◊[p218]CHAPTER VIIITHE EXPERIMENTAL ENGINE
[p218]
It will be recalled that the contract for the engine for the large aerodrome, which had been entered into on December 12, 1898, called for its completion on February 28, 1899. Between the time when the engine should have been completed and May, 1900, the engine builder had been engaged in a continuous series of changes on it, all connected with what might be briefly called its proper functioning. The actual mechanical construction of the more important parts had been admirably executed, and this main portion of the constructional work had been completed within the time called for by the contract. The trouble was that the engine, which was of the rotary cylinder type, would not furnish anything like the power which had been expected of it, and which the size and number of its cylinders indicated that it should furnish. No one who has not had practical experience in the development of gasoline engines, can understand or appreciate how fourteen months could be spent in changes in the minor details of the engine with the expectation that each contemplated change would bring success; and to anyone who has had experience in the matter, an attempt to explain the delays would merely seem like a history of his own experiences. It is, therefore, sufficient to say that the delay on the engine had now reached a point where it was necessary to bring it to a successful completion immediately or to abandon it definitely, and either find a competent builder who had already built engines which, while not necessarily light, were successful, and who would undertake to construct a light one on the same principles, or, as a last resort, to turn to steam; and even the contemplation of this was appalling.
On May 6, 1900, the writer went to New York to see what could be done towards assisting the engine builder to complete the large engine and also, if possible, the small one which had been ordered for the quarter-size model later described. He immediately made brake tests of the engine to determine accurately just what effects were being produced by the different changes the engine builder was making. Upon the first test the engine was found to develop only 2.83 horse-power, and this could not be maintained for more than a few minutes, when without any apparent cause and without any signs of overheating the engine would altogether cease to develop any power. After remaining in New York for several weeks, during which time many changes were made in the engine, he finally got it to the point where it would develop four horse-power continuously; but, as it seemed impossible to get any better results[p219]without an indefinite amount of experiment, it was decided that all hope of making this engine an immediate success would have to be abandoned.
Interest in the development of the automobile was increasing at a rapid rate all over the world, and while the builders in this country had not reached the stage of development which had been attained in Europe, especially in France, yet some American builders had succeeded in constructing cars propelled by gasoline engines which could be depended upon to run at least a short distance, and it was, therefore, hoped that some one of the more competent of these builders might be found who would undertake to construct a suitable engine. After making a most extensive but fruitless search for such a builder in this country, it was decided that it would be best to see what could be done in Europe, and as other administrative matters made it necessary for Mr. Langley to go to Europe about the middle of June, the writer accompanied him to see what could be done towards having a suitable engine built there. Some six weeks were spent in visiting all the important builders of gasoline engines in Europe, and the results were very discouraging. Everywhere the builders said that they did not care to undertake the work, and that they did not consider it possible to construct an engine of 12 horse-power weighing less than 100 to 150 kilograms (220 to 330 lbs.), or that, if they had thought it possible, they would already have built it, as they had had numerous inquiries for such engines, and also wanted them for their own use. The last hope of securing a suitable gasoline engine seemed to have vanished.
But, discouraging as was the refusal of the engine builders of Europe to undertake to build the engine, and still more so their opinion that such an engine was an impossibility, inspection of the engines exhibited at the Paris Exposition had so strengthened the writer’s conviction of the possibility of the undertaking that, before parting with Mr. Langley on August 3 to return to America, he personally assumed the responsibility of building an engine which would meet the requirements.
Upon returning from Europe on August 13, and finding that the engine builder in New York had made no progress whatever towards improving the engine during his absence, the writer condemned both the large engine and the small one. The engine builder had practically bankrupted himself in his attempts to construct these two engines, having spent something like $8000 or $10,000 in actual wages over and above the contract prices for the engines, to say nothing of remuneration for his own time or such expenses as shop rent and power. As all of the money for the large machine and practically all for the small one had been advanced to him at various times to assist him over financial stringencies—such advances, however, having been secured by suitable bonds—it was decided to take the various parts of the two engines in[p220]payment for the money which had been advanced, as it was hoped that some of the parts of the engines might prove of use in experimental work.
