Dayton, July 22, 1903
Your letters of 17th and 20th have been received. The table sent you last week is calculated for the surfaces, trussing, &c., used in our 1902 machine and includes the operator's body. It was figured on the basis of .8 lbs. per sq. ft. of surface. The front rudder in gliding carries a share of the load. Absolute accuracy is not claimed, but I think 10% will cover the errors, probably, except where numbers are small.
The following glide made Oct. 20th, 1902, was put down in our diary because the start, flight, and landing seemed to be at equal speeds, and we considered it a fair test of the machine under the conditions set forth.
Distance, 335 ft.; time, 16 1/2 seconds; wind, 6 1/4 meters (indicated); angle of descent, 7 5'.
You say in one letter that we put the speed required for support at 18 miles while the glides you took data of show speeds greater than this. You have probably forgotten the two glides of Oct. 9th numbered 24 & 25. In the table you sent me some time ago the wind speed is given as 56 meters in 10 seconds. It should be 56 meters in 20 seconds. The wind was too light for starting with comfort so no further attempts were made. These show speeds of about 18 miles and angles of descent of about 7 . In skimming along the ground at speeds much above 30 miles the front rudder framing was nearer the ground than the rear edge of the surfaces. As we were able to obtain speeds of more than 30 miles on hills of 10 or less our resistance could not have been greater than the table I sent you shows. Have you ever attempted to compute the performance of our machine at 18, 20, 22, 24, 26, & 30 miles according to your system of apportioning the resistances?
You say that you do not believe that computations of ordinary glides will lead to errors of 50 percent. In your letter of July 12 you make some computation of glide #10, Oct. 8th, 1902, and compute a negative tangential of about 25 lbs. Now I feel certain that it can be demonstrated that the tangential in that glide averaged + 12 lbs. or more, instead of 25 lbs. I am really a little rusty at figuring percents of error in such a case but, at a guess, say we put it at 100,000 percent at any rate it is rather more than 50 percent.
The values of drift, tangential, &c., given in degrees in the table sent you last week can be converted into lbs. by the formula (weight X sin. of angle). I prefer to think in degrees rather than pounds and thus avoid the constant necessity of considering the weight in lbs. to obtain the ratio to the resistances.
The curious swelling of the loss from superposing between 0 and 8 has a counterpart in our tables of surfaces. Compare #22, #23, & #24 (tangentials). It seems to fit the requirements laid down from our observations of our 1902 machine better than anything else.
I note that you say that you gave us a record of your 1896 glides some years ago. I have some recollection of having asked you at Kitty Hawk several years ago to give us a complete record of a day's gliding, but I do not now remember ever having had it, and we are unable to find it among our papers now. Would it be presuming on your good nature too much to ask for another copy? The data alone, without the computations, would be sufficient if you are busy.
The inaccuracies in the Revue des Sciences article in reference to our machine, to which I called your attention in a former letter, seemed to Orville and myself too serious to be allowed to appear in print. Other little errors such as the statement on page 11 that we tested "41" surfaces; (same page) that the surfaces are "straight from tip to tip" (page 12) that the wire was "piano wire" (p. 14, second par.) "that the rudder is turned to that side," &c., were not deemed of sufficient importance to really demand correction. But the statement in regard to the "twines" leading to the "hands" is more serious, and we hope will be omitted.
Prof. Langley seems to be having rather more than his fair share of trouble just now with pestiferous reporters and windstorms. But as the mosquitoes are reported to be very bad along the banks where the reporters are encamped he has some consolation. It would be interesting to attempt a computation of the possible performance of his machine in advance of its trial, but the data of the machine as given in the newspapers are so evidently erroneous that it seems hopeless to attempt it. It is a sure thing that the speed will not be from 60 to 90 miles an hour with an expenditure of 25 horsepower as the papers have reported its prospective flight. I presume that you are to be one of the guests of honor at the launching festivities. Our invitation has not yet arrived.
Octave Chanute to Wilbur Wright,
July 23, 1903