperating delays, the engine builder promising from week to week that certainly within the succeeding ten days he would be able to make delivery of the engine developing the full horse-power for which the contract called. After this delay on the engine had continued for some months—a delay which necessitated the cessation of the work on the main steel frame of the aerodrome, as it was deemed best to make certain tests of the engine running while supported by a portion of the frame to determine whether or not it was strong enough before completing the rest of it-—Mr. Langley decided to employ part of the time in the construction of a model of one-eighth the linear dimensions of the large aerodrome, which was to be used in testing a model of the newly designed launching apparatus described later, and which might also be flown as a kite in making check measurements on the proper balancing which should be employed for the large aerodrome.[p134]
The perfected launching apparatus which had been used for the steam-driven models Nos. 5 and 6 (described in Part I, Chapter Xâ—Š) had proved most satisfactory and reliable, but when the designs were made for a launching apparatus for the large machine it was found that an exact duplication of the plan of the small one involved serious difficulties in connection with the construction of the house-boat, owing to the very considerable weight and size of the turn-table necessary to permit the aerodrome to be launched in any desired direction, regardless of the direction in which the houseboat might be pointing under the influence of the wind and tide. A new design was accordingly made for a launching apparatus in which the launching car was to run on a track mounted directly on the turn-table, the launching car supporting the aerodrome from underneath, instead of being mounted in an inverted position on an overhead track with the aerodrome depending from it.
From the previous description of the launching apparatus, it will be recalled that, in order to provide that the aerodrome should drop slightly at the moment of its release from the car, and thereby avoid all danger of entanglement, the speed of the launching car at the point at which the aerodrome was released was purposely madelessthan the “soaring speed†of the aerodrome. Having this feature in mind, when designing the “underneath†launching apparatus, it was recognized that the danger of the aerodrome becoming entangled with this form of apparatus could be avoided by making the launching speedgreaterthan the velocity which it would be necessary for the aerodrome to have in order to soar,provided the balancing was correct and the aerodrome did soar. Nevertheless, it was deemed unwise to put too much dependence on the empirical calculations from which the balancing of the large aerodrome would necessarily be determined, and, therefore, some means seemed necessary for causing the launching car to drop out of the way immediately upon releasing the aerodrome. In the new design, more completely described below, in Chapter IV◊, this was accomplished by so arranging a portion of the front end of the track that, at the moment the launching car released the aerodrome, it dropped like a disappearing gun carriage, leaving the aerodrome free in the air with no possibility of becoming entangled, provided the aerodrome itself did not drop more rapidly than an angle of 15 degrees.
A small working model of this launching apparatus, one-eighth the linear dimensions of that which would be necessary for the large aerodrome, was first designed and constructed in the shop, the small one-eighth-size model of the large aerodrome being launched from it into a sheet stretched in front of it to act as a buffer. When it was found to work very satisfactorily, a large one, twice this size, was immediately built for use with the steam-driven models Nos. 5 and 6.[p135]
These models, Nos. 5 and 6, which had flown so successfully in 1896, had, during the preceding twelve months, been completely overhauled and thoroughly tested in preparing them for trials in actual flight. Many pendulum tests were made on both aerodromes, and it was found after repeated trial that each could be depended on to show a lift of sixty per cent of its flying weight.
This was more than sufficient for flight, but in order to insure successful trials and avoid delay no aerodrome was launched until it had shown previously its ability to generate enough power to maintain for at least two minutes a lift of at least fifty per cent of the total flying weight.
Models Nos. 5 and 6, having thus proved their readiness for trial in flight, were accordingly, in April, 1899, taken to Chopawamsic Island, together with the old “overhead†launching apparatus and the new one above described, and placed on a small house-boat similar to the one which had been used in 1896. Two men were detailed for this special work, and were first employed in mounting the old launching apparatus for a few preliminary tests with it, in order to make sure that the aerodromes were in proper working order before trying them on the new “underneath†one. After considerable delay, due to various causes, this apparatus and the aerodromes were got into proper working condition, and during June, July and August the following flights were made with these machines, the record being condensed from the reports made by the writer to Mr. Langley while he was abroad.
