Wilbur used to sit along the Miami River south of Dayton in a place called the Pinnacles and observe the birds flying. In his notes of 1900 he wrote, “The buzzard that uses the dihedral angle (v-shaped) finds greater difficulty to maintain equilibrium in strong winds than eagles and hawks which hold their wings level.”
The Wrights would remember that observation in designing the 1903 Wright Flyer. The Flyer had wings that drooped like an eagle in what is known as the anhedral configuration.
During their first flights of the 1902 glider on September 19, 1902 they found that while gliding down the slope of a sand dune, crosswinds would upset the glider. Orville first used the anhedral on the 1902 glider on the occasion of his first flight. (Wilbur didn’t let his younger brother fly before this time because he felt responsible to not let him hurt himself). This change, Orville said, would reduce the effects of unexpected winds that struck the glider from the side.
The brothers re-rigged the wings with a slight anhedral by trussing them so the wing tips drooped about 4 inches lower than the center of the wing.
They tried out the new configuration by flying the glider as a kite and found that it seemed to solve the problem. The glider-kite flew in crosswinds without an upset.
What they didn’t know was that they had created another problem. The anhedral configuration magnified the gliders already poor roll characteristic.
The next day Orville crashed when the glider suddenly rolled, turned up sidewise and slid into the sand in spite of all the warp that was applied. This happened on several occasions for no apparent reason. The brothers flew relatively low to the ground, so it didn’t take much of a loss of altitude for the lower wing to hit the sand and dig a small hole. Wilbur gave it the name, “well digging.”
Orville gave the following explanation of what occurred:
When the machine became tilted laterally it began to slide sidewise while advancing, just as a sled slides down hill or a ball rolls down an inclined plane, the speed increasing in an accelerated ratio. If the tilt happened to be a little worse than usual, or the operator were a little slow in getting the balance corrected, the machine slid sidewise so fast that this movement caused the vertical vanes to strike the wind on the side toward the low wing, instead of on the side toward the high wing, as it was expected to do. In this state of affairs the vertical vanes did not counteract the turning of the machine about a vertical axis caused by the difference of resistance of the warped wings on the right and left sides. On the contrary, the vanes assisted in the turning movement, and the result was worse than if there were no fixed vertical tail.
Orville thought of a solution one night when he had trouble falling asleep. He reasoned that making the stationary vertical tail movable would allow the pilot to turn the tail as a rudder to assist in making a controlled turn.
Wilbur liked the idea and improved on it by suggesting that the rudder be connected to the wing warping controls so that when the pilot warped the wings, the rudder would automatically move in the appropriate direction. The change significantly improved controllability, but did not solve it completely. That would have to wait until 1905.
The 1903 Flyer continued to use the anhedral design by incorporating a 10-inch droop in the wings.
The Wrights flew in a straight line into the wind on Dec. 17th. Their major control problem during their four flights that day was maintaining pitch.
It wasn’t until 1905 that the Wrights solved their major control problems and produced a practical airplane. By then they had made a number of design changes to their machine including eliminating the anhedral wing configuration.
The Wrights were never interested in designing a machine that was inherently stable. They wanted a machine that they could control in flight.
Flying like an eagle with drooping wing tips may have worked for their 1903 machine. They would later learn at Huffman Prairie during 1904/1905 that flying like an eagle was not the best configuration for handling pitch, roll and yaw and they produced the first practical flying machine in the world.