Octave Chanute was born in Paris, France, in February 1832, and died in Chicago, USA, Nov. 1910. Louis-Pierre Mouillard was born in Lyon, France, September 1834, and died in Cairo, Egypt, on 20 September 1897.
Cairo, Egypt, April 16, 1890
Louis-Pierre Mouillard to Octave Chanute
I thank you for your kindness in sending me your pamphlet on Air Resistance of Oblique Surfaces.
I have read it in L'Aeronaute, but I am going to read it once more with much attention and extreme pleasure.
I must confess that I have the deplorable habit of paying little attention to writings pertaining to pure mathematics, because of the difficulty I have understanding them. There is also my intellectual laziness which makes me go over most of these writings too lightly.
I have to admit that this is wrong. The best proof of it is your treatise, because in reading it I came across two items which interest me very much.
One is the reference to the narrow wing of speedy soaring birds. Then there is the plain truth, which you present mathematically at the end of your note in reference to the dirigible balloon, a truth which cannot be shouted loud enough, because the balloon is the enemy of the airplane.
It is the balloon that impedes the development of this difficult problem, which soon will need all support instead of obstacles. This means, Sir, that I am a partisan of the purest of aviation. I do not know whether you are acquainted with the fact that I took the liberty to write a book on this problems Empire de l'Air, published by G. Masson in 1881. At present I am preparing a continuation of this work which will be titled: Le Vol Sans Battement [Flight without Flapping Wing] and which will appear within a year or two.
I refer to the final part of your treatise which provided the stimulus of the present letter.
Sir, I cannot advise or criticize by means of mathematics, as this would be too difficult for me; but approaching the problem in another direction I could perhaps be of some assistance to you by means of observation, a field in which I am entirely at home.
In case some theoretical problems are confronting you in your experiments I would like to put my professors at your disposal. They are neighbors of mine, two vultures, which are brilliant demonstrators.
15 May 1890
Octave Chanute to Louis-Pierre Mouillard
I derived great pleasure from your letter, for I have the greatest estimation of your investigations and your book. I procured several copies of the latter at the time of my visit in France.
Not only have I found much confirmation of the theory which I had outlined, but also many facts which were new and interesting to me, and I am impatiently awaiting the publication of the new book you informed me about.
Science rests on observation and the principal advantage of theory is to give us general laws to coordinate and to verify the observations. I therefore consider your investigations to be of the greatest value, but it is possible that the mathematicians may be helpful to you by confirming or affirming the conclusions you arrive at by instinct.
For instance, I believe I am able to tell you, why you are absolutely correct when you say on page 272 (L'Empire de l'Air) that an airplane with cutouts operates almost as well as one without, for if I have reason to believe that the stream lines are deflected by the bottom surface, non-compressed air cones A A are formed which close these openings. In the sketch below.
I have the angles between them greatly exaggerated; they are about 10° for a speed of 10 meters per second.
On the other hand, I believe that you have found out long ago that the characteristics which you state on page 210 should be modified as follows: "If a body moves, its center of pressure is displaced and is transferred toward the front in the direction of the movement".
It is this continual displacement of the center of pressure, in proportion to the change of the angle of the wind which, to my mind, makes the longitudinal stability so difficult, so that almost the instinct of a bird is needed to maintain balance constantly. I would like to know whether your two vultures have imparted some knowledge to you on this subject.
I also would like to know whether you have made observations on the resistance of the fore part and the rear part of large soaring birds of which you speak on page 46. These observations would be very important, and if I should happen to be somewhere where soaring birds have their habitats I shall make these observations myself.
Do you read English? I take a chance in mailing you a booklet by Lancaster who spent five years in Florida to study large soaring birds. You will find some surprising remarks in this book, but it is not necessary to depend on his theory as to cause and effects, because he is entirely mistaken.
I should be pleased to receive another letter from you and to be of service to you if this is possible.
Cairo, 14 June 1890
Louis-Pierre Mouillard to Octave Chanute
I thank you very much for your kind letter and hasten to answer your questions.
It is a good thing that those who try to solve this irritating problem communicate with one another. There should be a fellowship comprising many individuals to overcome any kind of difficulty before it causes any damage. What someone knows, someone else does not know. This caused me to say in my second book that the greatest danger to aviation is the spirit of mystery in which those who take up the study of aeronautics generally cloak themselves.