After making a preliminary test of the engines and boiler, with the aerodrome mounted on benches inside the house-boat, to insure that everything connected with the power plant was in proper working order, the aerodrome was mounted on the launching apparatus on top of the house, the various parts were assembled and everything made ready for a flight. As it was calculated that this aerodrome would require a soaring speed of something like twenty-five feet a second, the springs which furnished the motive power for the initial acceleration of the car were adjusted to the proper tension to cause it to reach a speed of approximately twenty-three feet a second at the moment of launching. Everything being in readiness the burners were lighted but worked somewhat sluggishly at first, so that two minutes were consumed in raising a steam pressure of 110 pounds. Although this pressure should have been reached within one minute after lighting the burners, and the extra minute which had been consumed had made a drain on the supply of fuel and water which should have[p136]been left for consumption during flight, yet it was thought best to launch the aerodrome, so at 12.37 p. m. the car was released and the aerodrome launched. The launching apparatus worked perfectly; the aerodrome started off smoothly, and immediately after being released from the car it dropped slightly and began to turn to the right. It had been impossible to move the house-boat out into the stream so as to point the launching apparatus directly into the wind, as one end had settled slightly on the muddy beach in consequence of the existing low tide. For this reason it was necessary to launch the aerodrome due south, while the wind, which was very light, was from the north-northeast, and, therefore, blowing on its port quarter. The effect of the aerodrome turning to the right immediately after being launched was that it caused the wind to strike it to an increasing extent on the port side until, finally, it was going directly with the wind. It did not, however, continue in this direction, but kept turning to the right in a circle until it headed directly into the wind, which, now striking the under instead of the upper surface of the wings, immediately caused the aerodrome to rise. It continued circling, making three complete circles of approximately 200 feet diameter, dropping slightly when moving with the wind, but rising when moving against it, until, at the completion of the third circle, it had altered its path to such an extent that the left front wing touched a tree and caused the front of the machine to dip a little. It, however, kept up its flight, but the contact with the tree had so lowered its bow, and apparently also caused the wings to be twisted to such an extent, that it seemed unable to rise again, and after making another quarter circle it descended. Although the propellers were still turning when it struck the water, they had very greatly decreased their speed, making it apparent that the power had been very greatly reduced through the exhaustion of the fuel and water supply. The aerodrome did not sink, but slowly drifted with the current of the creek and was recovered in about five minutes and brought to the house-boat, where the wings were dismounted and dried, and the metal parts were carefully wiped off to prevent them from rusting. The path of this flight is plotted on a portion of a coast-survey chart and is shown in Plate33.
PL. 33. PATHS OF FLIGHT OF AERODROME NO. 6, JUNE 7, 1899â—Š
PL. 33. PATHS OF FLIGHT OF AERODROME NO. 6, JUNE 7, 1899â—Š
This erratic circling at first seemed unaccountable, but on closer examination, after the aerodrome had been brought into the house-boat, it was found that the pin which connects the synchronizing gear to the port propeller shaft had been sheared off. This had evidently happened while the aerodrome was still on the launching apparatus. The effect of this was to throw the total work of the water-circulating pump on the starboard engine, thus giving the port engine less work to do, and consequently making the port propeller run much faster than the starboard one, and thereby causing the peculiar and erratic circling of the aerodrome. It is evident that the undulatory motion of the[p137]aerodrome was due to the fact that, when it was moving against the wind, the speed relative to the air was greater than when it circled so as to go with the wind, and that this greater relative velocity increased the lifting power of the aerodrome.
The total time of the flight was 57 seconds, and the distance covered was between 2000 and 2500 feet, thus giving a speed of a little less than 30 miles an hour. Comparing this flight with that of November 28, 1896, made by the same machine, it will be noted that in the earlier flight the velocity was practically the same, but that the time of flight and the distance traversed then were nearly twice as great as in the present case.
A complete record of the details, not only of weight, but also of the position of the wings, the center of gravity, etc., which show the exact condition of the aerodrome when it made this flight, will be found in the appendix (Data Sheet, No. 3).
In the flight of June 7 there was a slight trembling of the aerodrome while it was in the air, and although this was probably due to the fact that the synchronizing gear was out of operation on account of the shearing off of one of the pins which held it, allowing the port engine to run faster than the starboard one, it was thought possible that some of the trembling might be due to the “wind-vane†rudder, which had been added to represent the equivalent of a steering device by which the operator would control the direction of the large machine. It was decided, therefore, to omit the “wind-vane†rudder in the present test, but to test the aerodrome with the same equipment of single-tier wings and Pénaud tail that had been used in the previous flight, the reel and float being moved to bring theCGthe same as on June 7.
