US 1470017 A
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V. LOUGHEED WING FOR FLYING MACHINES Filed Feb. 1919 2 Sheets-Shae; l
V. LOUGHEED WING FOR FLYING MACHINES Filed Feb. 4. 1919 2 Sheets-Sheet 2 y 453mm Patented Oct, 9, i923.
trait-ran stares hlmfil? FATENT QFE EQEO VICTOR LOUGHEED, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR T0 ALFRED J. OLEARY, OF SAN FRANCISCO, CALIFORNIA.
WING FOR FLYING MACHINES.
Application filed February 4, 1919. Serial No. 274,965.
To all 10 ham it may concern:
Be it known that I, VICTOR LOUGHEED, a citizen of the United States, residing at city and county of San Francisco, State of California, have discovered certain new and useful Improvements in lVings for Flying Machines; and I do hereby declare the following to be a full, clear, and exact description of the same.
My invention relates to a wholly-new class of sustaining surface for artificial flightone which (with the exception hereinafter noted) has not heretofore been recognized to exist; one which presents only remote and casual analogies to, and which therefore is not in any sense to be confounded with, established types of aeroplanes and aerocurves, the operation of which is based upon the long-recognized but radically-different principles, which concern the movement through an elastic fluid of an inclined plane. My device, on the contrary, finds its essential prototypes, in both form and functioning, in the wings of gliding and soaring birds, the functioning of which never heretofore has been soundly formulated, the performance of which is based upon profoundly-unique principles, and even the actual forms of which, during flight, had not been accurately or exactly determined, prior to my researches.
I recognize, however, that in the history of the prior art and in present engineering practice, flight of a sort has been often attempted and is now accomplished, with sustaining surfaces the details of which may be loosely construed to resemble those that are the subject of this specification, and of the claims hereof, and which, accordingly, upon superficial consideration might be regarded as differing therefrom in degree rather than in hind-but this specification is intended to explain, and the claims hereof are intended to define, the fact that my device is definitely new and without anticipation (except as hereinafter noted), in theessential details of its design as well as in the fundamental ones of its functioning.
The objects of my invention are tenfold- First, to reduce the total of the power necessary for flight (whether this be applied through propelling means actuated by a motor, or derived from the downward pull of gravity acting on the machine, or secured from the available energy that exists in fluctuating or rising currents of air), by substantially eliminating the application of power from the sustension of the machine, restricting it, instead, to the propulsion of the machine on one level, or to the lifting of the machine to a higher level;
Second, to increase the radius of flight with a given load and without descent, by the reduction in fuel load and the economy in fuel consumption, which are involved in the accomplishment of flight with a minimum of power;
Third, to reduce the size of the machine for a given capacity, by increasing the allowable loading per unit of area, through the introduction of a type of wing section with which high loading is not incompatible with high efficiency, nor with other advantageous effects;
Fourth, to add strength while at the same time eliminating the complication of resistance-creating struts and stays, extraneous to the wing structure, by providing in their place suflicient thickness, throughout the more heavily loaded portions of the wing, to accommodate adequately-strong and sufficiently-light internal bracing elements;
Fifth, to improve the inherent stability of the machine, by the use of a wing section in which the center of pressure does not shift away from the center of loading, except possibly to a relatively slight extent, and then in that direction which tends to recover the balance of the machine instead of to upset it further as in the case of all established present practice;
Sixth, to increase the maximum altitude of flight, by providing a structure which functions in rarefied air as well as in normal air, with the utmost of loading in combination with the utmost of power economy;
Seventh, to facilitate speed control or variability, by the use of a type of sustaining surface which, under the impulse of increased energy applied to its propulsion, tends to progress faster rather than to lift more;
Eighth, to simplify and chea-pen the sustaining structure, by favoring such selection and disposition of materials as tend largely to eliminate the usual thin, uncertain, and flimsy wooden members, for which in my wing it ispracticable to substitute deeply-webbed stamped metal members, without involving weight that is excessive per unit of area, in relation to the load carried per unit of area;
Ninth, to lengthen the useful life and facilitate the profitable'repair of the wing structure, by constructing it initially of materials that are strong and permanent, and by allowing the incorporation in its design of main and subsidiary elements which can be readily separated and replaced;
Tenth, to accelerate manufacturing processes, by the employment of details of design and structure which most advantageously involve only the use of elements that can be cheaply and quickly made, with a minimum of hand labor, from common materials and with ordinary facilities, to sufficient accuracy and in great quantities.
To explain clearly how my invention op-- erates and what it involves, so that any person skilled in the art or science to which it appertains can understand, make, and use the same, it is essential first to provide herein, for purposes of comparison, a statement of the manner in which present aeroplanes accomplish flight, defining the data and principles where-from they are designed, as attested by the entire standard and established literature, and the present recognized and universal engineering practice of, this art.
