Dayton, February 4, 1903
Since I wrote you last Orville and I have done a little experimenting to determine what shapes should be given to uprights, &c., to secure the minimum resistance. The results are not altogether what we expected. The basis of our experiments was a stick 2 ft. long, 7/8 in. wide and 1 1/2 in. deep. We found that rounding off the rear corners increased the resistance nearly 5 percent; while rounding the front corners reduced it to less than one half. Rounding both front and rear brought it down to about one third. A surface like this
rounded in front and tapering toward the rear gave a resistance of nearly one half. The same surface reversed gave a still greater resistance; and with both front and rear sharpened it was greater still. That rounded front edges were superior to sharpened did not surprise me as our experiments on the tangentials of surfaces gave similar results in our last year's experiments. But the effects of rounding and tapering the rear edge gave several surprises and some apparent contradictions. Thus rounding the rear edges of a stick which is left square in front will increase the resistance, while similarly rounding the rear edges of a stick which is already rounded in front will still further reduce the resistance. Why this rounding at the rear should cause an increase in one case and a decrease in the other is the puzzle. I have confirmed the fact by repeated experiments. The result is always the same.
A piece of strap iron 2 ft. by 1 inch gave a resistance of .21 lbs. in a wind blast moving 31 ft. per second. This would give a coefficient of a little less than .003, but if a deduction of 10 percent be made in the anemometer reading as per Prof. Marvin's report, then the coefficient would be about .0035. The coefficient of the stickrounded at front and rear
figures almost exactly .001.
I have not yet written up an account of our last year's gliding experiments, but have promised Mr. Warder that I will have a paper for the Western Society some time in June.
We are just now in the midst of the worst blizzard of recent years. Chicago is cut off from telegraph communication with the rest of the world and wires are down in many parts of the country. We envy you the sunny skies of Italy.
With kind regards to yourself and to the Misses Chanute, I am [&c.]