In the preparation of this Memoir, the writer has deemed it best to generally omit any mention of plans and ideas which were brought forth in the work, unless constructions or tests in accordance with them were carried to a sufficient extent to admit of some definite conclusion regarding them. However, owing to the important part played by the warping of the supporting surfaces, or the variation in the angle of auxiliary surfaces, in the methods of preserving the equilibrium of practically all flying machines of the present day, it may be of interest to here add a short mention of the direction in which plans along this line were originally proposed in this work. Mention has already been made of the importance which Mr. Langley attached to the study of the works of the great master-builder, Nature, though recognizing at the same time that owing both to the difference in the forces and methods of construction possible to man, it was not in general possible for him to produce the best results by attempting to too closely imitate the methods or plans of Nature.
Mr. Langley considered it not practicable or best to attempt to imitate the details of construction of the flying mechanism of birds. At the same time, he strongly believed that much was to be learned from them about the practical side of the art of balancing, and he therefore spent a great deal of time both in analyzing the methods practiced by the birds in preserving their equilibrium and in criticizing his own plans in this direction in the light of what Nature would seem likely to do if she had to construct a flying creature on such a large scale. In carrying on his investigations in the art as practiced by the birds, he made a trip to Jamaica during the early weeks of 1900, in order to study the species of buzzard which are so numerous and tame there and are known locally as the “John Crow.” After his return from this trip he wrote the following very interesting letter to Mr. Robert Ridgway, requesting certain data regarding the American buzzard, which he wished to compare with some data on the “John Crow” which he had obtained on this trip:
MARCH 29, 1900.
DEAR MR. RIDGWAY:
I have just returned from Jamaica, where among other occupations, I have been studying the evolutions of the buzzard locally called the “John Crow,” a soaring bird which is almost as much superior in skill to our buzzard as that is to a barn-yard fowl in its power of keeping itself in the air without flapping its wings, in what is very nearly a calm.
I have observed particularly the following points with the Jamaica specimen (which I can only give, however, approximately), and I should like to have you give corresponding ones for our Washington buzzard if you can oblige me. [p286]
I note here that the measurements were made on a live bird and that it was impracticable to get the separate weight of the wings except by estimate, but the two wings may be estimated collectively as 114 lbs., the whole weight being 234 lbs. to 3 lbs.
Approximate values:
When the bird is soaring in a nearly calm atmosphere, which it inexplicably does,—soaring I mean nearly in line of the observer’s eyes and coming directly to of going directly away from him,—it presents nearly the following appearance:
FIG. 1—Jamaica, Mch. 22, 1900. “John Crow.” Sketch soaring horizontally, by W. H. Holmes. Weight 3 lbs. Total wings area = 546 in. Perpendicular distance c below a b = 3.3 in. =
FIG. 2—Another.
FIGS. 1 and 2.—Type sketches of wings by Holmes from a mean of positions taken from his own sketches and photographs, and also from sketches and photographs by Langley.
FIG. 3.—Type sketch of same birds, average type, position of wings.—S. P. Langley.
FIG. 4.—Average typical position of wings in soaring gull. From memory by S. P. Langley. (The scale here may be taken approximately at 113).
I must preface what follows by a little statement of the things which particularly interest me here and which are not a naturalist’s ordinary concern.
First, I want to know the CG of the bird when in flight. You will understand that though there is but one center of gravity (here symbolized as CG), it may be considered (1) with reference to its position on the horizontal plan of the bird with wings extended, when it will always be found somewhere in the medial vertical plane, passing through the body, and usually nearly at a certain point with reference to length, the position thus considered being called CG, or (2) the position of the same CG with reference to a vertical plane passing transversely through the medial line, the position thus considered being called CG2. In the latter case you will understand that the CG which is that of the whole body, wings and all, will be carried more or less upward when the wings are thrown high up, and will be carried temporarily downward when the wings are at their lowest point of the stroke. It would have a certain position when the bird was at rest and another position when it was soaring and the wings were above the body.
The soaring bird is chiefly held upward by the pressure of the air under each wing, and just as the common center of gravity is a point where all the efforts of gravity are supposed to be centered, so there is a common center of pressure, or one point where all the efforts of the upper pressure of the air may be supposed to be centered, and it will be clear, on very little consideration that this latter point must be always nearly in a vertical line through the CG, and usually above it. Call it CP.
CG1 and CP1 are then, the symbols of CG and CP as referred to the horizontal plane. CG2 and CP2 are the symbols for the corresponding ones when referred to their position in the vertical plane.