How could you, by simple reasoning, arrive at the theory of the compressed air cones? This proves again that everybody acts according to his talents, and I have no talent for pure mathematics. I found the confirmation about slotted planes by means of plain and simple observation. I watched birds whose wings lacked some feathers and this lack had little effect on their flight motion. The next stop was to repeat this experiment with a paper airplane model. I did, and kept on doing it until it became quite absurd. The result led me straight to the consideration of superimposed planes.
Let us now discuss the law of attraction which I have promulgated and which, I must admit, has brought me considerable criticism.
First of all, Sir, I ought to tell you that I do not adhere absolutely to this mode of a statement; this puts us at ease in discussing it.
The first thought that comes to mind is certainly that of the displacement of the center of pressure and not that of the displacement of the center of gravity. That is the way I thought when I saw birds which were thrown out of balance; they changed their configuration and regained their equilibrium by means of their speed. In this case at the first view there is no possible error. It is very probable that a displacement of pressure takes place and that the body of the bird is moved by the action of this pressure to a point other than the center of the figure. I then reconsidered the law you refer to. However, several years before my book was printed, I had time to observe and to study the action of this displacement of the center of pressure on other objects besides birds.
I observed in succession: the moving steam ship whose fore part rises, the locomotive which at full speed seemed as if it wanted to take off from the tracks, so light became the front part. I asked myself whether the action of the air was sufficient to create such an unbalance on a mass so dense. Doubt impressed itself firmly in my mind. In order to clarify this perplexing case I tried to think of a way to eliminate the action of the air current, and I succeeded in the following manner. I simply took small scales which had no external beam such as are used in every shop. The mechanism is enclosed in a box and consequently beyond the action of the air current.
By imparting to these scales a motion in the direction of the longitudinal axis of their beams, the center of gravity if it is in question, will be put in arrear of the direction of the motion; the lever arm of the front platform becomes therefore longer, as the pivots have been fictitiously drawn back, and under these new equilibrium conditions the front platform should move downward, as was actually the case as soon as a motion was imparted to the scales. We have now before us a case which is explicable by a law such as promulgated and all one has to do is to substitute the word "pressure" for the word "gravity".
By pursuing this study further I find myself face to face with experiments which indicate also that the action of the center of pressure is very strong, so that now I begin to think that the two expressions are correct, because I have convinced myself that both actions exist.
In what proportion do they act? I do not know. Unknown roads are hard to travel. It would be necessary to devote to their study more time than I have left. In short, what I intended to describe is an unbalance in relation to the speed of the body, and since such a law is promulgated it permits an explanation of the motions of the bird airplane. That is all I have been looking for.
As to the air resistance of the front part and the rear part of a bird, I have considered it for quite a long time and observed not only winged creatures but also swimming creatures. This forms the subject of two long chapters of the book which I am writing, but owing to lack of space I am able to give you only the conclusion. Here it is: "In a creature perfectly endowed by nature to fly or to swim, drag may be disregarded."
You ask me, Sir, when my book will be published. I cannot tell you. First of all, I need some pocket money which I am lacking; then, and this is important, to be able to make an effort of self denial, upon which I have not yet decided. In this book I am telling everything I know not only about aviation but on other problems. For instance I speak about three balloons which would certainly bring fortunes if they were in other hands than mine. I come to the kites and discover there some curious machines. In these two chapters I tackle the problem profile of fast ships and all this always by the same procedure: observation. Yet, I confess, the profile of ships is one of my old hobbies. But if I had found this out twenty years earlier, I would have brought navigation twenty or more years ahead of time.
In short, I lay myself completely bare, and despite of being a good giver, I cannot decide to give this. Perhaps later, when I am absolutely convinced of my ineptitude to deduce even a little profit out of an idea, I shall bring myself to do it, but this time has not yet come.
In the meantime, Sir, if some points which I may know should be of interest to you, I shall be glad to be always at your service.
Chicago, 22 October 1890
Octave Chanute to Louis-Pierre Mouillard
The great frankness and the gloomy abnegation which your letter of June 14 expressed, touched me deeply and created my urgent wish to be of assistance to you if possible.
