Chicago, July 20, 1903
Answering your letter of 14th, I beg to say:
1st I do not know whether any of the records of Lilienthal's glides have been preserved, but I gathered the impression in Berlin that they had been destroyed after his death.
2d I gave you some years ago a record of our 1896 glides, with the speed of the wind added, but they are imperfect in there being no observation of the angle of the machine above or below the horizon, and so can only be very roughly calculated.
3d I fully agree that in order to compute a glide accurately the speed, angles, course, and wind should be uniform. You may remember that we proposed to measure those data, but did not.
4th Not having the speed at starting, rate of acceleration, maximum speed, rate of retardation, speed at landing, and path of undulations, you did very wisely in computing the average performance of your machine by angles as given, but I think this method leaves something to be desired, and may lead you astray when you come to drive your machine at higher speeds. I desire to compute the lift, drift, tangential, and head resistance in pounds, and do not agree that the computation of an ordinary glide will lead to errors of 50 percent. I believe that when there is no great variation in wind speed the other elements (retardation, acceleration, &c.) will equalize themselves, and that the foot pounds due to the descent will be pretty well accounted for. Perhaps as closely as in the table you have sent me.
I notice in the latter that, with 305 square feet of surface, the lift varies from 238 to 244 lbs., while the weight was from 251 1/2 to 260 pounds; that the percent of normal and the tangential do not coincide with those of any one of your surfaces; and that the loss due to superposing (which ought by rights to be included in the coefficients for surfaces) varies in an unaccountable manner, being smallest at 1 and at 8 , and greater at intermediate angles and at less speed than the maximum.
I shall be glad to have your views, and one computation of a glide which you think to conform with the requirements you lay down.
Wilbur Wright to Octave Chanute, July 22, 1903