The "Tangential" And Too Many Cups Of Coffee - Thursday, October 2, 1902
The History: Orville's notes provide additional information on Wilbur's last glide of the day: 550 feet. During the flight the machine "scraped" the ground then continued gliding for an additional 238 feet, but at an angle of 5°50´. This is the longest glide they have ever made.
The velocity of the wind during this last flight of the day was recorded: 0 feet - 6 m/s (meters/second); 100 feet - 4 1/2 m/s; 200 feet - 4 1/2 m/s; 300 feet - 4 m/s; 400 feet - 3 3/5 m/s; 550 feet - 4 m/s.
That evening they talked with George Spratt until 10 P.M. about the "tangential".
Here is a sample of their gliding tests today. (WW is Wilbur Wright and OW is Orville Wright.)
Last year, the Wrights returned home to Dayton after an unsuccessful summer of testing the 1901 glider. Convinced other researcher's data they based their glider's performance on was incorrect, they conducted their own systematic wind tunnel tests. Two instruments were built to measure the behavior of a variety of wing shapes: the lift and the drift (drag) balance.
The idea behind the drift balance had come from George Spratt. The drift balance had a moving needle which indicated the "tangential". Adding the tangential to the angle of attack gave the Wrights a gliding angle for that wing shape.
When George Spratt was at the camp, lively discussions and arguments on flight persisted until late in the evening. This particular night, Orville had one too many cups of coffee and could not sleep.
Although the 1902 glider's new fixed vertical tail had successfully corrected the machine's turning difficulties (at times the machine would turn in the wrong direction), now there was a new difficulty. Sometimes the glider would rapidly slide towards the ground in the direction of the lower wing. The wing tip would strike the ground and spin the machine around making a hole in the sand. The Wrights called this "well-digging" - today it is called a tail-spin. Although "well-digging" did not happen very often, it convinced the Wrights their control system was incomplete. Well-digging had not occurred with their previous gliders - none of which had tails.
Orville unable to sleep worked out a technical explanation for well-digging and a method of overcoming it - the design of a new vertical tail - a real rudder. Tomorrow at breakfast he would discuss the design with the others. This new rudder would perfect the Wrights' ability to control their glider. They would later file a patent for this system. Today all modern winged aircraft use these same basic mechanisms for control. This was a major discovery in the history of aviation - due in part to too many cups of coffee.