The Wright brothers had
designed two gliders using the accepted lift and drag equations,
Otto Lilienthal’s aerodynamic data, and Smeaton’s
coefficient. Neither glider produced the lift those calculations
predicted. Wilbur and Orville felt it was time to perform
their own aerodynamic research.
The Wrights examined all the terms in the lift and drag equations.
Some values—weight of the craft, wind speed, and wing
surface area—could be directly measured, so the Wrights
were confident of their accuracy. But the coefficients of
lift and drag and Smeaton’s coefficient were drawn from
the work of others. The brothers focused on these as the possible
source of their gliders’ poor lift performance.