[WalterBright]

Lilienthal's lift/drag numbers turned out to be off by a factor of 2, which is why the Wrights developed their wind tunnel and did exacting experiments to get the correct numbers, and developed the shape of their wing from it.

[andikleen2]

If you read Anderson "A history of Aerodynamics" it disagrees on this point. It states that the Wright's didn't have a good way to calculate drag, and they didn't understand many of the side effects from real wings (like flow separation) which caused wrong measurements initially. Later on they apparently came back to something that was closer to Lilienthal's numbers, even though the problem simply wasn't fully understood at the time.

This paper has a similar conclusion: https://corescholar.libraries.wright.edu/cgi/viewcontent.cgi...

"When the Wright brothers compared their results with those of Lilienthal, they found some disagreement, but not as much as they expected. As Wilbur states in his diary for October 16, 1901: "It would appear that Lilienthal is very much nearer the truth then we have heretofore been disposed to think." [Wolko, 21]. 17 The formulas were still not producing the lift and drag that were actually being produced. The only other possible source of error in these equations was the Smeaton coefficient of air pressure."

[WalterBright]

Thanks for the information. The bottom line was the Wrights needed a considerably bigger wing than that predicted by Lilienthal's numbers.