CHAPTER IVHOUSE-BOAT AND LAUNCHING APPARATUS

◊[p156]CHAPTER IVHOUSE-BOAT AND LAUNCHING APPARATUS

[p156]

The use of a house-boat seemed to Mr. Langley so indispensable in former years in making open-air tests of the models that he decided from the outset, though advised by the writer against doing so, to use the same plan on a much larger scale in connection with the large aerodrome. Aside from its supposed utility as a convenient and apparently safe place from which to launch the aerodrome, the house-boat was valuable as a portable workshop for making necessary repairs and as a temporary storehouse for the apparatus, thereby saving much packing and unpacking. It also provided sleeping quarters for the workmen.

It was early seen that this plan would require a boat at least 60 by 40 feet, which could be built only at a large initial cost. But as the experience with models had so firmly convinced Mr. Langley that it was necessary not only that the aerodrome be launched over the water, but also at a considerable height above it, and from a station that commanded all points of the compass, he decided to adopt this plan for the large aerodrome, and designs for such a boat were accordingly made in the latter part of 1898.

In order to insure the completion of this house-boat by the time the aerodrome was expected to be ready for trial, it was built under contract. Immediately after its delivery in May, 1899, work was begun on the superstructure which carried the launching track. This superstructure was a considerable undertaking, involving a turn-table weighing about 15 tons, supported on a double circular track, and this track in turn was supported entirely from the side walls of the house to avoid having columns in the middle of the floor. From the photographs, Plate38, Figs. 1, 2 and 3, it will be seen that the entire superstructure was supported by three trussed girders extending across the boat above the roof and carried by vertical posts built into the side walls of the house. The turn-table was 48 feet square and the launching track carried by it was 5 feet gauge by 80 feet long.

FIG.1.FIG.2.FIG.3.PL. 38. HOUSE-BOAT AND LAUNCHING APPARATUS, 1899◊

In making tests of the models, it had been the practice to carry the main body of the aerodrome up a ladder to the upper works of the boat, the wings being also carried up in the same manner. As the large aerodrome was expected to weigh at least 640 pounds, of which 350 pounds would be the steel frame with its undetachable parts, such as the engine and its appurtenances, it was seen that something more effective than a ladder would need to be provided for getting the aerodrome from the interior of the boat to the launching track[p157]above. It was therefore decided to place the upper works of the boat rather nearer the rear end than the front, thus leaving a space over the front end of the house through which a large trap-door might be cut in the roof, and it was thought that in this way the aerodrome might be passed up to the launching track by the use of suitable ropes and pulleys. The upper works were so arranged, and a sliding trap-door was provided in the roof, but more intimate knowledge of the difficulties of handling so large and heavy a frame made it certain, even before the aerodrome was ever placed upon the house-boat, that it would be impossible to transport it to the upper works by passing it through the trap-door. A different plan was then resorted to. A very large door was constructed at the rear end of the house, through which the completely assembled frame could be carried in a level position and placed upon a large raft, consisting of a lattice flooring over pontoons, moored at the rear end of the boat, as clearly seen in Plate38. In order to raise the aerodrome frame from the raft to the upper works, a large, but light, mast and boom, with suitable stays were provided. As the wings, when mounted in their proper position on the aerodrome, would be interfered with by such a mast, the mast and boom were so devised as to be capable of rapid erection and dismounting, only five minutes being necessary for either operation. In Plate38the mast and boom are seen in position in Fig. 3, while in Figs. 1 and 2 they have been dismounted.

The construction of the launching track and car was begun in November, 1899, but their completion was long delayed, as they were frequently put aside for the more immediately important parts of the work. Moreover, the arrangement of the struts and clutch of the launching car depended entirely on the form and dimensions of the frame of the aerodrome, which could not be entirely decided until a proper engine had been secured and tested in the frame to determine what modifications of it were necessary. In the spring of 1902, however, the launching car was entirely finished and a number of tests of the large engine were made in the shop with the frame mounted in position on the car.

From the description of the “overhead” launching apparatus (Part I, Chapter X◊) which had proved so successful in the tests of the models, both in 1896 and in the later experiments of 1899, it will be recalled that the essential features of it were a track and a light car with three hinged struts which extended below the body of the car, and against which suitable co-acting bearing points attached to the frame of the aerodrome were tightly drawn by means of a clutch which gripped a special fitting fastened to the aerodrome frame near the central point of its length. After the engine of the aerodrome had been started and got to running at full speed, the car was released and moved forward along its track by the combined force of the thrust of the propellers and the pull of the coiled launching springs. Just before the car reached the forward end of the track, a cam at this point caused the clutch to open and release[p158]the aerodrome, which immediately dropped slightly, as it had purposely not quite reached a speed sufficient to cause it to soar. This slight drop of the aerodrome, even if it were only a fraction of an inch, made it possible for the hinged struts, against which it had been held by the clutch, to be folded up by their special springs against the floor of the car, thus leaving the aerodrome free in the air without danger of entanglement.