Everything being in readiness, with the launching track pointed south, and the wind blowing only about512miles an hour from the southwest, the burners were lighted and 63 seconds were consumed before the steam pressure rose to 100 pounds. Although the valve which controlled the burner was open to its full extent the pressure showed no tendency to rise above 100 pounds, which was not considered quite high enough to furnish sufficient power for a successful flight, but as it was desired to determine at once at how low a steam pressure the aerodrome would fly successfully, it was decided to launch it even at this pressure. The launching apparatus was accordingly released and the aerodrome started off, gliding down about three feet immediately after being released, and then rising again, turning slightly to the right and then heading directly for the Virginia shore, where it seemed that it would smash itself in the heavy growth of timber, but when it was about 250 feet from the shore it turned towards the right and started back towards the island. The wind, however, which was blowing from its rear, evidently got down the smoke-stack and put out the fire,[p138]for the aerodrome commenced to descend as soon as it turned its back to the wind, and came down in the channel of the creek. The path of this flight is shown by the solid line in Plate34.
The total distance covered, as measured by plotting the course of its flight on the coast-survey chart, was about 1800 feet, and the length of time of flight was 40 seconds. The aerodrome was immediately recovered and brought into the house-boat, where it was found that there were still about 1000 grammes of water and 100 grammes of fuel unused in it, showing conclusively that the fire had been put out by the wind.
Upon inspection it was found that the aerodrome was uninjured, and although the burner had not worked at all satisfactorily, yet as the weather was exceedingly favorable it was decided to make another trial with it immediately, using the superposed wings.39
Everything being in readiness the burners were lighted, and 70 seconds were consumed before the pressure rose to 90 pounds, beyond which it was impossible to make it rise. Although it was felt certain that 90 pounds was not sufficient pressure to furnish the power necessary, yet as a storm was approaching in the distance, it was decided to launch the aerodrome, as it could at least be determined whether it was properly balanced for the superposed wings. When a total of 75 seconds had been consumed the car was released and the aerodrome was launched. The wooden arrangement for pressing down on the top of the wings to keep the aerodrome from being injured by the wind while it was on the car had been raised to the proper height for the superposed wings, but it had not been noticed that the sticks which support this arrangement had been elevated so much that they would come in contact with the beam extending across the boat, and from which the launching track was supported. Just as these sticks reached the cross-beam, however, it was noticed that they projected about three inches above the lower side of it; but the next moment they struck it, and although the force with which the car was running broke all four of them, the blow was sufficient to slow down the car, and thereby cause the aerodrome to be launched at a very greatly reduced speed; not over one-fifth of what it should have been. The shock of breaking these sticks evidently jarred the burners so that the fire was extinguished, for the aerodrome shot forward for about 25 feet and settled with everything intact, and with its midrod perfectly horizontal. The aerodrome itself sustained absolutely no injury, coming down as easily as though it had been lowered by a rope, and would have been given another trial immediately but for the fact that it was very late in the afternoon and darkness was rapidly approaching. The data on setting of wings, tail, etc., are shown on Data Sheet No. 4 (Appendix).[p139]
After several days’ delay, due to numerous small but exceedingly annoying troubles,—such as the leaking of boilers because of defects in the copper tubing, and the bursting of the air tank, due to its being pumped up to an excessive pressure, which a defective pressure gauge had failed to indicate,-—Aerodrome No. 6 was made ready for another trial, and it was decided to test it again with the superposed wings which had been used in the second experiment of June 13. The aerodrome was mounted on the “overhead†launching apparatus, which it will be remembered had been used in all the previous tests, and after 90 seconds had been consumed in raising a steam pressure of 110 pounds, it was launched directly into the wind, which was due south. After leaving the launching car, the aerodrome flew straight ahead for about 75 feet, when it suddenly turned its bow up into the air at an angle of about 15 degrees, and it seemed that the machine would be blown back onto the house-boat. However, when the rear end of the tail was within about 10 feet of the boat, and only about 10 feet above the water, it suddenly regained its equilibrium and went straight ahead again in the face of the wind with the guy-posts only about 4 feet above the surface of the water, flying almost exactly horizontally for a distance of about 100 feet, when the bow again suddenly became elevated. As the aerodrome was so close to the water, the wind forced it down until the burners were extinguished by coming in contact with the water. This brought the aerodrome to a standstill absolutely uninjured, the propellers being several inches above the water when they quit turning. The aerodrome was brought into the house-boat and thoroughly dried out, and another trial would have been made with it immediately but the wind which had been steadily increasing was now blowing something more than 12 miles an hour, and it was considered best not to attempt experiments in so strong and gusty a wind, for fear of the wings being broken by the wind suddenly veering and striking them on the side or rear while the aerodrome was still on the launching apparatus. The peculiar action of the aerodrome in the air appeared to be due to the fact that the propellers interfered more with the lifting power of the rear superposed wings, as they were then constructed, than they did with the “single-tier†ones. The data on the setting of the wings, tail, etc., are shown on Data Sheet No. 5 (Appendix).
