Dayton, July 14, 1903
I have your letter of July 12th enclosing translation of your article for Revue des Sciences and also a new computation of some of our glides of Oct 8th, 1902, from the data of yourself and Mr. Herring. Thank you. May I ask you to send me at your convenience a similar record of a dozen or fifteen consecutive glides from your records of 1896? Do you know whether or not any of Herr Lilienthal's records of glides are still preserved? I have not found in his published papers any data of actual glides.
I sent you a few days ago an estimate of the performance of our 1902 machine at various speeds. It agrees closely with all our observations of the relation of speed, angle of incidence, and angle of descent. The tangentials are estimated from our tables, and the head resistance calculated on the basis of an equivalent area of 3 sq. ft. for the uprights, wires, rudder framing, & man's body. The results obtained with the upper surface as compared with the results of the complete machine do not admit of any greater allowance for the head resistance than that named.
You will remember that for several years Orville and I have held the view that for purposes of computation a glide should be uniform in its course and rate of descent and in speed, and made on a hill of a slope equal to the rate of descent. The glides of Oct. 8th did not fulfill these conditions, consequently we have not used them for purposes of computation. In these glides the speed accelerated at the beginning and usually decreased toward the end. Sometimes the speed at starting was greater than at landing, and in a few cases less. The course was usually more or less undulating. If you will furnish us data of the speed at starting, rate of acceleration, maximum speed, rate of retardation, speed at landing, and a diagram of the path and undulations of the machine, with a mark to indicate the points at which observations of angle were taken, I think it would be possible to compute one of these glides though it might require some time. We have not had the necessary data and so have never tried it. The data of ordinary glides are, in my opinion, almost worthless for purposes of computation unless a possible error of 50 percent, or sometimes more, is no serious objection. The chief value of records of glides is to obtain a standard for comparing the performances of different machines but even in this respect it is far from infallible. Close comparisons are out of the question when the performances under consideration are accomplished under widely differing conditions. I did not feel it advisable to attempt any comparisons in my address at Chicago last month, but merely stated as clearly as possible what our machine had done under the conditions described.
In the Revue article sent us the depth of curvature of our 1902 machine is stated on page 11 to be 1/20. The correct amount is 1/25. And on page 14 it is stated that the tail is operated by "twines leading to the hand of the aviator." Really, this is news to me! Would it not be well to strike out that clause?
Have you noticed the amusing paradox in your table on page 17, which shows that the poorest machines are the best flyers? Compare Langley & Maxim with Tatin, Phillips, & Tatin & Richet.
Octave Chanute to Wilbur Wright, July 17, 1903