The balancing of a machine in mid-air is one of the most difficult problems in aviation. In the balloon this is easily accomplished because the principal weight, the basket with the passenger, is below the gas-filled sphere or compartment, and the balloon tends to right itself after any disturbance by the wind, much like a plummet when swayed out of its position.

Professor Langley, Lilienthal and others had sought to take advantage of this tendency in the construction of their machines by placing or arching the wings above the pilot or heavier portion of the mechanism. After a slight disturbance in mid-air the machine would then tend to right or balance itself and assume its former position. The practical difficulty of this arrangement, however, arose from the fact that when once set to swaying the gliders thus constructed continued to sway like the pendulum of a clock. The Wright brothers set themselves the task of finding some other method of preventing the biplane from dipping downward or upward at either side with the shifting of air currents. The first device to give steadiness of motion was a small movable horizontal plane, supported parallel with and in front of the two main planes, and by means of a lever, under control of the pilot.