It was also found after the experiment that one of the workmen, in assembling the machine on the launching car, had secretly increased the stiffness of the spring which controls the elasticity of the Pénaud tail. The effect of this increase in the stiffness of the Pénaud tail might at first thought appear to be similar to that of moving the center of pressure forward. Upon a closer analysis, however, it will be seen that the effect is very much greater, as excessive stiffness of the Pénaud tail not only causes the aerodrome to elevate its bow,[p140]but requires the overcoming of a strong downward force at the rear, even more serious than would be caused by placing an extra load at the rear of the machine without regard to its effect on the balancing. In experiments of this kind, however, the workmen get certain ideas of their own as to how the work should be conducted, and it is almost impossible in assembling the aerodrome to prevent them from making adjustments which are quite different from those which they have been directed to make, and which have been definitely planned with a view to determining the effect of slight changes which it is desired shall not be masked by changes of any kind in other details.
The wind, which had been blowing half a gale all day, gradually quieted down towards sunset and at five o’clock was very light, blowing only two miles an hour from the east-southeast. As one of the rear superposed wings had been injured on the previous day in carrying the aerodrome into the house-boat after its short and erratic flight, it was decided to use the “single-tier†wings in this experiment, and also to continue using the “overhead†launching apparatus for a few more flights. Everything being in readiness, the burners were lighted and 70 seconds were consumed in raising a steam pressure of 120 pounds, at which pressure the aerodrome was launched. It started straight ahead, dropping not more than a foot, and flying on an absolutely even keel for about 800 feet, when it suddenly turned to the left and made a short half circle of about 100 feet diameter, heading for a point about 150 feet east of the house-boat. When it was about 200 feet from the shore, a sudden gust of wind caught under the Pénaud tail, raising the rear portion of the aerodrome and causing the bow to point down at an angle of about 30 degrees. The aerodrome kept this angle and struck the shallow water only about 20 feet from the shore. The aerodrome was comparatively uninjured, and another flight would have been made immediately but for the fact that by the time the aerodrome had been properly inspected it was quite late, and entirely too dark, and there would have been danger of losing it in the adjacent marshes, which are difficult to traverse even under the best conditions of tide and light. The path of this flight is shown by the dotted line in Plate34.
While the preceding tests had been going on with Aerodrome No. 6, such time as could be spared for it was spent in getting Aerodrome No. 5 into proper condition. The copper tubing from which the boilers for both aerodromes were made was greatly inferior to that which had been used in previous years, and as this tubing could be procured only by having it specially drawn to order in France, and as it required several months after placing an order before the[p141]tubing could be delivered, it was necessary to make the best of what was already on hand. The copper tubing for the boilers which had been used in 1896, after being carefully annealed and filled with fine sand, could be wound into a perfectly smooth helix, free from all wrinkles, indentations, and so forth, on the inner side of the coil. But no amount of care, both in annealing and in winding this present lot of tubing, would produce a smooth helix, the tubing being badly wrinkled on the inner side of the coil in spite of every precaution. These wrinkles, however, were not so much the cause of serious trouble as was the fact that the tubing was not uniform in quality, each length of it having numerous rotten spots which did not always show up in the winding, but which gave way after the boiler had been completed and one or two preliminary runs in the shop had been made with it. While the effect of such small things cannot be appreciated from merely reading about them, yet they were the cause of the most exasperating annoyance and delay, as no sooner had the aerodrome been gotten into what appeared to be perfect working order than the boiler would break at one or more points, thus causing a delay which at the moment would seem to involve not more than a few hours, but before everything was again in working order would amount to several days.
