If their machine was capable, as they had demonstrated, of flying by its own power for 852 feet against a 20-mile wind, there was no reason why it shouldn’t go many times that far. But if the machine was to be practical, many improvements would be necessary, and they would need more experience in flying. Much practice would be required, and that would mean more expense in proportion to income, for they would have less time for building and repairing bicycles. But they decided to devote to aviation whatever amount of time seemed necessary. A number of bicycles at their shop were in various stages of completion. But no new ones were started after the Wrights’ return from Kitty Hawk, though some of those on hand were completed and sold. The brothers now began to turn over to Charlie Taylor, their chief mechanic, most of the routine work of the shop. In January, 1904, the brothers began building a new plane. It was similar to the one flown at Kitty Hawk, but there were a number of changes, including more sturdy construction throughout. The weight exceeded that of the original plane by about eighty pounds. (In flight, the weight, including the pilot, and 70 pounds of iron bars carried on the framework under the front elevator, was 900 pounds.[5]) The wing camber was changed from 1-20 to 1-25--that is, the curvature was decreased; and the ribs were tapered from front to rear spar instead of being of uniform depth, as in the earlier model. An entirely new engine went into the 1904 machine. In fact, the Wrights started to build three new engines. One of these had four cylinders of 4⅛-inch bore; another, four cylinders of only 4-inch bore, as the one used at Kitty Hawk; and the third was a V-type, of eight cylinders. The 4⅛-inch bore was the one installed in the 1904 plane and gave a satisfactory amount of power--but not so much as the Wrights later developed in the other four-cylinder motor of only four-inch bore. That motor they kept in their shop and used for a kind of guinea pig, trying various improvements and refinements until it produced as much power as they had expected from the V-type motor of eight cylinders and twice as much as the original motor used at Kitty Hawk. They then gave up the idea of completing the V-type motor. Another change in the 1904 machine was using white pine instead of spruce for the front and rear spars in the wings. Spruce was not available in Dayton at that time, and tests the Wrights made at their shop, in the manner usually employed for ascertaining the strength of woods, indicated that the two woods were about equally strong. (But in actual use, when stresses came suddenly, as in landing, the white pine spars snapped “like taffy under a hammer blow,” though spruce had always withstood such shocks. The brothers rebuilt the wings, with all spars of spruce.)