The History: During January, 1903 the Wrights began to investigate the shape of the uprights (the long posts which separated the upper and lower wings). Initially, a rectangular shape was used. However, from their experiments on wing shapes, the Wrights believed a shape with more curvature on the sides and without the sharp edges of the rectangle would be more aerodynamic. That is, the air would flow more smoothly around the shape. This would cause less air resistance and enable their machine to fly through the air with less effort.

Orville Wright Flying In the 1902 Glider

These charts from the Franklin Institute Science Museum are in Wilbur Wright's handwriting. You can see the different shapes the Wrights examined.