“WE NOW HOLD ALL
WHEN WILBUR GAVE HIS TALK in Chicago, in September 1901, he emphasized what he and Orville had already learned. On returning to Dayton, he turned his attention to what he didn't know. High on the list of things to determine were certain poorly-known numbers that he had been using when calculating lift and drag.
He had found values for these quantities by relying on standard equations that had been published many years earlier. Neither he nor Orville had to derive them; these equations were already in print, in the writings of Lilienthal and in the Aeronautical Annual. They called on investigators to find values for lift and drag by multiplying together a set of quantities:
Lift: L = k CL S V2
Drag: D = k CD S V2