Fig. 33.—A screw and fabric covered aeroplane in position for testing.
Fig. 34.—The rotating arm of the machine with a screw and aeroplane attached.
In constructing my apparatus, which is shown in the [photographs], and also in a side elevation ([Fig. 32]), I aimed at making the apparatus very light and strong, avoiding as far as possible atmospheric resistance. In the drawing, a, is a thick seamless steel pipe 6 inches diameter; b, is a cast-iron pedestal firmly bolted to d, and connected to a large cast-iron spider embedded in hydraulic cement; by this means great rigidity and stiffness were obtained. n, n was formed of strong Georgia pine planks 2 inches thick, and strongly bolted together. The two members of the long radial arm h, h, were made of Honduras mahogany, an extremely strong wood, and had their edges tapered off as shown at y, y. The power was transmitted from a small steam engine provided with a sensitive governor through the shaft f, f. In the base c, of the casting b, was placed a pair of tempered steel bevel gears, giving to the vertical shaft a high velocity. From a pulley on the top of this shaft, the belt i, was run through the arms h, h, as shown in section y, y. This gave a rapid rotation to the screw shaft in a very simple manner. The operation of the machine was as follows:—the aeroplane g, to be tested was secured to a sort of weighing apparatus which is shown in detail ([Fig. 36]), and the screw attached to the shaft. Upon starting the engine, a very rapid rotation was given to the screw which caused the radial arm to travel at a high velocity, the whole weight resting on a ball bearing at w. The radial arms and all of their attachments were balanced by a cigar-shaped lead weight s, which was secured to a sliding bar so as to make it easily adjustable. The thrust of the screw caused the screw shaft to travel longitudinally, and this was opposed by a spring connected by a very thin and light wire to the pointer of the index o. As the apparatus rotated rather slowly on account of its great diameter, it was quite possible to observe the lift while the machine was running at its highest speed. The aeroplanes were mounted after the manner of the tray of a grocer’s scales (see [Fig. 36]), and the lift of the aeroplane was determined by what it would lift at r—that is, while the machine was running at a given speed, iron or lead weights were placed in the pail r, until the lift of the aeroplane was exactly balanced, and then, in order to ascertain exactly what the lift was, the aeroplane was placed under what might be called a small crane, and a cord, running over a pulley, attached. The amount of weight necessary to lift the plane into the same position that it occupied while running was taken as its true lift. In order to facilitate experiments the gauge p, was provided. This gauge consisted of a large glass tube and the index p, with a quantity of red water at q. The centrifugal force of rotation caused the red water to rise in the tube. This was easily seen, so that if experiments were being tried, we will say at 50 miles an hour, it was always possible to turn on steam until the red liquid mounted to 50. This device was very simple and effective, and saved a great deal of time. In order to prevent the twisting of the radial arm, a piece of stiff oval steel tube 12 feet long was secured between the arms at j, and on each end of this tube were attached the wires u, u. This not only effectually supported the end of the arm, but at the same time prevented twisting and made everything extremely stiff. Of course, while the machine was running at a high velocity, centrifugal force had to be dealt with, and in order to prevent this from causing friction in the articulated joints of the weighing apparatus ([Fig. 36]), thin steel wires k, k were provided. As this apparatus was in the open, it was found that the slightest movement of the air greatly interfered with its action. On one occasion when a fabric covered aeroplane, 4 feet long by 3 feet wide, was placed in position, the four corners being held down by the wires v, v, and the apparatus driven at a high velocity, a sudden gust of wind snapped two of the wires, broke the aeroplane, and the flying fragments smashed the screw, and this notwithstanding that each of the four wires was supposed to be strong enough to resist at least four times any possible lifting that the whole aeroplane might be subjected to.
Fig. 35.—The little steam engine used by me in my rotating arm experiments; the tachometer and dynamometer are distinctly shown.
In order to ascertain the force and direction of the wind, I made an extremely simple and effective apparatus which is fully shown (see [Fig. 38]). Whilst conducting these experiments it occurred to me, when a large aeroplane was used, that after it had been travelling for a considerable time, it would impart to the air in the path of its travel, a downward motion, and that the lifting effect would be greatly reduced on this account. In order to test this, I provided four light brass screws and mounted them, as shown at [x], on a hardened polished steel point much above their centre of gravity, so that they balanced themselves. On account of the absence of friction, they were easily rotated, and responded to the least breath of air that might be moving. One morning when there was a dead calm, I placed four of these screws equidistant around the whole circle. Some of them rotated very slowly in one direction and some in another; some alternated, but all their motions were extremely slow. However, upon setting the machine going with a large aeroplane and a powerful screw, I found after a few turns that the air was moving downwards around the whole circle at a velocity of about 2 miles an hour, but as the screw was a considerable distance below the aeroplane, I estimated that the actual downward velocity of the air in which the aeroplane was travelling was about 4 miles an hour. The result of my experiments are clearly shown in an unpublished paper which I wrote at the time, and as it is of considerable historical interest, I have placed it in the [appendix], notwithstanding that there may be certain repetitions.
Fig. 36.—The machine attached to the end of the rotating shaft—a, a, the body of the machine; b, b, four-legged spider secured to a, a; c, c, parallel bars; d, d, vertical member to which the aeroplane g, g is attached; h, h, the screw; f, f, wires for preventing distortion of the aeroplane.