PL. 75. QUARTER-SIZE MODEL AERODROME EQUIPPED WITH SUPERPOSED SURFACES, JUNE 11, 1901, SIDE VIEW [◊]
PL. 76. QUARTER-SIZE MODEL AERODROME EQUIPPED WITH SUPERPOSED SURFACES, JUNE 11, 1901. END VIEW [◊]
PL. 77. CYLINDERS OF ENGINE OF QUARTER-SIZE MODEL AERODROME [◊]
After much delay, due to various causes, the quarter-size model, as shown in plan, end elevation, side elevation and three-quarter elevation in Plates [71] and [72], respectively, was taken down the river in June, 1901, in order to make some tests with it from the small house-boat, which had been previously moved to the middle of the river opposite Widewater, Va. A test of it in free flight was made on June 18, its condition at this time being shown by Data Sheet No. 12 in Appendix. The launching apparatus worked perfectly and the aerodrome started off on an absolutely even keel, dropping only a few inches immediately upon leaving the launching apparatus, and continuing straight ahead directly into the light wind of something less than 2 miles an hour. After it had gone only about 100 feet, however, it began to descend slowly, but still maintained a perfectly even balance, and finally touched the water about 150 feet from the house-boat, having been in the air between 4 and 5 seconds. It was immediately recovered, and as soon as the wings could be dried out another test was made, as it was thought probable that the wind had interfered with the carburetor to such an extent that the engine had not received the proper mixture of gas. Upon this second test the launching apparatus again worked perfectly and the aerodrome again flew straight ahead on a perfectly even keel, and at a uniform height from the water until it had gone about 300 feet, when it again began to descend slowly and finally touched the water about 350 feet from the house-boat, having been in the air about 10 seconds. While the tests were very disappointing, owing to the extreme brevity of the flights, yet they showed conclusively that the balancing of the aerodrome was correct, at least as far as motion in a straight line and in a quiet atmosphere was concerned. As one and a half horse-power, which was felt to be the very minimum which would successfully propel the aerodrome, was furnished by the engine only when working at its very best, and as the change in conditions from a quiet state to a velocity of something like 40 feet per second evidently caused a considerable drop in the power because of the change in the gaseous mixture which the carburetor furnished to the engine, it was decided not to make any further test of the aerodrome until the engine cylinders could be reconstructed so as to provide more effective means for cooling it, and thereby a reasonable margin of power above that actually necessary. The aerodrome was accordingly returned to Washington for the purpose of making new cylinders for the engine. In constructing these new cylinders the old cylinder heads from the previous cylinders were used in order to expedite their completion. This proved in the end to be a very great mistake, though at the time it seemed probable that the use of them would save much delay and considerable expense. The new cylinders were constructed of steel tubing originally one-half inch thick, which [p233] was machined to the form clearly shown in the photograph, Plate [77], where it will be seen that thin radiating ribs spaced one-quarter inch apart were formed integral with the cylinder, the combustion chambers or heads being screwed on and brazed to the cylinders. After much delay the new cylinders were completed, and upon test it was found that while the radiating ribs assisted very greatly in keeping the engine cool, yet the valves were so small that the gas was not able to get in and out of the cylinders rapidly enough to permit the engine to furnish its full power. Even at this stage it would have been better either to have made new cylinder heads with larger valves or to have made entirely new cylinders and cylinder heads, but in the effort to economize time and money it seemed best to try to overcome part of the defect by adding an auxiliary inlet valve. This was constructed, and upon test it was found that, although the engine developed 3.2 horse-power on the Prony brake at 1800 R. P. M., and even maintained 5.1 horse-power on the brake for a few seconds when running at 3000 R. P. M., the ports leading from the valve chamber to the cylinders were so small that they became heated after the engine had run for 2 minutes and premature ignition occurred, which, of course, immediately and very greatly reduced the power developed.
It was decided, however, in view of the tests in which the engine had developed 3.2 horse-power at 1800 R. P. M., that there was sufficient margin of power to enable it to propel the quarter-size model, even if it was not working at its best. After concluding the Prony-brake tests on the engine, it was mounted in its proper position in the aerodrome frame and connected to the propeller shafts. Some pendulum tests were then made, showing an average lift of approximately 57 per cent of the total flying weight. But it was found that the propeller and transmission shafts and their bearings would not stand the strain due to the increased power of the engine. Newer and stronger shafts and bearings were, therefore, constructed and further pendulum tests were made. It was then found that the transverse frame which supported the shafts and bearings was too weak, and this was strengthened by substituting newer and thicker tubing where it seemed necessary.
These changes and repairs were all completed by October, 1901, and the quarter-size model was at last, after months of delay, felt to be in a condition which justified the expectation that its next flight would be entirely successful. In view of the much more important work on the large aerodrome which demanded immediate attention the quarter-size model in this completed condition was put aside. Nothing more was done with it until April, 1903, when some shop tests were made preliminary to taking it to Quantico, where, on August 8, it made a successful flight, which is described in Chapter XII [◊].