[Illustration: Fig. 53.--In order to adjust the lifting effect so that it was directly over the centre of gravity, and to test the action of my fore and aft horizontal rudders, I ran the machine along the steel rail _i_, _i_, and adjusted my weights and aeroplanes in such a manner that, when the machine was run at a speed of 30 miles an hour along the track, with the rudders adjusted in the manner shown, the front wheel _j_, was raised from the steel track and the small wheel _m_, brought into contact with the upper track _h_. When the rudder _b_, _b_, is in this position, it produces a strong lifting effect, while the rudder _c_, _c_, does not lift at all.] [Illustration: Fig. 54.--This shows the rudders placed in such a position that _b_, _b_, does not lift at all, while _c_, is placed at such an angle as to produce a strong lifting effect, especially so as it is in the blast of the screws _d_, _d_. With the rudders in this position, and at a speed of 30 miles an hour, I was able to lift the rear wheels _k_, _k_, off the steel rails and to bring the small wheel _l_, in contact with the upper track _h_. These experiments showed that the machine could be tilted in either direction by changing the position of the rudder.] [Illustration: Fig. 55.--When the rudders were placed in the position shown, and the machine was run over the track at a rate of 40 miles an hour, all the weight was lifted off the wheels, _j_, and _k_, and both the small wheels _m_, and _l_, engaged the upper track.] [Illustration: Fig. 56.--In case of a breakdown or failure of the engines when the machine is in flight, it is necessary to place the rudders in the position shown, in order to prevent the machine from diving to the earth. When the rudders are in this position, a rapid and destructive descent is not possible, as the machine will preserve an even keel while falling.] CHAPTER VII. THE SHAPE AND EFFICIENCY OF AEROPLANES.