Immediately after the writer’s return to Washington he began work on the development of an engine. Taking some of the parts of the engine which had been condemned and constructing others, he was able by September 18 to have an experimental engine at work which, while not water-jacketed, but provisionally cooled by wrapping wet cloths around the cylinders, developed1812horse-power on the Prony brake at 715 R. P. M., the engine, including these wet cloths, weighing 108 pounds. Of course these wet cloths sufficed to keep the engine cool for only a short time—three to four minutes being the maximum. This was only a temporary expedient for enabling the engine to run for a sufficient time to make brake tests and determine the power it developed, but the results obtained were so very encouraging that it was decided to make water jackets for the cylinders of this engine and see what power it would then develop for more extended periods.
This experimental engine, which was merely a “patched-up” affair, was first equipped with a sparking arrangement built on the wiping-contact principle. With this sparking arrangement several important difficulties presented themselves, among which may be particularly mentioned the great difficulty of so adjusting the sparking arrangements that the explosion in each cylinder occurred at exactly the same point in its cycle that the explosions occurred in all the other cylinders, it being necessary to secure this result to a reasonably accurate degree in order to cause the engine to run smoothly enough to be used in the aerodrome. Where an engine has a large and heavy fly-wheel running at a high rate of speed, the nicety of adjustment of the sparking arrangement is not so essential, for the fly-wheel acts as a reservoir of energy and tends to smooth out the rough and jerky impulses which would be otherwise introduced by slight variations in the force of the explosions in the cylinders. In constructing an engine for an aerodrome, however, the permissible weight of the engine is so very small that the use of a fly-wheel having sufficient weight to act as an energy reservoir is practically prohibited. Another serious difficulty which was encountered with the wiping-contact type of sparking arrangement was that of keeping the stuffing boxes around the rotating contact rods tight enough to prevent leakage, without at the same time binding and causing excessive friction. Although it seemed probable that the difficulties which have been mentioned, and other minor ones which were apparent, could be remedied by further experiment, yet the high tension or “jump-spark” type of sparking apparatus seemed to offer much greater advantages. Since it had fewer moving parts, and furthermore since the wiping-contact sparking arrangement would have to be considerably modified in order to permit the construction of water jackets around the cylinders, it was decided to construct a[p221]new sparking arrangement for the engine on the jump-spark principle. After introducing this change in the engine it was found to run very much more smoothly and to require a minimum amount of care in adjusting it.
At the time that this engine was being developed it was practically impossible to obtain any outside information regarding the proper way of constructing it. The little that was then known had been learned through laborious experience and at great cost by the experimenters who were attempting to build automobiles, and was zealously guarded in the hope of preventing their rivals from utilizing the results of their labors. It was the known custom, however, of all engine builders at this time to use a separate spark coil and a separate contact maker for each cylinder of an engine, no matter how many cylinders there were. This multiplication of the spark coils, which at that time were very heavy, not only added greatly to the weight but also had the same defect that the wipe-spark type of sparking arrangement had of being exceedingly difficult to so adjust that all of the contact makers would perform their functions at exactly the same point in the cycle for each cylinder. To obviate these difficulties, both of adjustment and of excessive weight, the writer devised what is supposed to have been at that time a new and valuable multiple-sparking arrangement whereby only one battery, one coil and one contact maker were utilized for causing the spark in all five cylinders, a small commutating arrangement in the high-tension circuit distributing the sparks to the proper cylinders at the proper time. This form of sparking arrangement was found upon test to work so satisfactorily that it was afterwards adopted for the small engine of the quarter-size model, and also for the new and larger engine which was afterwards built and which will be described further on. It is needless to describe in detail the many and perplexing difficulties which were experienced in procuring suitable spark coils, spark plugs and other appurtenances of the sparking apparatus, all of which at this time were in a very crude state of development, there being only a few different makes on the market, and most of these being very unsatisfactory. One important minor improvement connected with the spark plugs may be described, as the beneficial effect produced by it was so very great that its use was continued in all future spark plugs for all of the engines. This improvement, however, is now incorporated in many of the plugs which are on the market, and in some cases patents, covering the particular form in which the improvement is incorporated, are exploited by the manufacturer. Considerable difficulty was at first experienced with the spark plugs from a coating of soot (resulting from the incomplete combustion of the gas and oil in the cylinder at the time of explosion) which formed on the porcelain and thereby caused a short-circuit, preventing the plug from working properly. This was overcome by extending the metal portion of the plug for some distance into the cylinder, and for something like three-quarters of an[p222]inch beyond the end of the porcelain insulator. The terminal which passed through the insulator was also extended for something like half an inch beyond the porcelain and bent to a proper extent to co-act with a piece of platinum wire inserted in the interior wall of the plug which formed the other terminal. After making this improvement in the plugs practically no difficulty was experienced from short-circuits caused by the soot.