You are perfectly right, indeed, if you do not wish to lay all your cards on the table as long as long as there is some hope of success. Although you justly blame the spirit of mystery, there are many things which one cannot lay bare to everybody.
I asked myself very seriously whether it is the element of success you are lacking and whether the theory could not point to a solution. In order to go deeper into this matter I have read your book again very carefully and it seems to me that what you are lacking in attaining your goal to rise in the air when there is a strong wind, is the longitudinal equilibrium and the certainty that your machine does not turn a somersault under any condition.
It is rather easy to get the transverse equilibrium; either by the application of the V shape which increases resistance, or by giving the machine a vertical keel or by applying both suggestions. However it is much harder to get longitudinal equilibrium without an increase of resistance. But none of the solutions offered are in my opinion satisfactory for a machine larger than a bird.
The shape of the bird and the necessity to fold its wings give it an unstable equilibrium and for these reasons the bird became an acrobat. I believe, as far as I am concerned, that it is true I should not even dream of imitating the bird, but I also believe that it is possible to apply the same principles in a different manner, and that perhaps the theory will indicate the means with which to obtain a stable equilibrium.
Before I approached this problem to make it applicable to your purpose I had hardly devoted myself to it. Up to now I studied the laws of flight rather than thinking of a design, and if I make one, it will be a machine powered by an engine, to be flown fast in any kind of weather.
In reference to your case, I had to make some experiments which explains why I did not answer your letter sooner. I believe I have found something useful which I think to be new. I am sending it to you under two conditions which I kindly ask you to accept mentally before reading the enclosed sheet (No. 3 & 4).
1. The idea is for you only. If it is successful I want you to say afterward that you received it from me.
2. If afterward a patent for its application should be taken out, the European patents are for you and the American patents are mine for the entire machine.
This is to show how I was guided by reasoning, based on the idea that the streamlines separate in front of the lower plane:
A B is the section of the plane and ABDE is the air prismoid which rests on a thin plane. If the plane takes the position AC, the prismoid having the same separation of the sides, is now indicated by ACFG. It is evident that there will be a relatively large preponderance of molecules on the front of the plane and that the center of pressure moves forward.
According to the ratio in which the angle of incidence becomes more pointed the center of pressure moves forward. The arm of the lever increases toward the front edge and the equilibrium is disturbed.
The question now is to limit as much as possible any movement of the center of pressure, yet without decreasing the lifting surface. A bird is able to act against the motion of pressure simply by varying its center of gravity. But take a large machine which has a wing 5 meter wide. The center of pressure may vary by 11/2 meters between 45° and 1° of inclination but there is no chance to vary the center of gravity quickly enough over this distance.
In order to resolve such a difficulty on a machine it will be sufficient to cut the plane or the wing into narrow strips and place them one behind the other at such a distance that the pressure prismoids which rest on the strips do not interfere with one another. Next, to suspend the weight of the body as low as it reasonably can be done. The centers of pressure are easily displaced across the strips at the same distance according to the width of the latter. But this distance is small, if the wing of 5 meters is cut into 10 strips, the displacement of the center of pressure will only be 0.15 m instead of 1.5 m. This leads to the idea of superimposed planes, but it will be well to guard against any overconfidence. For the machine no longer would be a parachute if the planes were concealed behind one another and so to prevent the creation of vertical prismoids during the descent.
Take your piece of cardboard of page 210, cut it in four or eight strips and paste them behind one another on one or several keels in such a way as to leave a slight space between these strips. Then make a very slight "correction fold" of about 3° to 5° toward the rear and drop the carton by the edge as before. You will note that, instead of making a turning motion, it will straighten out and drop vertically, without fail.
I believe this is the principle of the longitudinal equilibrium for a machine. For very good reasons the bird does not need it, but it makes the "correction fold" by means of its tail, and changes its center of gravity. As to the practical application, I have several ideas about it, but I do not wish to send them to you until I know whether I have guessed correctly what you are looking for and what your designs are for a machine. Please answer me soon.
Cairo, 20 November 1890
Louis-Pierre Mouillard to Octave Chanute
Thanks for your kind letter and for the sympathy expressed therein.
Thanks also for the idea which you intend to send me.
Today I am forced to make a confession which becomes very painful to write down, but there is no use to conceal it; It is disgraceful, but here it is: I did not understand!
