The main connecting rod was 78-inch diameter and solid, while the other four were of the same diameter but with a 58-inch hole in them. The gudgeon pins in the pistons were hollow steel tubes 78-inch diameter and case-hardened, and were oiled entirely by the oil thrown off by centrifugal force from the crank-pin bearing, the oil running along the connecting rods and through suitable holes at the heads into oil grooves in the bronze bushings in these heads.
Since on an engine for an aerodrome the best plan for releasing the exhaust gases from the engine is to get rid of them as soon as possible, so long as they are released behind the aviator and do not interfere with his view in the direction of motion, it was decided to have the gases exhaust immediately from the combustion chambers; but in order to prevent their playing on and heating the main bearing of the crank shaft in the port drum the combustion chambers were each provided with a chamber below the exhaust-valve seat, with a side outlet therefrom. The manifold pipe through which the gaseous mixture was supplied to the inlet valves of the engine consisted of a tube bent to a circle and having five branch tubes, each leading to one of the automatic inlet valves, which fitted removable cast-iron seats fastened by a nut in the upper part of each combustion chamber. The very small amount of clearance between the engine and the frame necessitated that this pipe be cut in three places and joined by flanges in order to properly assemble it on the engine when the latter was mounted in the frame. The carburetor, which was placed near the rear of the aviator’s car, was connected through suitable pipes to this circular inlet pipe, at a point horizontally in line with the center of the shaft. The auxiliary air valve consisted of a sleeve rotatably mounted on the vertical pipe leading from the carburetor to the manifold, holes in the sleeve being brought to coincide more or less with holes in the vertical pipe, by the operator, when more or less air was required or when he wished to vary the speed of the engine. The cooling water for the jackets of the cylinders was led to them through a circular manifold pipe on the starboard side connected by a vertical pipe with the centrifugal pump situated at the lower point of the lower pyramid of the aerodrome frame. The heated water was led from the jackets through another [p241] circular manifold pipe on the port side, through two connections to the radiating tubes at the front and rear, respectively, of the cross-frame. These radiating tubes, which were provided with thin radiating ribs soldered to them, finally led the cooled water to the tank situated in the extreme rear of the aviator’s car, a suitable pipe from the bottom of this tank being connected to the inlet side of the centrifugal pump. The centrifugal pump was driven by means of a vertical shaft connected to the crank shaft through a set of bevel gears which drove it at three times the speed of the engine. The bearings through which these gears were connected were mounted on the port bed plate, and in order to allow for a certain amount of vibration between the engine and the pump this vertical connecting shaft had a telescoping section connected through suitable splines.
The sparking apparatus comprised, first, a primary sparker similar to the simplest form of such devices which have since come into common use, where a cam driven by the engine co-acts with a pawl on the end of a spring, but in this case, as this sparker was used for all five cylinders, the cam was driven at a speed of two and one-half times that of the engine shaft, thus making and breaking the primary circuit five times in each two revolutions of the engine. Second, a spark coil, the primary terminals of which were connected to the primary sparker and to a set of dry batteries. Third, a secondary distributor consisting of a disc carrying a contact brush and driven at a speed one-half that of the engine, this brush being constantly connected through a contact ring to one of the terminals of the high-tension side of the spark coil and running over the face of a five-section commutator, each of the sections of which was connected to a spark plug, the other high-tension terminal of the spark coil being, of course, grounded on the engine frame. This sparking apparatus was first constructed by using blocks of red fibre for insulation. After the engine was completed and was being tested difficulties were met with in the sparking apparatus which at that time appeared inexplicable. After a great deal of annoyance and loss of time it was finally discovered that the red fibre was not as good an insulating medium as it was supposed to be, owing to the zinc oxide used in making it. In damp weather the sparking apparatus absolutely refused to work, and it was found that the moisture in the air caused the zinc oxide in the fibre to nullify its insulating qualities. This trouble, after being located, was cured by substituting hard rubber for the red fibre.
At the time when this engine was built, as well as earlier when the experimental engine was built, it was impossible to procure any wire which had been properly insulated to withstand the high voltages necessary for the connections between the high-tension side of the spark coil and the secondary distributor, and from the secondary distributor to the spark plugs in the cylinders. While at this time this appears a very simple matter, yet the trouble experienced and [p242] the delays caused by the lack of such small accessories which are now so easily procurable were very exasperating, and it was finally necessary to insulate these wires by covering them with several thicknesses of ordinary rubber tube of different diameters telescoped over each other.
In the early tests of this new engine, which were made with it mounted on a special testing frame and delivering its power to the water-absorption dynamometers, the engine was operated without any fly wheels, and, so far as its smoothness of operation was concerned and its ability to generate its maximum power, it did not require any.
After the completion of the tests on the testing frame the engine was assembled in the aerodrome frame, which was first mounted on the floor of the launching car. The car itself was mounted on a short track in the shop, which arrangement provided a smoothly rolling carriage which could be utilized for measuring the thrust of the propellers by merely attaching a spring balance between the rear of the car and a proper holding strap on the track. In the first tests of the engine under these conditions, it was found that while the engine itself did not require any fly wheels, yet the lack of them caused trouble with the transmission and propeller shafts, which, while it had never been anticipated, was easily understood when it was encountered. This difficulty was caused by the “reverse torque,” which fluctuated from a maximum to a minimum five times during each double revolution of the engine, and which set up fluctuating torsional strains of such magnitude in the transmission and propeller shafts that the shafts themselves became exceedingly hot after a few minutes operation of the engine, and under more prolonged periods of operation these fluctuating torsional strains caused a permanent twisting and bending of the shafts. The transmission and propeller shafts were at first made of tubing one-sixteenth of an inch thick, but these were abandoned both on account of the necessity of abandoning the screw-thread method of attaching the flange couplings and gears, and also because these shafts had been designed when it was expected to transmit only twelve horse-power to each propeller, while the increase of power in the large engine necessarily required much stronger shafts. The first shafts which were actually tested in the frame were, therefore, one and one-half inches in diameter by three-thirty-seconds of an inch thick, the tubing having been one-thirty-second of an inch larger originally and turned down to this size to insure a straight shaft. When these shafts twisted under the action of the reverse torque of the engine, a very much heavier set, practically twice as thick, were constructed. When used in the tests these heavier shafts, while much stronger, still showed a large amount of heating due to the fluctuating torsional strains.