In making the tests of this experimental engine it was found practically impossible to absorb the power by a Prony brake in a sufficiently uniform manner on account of the fact that the engine was being run without a fly wheel. The consequent variation in the torque and speed during each revolution caused such great fluctuations in the reading of the scales which measured the pull of the Prony brake that no confidence could be felt in the accuracy of the readings and, therefore, no confidence could be placed in the determinations of the effect which different changes in the engine produced. A water-absorption dynamometer consisting of a number of flat, circular discs fastened to a shaft and rotating between other parallel flat discs arranged in a circular drum which was filled to any desired extent with water was immediately planned, and the construction of two of them was begun so that power could be taken from both ends of the engine shaft, which, on account of its necessary lightness, was apt to be injured by being twisted when all the power was taken from one end of the shaft. In order to continue the tests on the engine while this dynamometer was being made it was decided to employ one of the propellers as a dynamometer. Although no accurate tests had been made to determine just how much power was required to drive these propellers at various speeds, yet the fundamental law was known that under the same conditions the power required to drive any propeller would vary as the cube of the number of revolutions, and since the Prony-brake tests had given an approximation as to the amount of power which the engine developed at certain speeds, the law of the propeller, and extrapolations from the data obtained in the tests of the smaller propellers in 1898, enabled further approximations to be made as to the amount of extra power which the engine developed when certain changes enabled it to drive the propeller at increased speeds. This method had also the great advantage that, since the power required varies as the cube of the number of revolutions, it is practically impossible for the engine to “run away” with the propeller and cause serious damage through the possible excessive strains introduced by high speed. This feature is also possessed by water-absorption dynamometers of the type which were built and used in the later tests.
The construction of water jackets for this engine proved an exceedingly formidable task, it being impossible to braze the jackets directly to the walls of the cylinders without risk of ruining them. It therefore became necessary to attach them by means of stuffing boxes, which, on account of their large size[p223]and the necessity for keeping the weight a minimum, was a most difficult piece of work. The work was rendered still more difficult by the fact that the water jackets had to be made in halves which were brazed together after they had been fitted over the head of the cylinder. Even when the work was done in the most careful way this method of construction gave a great deal of trouble from the leaking of the stuffing boxes or the jackets themselves. However, after much delay, the water jackets were finally completed, and upon test the engine was found to develop 21.5 horse-power at 825 R. P. M., the engine itself weighing 120 pounds.
Further changes were made in this engine, especially in the pistons, a new set of which were constructed which weighed 15 pounds less than the original set. On account of the difficulty with the leakage of the water around the stuffing boxes of the water jackets, and also from imperfections in the brazed joints of the jackets themselves, it was found impossible to rely on the power that the engine would develop at any particular time, as the water leaking from the jackets and running down on the spark plugs of the lower cylinders caused these cylinders to work erratically, and this not only materially reduced the power but also caused jerky impulses in the absence of fly wheels.
It seemed so desirable to obtain as soon as possible a first test in actual flight of the large machine that the writer offered to put this engine in the aerodrome frame and make a test with it if the machine were launched over the water, but with the launching track mounted directly on the river bank. However, Mr. Langley felt it so necessary to make the initial test from the top of the house-boat and at an elevation of 30 feet or more that he would not consent to this, and as the engine at its best did not develop quite 24 horse-power, which had been calculated as the minimum which should be provided, it was thought unwise to attempt to make the first test from the top of the house-boat until the aerodrome had been provided with engines that could be depended on to develop continuously not less than 24 horse-power.
