Dayton, December 1, 1900
We have your letter of Nov. 29th with pages of manuscript enclosed. We see nothing in it requiring correction, but would suggest that you use names instead of initials in your reference to ourselves, and that our business be omitted unless you are following the names of other experimenters with a similar reference. We merely offer this as a suggestion.
In your letter you give the following figures:
|For man||1||sq. ft. instead of||5||sq. ft. in my double-decker|
|For framing||2.25||sq. ft. instead of||4.02||sq. ft. in my double-decker|
|Making||3.25||sq. ft. total||9.02||sq. ft. in my double-decker|
|___2||lbs. per sq. ft.||___2||lbs. per sq. ft.|
There is a small error in this. The resistance of our machine without load was 6.5 lbs. The body of the operator is extra. Our figures would be as follows:
|For man||1/2||sq. ft.||5||sq. ft.|
|For machine||3 1/4||sq. ft.||4.02||sq. ft.|
|Total resistance||3.75||X 2 = 7.5 lbs. instead of||18.04||as figured for yours|
But our machine had an area of 165 sq. ft. wing surface as compared with 134 sq. ft. in your machine. Allowing for difference in size of machines, the drift of our machine as we measured it, is about >i of the drift of your machine as calculated by yourself. Do you think it probable that you overestimated the resistance of your machine and operator, and underestimated the drift of surfaces in your calculations of power consumed in gliding? We have never made a direct measurement of the resistance of a man's body in the upright position, but calculations based on bicycle riding show that in a semi-upright position the net resistance is equal to but little over one square foot although his cross-section is nearly or quite three sq. ft. in racing position. This gives a coefficient of l<. It would seem probable that even in the upright position the coefficient would not exceed 1/2; or, 2 1/2 sq. ft. net area, instead of 5 sq. ft. If this should really be the case it would seem probable that the Lilienthal tables of proportion of drift to lift are not correct for large surfaces, or that you underestimated the speed of the relative wind. Have you ever attempted a direct measurement of the resistance of your machines unloaded?
In our experiments we found that loading the machine increased the horizontal pull more than the tables led us to expect. We attributed this to the facts that our wings were not varnished to render them airtight, and that our curvature was only one in 22 instead of one in twelve. We could not get our angle down to three degrees with less than 30 miles wind. When carrying a man the pull decreased as the wind increased between twenty and thirty miles.
Chanute's response, December 2, 1900