[Illustration: ELECTRIC FAN(A) FURNISHED AIR PRESSURE WHICH ACTED ON WING SECTION(B). WING SECTION(B) WAS MOUNTED ON A SWINGING FRAME(C). THE MOVEMENT OF(B) CAUSED(C) TO MOVE A POINTER ON DIAL(D) WHICH INDICATED THE AMOUNT OF MOVEMENT OF(B). (E) ARE WEIGHTS ATTACHED TO WING(B). (E) REPRESENTED _WEIGHT_ AND _DRAG_. THEY REGISTERED THEIR EFFECT ON WING LIFT.] The Wright Brothers were not only inspired mechanics (as many people still believe today) but serious scientists, working along the soundest lines. In their keen desire to know what air pressure on wings really was, they cleared a corner of their bicycle shop and built a small wind tunnel with spare lumber and an old electric fan. They built small wing sections of various shapes and experimented with them in their wind tunnel. The electric fan was used to create the moving air around the wing section. By attaching the wing sections to a supporting frame and connecting the frame with a pointer and dial, they were able to keep a record of the effect of moving air on each experimental wing section. Through their wind tunnel research the Wright Brothers discovered the four forces that control all heavier-than-air flight: _lift_, _thrust_, _weight_, and _drag_. They found that a slight curve or camber in the wing section would cause the moving air to travel farther over the top of the wing surface than along the under side. This made the air pressure greater under the wing, gave a suction effect above the wing, and caused it to rise, creating _lift_. They discovered that a wing section of the proper camber would counteract the _weight_ of gravity. Thus, a wing must be so designed that, with a certain amount of air flowing around it, it would lift a certain _weight_. They also discovered that air flow against any surface attached to the wing would cause a resistance or _drag_. Hundreds of experiments in their wind tunnel with various types of wing shapes gave the Wrights a series of tables from which to design a wing that would create the _lift_ for a designed weight. [Illustration: THE FOUR FORCES THAT CONTROL THE FLIGHT OF THE AIRPLANE LIFT TRUST DRAG WEIGHT]