PL. 34. PATHS OF FLIGHT OF AERODROME NO. 6,JUNE 13 AND 23, 1899â—Š
PL. 34. PATHS OF FLIGHT OF AERODROME NO. 6,JUNE 13 AND 23, 1899â—Š
However, after much perseverance, Aerodrome No. 5 was put in satisfactory working condition, and on June 27 was launched with its “single-tier†wings and Pénaud tail. The data on settings of wings, tail, etc., are given on Data Sheet No. 6. After lighting the burners, 70 seconds were consumed in raising a steam pressure of 120 pounds. Immediately upon leaving the launching car the aerodrome started to rise with its bow elevated to an angle of about 15 degrees. It flew straight ahead about 80 feet, when it came backward and downward and touched the water about 40 feet from the boat. The failure of the aerodrome to fly properly was evidently due to its not being in proper balance. The cause of this lack of proper balance was not immediately apparent, but was very soon detected and will be discussed later on.
After several days of incessant rain and strong winds, which prevented an experiment, the weather became brighter and the wind quieted down and the afternoon of June 30 was almost ideal for an experiment. At five o’clock Aerodrome No. 5, with “single-tier†wings and Pénaud tail, was placed on the launching apparatus, a few minutes later the burners were lighted, and just as the propellers started to turn a racking noise was heard. Upon investigation it was found that the circulating pump had broken. The break was a very small matter and could have been repaired in an hour, but it was then too late to repair the damage and get a flight before dark, so the aerodrome was reluctantly dismounted and the men put to work repairing the broken pump.[p142]
The great disadvantage of conducting the experiments at a point forty miles from the city and the shops was felt at all times. Workmen, even of the very best class, cannot be kept contentedly at work at a point so far removed from their homes, even by bringing them to the city on Saturday afternoon and carrying them back to the experimental grounds the following Monday. Moreover, it is worse than useless to try to get even as much as one-third the ordinary amount of work done if there is the slightest excuse for tightening anchor ropes, watching passing boats, or wasting time on any of the multitudinous small variations from their usual routine of life.
On July 7, Aerodrome No. 5, equipped with “single-tier†wings and Pénaud tail, was made ready for a flight in the afternoon. The settings of the wings, tail, etc., are given on Data Sheet 6. Using the “overhead†launching apparatus, the aerodrome was launched with a steam pressure of 115 pounds. Immediately upon being launched its bow rose to an angle of about fifteen degrees or more, and the aerodrome came backward and downward and touched the water about three or four feet from the house-boat.
It may be well to recall from what has been said in Part I, Chapter IX◊, that Aerodrome No. 5 is the one with the very low thrust line, and in 1896 had its “separator†several centimetres in front of its center of gravity. When this aerodrome was overhauled just previous to these experiments, the separator was moved back to the same relative position as that in Aerodrome No. 6, so that the gradual depletion of the water supply during flight would not cause it to become light in front of the center of gravity.
In the launching of Aerodrome No. 5, above described, it showed no tendency to drop immediately upon leaving the launching ways, but on the contrary its bow in every case rose almost immediately until it was at an angle of about fifteen degrees or more. From the photograph (Plate35) it will be noticed that the wings of the aerodrome are held down by the longitudinal strips,A, fastened to cross-beams attached to the launching car. If, now, the launching speed is too great and the aerodrome tries to rise immediately upon being released, the front end, which passes from under the launching car before the rear does, and is thus free to rise, will immediately rise, while the rear cannot rise until it has passed entirely in front of the car, which being a distance of several feet requires an appreciable fraction of a second, during which time the bow of the machine has been able to rise to quite a steep angle. This has the effect of slowing down the aerodrome so that it does not get quite the proper chance to start on its flight with a minimum head resistance.
In view of the above facts, it was decided to decrease the speed of the launching car slightly when using Aerodrome No. 5, so that this matter could be thoroughly tested out.
PL. 35. AERODROME NO. 5 ON LAUNCHING-WAYSâ—Š
PL. 35. AERODROME NO. 5 ON LAUNCHING-WAYSâ—Š
[p143]
The very early morning preceding actual sunrise on July 11 was undoubtedly as calm as it is possible to find; there was absolutely no breeze stirring and the water in the river was as smooth as glass as far as one could see. The anemometer cups were stationary, the wind vane stood absolutely parallel to the launching apparatus and everything promised a most successful experiment. After mounting the aerodrome on the “overhead†launching apparatus the burner was lighted, and while the steam pressure was still rising and the propellers were revolving faster and faster all the time, there was a snap and they ceased to turn. The fire, which was burning fiercely, ran the pressure immediately to 150 pounds. An attempt was at once made to start the propellers again by giving them an initial turn by hand, it being thought possible that a sudden gush of water had taken place and, accumulating in one end of the engine cylinder, had blocked the engine. However, as the engine refused to keep the propellers going after they were started, and as the pressure was still rising very rapidly, the burner was shut off and an investigation made. Upon removing the hull covering, it was found that the connecting rod bearing had broken off short near the crank pin of the engine, and that it would be necessary to take the part to Washington in order to repair it, as there were no machine tools on the house-boat.
