Dayton, November 16, 1900
In October my brother and myself spent a vacation of several weeks at Kitty Hawk, North Carolina, experimenting with a soaring machine. We located on the bar which separates Albemarle Sound from the ocean. South of Kitty Hawk the bar is absolutely bare of vegetation and flat as a floor, from sound to ocean, for a distance of nearly five miles, except a sand hill one hundred and five ft. high which rises almost in its center. The main slope of the hill is to the northeast, which is facing the prevailing winds. The slope is one in six (9° 28'). To the north, northeast, east, and southeast there is nothing but flat plain and ocean for a thousand miles nearly. It is an ideal place for gliding experiments except for its inaccessibility. The person who goes there must take everything he will possibly need, for he cannot depend on getting any needed article from the outside world in less than three weeks.
The machine we used was a double-decker with surfaces 17 ft. by 5 ft. A space eighteen inches wide was cut out of the lower surface, so the net surface was about one hundred and sixty-five feet, and the weight with operator was 190 lbs. The ribs were of ash bent to this shape. The depth of curve was two and one half inches, or about one in twenty-three. The main cross- pieces were of white pine. The forward pieces were triangular in cross section and located at the extreme front. The rear pieces were square and located about a foot from the rear edge. An extra piece of cloth ran up over it to lessen resistance. The covering of the machine was French sateen, and it was put on bias so that no wire stays were needed to brace the surfaces diagonally. All the ribs were enclosed thus The uprights were jointed to the surfaces with flexible hinges and the whole machine trussed the long way, that is laterally, but not in the fore-and-aft direction We used fifteen-gauge spring steel wire. By tightening the wire a every other wire was tightened. The surfaces were thus left capable of torsion, and this was the method we used to maintain lateral equilibrium. We laid down flat on the lower surface and maintained fore-and-aft balance by means of a forward rudder. We used no rear rudder; and neither horizontal nor vertical tails. At first the machine was curved laterally to obtain the effect of dihedral angles, but we found the effect very unsatisfactory in gusty winds. Control was much easier after we made it straight. We began experiments by testing the machine as a kite, and found that a wind of twenty-five miles would more than support it with operator on it. Our final estimate of its soaring speed was twenty-two miles. We soon found that our arrangements for working the front rudder and twisting the planes were such that it was very difficult to operate them simultaneously. As we had neither the material nor the tools to change these so as to correct the trouble we were compelled to test them separately. Two minutes' trial was sufficient to prove the efficiency of twisting the planes to obtain lateral balance. We also found our system of fore-and-aft balancing quite effective but it was only when we came to gliding that we became positive of this.
We spent quite a large portion of our time in testing the lift and drift of the machine in winds of different velocities, and with various loads. I will not go into this matter deeply just now but will say that in a wind blowing twenty miles per hour the drift of the machine when loaded to bring its weight up to fifty pounds was eight pounds. With the same wind blowing up a hill having a rise of one in twelve the drift was only three or four pounds and on a still steeper hill but with a lighter wind the drift became a negative quantity and the machine both rose and made its way against the wind till it lost its balance. The resistance of the framing is certainly much less than Mr. Herring estimates in his article in the '97 Annual, for our machine is 25% larger than his, yet the drift due to a lift of fifty lbs. added to the drift of the framing is less than his estimate of framing drift alone. Our experiments also indicate that with the operator lying down, the resistance is less than one tenth of the estimate of Mr. Herring for the upright position. On the other hand we found the drift of the surfaces under full load was greater than the Lilienthal tables would indicate, but it may be that this is due to the fact that our curve was only one in twenty-three instead of one in twelve. The fact that our cloth was not varnished may also partly account for it.
After we found the difficulty of simultaneously maintaining both fore-and-aft and lateral balance we almost gave up the idea of attempting to glide, but just before returning we went down to the big hill which was about three miles from our camp and spent a day in gliding. Our plan of operation was for the aeronaut to lie down on the lower plane while two assistants grasped the ends of the machine and ran forward till the machine was supported on the air. The fore-and-aft equilibrium was in entire control of the rider, but the assistants ran beside the machine and pressed down the end which attempted to rise. We soon found that the machine could soar on a less angle than one in six and that if the machine was kept close to the slope (which was one in six by measurement) the speed rapidly increased till the runners could no longer keep up. The man on the machine then brought the machine slowly to the ground, so slowly in fact that the marks of the machine could be seen for twenty or thirty feet back from the point where it finally stopped. We had intended to have the operator turn his body to an upright position before landing but a few preliminary tests having shown that it was feasible to let the machine settle down upon its lower surface with the operator maintaining his recumbent position, we used this method of landing entirely. And although in appearance it was a dangerous practice we found it perfectly safe and comfortable except for the flying sand, and the machine was not once injured although we sometimes landed at a rate of very nearly thirty miles per hour. The operators did not receive a single bruise. With the conditions which obtain at Kitty Hawk there is no need at all of using the upright position. The distance glided was between three and four hundred feet at an angle of one in six and the speed at landing was more than double that of starting.
The wind was blowing about twelve miles. We found no difficulty in maintaining fore-and-aft balance. The ease with which it was accomplished was a matter of great astonishment to us. It was so different from what the writings of other experimenters led us to expect. This may have been partly due to the steadiness of the wind, partly to the fixed position of the operator, and partly to a fortunate combination of circumstances of which we were not aware, but it is our hope that it was due to a new method of grouping our surfaces and to the particularly efficient rudder which we used. I will write to you later in regard to these. Our rudder had an area of twelve square feet, and it was our sole means of guiding and balancing longitudinally. We never found it necessary to shift the body.
Kitty Hawk is a splendid place to observe soaring flight. I think at least a hundred buzzards, eagles, ospreys, and hawks made their home within a half mile of our camp. We were enabled to make a number of observations and settle conclusively to our minds some points which have been much disputed among writers on the soaring problem.
Octave Chanute to Wilbur Wright