Dayton, August 31, 1903
Your letter of 27th is at hand. The supporting area of our machine at 18 miles an hour is probably a very little over 305 sq. ft. As the speed increases the front rudder becomes more and more a supporting surface, till at 30 miles it is lifting about twice as much per sq. ft. as the main surfaces its angle of incidence being four or five degrees while that of the main surfaces is only about 1 degree. The supporting area is therefore equivalent to about 335 sq. ft. I have never figured the matter very closely, but in the table I sent you I made a little allowance for the front rudder at the smaller angles, that is, I allowed a little more lift than the angles of incidence named would show in the tables. I figured the column of " % of normal" on the basis of .8 lb. per sq. ft. for all, and made the allowance in the angles. The table1 was based on a rough average of #9, #12, & #35 in figuring the support. The tangentials were estimated from the principles shown by comparisons of various curvatures & thicknesses. We never tested a surface exactly corresponding to those used in our 1902 machine, and consequently are compelled to make various allowances in our estimates.
We received our copies of the address and were much pleased with them. So far we have sent copies only to a few persons with whom we have had correspondence, such as Profs. Ferguson, Zahm, & Langley.
We have been very busy with our preparations, and also with some outside matters which have consumed much time. We are hoping to get away within the next three weeks. The extra power we carry, as compared with our original estimates, has made it advisable to rebuild some parts, such as axles for the screws, &c. The total weight will probably reach 675 lbs.
1 These comparisons were made from an undated table which appears in four of the early notebooks. The table is given in note to Wilbur Wright to Octave Chanute, Jan. 10, 1902.