After several days of exceedingly bad weather, the conditions grew more favorable. Late in the afternoon of July 14, Aerodrome No. 5 was again placed on the “overhead†launching apparatus and prepared for a trial. After lighting the burners, 95 seconds were required to raise a steam pressure of 120 pounds. Upon leaving the launching apparatus the aerodrome went directly ahead for a few feet, but immediately commenced to rise, elevating its bow to an angle of 20 degrees by the time it had travelled 40 feet. With its bow in this position, it was blown back towards the house-boat and a little to the right of it, and, when within about 5 feet of the water, suddenly righted itself and started ahead again, rising all the time and reaching a height of about 20 feet by the time it had travelled 100 feet. In the meantime the bow had again become elevated to an angle of about 15 degrees and the aerodrome was blown backwards and downwards again. Just before reaching the water it started to right itself, but it had descended so that the front guy-post was in the water, thus destroying its equilibrium and causing it to settle into the water. The path of this flight is shown by the peculiar S-shaped line in Plate34.
In the adjustments preliminary to the above trial the Pénaud tail was elevated to an angle of712degrees when the aerodrome was stationary in the shop. This excessive elevation, coupled with the fact that the center of gravity was also probably a little too far forward, no doubt accounts for the erratic flight. The data on setting of wings, tail, etc., are given on Data Sheet No. 7 (Appendix).[p144]
After several days of exceedingly bad weather the conditions were more favorable on July 19. Since the last experiment on July 14 the coefficient of elasticity of the Pénaud tail had been decreased, the rear wings moved back 5 centimetres, and the “float†so placed that the center of gravity of the machine was brought to the same position it had had on that day, that is, 2 centimetres back of the line of thrust. With this arrangement, assuming that theCPis over theCG, we should have an apparent efficiency of the rear wings of 63.6 per cent, since the distance betweenCPfw, andCGis 79.7 centimetres, and the distance betweenCPrwandCGis 125.3 centimetres. With the adjustment of July 14, the distance betweenCPfwandCGwas 79.7 centimetres, and the distance betweenCPrwandCGwas 118.3 centimetres, thus allowing for an apparent efficiency of 67.37 per cent for the rear wings. It will be recalled that in the unsuccessful flight of July 14 the midrod of the aerodrome was inclined at an angle of about 20 degrees during most of the time that it was in the air, thus indicating that the front wings were lifting proportionately more than they should. On July 14 the Pénaud tail had a negative elevation of 7° 30′, and it required 1240 grammes placed at its center to bring it to the horizontal. On July 19 the elevation of the tail was changed to 5° and a weaker spring for controlling the elasticity was substituted, so that it required only 200 grammes placed at the center of the tail to bring it to the horizontal. A rubber band, of about one-half the strength of the upper spring, was attached by means of a cord to the lower guy-post and the lower vertical ribs of the tail, so that the tail would be elastic both ways. This rubber band was in place and acting to help draw the tail down when the above measurement of the coefficient of elasticity was made. A rubber band connected to the lower side of the tail was also used in the flight of July 14, but it was so very weak, compared to the upper spring, that its effect was negligible.
The effect of this change in the balancing of the aerodrome, and also the more considerable effect which the coefficient of elasticity of the tail has on the balancing, will be immediately noticed from the description of the next flight. The data on setting of wings, tail, etc. are given on Data Sheet No. 8.
