However, in a few months the brothers untangled the conflicting factors and calculations. After studying the problem, they felt sure of their ability to design propellers of exactly the right diameter, pitch, and area for their need. Estimates derived from their formulas led to their propellers operating at a higher rate of efficiency (66 percent) than any others of that day. The tremendous expenditure of power that characterized experiments of other aeronautical investigators up to that time were due to inefficient propellers as well as inefficient lifting surfaces. The Wright propellers, designed according to their own calculations, were the first propellers ever built by anyone for which the performance could be predicted. After tests, their propellers produced not quite 1 percent less thrust than they had calculated. In useful work they gave about two thirds of the power expended—a third more than had been achieved by such men as Sir Hiram Maxim and Dr. Langley. [Illustration: Arrangement of propeller-driving chains and casings on original Wright 1903 machine displayed in the Smithsonian Institution. _Courtesy, Smithsonian Institution._] The brothers decided to use two propellers on their powered machine for two reasons. First, by using two propellers they could secure a reaction against a greater quantity of air and use a larger pitch angle than was possible with one propeller; and second, having the two propellers run in opposite directions, the gyroscopic action of one would neutralize that of the other. The two pusher-type propellers on the 1903 powered machine were mounted on tubular shafts about 10 feet apart, both driven by chains running over sprockets. By crossing one of the chains in a figure eight, the propellers were run in opposite directions to counteract torque. The propellers were made of three laminations of spruce, each 1⅛ inches thick. The wood was glued together and shaped with a hatchet and drawshave. _The Powered Machine, 1903_ The 1903 machine had a wingspan of 40 feet, 4 inches, a camber of 1 in 20; a wing area of 510 square feet; and a length of 21 feet, 1 inch. It weighed 605 pounds without a pilot. The machine was not symmetrical from side to side; the engine was placed on the lower wing to the right of center to reduce the danger of its falling on the pilot. The pilot would ride lying prone as on the gliders but to the left of center to balance the weight. The right wing was approximately 4 inches longer than the left to provide additional lift to compensate for the engine which weighed 34 pounds more than the pilot.