I am so impervious to any mathematical statement that it does not surprise me; but what will somebody else think of it; it seems strange, I admit. I am one of those who solve a problem, even a difficult one, very easily in their own way, but who are unable to understand a statement of it, if this statement assumes the aspect of a formula. That's how matters stand and I have not succeeded in reforming myself. I have picked up your letter ten times, trying each time, with an enormous effort, to comprehend it. I could not understand that letter if you would kill me, those prismoids keep on dancing in my head, I am getting dizzy. And yet I have spent my life studying them, but always in my own way.
I never was able to make an algebraic division, a fact which instilled a holy terror into me against algebra. This fact stands out vividly in my books to the great dismay of those who understand that there is still something in my brains.
While I am in a confessing mood, I may as well go the whole way. I never use formulas for simple cube calculations; also to determine the volume of a sphere I do not use (4 * PI * r3)/3.
No! This frightens me. I am afraid that I may make a mistake. I prefer each time to say to myself: A sphere may be considered to consist of a series of cones, the surface of a circle as a multitude of triangles, etc. This is always the very same thing but without a formula.
In spite of all this, I calculate very easily and correctly. Very often it happens that I arrive at my results so quickly as to enable me to check whether the others have made a mistake in their calculations. Physics I know fairly well, am rather skilled in chemistry and not bad in the sciences ending with "gy". I even have been a surveyor, always using my own methods which are of mystifying accuracy. In short, alas! I am as usual different than anybody else. My family claims that I acquired this trait from my foster mother who was a she-goat. There certainly seems to be some truth to it, because if I look back to other phases of my life I notice that I am always off the beaten path.
This is my great misfortune, I know it. But is it possible to reform without becoming a nonentity? I do not believe it.
However, if you would explain to me by word of mouth what I could not understand even by reading your letter ten times, I am convinced that I probably would grasp it in five minutes.
Your good letter contains also one other point which I could not understand and which surprised me very much. You say that the longitudinal equilibrium which I have expounded is very hard to achieve and requires an amount of energy much larger than the human body is able to furnish.
The vertical equilibriums obtained by the airplane (fig. 30) is a simplified copy of that of the bird; that is the method it uses. Experiments with well-designed machines, especially when they attain a largeness, give surprising results. I have tried it with an airplane which had a span of five meters and during the second test I obtained this perfect equilibrium. There is nothing more steady and more regular than the motion of translation. The airplane was thrown from the top of a quarry, a height of 70 meters, and it landed about 300 steps away in absolute still air.
I can no more go back to that quarry, because it is too far for me. However there will be a chance some day. They propose to build a railroad in order to establish a sanitarium on top of the mountain. Thanks to this railroad I hope to renew the experiment next summer and to use an airplane which has a surface of about 20 square meters and which has been built some years ago. This machine is designed to carry a man, but due to my inability to move I have never tried it.
The experiment will therefore be extremely momentous. I shall write you the results of it as soon as I have done it. I refer to figure 30.
I am going to put progressively (!) sand bags in the machine in the place where the aviator is supposed to be, and some young men whose lives have been poisoned by my book are going to launch the machine. I am going to provide its front part with cane to ward off shocks, and hope that it will perform well.
It seems to me that you gained this impression because you had little occasion to observe very large birds. The minute you will be able to study the great vultures or the condors you will change your mind. The sight of a vulture makes it perfectly easy to believe that vertical control is a difficult feat, but seeing a large vulture take off or in flight or alighting, simplifies this question completely. By seeing its slow and simple maneuvers one understands that the average human energy is perfectly capable to reproduce them.
As to the problem of horizontal control I have not been explicit enough in my book.
As you have been so kind to favor me with an idea, which alas! I could not digest, I, on my part am going to augment this point which is entirely incomplete.
This control as explained in my book is taken directly from nature, but these control actuations are slow. The fast ones are produced in a different way. I assert that when a bird is going to make a turn to one side, it deflects the wing of this side and the small wing always points toward the center. This is a fact, but entirely insufficient.
Here is the complement of this maneuver: The sixth and the seventh feathers of the "hand" of a bird (see figure 12) where they are easily visible are, what I call, annular feathers. They have the largest surface of all the feathers of the entire wing. When the bird is about to turn, it cuts the air with these feathers. The wing tip twists ... That warped part of the airplane does not glide any more as compared to the corresponding part of the other. These feathers obstruct the motion, they stop it, forming a long lever on this point. This causes a variation of motion and a rapid change of direction.
