In Pursuit Of Thrust - The First Propeller Tests - Monday, December 15, 1902
The History: Orville and Wilbur Wright had returned home to Dayton after their successful gliding experiments in North Carolina just six weeks ago. Nonetheless, they are already prepared to conduct their first propeller tests.
The Wrights had diligently conducted wind tunnel tests of airfoils in 1901, which had helped them determine better wing shapes. These tests laid the foundation for the success of the wings on the 1902 glider.
Propellers are actually a series of small airfoils laid out next to one another and combined together. The Wrights knew they could calculate the forces created by an airfoil as they had in the wind tunnel tests. Consequently, they felt they could determine the forces generated by the propeller. After all, instead of flying straight the propeller was just a set of spinning airfoils, in their minds. They soon realized that the propeller's motion was more complicated than this.
They could try different shapes and see what worked best and evolve their propeller design this way (known as "trial-and-error", to keep trying different alternatives until one is successful). This could be very time consuming. Instead, the Wrights decided they would need to develop a theory - a set of principles which would explain propeller performance. This would provide a more systematic way of developing propeller shapes. If they had a plausible theory they would be able to predict and estimate their propeller shape and performance.
As a first step, the Wrights decided to build a propeller, observe its motion and take a few measurements, to begin to develop their theory. Their propeller blade was 28 inches in diameter (long). The blade was 7 inches at its widest point. Powered by a motor [most likely the same one which powered their wind tunnel] spinning the propeller at 1600 revolutions per minute, they estimated that the shape provided 12 pounds of thrust.