I shall be glad to explain to you, if you are not familiar with it, the simple method of finding the CG1 and CG2. It consists in bending the wings into just the position that they would ordinarily occupy above the body in plain soaring flight, keeping them there by a very light bent stick or wire, then hanging the bird up by a line attached to the tip of one wing, and see where this line would pass through the body of the bird, for the CG will be somewhere in this line. After marking then, on the body of the bird its position, hang it up a second time by the head or tail and note again where the new vertical line runs in the new position. There is but one CG and but one point in which two straight lines can cross, and that will be the CG necessarily. Note with all care just where this is above or below the center of the body of the bird.
As for the CP for either wing, that may be nearly found by tracing the wing on a flat piece of thick paper or cardboard strong enough not to bend much—cutting out the tracing and balancing it well on the point of a pencil—the point about which it balances is very near CP2 or the center of pressure in the vertical plane. There is such a point of course in each wing, and when they are thrown up in the actual position that they have in calm soaring flight, we may suppose a horizontal line drawn between them, and it is the distance from this horizontal line to CG2 compared with the area of the wings or with the distance between their extended tips which we want to know, which gives the vertical distance which the CG is below the CP, the thing we want to know.
It will be very convenient also to have a wing dissected from the body and the wing itself held in about the soaring curve by a bit of light stick balanced on a pencil point, which will give the CG of the wing as distinct from that of the body. However, the three things I principally want, beside a sketch or [p288] photograph of the bird from about its own level coming directly toward or going directly away in soaring flight, are these:
Approximate weight of the bird,—and approximate tracing of its extended wing with the area, so that we can tell the area of the supporting surface relative to the weight, and finally, the distance between CP2, and CG2, which is obtainable by the process which I have explained.
I am afraid that what I have just been describing at such length may have a certain obscurity to you, but if you will give me an opportunity, I shall be pleased to illustrate it with the actual experiment when the bird is hung up by a string, and you will see that it is in reality simple.
Referring to the sketches on page 3 of this communication, a and b correspond to the centers of pressure on either wing where the upward pressure of the air distributed over each wing may be supposed to be gathered in a single point. This, as I have said, is called the center of pressure with reference to the vertical flight, and its symbol is CP2, while the horizontal dotted line between them represents the level of CP2, from the best estimate that I could make when the wings are in their natural position of soaring. It is evident that this line passed far above the body of the vulture, and if (the corresponding symbol for the height of the center of gravity being CG2), the CG2, of the entire bird be taken, it will be found to lie nearly in the point c. Where c is in the present case, I could not determine exactly in my hasty examinations in the live bird, but I assume that it is about 12 way between the central horizontal axial line of the bird’s body and the upper portion. I repeat that it is important to me to know what the vertical distance is between CP2 and CG2 in each specimen of soaring bird. I may observe in illustration that in the common sea-gull, it is nearly as shown in the faint sketch; that is to say, that the corresponding line a b in the soaring gull passes distinctly through the upper part of the body, and the distance down to the CG2 of the whole in the gull is almost nil, while in the buzzard it is very considerable as shown by the corresponding distance in the “John Crow.”
Now, what I want to get from you is the corresponding figures for an average specimen of our Washington buzzard. If you will kindly have one killed and weighed while fresh, and before the rigor-mortis has set in, first noting the position of its wings when soaring in a calm, and (if possible) when coming toward you or going away in about a horizontal plane with your eye, in which position the wings will be elevated and bent somewhat as in the case of the above sketch of the “John Crow”; if you will kindly do this, so as to give me corresponding facts with reference to the buzzard, namely weight, area of extended wing surface, distance between tips as bent up in ordinary flight, distance between extended tips, the quantity CP2−CG2, and also will make such a tracing of the buzzard’s wing as Mr. Manly will show you of the “John Crow’s,” I shall be obliged.
My impression is that the buzzard is a considerably heavier bird than the “John Crow,” without, however, very much greater spread of wing. I may observe that when the wings of the Jamaica bird were spread out, they were spread quite to their utmost extent, and the distance between the tips of the terminal feathers was much greater than when in flight. I wish you would kindly also add the scientific name of the “John Crow,” with any particulars that you would think of interest.
If there be any special expenses incurred in the preparation of this memorandum, including the time of a photographer, I will direct them to be paid from the Smithsonian fund. [p289]
If you could get Mr. Holmes (who made most of the sketches and all of the photographs of the “John Crow”), to try and do something like this for your buzzard, especially getting such a photograph of it in flight, as will give the position of its center of gravity relative to the center of pressure on the wings, it would add very greatly to the value of your memoranda, and I think Mr. Holmes takes so full and intelligent an interest in the subject, that he might be pleased to give his help.
