Note 7 — Chapter I · INTRODUCTORY

Communication to the French Academy. Extract from the Comptes Rendus of the Sessions of the Academy of Sciences, Vol. 122, Session of May 26, 1896.

(Translation.)

A Description of Mechanical Flight. By S. P. Langley.

In a communication which I addressed to the Academy in July, 1891, I remarked that the results of experimental investigation had shown the possibility of constructing machines which could give such a horizontal velocity to bodies resembling in shape inclined planes, and more than a thousand times heavier than air, that these could be sustained on this element.

While I have elsewhere remarked that surfaces other than planes might give better results, and that absolutely horizontal flight, which is so desirable in theory, is hardly realizable in practice, so far as I know there has never been constructed, up to the present time, any heavy aerodrome, or so-called flying-machine, which can keep itself freely in the air by its own force more than a few seconds, the difficulties encountered in absolutely free flight being, for many reasons, immeasurably greater than those experienced when the flight is controlled by the body’s pressing upward against a horizontal track, or whirling-arm. No one is unaware that many experimenters have been engaged in trying to execute free mechanical flight, and although the demonstration which I furnished in 1891 [“Experiments in Aerodynamics,” 1891] of its theoretical possibility with means then at our disposition, seemed conclusive, so long a time has elapsed without practical results, that it might be doubted whether these theoretical conditions are to be realized. I have thought it well, then, to occupy myself with the construction of an aerodrome with which I might put my previous conclusions to the test of experiment.

The Academy will, perhaps, find it interesting to read the narrative given here by an eye-witness, who is well known to it. I am led to present it not only by the request with which he honors me, but by the apprehension that my administrative duties may put a stop to these researches, so that it seems to me advisable to announce the degree in which I have already succeeded, although this success be not as complete as I should like to make it.

The experiments took place on a bay of the Potomac River, some distance below Washington. The aerodrome was built chiefly of steel, though lighter material entered into the construction, so that its density as a whole was a little below unity. No gas whatever entered into the construction of the machine, and the absolute weight, independent of fuel and water, was about 11 kilos (24 pounds). The width of the supporting surfaces was about 4 metres (13 feet), and the power was furnished by an extremely light engine of approximately one horse-power. There was no one to direct it on board, and the means for keeping it automatically in horizontal flight were not complete. It is important to remark that the small dimensions of the machine did not allow it to include any apparatus for condensing the steam, so that it could only carry water enough for a very brief course—a drawback which would not be encountered in one of a larger construction.

It is also to be noted that the speed estimated by Mr. Bell was that obtained in a continuous ascending flight, and much less than would have been attained in a horizontal course.

On Mechanical Flight. Letter of Mr. Alexander Graham Bell to Mr. Langley.

Washington, May 6, 1896.

I am quite aware that you are not desirous of publication until you have attained more complete success in obtaining horizontal flight under an automatic direction, but it seems that what I have been privileged to see to-day marks such a great progress on everything ever before done in this way, that the news of it should be made public, and I am happy to give my own testimony on the results of two trials which I have witnessed to-day by your invitation, hoping that you will kindly consent to making it known.

For the first trial, the apparatus, chiefly constructed of steel and driven by a steam engine, was launched from a boat at a height of about 20 feet from the water. Under the impulse of its engines alone, it advanced against the wind and while drifting little, and slowly ascending with a remarkably uniform motion, it described curves of about 100 metres in diameter; till at a height in the air which I estimate at about 25 metres (82 feet), the revolutions of the screws ceased for want of steam, as I understood, and the apparatus descended gently and sank into the water, which it reached in a minute and a half from the start. It was not damaged, and was immediately ready for another flight.

In the second trial it repeated in nearly every respect the action of the first, and with an identical result. It rose smoothly in great curves until it approached a prominent wooded promontory, which it crossed at a height of 8 to 10 metres above the tops of the highest trees, upon the exhaustion of the steam descending slowly into the bay, where it settled in a minute and thirty-one seconds from the start. You have an instantaneous photograph of it, which I took just after the launch. [See plates 20, 21, and 22 of present work.]

From the extent of the curves which it described, which I estimated with other persons, from measurements which I took, and from the number of revolutions of the propellers, as recorded by the automatic counter which I consulted, I estimate the absolute length of each course to be over half an English mile, or, more exactly a little over 900 metres (2953 feet).

The duration of flight during the second trial was one minute and thirty-one seconds, and the average velocity between twenty and twenty-five miles an hour, or, let us say 10 metres a second, in a course which was constantly ascending. I was extremely impressed by the easy regular course of each trial, and by the fact that the apparatus descended each time with such smoothness and gentleness as to render any jar or danger out of the question.

It seemed to me that no one could have witnessed these experiments without being convinced that the possibility of mechanical flight had been demonstrated.