At 3 p. m., the wind having died down, Aerodrome No. 5, equipped with its “single-tier†wings and Pénaud tail adjusted as above, was placed on the “overhead†launching apparatus. After lighting the burners, one minute and thirty seconds were required to raise a steam pressure of 120 pounds. Immediately upon leaving the launching apparatus, the aerodrome started straight ahead, dropping about 3 feet by the time it had gone 100 feet; it then rose with its midrod at an angle of about 6 or 8 degrees, regaining its level very quickly, however, and making three of these undulations by the time it had gone[p145]300 feet. It continued straight ahead for another 300 feet and began to circle to the left, the diameter of the first circle being about 200 feet. As soon as it started to circle, it rose with its midrod at an angle of about 15 degrees, and by the time it had made its first half turn it started to descend, coming down to within 15 feet of the water. As soon, however, as it had completed this first turn, it again rose, making another half circle, then, upon the completion of this half turn of the second circle, descended, this time to within 10 feet of the water, rising again for the third half turn, but again descending to within 2 feet of the water at the completion of this third circle, and then rising and completing the first half turn of the fourth circle. By this time, however, it had sunk so near to the water that the guy-posts caught in the tall grass while it was descending just before the completion of the fourth circle, thus pulling the aerodrome down into the water with the propellers still running. The total time the aerodrome was in the air was 46 seconds. The total number of revolutions of the propellers was 488, or at the mean rate of 637 R. P. M. Upon examining the aerodrome, after it was recovered, it was found that there were 925 grammes of water left in the separator, the fire having been put out by the aerodrome coming down into the water.
When the aerodrome first commenced to circle during its flight, it was noticed that the front wing clamps had twisted on the midrod, the left wing being dipped downwards, and the right one, of course, being elevated, and the peculiar circling of the aerodrome was undoubtedly due to this fact. The cause of the wing clamp twisting on the midrod was that one of the workmen forgot to tighten one of the screws of the wing clamp when the wings were being adjusted on the aerodrome. But for this unfortunate twisting of the wings, it is probable that the flight would have been perfectly straight and the distance covered would have been considerably greater than it was, the total path traversed being about 2600 to 2800 feet, found by plotting the path on the coast-survey chart and measuring it.
As the proper balancing of both Aerodrome No. 5 and No. 6 had now been determined with reasonable accuracy, and as much more time had already been given to the experiments than had been intended, it was decided to dismount the “overhead†launching apparatus at once and substitute the “underneath†one, so that it could be immediately determined whether this newer plan for launching the aerodrome by a car supporting it from underneath would be suitable for use with the large machine. After a considerable period of exceedingly bad weather, during which time the change was made in the launching apparatus, the weather conditions became more favorable on July 27. Aerodrome No. 6, equipped with “single-tier†wings and Pénaud tail, was mounted on the[p146]“underneath†launching apparatus, and everything was got ready for a flight. On lighting the burners, they failed to work properly, and, upon investigation, it was found that the air valve controlling the air pressure on the gasoline tank, was out of order. While this was being repaired, the wind rapidly increased in velocity and became very gusty, thus endangering the aerodrome, as the wings were very liable to be broken by the wind suddenly veering more rapidly than the house-boat could turn or the turn-table could be moved, and thus striking the wings from the side and putting an enormous upward pressure on them, owing to the fact that the diedral angle between them gave to each wing an elevation of712degrees from the horizontal. The aerodrome was accordingly dismounted and everything kept in readiness for a trial, with the hope that the wind would die down, or at least become steady, but it did not do so until after dark.
Aerodrome No. 6, equipped with “single-tier†wings and Pénaud tail, was launched from the “underneath†launching apparatus. There was a dead calm, the river not showing a ripple; the wind vane pointed to the northeast, but as the tide was low and the boat was aground, the launching track was pointing due south. At 7 a. m. the burners were lighted, and 80 seconds were consumed in raising a steam pressure of 120 pounds. Everything worked perfectly; the uprights on the car, which initially support the aerodrome and upon its being released are instantaneously pulled down by rubber springs, as well as the disappearing part of the track, acted without the slightest hitch. Immediately upon leaving the launching apparatus, the aerodrome depressed its bow to an angle of between 3 and 4 degrees and made a direct line for the water. At this angle it struck just on the opposite side of the channel, about 300 feet from the house-boat, and while several minor parts, such as guy-posts, were injured no damage of importance was done. Owing to the difficulty of getting through the marsh and recovering Aerodrome No. 6, it was found impossible to make another trial with No. 5 before the wind had increased to a prohibitive velocity. The path of this flight is shown by the dotted line in Plate36. The data on setting of wings, tail, etc., are given on Data Sheet No. 9.
