| DETAILEDWEIGHTOFNEWLARGEENGINE. | |
| Name of part. | Weight in grammes. |
| Crank shaft | 5,225 |
| Connecting rods (total) | 5,005 |
| Pistons— | |
| No. 1 | 1,652 |
| No. 2 | 1,647 |
| No. 3 | 1,655 |
| No. 4 | 1,660 |
| No. 5 | 1,646 |
| Cylinders— | |
| No. 1 (including exhaust and inlet valves, oil cups, etc.) | 4,768 |
| No. 2 (including exhaust and inlet valves, oil cups, etc.) | 4,685 |
| No. 3 (including exhaust and inlet valves, oil cups, etc.) | 4,638 |
| No. 4 (including exhaust and inlet valves, oil cups, etc.) | 4,637 |
| No. 5 (including exhaust and inlet valves, oil cups, etc.) | 4,796 |
| Port crank chamber drum, including cam, cam gears, punch rods, etc. | 5,225 |
| Starboard crank chamber drum | 3,440 |
| Spark plugs (5) | 450 |
| Outlet water pipe | 450 |
| Inlet water pipe | 360 |
| Inlet gas manifold | 1,700 |
| Primary and secondary sparkers and wires | 512 |
| Balance arm with braces for same—starboard | 1,040 |
| Balance arm with braces for same—port | 1,067 |
| Total | 56,323 gm.=124.17 lbs. |
| Starboard fly wheel | 3,946 |
| Port fly wheel | 3,234 |
| Total weight of engine and fly wheels | 63,503 gm.=140.00 lbs. |
| Spark coil and batteries | 6,800 |
| Carburetor | 3,751 |
| Inlet gas pipe from carburetor to manifold | 756 |
| Gasoline tank | 1,004 |
| Water tank | 717 |
| Water circulating pump and shaft | 807 |
| Radiator | 7,700 |
| Total weight of power plant | 85,038 gm.=187.47 lbs. |
[p251]
CHAPTER XI
SHOP TESTS OF THE AERODROME
In June, 1902, after the proper adjustments of the carburetor and other accessories of the engine had been accurately determined in the tests on the testing frame, the engine was assembled in its proper position in the aerodrome frame and connected to the propellers. The aerodrome frame was then mounted directly on the floor of the launching car, which was placed on a short track laid on the floor of the shop, as previously described. A large spring balance, which had been previously calibrated, was then connected between the car and an upright fastened to the track, and tests were made to determine the thrust developed when the engine drove the propellers at different speeds. Upon finding that there was comparatively little vibration when the engine was driving the propellers even at its maximum speed, it was felt safe to raise the aerodrome from the floor of the car and place it upon the uprights on which it would be supported in launching it. Quite an extended series of tests was then made, and although the uprights raised the aerodrome frame until the midrod was practically 9 feet from the floor of the car, and in the tests at maximum power the propellers developed an average thrust of 450 pounds, yet it was found that the clutch hook held the bearing points of the frame so securely on the uprights of the car that all fear that the aerodrome might break loose from the car during the launching process was removed.
Upon the completion of these tests, which had proved most satisfactory, the aerodrome frame was supported from the ceiling of the shop by means of four short coil springs which reproduced as nearly as possible the elastic or flexible suspension which the aerodrome would have when supported by its wings in the air. These springs were attached at the same points on the main frame of the aerodrome at which the wings would be attached, thus permitting a careful study of the amount of flexure and vibration which it would undergo in actual flight. The most remarkable difference in the nature of the vibration induced in the frame was found when the aerodrome was thus supported by springs. When it was supported on the rather unyielding launching car, the general tremor set up in the frame by the engine and propellers was, while small, yet harsh, the effect on a person standing in the aviator’s car being rather unpleasant in the joints of the knees when experienced for several minutes. When the frame was suspended by the springs it was found that all this harshness of tremor disappeared, it being replaced by a slight general and rapid tremor of the whole frame, which was not at all unpleasant, and which [p252] had no tiring effect on one standing in the aviator’s car. In fact, the vibration in the first case resembled rather closely that of a motor vehicle supported on wheels having metal tires, and in the second case a motor vehicle supported on wheels having pneumatic tires.
As in these tests in the shop it was impossible to keep the engine cool by circulating its cooling water through the radiator, since there was no air current blowing across the latter to carry away the heat, it was necessary to connect an extra water tank in the cooling-water circuit. A tank holding about ten gallons was used, and this sufficed for about ten minutes before the water was raised to the boiling point.
During one of these tests when the frame was supported from the springs, and while the engine was developing about fifty horse-power, without any warning whatever, both propellers suddenly twisted off from the flanges by which they were connected to the propeller shafts, thus leaving the engine entirely unloaded. The propellers both dropped quietly to the floor, making only about one or two turns in falling the distance of approximately 10 feet, and the engine, which had been running at about 850 R. P. M., immediately speeded up to an exceedingly high speed, which, while not exactly known, since the tachometer only read to 2000 R. P. M., yet from the deflection produced on the tachometer needle must have been considerably higher than this. Although the fly wheels, which were 33 inches in diameter, with the aluminum rims and wire spokes, had been exceedingly well made, yet it was not considered safe to run them at this speed, and the engine was immediately shut down. At the moment, however, that the engine had broken loose from its propellers and also momentarily jumped to this exceedingly high speed there was absolutely no vibration that could be noticed, the unloaded engine running as smoothly as an electric motor. This showed very clearly that the running balance of the engine was as near perfect as it would be possible to get it, except with a seven-cylinder engine, which is theoretically capable of more perfect balance. It was evident that what small vibration there was in the frame while the engine was developing its power was due almost entirely to the reverse torque, and, of course, could never be entirely eliminated.
In the tests of the engine working in the frame, both while mounted on the car and also when suspended from the springs, a great amount of delay was caused from the fact that the ball-bearings on the transmission and propeller shafts frequently went to pieces. There were two reasons for this: In the first place, although carefully selected balls were used, defective ones were continually encountered. Even a slight defect in a single ball resulted in its breaking under the rather severe test to which they were subjected, and, as is well known, the breaking of one ball in a ball-bearing usually results in the destruction of the whole bearing, especially if the races are light. The second cause was that [p253] the whole aerodrome had been originally designed with the expectation of using a maximum of 24 horse-power, and as no margin had been left to provide for possible increases in the size of the bearings, there was no room to permit them to be increased without almost completely reconstructing portions of the transverse frame. While in the end it would have been cheaper to have reconstructed these portions in order to put in larger bearings, yet, as is always the case in experimental work of this kind, small changes which seem to hold out hope of overcoming difficulties are usually followed, rather than reconstructions which can be seen to involve considerable expense and delay. After a number of minor changes had been made in the bearings, they were finally able to stand up fairly well under the severe strain to which they were subjected when the engine developed its full power, and no further changes were made in them; a defective race being, however, replaced by a new one as occasion demanded.
These tests demonstrated very clearly that at speeds of approximately 1000 revolutions per minute ball-bearings which are subjected to considerable loads should be calculated with a considerable margin of safety, as the yielding of the frame, which must necessarily be far from rigid, causes more or less error in the alignment of the shafts and bearings, and this introduces considerably increased strains on the bearings. In the early tests before the bearings were strengthened, the balls in some of the races were on a few occasions ground to a very fine powder before it was discovered that they had failed. Such a result, it will be understood, could and did occur in the course of a very minute length of time.