Very truly yours,
S. P. LANGLEY,
Secretary.
MR. ROBERT RIDGWAY,
Smithsonian Institution,
In response to this request, Mr. Ridgway submitted the following very interesting information:
PROF. S. P. LANGLEY,
Secretary, Smithsonian Institution.
I have the honor of submitting herewith the data obtained by Mr. Rolla P. Currie concerning measurements, etc., of the common Turkey Buzzard (Cathartes aura) of the United States, as requested by you in your letter of March 29, last.
The difficulties in the way of securing these data, already explained by me in previous communications, are responsible for the delay in submitting them.
Hoping that this material may prove of use to you, I am,
Very respectfully,
R. RIDGWAY,
Curator, Division of Birds.
MEMORANDA IN REGARD TO THE TURKEY BUZZARD (SECOND SPECIMEN)
1. Weight.—1850 grammes.
2. Area of outstretched wings.—641 square inches. (Computed from three sheets of tracings, A1 and A2 comprising the entire area of both wings; B, a single wing.)
Note.—As the bird was in process of moult, one of the large wing quills, as shown by the tracings and compo-board patterns, is but partially developed, thus slightly modifying the results obtained. Its length, if full grown, would be nearly the same as that of the quill just above it.
3. Distance between the tips of these wings.—5 feet, 8.7 inches.
4. Distance between the tips of the same wings when the bird is in horizontal soaring flight.—Estimating the dihedral angle of the wings to be 150°, and elevating the wings so as to make this angle, the distance between their tips [p290] measures 5 feet, 5.7 inches, or 3 inches less than when fully extended in the horizontal plane.
5. The position of the center of pressure of the wing.—This is indicated on two compo-board patterns, C and D. C was made from a fully extended wing, while D was made from the wing in the soaring position. The centers of pressure of the wings are about 2 feet, 0.5 inches apart, or 1 foot, 0.25 inches from the central point of the bird’s body.
6. The position of the center of gravity of the soaring bird.—(Length of buzzard, 26 inches.) The center of gravity of the soaring buzzard in the horizontal plane, CG1, was found to lie 912 inches behind the tip of the beak and 1612 inches in front of the tip of the tail.
The center of gravity of the soaring bird in the vertical plane, CG2, was found to lie 2.8 inches above the ventral point of the body and 1.6 inches below the dorsal point, the depth of the bird’s body at CG1, being 4.4 inches.
In determining the center of gravity, the bird was frozen in the soaring position, its wings making a dihedral angle of 150°. It was then hung up, first horizontally and then vertically, and balanced till the line from which it was suspended coincided with a plumb-line placed in front of it; the measurements were then made.
The bird was afterwards, and while still frozen, hung up in the same way in Mr. Smillie’s photographic room, and exposures made by him in both positions. These photographs, E1 and F1 were enlarged to natural size, and measurements made on the enlargements yielded, as nearly as could be determined, the same results as when taken directly upon the bird.
As determined by measurements upon the buzzard in soaring position, the center of gravity was found to be 2.65 inches below the center of pressure (estimating the center of pressure to be at the bend of the wing); or, employing the compo-board pattern in a corresponding position, the distance was seen to be a small fraction of an inch less.
7. The position of the root of the wing.—This is indicated on the tracing A1.
a. (Depth of the body on a vertical line with root, 3.5 inches.) The root lies 1.6 inches below dorsal line, 1.9 inches above ventral line.
b. (Length of body, 26 inches.) The root lies 7.6 inches behind tip of beak, 18.4 inches in front of tip of tail.
8. The dihedral angle between the wings.—The photographs taken previously were not sufficiently large or distinct to enable us to determine this with exactness. It was estimated, however, as 150°, and experiments were made on this basis.
9. The center of gravity of the dissected wing.—This was found, first, for the wing having all the muscles, up to the ball and socket joint, intact. One of the wings was frozen in the soaring position and its center of gravity found by balancing on a point. Its position was marked by a wire thrust through the wing at this place, and the wing (H) is preserved in formalin. This position is also marked on a special tracing, I. It lies 6 inches from the base of the humerus bone (root of wing). Secondly, it was found for the wing denuded of all muscle. Its position was marked on the other wing of the bird, which is preserved dry, spread in the soaring position. It lies 934 inches from the base of the humerus. [p291]
10. The weight of the dissected wing.—
a. With all muscle up to the ball and socket joint intact, 325 grammes.
b. With all muscle removed, 190 grammes.