The struts referred to above were three in number, two being placed near the rear and one at the center of the front of the car. The use of three points of support had the advantage of furnishing a rather rigid foundation against which the frame could be tightly drawn by means of the clutch-hook without risk of straining it. In designing the “underneath” launching apparatus, which was very thoroughly tested in the experiments with the models in the summer of 1899, the plan of having three struts with the aerodrome drawn tightly against them by means of a central clutch-hook was continued with most satisfactory results.

When the position of the struts on this launching apparatus had been changed so as to permit it to be used for the quarter-size model, it was found, in making shop tests of the engine with the aerodrome mounted on the launching car, that, owing to the greater vibration produced by the gasoline engine, the three points of suspension did not hold the model in a sufficiently rigid manner. It became necessary, therefore, to use four struts, the two rear ones being left as before, and the single one in front being replaced by two interconnected ones arranged similarly to those in the rear. After making this change no difficulty was found in holding the aerodrome rigidly against the struts, and this modification was therefore immediately introduced in the designs for the large launching car which was already under construction.

PL. 39. METHOD OF ATTACHING GUY-WIRES TO GUY-POSTS TO RELIEVE TORSIONAL STRAIN◊

Experience, both with models 5 and 6, and with the quarter-size model, had also demonstrated the necessity of providing some means whereby the aerodrome frame would be relieved of the torsional strains produced upon it by a side wind striking the under surface of the wings when the aerodrome was mounted on the car preparatory to a test. The means for preventing these torsional strains in the case of the models, when “overhead” type of launching car was used, has been described in Chapter X of Part I◊. However, with the “underneath” type of launching car, a different means was necessary. A plan, in which outriggers projected from the body of the car and wires running from these outriggers up to the main ribs of the wings, with means for releasing the wires just before the car reached the end of the track, was used with the “underneath” car in the tests of models 5 and 6 in the summer of 1899, but the outriggers were frequently deranged by the sudden stopping of the car at the end of the run and they were replaced by a simpler arrangement. In this plan the torsional strains were relieved by providing, at the forward and rear ends[p159]of the car, smaller hinged uprights furnished in their upper part with a small slot into which a pin projected from the bottom of the forward and rear guy-posts, respectively. The guy-wires from wings being connected to the lower ends of the guy-posts the torsional strain produced by a side wind was immediately transmitted from the wings through the guy-wires to the guy-post, whence it was transmitted to the car itself, and thus prevented from acting on the metal frame of the aerodrome, as shown in Plate39. These additional short struts for taking up the torsional strain were first added to the small launching car in 1901, and in the succeeding tests made with the quarter-size model no trouble of any kind was indicated as likely to be caused by them. As it was these extra struts which were directly responsible for the accident in the launching of the large aerodrome October 7, 1903, at the time of its first trial, and possibly also for that on December 8, 1903, at the time of the second trial, special attention is here called to them.

The length of travel which could be provided for the launching car in the case of the large aerodrome, as well as in that of the models was necessarily very limited, owing to the fact that the track had to be constructed on the top of the house of the boat. It was therefore necessary, in order that the aerodrome might attain a speed sufficient for soaring before being launched, to keep the weight of the launching car as small as possible, a given spring tension being capable of accelerating a given mass a definite amount in a given length of travel. With a heavier launching car the spring tension would have to be increased. Moreover, since the blow which would be struck when the car was suddenly stopped at the end of the track, would depend on its mass as well as its velocity, there was an additional reason for trying to keep the weight of the car as small as possible.

While it was found perfectly feasible to keep the weight of the launching car for the model low enough for practical purposes, in designing the launching car for the large aerodrome it was only by eliminating all flooring of the car and providing merely a box frame with necessary cross-braces, that its weight was kept within what appeared reasonable limits. Even then the blow which it would strike when it reached the end of the track was found by calculation to be exceedingly formidable.

