The total flying time during 1904 was only 45 minutes. But the knowledge and experience gained from that three quarters of an hour were of almost inestimable importance. Toward the end of May, 1905, the Wrights began assembling a machine all new with the exception of the motor and the propeller-driving mechanism. Strengthening of the structure at places where the previous machine had been too weak in making landings added about 25 pounds more weight. The principal changes, however, were in wing design, addition of some new features not in the earlier machines, and in making the wing-warping and operation of the tail rudder independent of each other. The camber of the wings was changed from 1-25, used in 1904, back to 1-20 as used in 1903 at Kitty Hawk. This change was to enable the machine to get off at a slower speed. The most radical change was the addition of two semi-circular vanes, called “blinkers,” between the two surfaces of the front elevator. This device was later patented by the Wrights. The purpose of the “blinkers” was to assist the rear rudder in overcoming the unequal resistances of the two wings when they were warped while making a turn. Gliding experiments in 1902 had shown that the pressure on a fixed vane in the rear of the wings tended to speed the higher wing when the machine slipped in the direction of the lower wing, and caused a tail-spin. The vane had to be made movable to relieve this pressure. It now occurred to the Wrights that if a fixed vane were placed in front of the wings, instead of behind them, its effect would be the reverse of that when the vane was in the rear, and that there would be less need of operating the rear rudder to overcome the unbalanced resistance of the two wings. Moreover, when the machine slipped inward while “banking” a turn, the speed of the low wing would be increased and a tail-spin avoided. The operation of the rear rudder could now be made independent of the wing-warp without danger. It was found that the “blinkers” entirely removed the danger of tail spinning but that they added to the difficulty of steering, both when flying straight and when making turns. Consequently they were not used in all the flights. (In modern planes the effect of the “blinkers” is gained by extending the fuselage far out in front of the wings.)