Weight of muscle, therefore, 135 grammes.
The position of the root of the tail.—
a. In the horizontal plane, 11.8 inches in front of the tip of the longest tail feather; 14.2 inches behind tip of beak.
b. In the vertical plane: (depth of body from ventral point below root of tail to a point directly above, which is on a level with the highest point of the back, 2.5 inches.) 1.5 inches above ventral point, 1 inch below dorsal point.
Weight of tail.—With muscle, 40 grammes; without muscle, 30 grammes. Weight of muscle, therefore, 10 grammes.
EXHIBITS ACCOMPANYING THESE MEMORANDA
A1 and A2. Two sheets, comprising a tracing of the entire turkey buzzard with fully outstretched wings. From these the area of the wings and the distance between their tips was obtained. The position of the root of the wing and the root of the tail is also marked on one of these sheets.
B. One sheet, comprising a tracing of a single wing, and from which the area was also computed. This area, multiplied by 2, gives the same result as the sum of both wings on A1 and A2. The compo-board pattern C was made from this tracing.
C. Compo-board pattern of fully extended wing, on which the center of pressure is indicated.
D. Compo-board pattern of wing in soaring position, on which the center of pressure is shown. [p292]
E1. Photograph of bird in soaring position, suspended horizontally.
E2. Same, enlarged to natural size.
F1. Photograph of bird in soaring position, suspended vertically.
F2. Same, enlarged to natural size.
G. Tracing of wing in soaring position, from which the compo-board pattern D was made.
H. Wing preserved in formalin, on which the center of gravity is recorded.
I. Tracing of wing H when frozen in soaring position, on which the center of gravity is marked.
J. Wing with muscle removed, on which the center of gravity is shown.
Several persons connected with the Smithsonian Institution and U. S. National Museum have contributed towards securing the results herewith submitted. Among them, I desire especially to mention Mr. W. H. Holmes, Mr. [p293] F. A. Lucas, Mr. N. R. Wood, and Mr. R. L. Reed. Mr. Holmes superintended the experiments in connection with No. 6 (finding the bird’s center of gravity), and by his suggestions and criticisms helped me in many other particulars. The photographs and enlargements were made by Mr. T. W. Smillie.
Respectfully submitted,
ROLLA P. CURRIE,
Aid, Division of Insects, acting in the Division of Birds.
OCTOBER 16, 1900.
The feats of airmanship performed by the “John Crow” seemed to greatly impress Mr. Langley and shortly after this trip he wrote the following letter to the writer:
SMITHSONIAN INSTITUTION
WASHINGTON, D. C., April 16, 1900.
DEAR MR. MANLY:
I am reminded of the consequence that I have, in connection with Mr. Chanute and perhaps Mr. Huffaker, attached in the past to the possibility of directing the bird, and consequently the flying machine, by the mere inflection of the wing, that is, by changing its angle; and you recall to me that Mr. Huffaker at one time proposed to arrange a wing, with some provision of a spring, which should enable it to change its angle automatically. . . . .
I have been noting this ability to guide by the slight inflection of the wing, in my studies of the Jamaica buzzard, and am ready to say that I think, while the quarter-sized working model of the great aerodrome is building, it will be worth while to make some arrangement of the frame or wing-holder which will make it possible to test this idea. I will endeavor to work out something of the kind more in detail myself, but whatever it is, it will apparently involve the ability of the wing to rotate about a line passing nearly through it lengthwise, and an allowance for this; if not in the wing itself, then in the wing-holder; will need to be made while the present model is under construction.
I will request you to especially look out for this, as far as you can on these indications.
Very respectfully yours,
S. P. LANGLEY,
Secretary.
The instructions and suggestions contained in this letter and in many conferences on the subject were never carried out by the writer, on account of the extreme pressure of the work already on him which had for its object, not the production of a flying machine which would embody all of the control which we wished it to have, but which would be burdened only with such devices and arrangements as would enable it to transport a human being, and thus demonstrate the practicability of human flight.
SMITHSONIAN INSTITUTION, WASHINGTON, D. C., November 30, 1895.
DEAR SIR:
The following instructions are to replace those of May 13, 1895:
1. The minimum fraction of its own “flying weight” (that is, weight complete with initial water and fuel), which the aerodrome shall lift on the pendulum, is 50 percent,50 under such engine power as can certainly be gotten up in the field and maintained during forty seconds from the time the aerodrome is let go.