Referring to the drawings of Plate40, Figs. 1, 2 and 3, it will be seen that the large launching car consisted essentially of two parallel longitudinal side members 6 inches deep by 1.5 inches thick by 19 feet long, connected by three main sets of cross-members: one set near the rear, at the point at which the rear struts for supporting the aerodrome were mounted; a second rather heavier set about the middle of its length, at the point where the strut which carried the clutch-hook was mounted; and a third near the front, at the point where the front struts were mounted. Projecting from the forward end of each of the[p160]longitudinal side members were piston rods, on which were mounted leather-cup pistons, which co-acted with buffer cylinders fixed at the extreme front of the track to absorb the blow when the car reached them at the end of its travel. The car was supported on each side by means of four hangers (Figs. 4 and 5) which carried grooved wheels having ball-bearings and running on a steel track consisting of flat plates fastened on the side of the timbers of the launching track. On the extreme lower point of these hangers were small guide pulleys, so placed as to be just below and out of contact with a guard rail on the side of the launching track, thus preventing any possibility of the launching car being raised from the track either during its forward motion or by a side wind striking underneath the wings.

Aerodrome “A.”(Details13Full Size)PL. 40. GENERAL PLAN AND DETAILS OF LAUNCHING-CAR◊lgr

FIG.1.FIG.2.FIG.3.PL. 41. AERODROME ON LAUNCHING-CAR◊

PL. 42. DETAILS OF CLUTCH POST FOR LAUNCHING-CAR◊lgr

PL. 43. FRONT END OF TRACK JUST PREPARATORY TO LAUNCHING AERODROME◊

On the large launching car the arrangement of the struts against which the bearing points of the frame were tightly drawn by the clutch was similar in all respects to that used on the model car, there being only slight differences in details. The details of the uprights on which the bearing points of the aerodrome frame rested are clearly shown in Figs. 6, 7, 8, and 9 of Plate40. From the photographs (Plate41, Figs. 1, 2, and 3) which show the large frame mounted on the launching car, the general arrangement of the struts and the clutch-hook can be readily seen; and from Plate42, Figs. 1, 2, and 3, which show in detail most of the important features of the clutch-post and its clutch, a very good idea of the size of the different parts may be had by observing that the distance from the fulcrum of each half of the hook to the pin by which it was connected through the universal joint to the vertical rods is five inches. As previously stated, this clutch-hook gripped the lower pyramid and pulled the bearing points of the frame firmly against the forward and rear struts of the launching car, and in launching the aerodrome the triggers arranged on the bottom of the car, which at the proper time pull on the vertical rods and thereby force the two halves of the clutch-hook apart, are so arranged that they strike a cross-beam at the front end of the track one inch before the triggers, which keep the struts from being pulled down by their springs, which tend to fold them up and force them down against the car. The triggers, which prevent the struts from being folded down, strike a cross-beam in the track one foot before the buffer pistons on the end of the car begin to enter the buffer cylinders at the end of the track, and, consequently, one foot before the folding prop, which supports the front end of the track, is knocked out by the car striking a special trigger which allows this folding prop to swing forward when the front end of the track folds down to insure that the aerodrome will not become entangled with the car, even though the aerodrome be not quite up to soaring speed at the moment of launching. The manner in which this front end of the track folds down can be very readily seen by comparing Plate43with Plate95of Chapter XII◊, the former showing the front end of the track in horizontal position, with[p161]the aerodrome at the extreme rear end just preparatory to launching, and the latter showing the front end of the track folded down with the hinged prop standing outward in its downward path and the aerodrome just launched. These photographs will be more particularly referred to later, but attention is here called to them so that the description immediately following may be more easily understood.

Although this method of launching the aerodrome seemed to Mr. Langley, both theoretically and from the experience with the models, to be a satisfactory and feasible plan, there were two very important respects in which it seemed from the very first open to objection. In the first place, it was necessary that the aerodrome should be launched as nearly at its soaring speed as possible, because either an excess or deficiency of speed interfered to some extent with the equilibrium of the machine. So many factors were involved in the determination of what this final velocity should be that it seemed almost impossible to be sure of the results until at least one test of the aerodrome had been made. In the second place it was not known whether the rapid acceleration of the car would seriously interfere with the equilibrium of the aviator.