I have reproduced this effect several times, using various means, always with success. This is the fast action of horizontal control. The shifting of the mass to one side and the decrease of the surface on the same side are not to be compared as an action of direction with the rough means of direction control.
The first ones are applied in soaring flight when a circle is about to be flown, and the latter in free navigation.
Here you have then the picture of a bird at its two aspects of useful motions which we wish to reproduce. The other faculties of the bird, which enable it to fold its wings etc. are of no interest to us. With these two modes of control we will be able to reproduce cross-country flight at an average time: That is all I want to reproduce.
Actually I am going deeper into this matter to consider construction details. At the same time I have put aside the airplane type represented in figure 30 in order to construct a simpler and more perfect one. Then I am going to resume work on the engine-powered airplane fig. 31 by simplifying it considerably. That is the one I call the "machine for those who are impotent" that means me. With this I want to say that I am trying to get around the difficulties which a personal airplane presents, and besides to have the experience of getting a ride in the air.
As you see, dear sir, despite my discouragement, despite the gloom to which I am resigned and to which I seem to be condemned, I do not let loose of the problem. I am holding on to it cold bloodedly and have my reasons for doing so. How would it be possible to forget such a problem, especially when the soaring birds are always performing in front of one's eyes.
What I need to succeed is a little comfort, a little freedom of action. I am frustrated too much by the necessities of life, to be able to act with success, and not means enough to evolve an idea with a chance to succeed. I discover that in my files some designs are getting mouldy which, in more active hands than mine, would be quickly executed and made profitable. First of all, those pertaining to aviation which I am giving to the whole world. My life has been such a disillusioned one that not only do I not believe in anything but I do much thinking and little acting: This is my shortcoming. I should have two masters, one for thinking and the other one for action and to get the better of the thinker.
In 1881, I surely thought that the time of my freedom of action had come. While I was publishing my book in Paris, I tackled another problem just as important as that of aviation. It had to do with changing extant conditions in the French Navy from top to bottom. I had been received several times by Gambetta in a way which looked very promising. This great man showed great interest in my ideas. Unfortunately all my hopes collapsed with the death of this brilliant man. Today I am in touch with Admiral Aube, former Minister of the Navy, the man who said that the day of floating "cathedrals" has passed, and that it is necessary to apply new ideas. Who knows whether he will got back into power?
This blow drove me back into my hole in Cairo which I shall never leave again. And yet this idea is so new, as up-to-date as it was twenty years ago when I evolved it.
Last summer I had the pleasure of receiving a call of one of your acquaintances, the Russian engineer Drzewiecki. He told me about you and about the exposition in Chicago where he said he went. According to what he had to say you gentlemen of the United States are doing well. You want to do everything in great style and beautiful. He spoke to me about a flying machine which he intends to build. During his entire conversation he watched the small vultures and the crows nearby. Unfortunately M. Drzewiecki was out of luck, during his two weeks' stay I could not show him a single large vulture. This was too bad as I might have been able to convert him to flight without flapping wings.
However this extraordinary exposition and the daring people who arranged it keep running in my head. I wonder whether there would not be any possibility to exhibit in your country some new ideas and get something out of it. As far as France is concerned I have given it up because they are all wet hens.
Would you be kind enough to tell me whether among the following ideas would be some which could be utilized profitably. I selected those which may have some connection with an exhibition:
In case something among these ideas looks usable to you, please let me know whether you want to take it up with me and under what conditions. My share would be the idea. I do not need to tell you that I am not a capitalist. I have proclaimed it from the housetops and everybody knows it. I would not dare to offer my active participation due to my poor health. Chicago is too far away, above all from New York. If this trip could be made by ship it would be all right but a thirty hour ride on the railroad seems rather somewhat too long for my constitution.
After reading this long letter you must think me to be very verbose, very bold, and very inquisitive. Please excuse me and blame it on the charming kindness which radiates from your kind letter. So if I have been too long winded, it could not be helped.
