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.