Upon calculation it was found that by providing specially light fly wheels the major portion of this reverse torque could be eliminated for a less increase [p243] in weight than would be occasioned by sufficiently increasing the thickness of the transmission and propeller shafts to safely stand it. Since it was desired to concentrate as much as possible of the weight of the fly wheels in the rims, the idea at once suggested itself of building them up like a bicycle wheel by means of tangent spokes. Two steel automobile-wheel rims were therefore procured thirty-three inches in diameter, and these were provided with tangent spokes connected to special steel hubs fitted to the crank shaft of the engine. The rims themselves not being quite heavy enough, and constructional reasons necessitating their being at different distances from the center of length of the crank pin, the extra weight which it was desired to give to these rims was provided by means of steel wire wound tightly around and fastened to the rims, the weight of each rim being made inversely proportional to its distance from the center of the crank pin. The first spokes which were used for these wheels were standard bicycle spokes three-thirty-seconds of an inch in diameter, but these were soon found to be entirely too weak to withstand the sudden strains due to the rapid starting of the engine. They were therefore replaced by standard spokes one-eighth of an inch in diameter, but these also proved too weak and were later replaced with special spokes made in the shop out of No. 10 coppered-steel wire, which by test was found to have a tensional strength of 2192 pounds. As these steel rims were only one-sixteenth of an inch thick and had not been made exactly true, but had been straightened before being used, it was found that they very quickly went out of shape under the strain due to the centrifugal force at high speeds, and also when the engine was suddenly accelerated. As long as they did stay true, however, it was found that they were sufficiently heavy to provide all of the fly-wheel effect it was necessary to have in order to eliminate all trouble from the reverse torque.
After further consideration, it was decided that the only means of constructing a fly wheel which would have a stiff rim and at the same time would not be heavier than the steel ones, which had been found adequate, was by perpetrating what would at first sight appear to be an absurdity. A new set of rims for the fly wheels was made by constructing them of an aluminum casting, the section of the rim being U-shaped. After machining these rims and assembling the fly wheels with them, it was found that they were many times stiffer than the previous steel ones of the same weight, and after this change no further trouble was experienced in keeping the fly wheels perfectly true, even under the most severe strains. In fact, on one occasion when the engine broke loose from the propellers, it ran to a speed, which, while not exactly known, yet reached the limit of the tachometer, which was 2000 R. P. M., without injury to the fly wheels.
It will be recalled that in starting up the engine on the quarter-size model, the initial “cranking” necessary with a gasoline engine was accomplished by [p244] having two of the mechanics turn the propellers. While this same plan might have been followed in the case of the large aerodrome, yet it would have involved some danger to the mechanics and would also have left the aviator without any means of restarting the engine should it for any reason stop while in the air. Believing it to be very important to provide means for enabling the aviator to restart the engine in case it stopped in the air, the writer devised the starting mechanism shown in the drawings, Plates [78] to [80]. Fastened by tongues and grooves to the port side of the engine crank shaft, just outside of the bed plate, is a worm wheel, on the hub of which is mounted the bevel gear which drives the water-circulation pump through the bevel pinion, as already described. Mounted on the web of the bed plate are two brackets, in which the shaft for the starting crank is journaled, this shaft passing forward and downward through the front of the cross-frame of the aerodrome, where it is journaled in a bracket secured to the brace tubes thereof. At the front or lower end of the shaft a crank handle is connected thereto by a ratchet mechanism. The upper end of the starting shaft, between the bearings of the two supporting brackets, is tongued and grooved, and slidably mounted thereon with co-acting grooves and tongues is a worm screw which, in the position shown in Plates [79] and [80], is in gear with the worm wheel just described. However, when the worm screw is slid along on the shaft until it is against the upper bracket it is out of gear with the worm wheel. Mounted in the interior of the tubular starting shaft is a spring-pressed pawl plug, not shown, but which projects through one of the tongues on the shaft near the upper bracket. If the worm screw is slid up against this upper bracket, this pawl catches in a radial hole in the worm screw and holds it in this position out of gear with the worm wheel. Connected to this pawl plug and passing longitudinally through the center of the shaft is a wire which terminates in a button just at the end thereof. By pulling on this button the operator may release the worm and thus permit it to slide downward so that when the starting crank is turned in a clockwise direction the worm will screw itself into gear with the worm wheel, and any further turning of the starting crank will cause the worm to force the worm wheel, and, consequently, the engine shaft, around in a clockwise direction. As soon as the engine gets an explosion the worm wheel slides the worm along against the upper bracket, where the spring pawl catches and holds it till it is again released by the operator as before.
This starting mechanism was a success from the first, and the engine was never started up in any other way. With an aerodrome having the qualities of automatic equilibrium, which the Langley machines have, it was felt very certain that by this mechanism the engine could be easily restarted while in the air, in case it was inadvertently stopped. [p245]