The blast, the pumps, and all other essential parts must, in other words, be in such a condition that steam enough for this lifting over 50 per cent of weight can be gotten up readily and surely in the field and in a time which will still leave at least forty seconds’ supply.
2. The minimum relation of supporting area to weight in any aerodrome constructed hereafter, is to be two feet to the pound,50 and the minimum of power at the rate of one steadily-maintained horse power50 at the brake under ordinary conditions, to not over twenty-two pounds (ten kilos) of flying weight. In absence of a brake determination horse power may be taken—
H. P. =
revs. per min. at rest × pitch × diameter (in ft.) × thrust (in lbs.)33,000.These rules do not apply to No. 5, but they do to No. 6, which is to be built over, if necessary, to meet them.
3. In balancing an aerodrome, unless otherwise instructed, set wings at a root angle of either 10°, 7°, or 5°, after being certain from previous inversion and sanding, that the tip angle in motion will not differ from this root angle as much as 5°.
The object in balancing any aerodrome with a single pair of wings is to be able to bring the c g2 under their c p2 without any reference to the tail, which supports nothing, unless specially ordered. But as this condition cannot now be obtained in Nos. 5 and 6, these at any rate, and perhaps future aerodromes, are to carry a second pair of wings. When this second pair of wings is of nearly equal size with the first it is to be assumed in preliminary adjustments for weight and center of pressure, that the second pair has two-thirds the lifting efficiency per unit area of the first.
Calling the whole distance from the mean center of pressure of the wings to the center of gravity M. M is to have a definite relation to the breadth of [p295] wings from tip to tip (b) and total fore and aft length (1), which is provisionally fixed at M =√(bl)8, and the line of thrust is to be not over one-fourth the way from c p2 to c g2.
Generally speaking the front pair of wings will be fixed in position and the adjustment for balancing made by moving the rear pair.
The individual weights of all parts checked by lump weighing are to be given by the caretaker (Mr. Huffaker), under the general scheme shown in the note. The work on the aerodromes being divided into two classes, viz.: metal work and all which is not metal, the two in charge of this work (Mr. Reed and Mr. Maltby) are severally responsible for knowing the weight in grammes of any of the parts they have put into their work, giving these weights to Mr. Huffaker, together with any data for filling out the annexed tables,51 on his request.
Until further orders, Mr. Huffaker is charged with the responsibility of seeing that these conditions are met before any aerodrome is boxed, and will keep the record of weights of the aerodromes and their principal parts as already completed, in a book, to be preserved in your keeping, which will also be arranged to show with signed photographs and descriptions, and with sketches where needed, the condition and weight (as far as constructed) of every aerodrome, and of any new construction of any part, on the first of each month.
Particular attention is directed to the preceding paragraph, and to the need that evidence of a definite character is to be obtained and preserved of everything already done, and being done.
Without special orders to the contrary, you will not authorize the boxing of any aerodrome which does not, to your knowledge, meet these conditions.
Each aerodrome is to have the following parts in duplicate or in triplicate:
with any other parts in duplicate or triplicate, which experience has shown to be necessary.
Mr. Reed will not box any aerodrome till a certificate from Mr. Huffaker can be put on the inside cover, with the list of contents, showing what the conditions are as to weight, wing area, power, etc., and the person in the field charged with the duty of launching the aerodrome (at present Mr. Reed), is authorized not to let it go unless he is satisfied that it has a full forty seconds’ supply of steam. [p296]
I am satisfied that a great deal of time is lost in putting the aerodrome together for flight, owing to the absence of any preliminary drill in doing this. Before it goes into the field the whole is to be completely boxed, and then taken out from the box and set up on the clutch, and steam gotten up for flight. All this is to be done in the shop before the final boxing, and provision is to be made so that no wiring or adjusting of parts is to be done in the field which can possibly be avoided by forethought in the shop. The tail-piece, for instance, is to be bushed with brass, so that it will always come into the same place, and make a tight fit, in spite of wetting or shrinking, in the steel tube, where it is to go into a guide-way with a bayonet spring, or a like contrivance for setting it at once securely into position.
The mean positions of the wings and tail are to be laid out in some way permanently on the mid-rod, but every guy-rod or adjustable piece is to be arranged so as to fit at once securely and permanently in its position without wiring or like slow process.
Very truly yours,
S. P. LANGLEY,
Secretary.
W. C. WINLOCK, Esq.,
Assistant in Charge,
Smithsonian Institution.
A copy to be communicated to:——