30 December 1890
Octave Chanute to Louis-Pierre Mouillard
I received your kind letter and I must admit it is I who was mistaken. As you have guessed correctly I never have observed any large bird. We do not have them here. But according to what you said of their maneuvers to maintain their equilibrium and the precautions you point out on pages 256 and 257 "In order not to be in distress every minute and obliged to put the machine in V", I thought that it was the longitudinal equilibrium which made you hesitate, and that I might render you a real service by sending you a solution.
I am certain that you grasped that solution since the time you wrote me. It is so simple to divide the wing surface into a series of narrow strips which are placed behind one another with a very small space between each of them. Enclosed you find a pasteboard which explains the whole matter. When you drop it sideways it will start to rotate and when you drop it tail first it will fall straight downward.
I ask you to keep this experiment a secret. Since I am in the mood of confessing I must tell you also that I did not understand at all the figure . . . . . . . I therefore ask again whether this is a machine as seen from the top or from the side . . . . . I would be very pleased to get some information on this subject, as I am ashamed of not having understood everything you said.
Neither did I understand Fig. 31. However as a compensation I want to tell you that two American inventors made the announcement that they have designed very light engines. One, Mr. Maxim, says that his engine (internal combustion) weighs 2.72 kilograms per H.P., and the other Mr. Pennington has a gas engine which weighs 1.18 kilograms per H.P. I am sending you a newspaper article which gives a sketch of the latter. I believe that three quarters of these claims may be discounted. Yet even if it weighs 5 kilograms per H.P. your motorized airplane is very close to being realized. I have been promised some more details on this matter shortly.
Therefore please let me know whether you have obtained an equilibrium which is stable and automatic in every direction, as your letter seems to indicate, and (if this is not a secret) its principle. Yet I want you to feel certain that I do not want to pry into your invention. I have some means and would like to see my name be associated with the conquest of the "empire of the air," but I do not want to expose myself of being accused to have appropriated the ideas of somebody else. This is the reason why I have been hesitating to decide what I could do with the various devices you proposed for our World's Fair. Almost all of them are what we here call "inventions on paper" which means inventions which are not yet perfected. This type of idea is not only hard to sell but very easy to steal. However I am willing to consider some of them under the following conditions:
Following are the ideas which in my opinion are easiest to make use of at our Fair:
4. Alpine balloon for an exposition
6. Dirigible balloon without propulsion device
7. Mineral sorting device using very little water
8. Dew condenser - a complement to the preceding device
It may be perfectly possible that with more explicit information I could raise some money for the other ideas especially if they are in such a stage that they may be patented. It seems to me that you could patent and sell the following in Europe:
1. Constant propeller of higher efficiency
3. Look-out post for the Navy
9. Balloon valve
10. Torpedoes for the Navy
I believe that you would get less for them in America, because less attention is paid in this country to matters pertaining to war.
You may be interested to learn that you have converted Mr. Drzewiecki to flight without flapping wings. He wrote me from St. Petersburg that he has just put the finishing touches on a book which deals with this subject. He is going to go to Paris where he wants to build an engineless airplane.
Mr. Langley the Secretary of our "Smithsonian Institution" or Museum of Arts and Sciences asked me to tell you that he has read your book with great interest. He says that he shares your ideas and that he would be glad to be of assistance to you.
31 December 90
P.S. Rereading my letter I notice that I have not thanked you for the explanation you gave me on the way in which a bird attains an abrupt change of horizontal control. I want to make good for this oversight by thanking you very sincerely for this interesting observation which should be of real importance when air navigation becomes a fact.
I notice also that I told you to protect you so that your ideas may not be appropriated either by me or by somebody else. I advised you to have them patented before divulging them to me, but I have not provided for the money you would have to spend to do so. I therefore am sending you 500 Francs which you may either use for this purpose or else to have copies made of the papers and the explanations you want to send me.
There is a passage in your letter of June 14th which I have not quite understood, probably due to my lack of perfection of the French language. You said: "Dans L'Etre parfaitement doue pour le vol, ou la nage, le trainement peut etre neglige." By using the word "trainement" do you want to say friction or else total resistance? In the latter case we are directly pushed back to the dirigible balloon which however is not commended by you.
I am also very anxious to know what you have actually found out about tailless kites. So far I am acquainted with the Japanese kite or rather the Chinese kites, the military kite
And the Bazin kite
They all are based on the same principle and I wonder whether you have discovered a better form.
On to 1891