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 The creator of the ""Blade Element Theory"" is Stefan Drzewiecki and not the Wright Brothers. 

Tom Crouch, a pro Wright brother historian, claims the two US inventors realized that a propeller was in fact a rotating wing and that they discovered a method to design propellers (see 1).

(1) ""The design of effective propellers presented a far greater challenge. The Wrights, who had initially hoped to learn from experience with ship propellers, discovered that little thought had been given to basic theory in this area. In another of their brilliant flashes of insight, the brothers reasoned that a propeller could be regarded as a rotary wing in which the lift being generated becomes the thrust that moves the aircraft forward. Knowing the number of revolutions per minute at which the propeller would be turning, they calculated the speed at which the blade would be moving at any point along its length and selected an appropriate airfoil from the tables developed during their wind tunnel tests. It sounds simple enough, but as Orville explained, ""on further consideration it is hard to find even a point from which to make a start, for nothing about a propeller, or the medium in which it acts, stands still for a moment."""", Tom Crouch, ""First Flight: The Wright Brothers and the Invention of the Airplane"", pag. 57, 2002, https://archive.org/stream/firstflightwrigh00crou#page/56/mode/2up 

However, the letter of Wilbur Wright to Octave Chanute (see 2) shows the two brothers had already been informed about the theory of Stefan Drzewiecki, before their alleged powered flight in Dec. 1903.

(2) Letter of Wilbur Wright to Octave Chanute
Dayton, July 2, 1903,

""My delay in writing you was chiefly due to a desire to first obtain a clear understanding of the Drzewiecki article on screws. [2] This author's methods of thought and expression are so different from my own that it has been no easy matter to master his paper. It shows a very clear understanding of some features of the question, but as the author seems unacquainted with negative tangential, and with the effect which weight of water acted upon by each part of the screw has in fixing the angle of incidence, the paper leaves much to be desired as a complete discussion of the subject. I am quite certain that his method of constructing a screw of uniform angle of incidence will not give the result intended. The speed imparted to the water by suction before the screw actually has a chance to strike it is also ignored; and no method of calculating the loss from this source is given. Some of his conclusions seem to Orville and me to be rank heresy, but of course we are like the theologians and judge the ""soundness"" or ""unsoundness"" of others by the closeness of their agreement with ourselves."", Source: http://invention.psychology.msstate.edu/inventors/i/Wrights/library/Chanute_Wright_correspond/1903/Jul2-1903.html

(3) ""[2] Stefan Drzewiecki, born in 1844, was the originator of the blade element theory of screws, which considers the blades of a screw as being composed of an infinite number of aerofoil sections. The blade element theory, together with the momentum theory of Froude and Rankine, is almost universally used today to explain the action of aerial screws. In 1900, Drzewiecki presented a paper, ""Des Helices propulsives,"" to the Congres d'Architecture et de Constructions Navales in Paris. In 1901, a second paper by him, ""Du Choix des elements determinant les helices propulsives permettant leur facile comparaison entre elles,"" was published in the Bulletin de l'Association Technique Maritime (no. 12, 1901). The papers were reprinted in Paris in 1900 and 1901 respectively. It is not known which of the two Chanute sent to the Wrights."", Source: http://invention.psychology.msstate.edu/inventors/i/Wrights/library/Chanute_Wright_correspond/1903/Jul2-1903.html

These two brothers were ignorant people, they made fun of Drzewiecki in front of Chanute, and finally, in 1908 when they flew in France and US in front of witnesses, started to claim the theory of this Polish scientist as their own. Historians, like Tom Crouch, who do not have any technical background, simply believed the two brothers and propagated this false information around the world."