Lift-generating surfaces--these are the bases of all flying. Every one knows, for instance, that a paper dart, instead of falling directly to the floor, sails in a gliding angle for some distance before crashing. Lift is generated under those plane surfaces moving through the air--and the lift keeps that paper dart gliding. Little eddies of air are compressed under its tiny wings. Imagine an engine in the dart, propelling it at some speed. Instead of having to nose down to get enough speed to generate lift under its wings, the dart would be able to fly on the level, or even climb a bit. Just so with an airplane. A gliding airplane about to land with power shut off is that paper dart on a large scale. The airplane flying is the dart with power. To make the airplane safe to fly, to give control to the pilot so that he may steer it where he wants to, there is a rudder, moved by a rudder-bar under the foot of the pilot. It is impossible to turn a swiftly moving airplane in the air by the rudder alone. It must be banked to prevent skidding, even as a race-track is banked high on the turns. On its side an airplane will cushion its own bank of proper degree by the use of ailerons. These ailerons are sections of the wing-tips which may be moved either up or down. They are counterbalanced so that movement of the left down gives you the right aileron up. With left aileron down, the lift of the left wing is increased, and it tips up; at the same time the lift of the right wing is decreased, and it sags down. In that way the airplane is tipped up for a bank. These ailerons, wing sections, really, are controlled by a device known as the joy-stick in the cockpit. We have seen how an airplane is made to tip and turn. Before a machine is under control we must be able to climb, or come down to the ground for a landing. Vertical control of an airplane is attained by the use of elevators, flaps on the tail plane acting as horizontal rudders. A pull-back on the joy-stick lifts the flaps, raises the nose of the machine, and causes it to gain height. Push the joy-stick forward, the elevators are turned down, and the machine goes into a dive for the ground. In making many maneuvers all three controls, rudder, ailerons, and elevators, are used at once and the pilot feels his way with the machine, guiding it with the stick and the rudder-bar.