In reference to the first question it was, of course, known that a freely falling body acquires a speed of 32 feet per second at the end of the first second after having fallen a distance of 16 feet. It was proposed to launch the aerodrome at approximately 35 feet per second; and, since the distance over which the car would pass in acquiring this speed was approximately 60 feet, the rate of acceleration would, of course, be less than that for a freely falling body. The conditions in the two cases, however, are quite different. In the case of the freely falling body there is the constant force of gravity which causes the acceleration. In the case of the aerodrome the car is initially standing still but ready to be acted upon by the combined force of the thrust of the propellers and the tension of the springs. The propeller thrust is approximately 450 pounds at the moment of releasing the car, while the spring tension adds approximately 400 pounds more pull, giving a total pull of 850 pounds acting on the car at the start. The weight of the aerodrome including the aeronaut being approximately 850 pounds, and the weight of the car being approximately 450 pounds, the total weight to be accelerated is 1300 pounds. The resistance of the car and the aerodrome is zero at the moment the car is released, and increases approximately as the square of the velocity until it reaches approximately 300 pounds at the soaring speed of the aerodrome; while on the other hand the spring tension decreases uniformly from 400 pounds at the start to approximately 76 pounds at the end of the track, and the thrust due to the propellers decreases from 450 pounds at the start to approximately 250 pounds at the moment of launching. Consequently, it is in a general way clear that the rate of acceleration of the aerodrome and car decrease, probably in a geometric ratio, the rate of acceleration[p162]at the moment of launching the aerodrome being much less than that of a freely falling body. Since so many factors enter into the problem no confidence was felt in calculations as to what the rate of acceleration would be. It was, therefore, decided to determine it experimentally at the same time that tests were made on the car to determine what spring tension would be necessary to enable the aerodrome and car to acquire soaring speed by the time they reached the end of the track.

It was obviously impossible to make this initial test with the aerodrome mounted on the launching car, as the aerodrome would certainly wreck both itself and the car were it allowed to remain fastened when the car was stopped at the end of the track. It was, therefore, decided to make the tests by mounting on the car boards which would have a head resistance equal to that of the aerodrome. In order to minimize as much as possible the blow due to the car striking the buffers at the end of the track, the car had been made as light as possible. On this account it was felt to be unwise to risk adding to it a weight of 850 pounds to represent the aerodrome, and supplying an additional spring tension to represent the thrust of the propellers, as the total effect of the added weight and the added pull would certainly completely demolish the car. By calculation it was found that the omission of the 850 pounds weight of the aerodrome and the spring tension to represent the thrust of the propellers would practically counterbalance each other; and that if sufficient spring tension were provided to cause the car, with the light boards representing the head resistance of the aerodrome, to reach the soaring speed by the time it arrived at the end of the track, it would be safe to assume that this spring tension would be sufficient for use in launching the aerodrome.

The method of measuring the final speed of the launching car for the models consisted in fastening a strip of smoked paper to the launching car in such a position that it was drawn past a stylus fastened to the end of a vibrating tuning fork placed at the end of the track. This had proved perfectly successful, but it gave a record merely of the final speed attained by the car at the moment of launching the aerodrome. In the case of the large aerodrome it was desirable to have a record of the speed of the car during the first few feet, and also at several other points in its travel down the launching track, and the more numerous these points the better. Short strips of copper were accordingly placed every twelve inches along the length of the track, and these were connected by a wire to one terminal of a small electric battery. Mounted on the car, in such a way that it would be drawn across these contact strips, was a copper brush arranged to make continuous contact with another wire stretched along the track, this second wire being connected to the other terminal of the electric battery and having in its circuit the magnet which actuated a pen on a chronograph. Since the rate of revolution of the chronograph barrel was known, the[p163]distance between the marks which the magnet would cause the pen to make when its circuit was closed by the brush on the car passing across the contact strips on the track would give correct measures of the time consumed by the car in passing over each twelve inches of its travel. Upon test, however, it was found impossible to get the chronograph magnets to work rapidly enough to respond to the very rapid opening and closing of the circuit after the car had passed over the first one-quarter of its length of travel. As a large part of the slowness of action seemed to be due to the weight of the fountain pens, they were replaced by small glass tubes drawn out to a fine point and containing a small amount of ink. These seemed, however, to be still too heavy to respond to the rapid closing of the circuit unless the contacts were made unduly long. The contacts were finally made three inches long and placed only every three feet along the track, but just as these contacts were completed and placed in position the clock-work of the chronograph itself became deranged. Before it could be repaired, the tests were discontinued, as everything was in readiness for the boat to proceed down the river where the actual tests in free flight were to be made. Tests of the final speed of the car were, however, made by the tuning-fork method, and the springs were adjusted until their tension was sufficient to cause the car to attain a speed of thirty-five feet a second at a point three inches in front of the point at which the aerodrome would be released from the car.

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