The last previous trial of Aerodrome No. 6 was made on June 23, and the balancing at that time was evidently correct for the settings of the tail which were then used. The Pénaud tail then had an elevation of712degrees, and the coefficient of elasticity was such that 1240 grammes were required at the center of the tail to deflect it to the horizontal. In the trial above recorded, on July 28, the adjustments of the wings were practically what they were on June 23, theCGbeing moved forward 1 centimetre, but the Pénaud tail had an elevation of something less than 5 degrees, and the coefficient of elasticity was such that[p147]200 grammes placed at the center were required to deflect the tail to a horizontal. It was not intended that the angle of the tail should have been less than 5 degrees, but it was found that one of the workmen had improperly attached the fastening wire, and had considerably decreased the angle. This last adjustment of the Pénaud tail should have been the same as that used on Aerodrome No. 5 in its flight of July 19. TheCGhad purposely been moved forward slightly, but the effect of moving theCGforward and at the same time decreasing the stiffness and angle of the tail was shown by this flight.
The above trial not only very clearly emphasizes the importance of carefully determining what the elasticity of the Pénaud tail should be, but also emphasizes the fact that even the best workmen, who have had several years of experience, cannot be relied on in anything which requires that everything be doneexactly rightand notnearly right.
The aerodrome equipped with “single-tier†wings and Pénaud tail was launched from the “underneath†launching apparatus at 9 a. m., 1 minute and 30 seconds having been required to raise 120 pounds steam pressure. The wind was from the southeast, with a velocity of 3 miles an hour, and the launching track was pointed directly into it.
The launching apparatus, with the disappearing track, worked perfectly, and the aerodrome started straight ahead, dropping slightly at first, but immediately regaining its level and going ahead, gradually raising its bow to an angle of about 8 or 10 degrees, and slightly slacking up its speed by the time it had gone about 300 feet. It then made a circle to the left of a radius of about 75 feet and started back. As soon as it had made this turn it regained its level and directly regained its speed. But as soon as it had speeded up again it elevated its bow, which slackened its speed as before. It then again righted itself, still going in the same direction and crossing the sand-bar on the point of the island at a height of about 40 feet. As soon as it had crossed the sand-bar, it again made a circle to the left with a radius of about 75 feet, heading directly for the house-boat, but when it had got back above the sand-bar it again circled to the left, passing directly between two tall trees, and barely missing them, and still circling to the left, when it again reached the opposite side of the sand-bar. It, however, kept on circling to the left and once more started back towards the house-boat, this time passing to the left of the trees and again barely missing them, and completing this, its second, circle over the sand-bar. It then started due north, heading directly for Quantico, but by this time something had evidently happened to the burners as the fire went out, and the propellers gradually slowed up. However, it kept on towards Quantico, gradually descending on an even keel, and came down in the water at a point about 500 feet[p148]from the sand-bar and about 1000 feet from the house-boat. The propellers had almost ceased turning when the aerodrome came down into the water, and it settled almost as quietly as though it had been picked up and placed there, so that no damage was done to it.
The total time that the aerodrome was in the air was 63 seconds, and the total length of flight was about 2500 feet. The path of this flight is shown by the dotted line with the double circle in Plate36. The data on settings of wings, tail, etc., are given on Data Sheet No. 10.
As soon as the workmen had had their breakfast, Aerodrome No. 5 was again placed on the launching apparatus, equipped this time with the superposed wings and Pénaud tail. Upon lighting the burners, it was found that they did not work properly, a small piece of soot having clogged up the tip of the vaporizing coil. While this trouble with the burners was being remedied, the wind increased to such an extent that it was found necessary to remove the aerodrome from the launching apparatus to prevent its being injured by side gusts. As it was Saturday and the wind showed no signs of quieting down, the experiments were discontinued until the next week.
After placing the aerodrome on the launching apparatus and getting everything in readiness for a flight, upon lighting the burners a sudden sheet of flame shot out of the smoke-stack and so seriously charred three panels of each of the rear wings that they had to be removed for repairs. The silk covering of the wings had been coated with a special fire-proofing preparation, but the intensely hot flame, of course, charred all the silk that it came in contact with.
By the time that the wings had been repaired, and the defect in the burner which caused the accident had been remedied, a severe storm had arisen, making it necessary to remove everything to the interior of the boat. While waiting for the weather to become more suitable, a test of the engine of Aerodrome No. 5 was made inside of the house-boat. In this test a steam pressure of 140 pounds was obtained, giving 650 R. P. M. of the round-end, 100-centimetre propellers, which previous tests had shown to mean a thrust of 7480 grammes. As the flying weight of the aerodrome was now 14,104 grammes, the thrust obtained would correspond to a lift of 53 per cent of the flying weight, which was maintained in this test for 90 seconds.
As theCGof Aerodrome No. 5 seemed to be a little too far forward in the flight of July 28, it was decided to change it slightly, and it was moved back 4 millimetres.