The much celebrated 66% efficiency of the 1903 propellers not confirmed by wind tunnel tests
"Flyer I 1903" used anachronistic propellers!!
In a March 6, 1903 note, with calculations regarding the efficiency of their propellers (see
Local Hangar: Wright Flyers (Demo Site) - Picture Page ), the Wright brothers just applied a known elementary relation:
Efficiency_propeller = Thrust * Plane_speed / Power_available
66%=90lbf*24mph/8.73HP
They simply needed a 90lbf propeller at 24mph considering a 8.73HP engine was available and they calculated that their propeller should be at least 66% efficient otherwise the required 90lbf thrust to keep the plane aloft would not have been reached.
Their calculations show just how great the performance of the propeller should have been not how great it really was.
This efficiency was never obtained by people from the Wright Experience project. The site
Mechanical Engineering "100 Years of Flight" supplement, Dec. 2003 -- "Prop-Wrights," Feature Article says that many tests were effectuated and efficiencies between 75% and 82% were obtained, which is not 66%. They also say they reconstructed, with the help of computers, the propellers using badly damaged parts of the originals. However, in their reconstructions, they acknowledged they had made some assumptions that could have alter the efficiency. In conclusion that 66% efficiency is not confirmed. When a team wants to replicate the results or predictions of some inventors the team has to obtain exactly the same results not much better!
In the article "The Wright Brothers' Aeroplane, O. and W. Wright, The Century Magazine, September 1908, pag. 648-649,
The Wright Brothers' Aeroplane [Orville and Wilbur Wright, The Century Magazine, September 1908] | Library of Congress ", the Wright brothers wrote:
"Our first propellers, built entirely from calculations, gave in useful work 66 per cent. of the power expended. This was about one third more than had been secured by Maxim or Langley."
The text is clear, based on calculations the two brothers built a 66% efficient propeller, a claim not backed by that March 6, 1903 note (
66%=90lbf*24mph/8.73HP).
An advanced high efficiency propeller, made by Lucien Chauviere, can be seen in L'Aerophile from May 15, 1908, pag. 182 (see
L'Aérophile (Paris) ). It is above the propellers presented by the brothers starting with Aug. 8, 1908 and clearly made before their propellers became known. Definitely, Europeans did not learn from the Wright Brothers how to make efficient propellers. The opposite seems to be true.
Basically, the two brothers came in Aug. 1908 with propellers of a type already existent since 1907 and claimed they had invented them in 1903. The existence of these propellers in pictures allegedly made in 1903 increases the number of doubts the photos were made in that year indeed.