It then became necessary either to build a duplicate engine and use both of them in the aerodrome, the original plan as already explained having been to have two engines developing the 24 horse-power together; or, second, to construct an entirely new engine large enough to furnish a minimum of 24 horse-power and use this single engine.
As the construction and tests of this experimental engine had shown many places in which the weight might be safely reduced, the writer decided to construct an entirely new and larger single engine, and thereby avoid the extra weight and difficulties which would be introduced by having to use synchronizing gears where two engines were used, it being impossible, of course, to run the two propellers from the two engines independently without risk of serious disaster.[p224]
It will be recalled that when the aerodrome was originally planned in 1898 it was proposed to have two engines of 12 horse-power each, and the contract for the single engine of 12 horse-power provided that a duplicate was to be supplied, if desired, immediately upon the completion and delivery of the first one. The calculations, both from the whirling-table tests and from the results with the steam-driven models in actual flight, indicated that 24 horse-power would be ample for the aerodrome, which it was then expected would not exceed 640 pounds in weight, with a supporting surface of 960 square feet. But it was found that the total weight of the machine was rapidly increasing on account of slight increases in the various details, which when added together made a considerable increase in weight. Furthermore, as it had been found difficult to keep all five of the cylinders of the experimental engine working uniformly, it was thought best to build this new engine sufficiently large to provide not only the extra power necessary because of the increased weight of the aerodrome, but also to provide for further inevitable increases in weight, and over and above all this, to provide also that the engine would furnish all the power necessary, even though one of its cylinders should absolutely fail to work and act as a dead load on the others. The writer accordingly designed this new engine to give 40 horse-power when all five of the cylinders were working, and 28 horse-power even though one cylinder should act as a dead load on the others.
The various materials for the construction of this engine were ordered early in December, 1900, with the promise of delivery not later than January, 1901. Owing to various causes, however, the major portion of the materials could not be obtained until late in the spring, and, in fact, a portion of them were not obtained until the summer of 1901. During this period of delay, however, the engine for the quarter-size model was completely reconstructed and further tests were made with the experimental engine in developing accessories, such as carburetors and spark coils.
The float-feed type of carburetor which was then coming into prominence in automobile work proved at that stage of its development to be totally unsuitable, as the slight but constant tremor of the aerodrome frame, when the engine was working at high speeds under a heavy load, caused the float to act as a pump and periodically flood the carburetor. This resulted in an irregularity of action of the engine which at times injured not only the transmission shafts, gears, and frame, but the engine itself by the serious pounding which occurred. A form was next tried in which the gasoline was fed in through the valve seat of a lightly loaded valve which raised whenever there was suction in the inlet pipe, the amount of gasoline fed being regulated by a pin valve. Later there were built several shapes and sizes of tanks filled with absorbent material, which was saturated with gasoline and the surplus drawn off before starting the engine. Some of these tanks were provided with a jacket through which[p225]a portion of the exhaust gases was passed in order to compensate for the cooling of the tank caused by the evaporation of the gasoline. As a result of these tests it was found that a type consisting essentially of a tank filled with small lumps of a porous cellular wood (tupelo wood) which was initially saturated with gasoline, and into which the gasoline was fed through a distributing pipe as rapidly as it was taken up by the air, which was sucked through it by the engine, gave the best results. Instead of jacketing this tank, the cooling effect due to evaporation was compensated by drawing the somewhat heated air from around the engine cylinders up through the loosely packed lumps of wood. When tested in the shop this type was found to give such a very uniform mixture that the engine ran as smoothly and regularly as an electric motor, the vibration in no way interfering with it, and even when the sudden change from a state of rest to one of rapid motion through the air was imitated by suddenly turning on the carburetor the blast of several large electric fans from various angles, it was found to have no appreciable effect on the running of the engine, thus indicating that the trouble which was experienced with the model aerodrome in the trials of 1901 was not likely to be repeated with the large aerodrome. Somewhat more than a dozen carburetors of various forms were constructed before this last type was devised, but this proved so satisfactory that there were never thereafter any carburetor troubles. In fact, as will later appear, a carburetor of this type kept the engine on the large aerodrome running at full power not only when the aerodrome was in a vertical position in the air, but also after it had turned completely over on its back.