Fig. 24.—Cross-sections of bars of wood employed for ascertaining the coefficient of different forms.
Fig. 25.—Transverse sections of bars of wood experimented with for the purpose of ascertaining their coefficients as relates to a normal plane.
Fig. 26.—A flat aeroplane placed at different angles.
In order to ascertain the resistance encountered by various shaped bodies driven at various speeds through the air, the best form of aeroplanes, and the efficiency of atmospheric condensers, I made the apparatus shown in [Figs. 22] and [23]. The smaller and straight portion of this apparatus was 12 feet long and exactly 3 feet square inside, and was connected as shown to a shorter box 4 feet square. Two strongly made wooden screws b, b and d, were attached to the same shaft. These screws had two blades each, and while one pair of blades was in a vertical position, the other was in a horizontal position. I interposed between the screws, slats of thin wood arranged in the manner shown at d, d; this was to prevent rotation of the air. At e I placed vertical slats of thin wood, and horizontal slats of the same size at f. At g two wide and thin boards, sharp at both edges and made in the form of the letter X, were placed in the box as shown in section XY. An engine of 100 H.P. with an automatic variable cut-off was employed which gave to the screws a uniform rate of rotation, and as the engine had no other work to do, the governor could be arranged to give varying speeds such as were required for the experiments. The objects to be tested were attached to the movable bars. In the drawing, the aeroplane k, k is shown in position for testing. This apparatus was provided with a rather complicated set of levers, which permitted not only the measurement of the lift of the objects experimented with, but also that of the drift. The principle employed in this apparatus was a modification of the ordinary weighing apparatus used by grocers, etc. The first object tested was a bar of wood exactly 2 inches square shown in [Fig. 24]. This was placed in such a manner that the wind struck squarely against the side as shown in the drawing, and with a wind of 49 miles per hour, it was found that the drift or tendency to move with the air was 5·16 lbs.; at the same time, the wind on my instrument gave a pressure of 2 lbs. on a normal plane 6 inches square. The velocity of the wind was ascertained by an anemometer of the best London make. Upon turning the same bar of wood in the position shown at b, the drift mounted to 5·47 lbs. A round bar of wood, 2 inches in diameter, shown at c, gave a drift of 2·97 lbs. These experiments were repeated with a wind velocity of 40 miles per hour, when it was found that the drift of a was 4·56 lbs., and that of the round bar, 2·80 lbs. It will be seen from these experiments that the power required for driving bars or rods through the air is considerably greater than one would have supposed. The next object experimented with was a, [Fig. 25]. When this was subject to a wind of 40 miles an hour, the drift was 0·78 lb. Upon reversing this bar—that is, putting the thin edge instead of the thick edge next to the wind—the drift mounted to 1·22 lbs.; b showed a drift of 0·28 lb. with the thick edge to the wind, and 0·42 lb. with the thin edge to the wind; c showed a drift of 0·23 lb. with the thick edge to the wind, and 0·59 lb. with the thin edge to the wind; and d, which was the same thickness as the others and 12 inches wide, both edges being alike, showed a drift of only 0·19 lb. These experiments show in a most conclusive manner the shapes that are most advantageous to use in constructing the framework of flying machines. Aeroplane e, [Fig. 26], when placed on the machine in a horizontal position showed neither lift nor drift, but upon placing it at an angle of 1 in 20, as shown at f, the lift was 3·98 lbs. and the drift 0·30 lb. with a wind velocity of 40 miles per hour. At this low angle the blade trembled slightly. Upon placing the same plane at an angle of 1 in 16 as shown at g, the lift was 4·59 lbs. and the drift 0·53 lb. It will be observed that the underneath side of this plane is perfectly flat. The next experiment was with planes slightly curved, as shown in [Fig. 27]. The aeroplane a was 16 inches wide, very thin, and only slightly curved. When set at a very low angle, it vibrated so as to make the readings very uncertain, but when set at an angle of 1 in 10 it lifted 9·94 lbs. with a drift of 1·12 lbs. By slightly changing the angle it was made to lift 10·34 lbs. with a drift of 1·23 lbs., the wind velocity being 41 miles per hour. Aeroplane b, 12 inches wide, [Fig. 27], when placed at an angle of 1 in 14 with an air blast of 41 miles per hour, gave a lift of 5·28 lbs. with a drift of 0·44 lb.; at an angle of 1 in 12 the lift was 5·82 lbs. and the drift 0·5 lb.; at an angle of 1 in 10 the lift was 6·75 lbs. and the drift 0·73 lb.; with an angle of 1 in 8 the lift was 7·75 lbs. and the drift 1 lb.; with an angle of 1 in 7 the lift was 8·5 lbs. and the drift 1·25 lbs.; at an angle of 1 in 6 the lift was 9·87 lbs. and the drift 1·71 lbs. Aeroplane c, [Fig. 27], which had more curvature than b, when run in a horizontal position, gave a considerable lift, and when raised to an angle of 1 in 12 it gave a lift of 6·12 lbs. with a drift of 0·54 lb. In another experiment at the same angle, it gave a lift of 6·41 lbs. with a drift of 0·56 lb.; at an angle of 1 in 16 it gave a lift of 5·47 lbs. with a drift of 0·37 lb.; at an angle of 1 in 10 it gave a lift of 6·97 lbs. and a drift of 0·70 lb.; at an angle of 1 in 8 it gave a lift of 8·22 lbs. with a drift of 1·08 lbs.; at an angle of 1 in 7 it gave a lift of 9·94 lbs. with a drift of 1·45 lbs.; at an angle of 1 in 6 it gave a lift of 10·34 lbs. and a drift of 1·75 lbs. This plane was then carefully set so that both the forward and aft edges were exactly the same height, and with a wind blast of 41 miles per hour it gave a lift of 2·09 lbs. with a drift of 0·21 lb. It was then pitched 1 in 18 in the wrong direction, and at this point, the lifting effect completely disappeared, while the drift was practically nothing.
Fig. 27.—Group of aeroplanes used in experimental research. Although shown the same size in the drawing, aeroplane a was 16 inches wide, and b and c, 12 inches wide.
Fig. 28.—An 8-inch aeroplane which did very well. This aeroplane gave decided lifting effect when the bottom side was placed dead level, as shown at a.