Every aeroplane, from the thin flat surfaces that formed the subject of so many early experiments. down to present successful aeroplanes which are not flat, and which in some cases are moderately thick, is an inclined planein the common understanding of this term-which, when placed at an angle of incidence with the line of relative air movement, and in this position propelled through the air by any suitable means, then compresses air beneath it and rarefies air above it, so that a sustaining effect, termed the lift, is secured at the cost of a related resistance, termed the drift, against which a continuously-applied propelling effort must be exerted to maintain the sustention. It is of incidental importance here to mention that, in the total resistance opposed to propulsion by the conventional aeroplane, there are two other componentshead resistance and skin friction. incidental, respectively, to the necessity for forcing through the air the volumes of the machine structure. and for sliding against the air the. areas of the machine surfaces. But these resistances are apart and distinct from the resistance component that has for its warrant the securing of the lift.
In this method of accomplishing flight, it is now known that both head resistance and skin friction can be reduced to very small magnitudes, by making the plane relatively thin, by the use of bodies, struts, stays, and other members designed in suitable streamline forms (whereby the air reacting on the rear thereof may largely return the energy initially expended by the front there of in compressing it out of the way), and by the use of surfaces of suitable smoothness or other quality to minimize the friction of the air thereon. These components, which constitute the direct resistance to propulsion, may be thus made to absorb only a very small proportion of the total power used, so that a very large proportion of the total power used, therefore, is expended against the indirect resistance to propulsion by which the machine is sustained.
l'n consequence, the modern aeroplane is exceedingly ineflicient, and prodigiously wasteful of energy, as is further established by the fact that it is the present standard of military-aeroplane practice to sustain no more than twelve or fifteen pounds per horsepower--whereas a twelve-pound eagle, to turn to natural flight for an example, has an absolute maximum of not over one twenty-fifth part of a horsepower available, and is unquestionably able to fly by the utilization of only a small fraction of this maximum, probably with as little as the two hundred and fiftieth part of a horsepower. and possibly no more than the twelve hundredth part! These figures are derived from well-known researches made bv Lilienthal, (lhanute, Marey, Langley, lvlontgomcry, and other famous investigators. and have been confirmed in experiments made by me.
The inferences from so extraordinary an economy of energy are such as inevitably to present the entire problem of artificial flight in a whollynew aspect. Concerning natural flight. they lead directly to two most important conclusions-the first, that it is a very-easy rather than ,a very-severe tax u on the birds strength to supply the trifl ng amount of energy required to maintain flight. and. the second. that it is quite practicable in many atmospheric conditions that commonly obtain, to secure from rising and fluctuating currents of air, or from the wei ht of the device. descending at an exceedino'ly flat angle under the influence of gravity, the small amount of power necessarv to continue the operation of a properlydesigned flight mechanism.
The reason for the extreme inefficiency of an inclined plane as compared with a wing. lies in the fact that the air it compresses and rarefies, in the course of securing sustention therefrom. and in the compression and rarefaction of which so much energy is employed. and in the momentarily-abnormal pressure of which, therefore, the energyexpended i temporarily-existent and potentially-available, is permitted to recover its normal volume, at such a distance from, or in such relations to, the inclined plane, that the energy it yields up in recovering its normal volume does not produce any useful effect, since it is not returned to the machine, and therefore can be of no help in reducing the power demanded to propel and sustain it.
To avoid various shortcomings of and objections to the inclined plane, therefore, my invention consists in the use, for a sustaining surface, of a wing, into the design, construction, and operation of which certain new and useful principles are incorporated, which I will now describe.
Referring to the accompanying drawings, in which similar letters designate similar parts, throughout the several views, and amongst which there are necessarily included several views which are illustrative of principles involved, rather than of the actual invention, Figure 1 is a plan or outline view of a wing. Fig. 2 is a cross section on the line A A of Fig. 1. Fig. 3 is a cross section on the line B B of Fig. 1. Figs. l, 5, 6, 7, and 8 are explanatory drawings, not necessarily illustrating actual mechanisms, but introduced to explain principles involved in the variations in thickness of my wing section. Figs 9 and 10 are explanatory drawings, not necessarily illustrating actual mechanisms, but introduced to explain principles involved in the variations in curvature of my wing section.
Concerning Fig. 1, it is to be explained that although this represents one of the outlines to which I prefer to design a Wing, many possible deviations from this outline may be made without seriously conflicting with the advantages I gain from the peculiar cross sections, the forms and the functions of which are essential features of my invention.
Considering Fig. 2, the basic feature of this cross section is its division into two primary elements CDD and DD-E. These are each divided into two secondary elements, C-DD into C-aa and aaDD, and DDE into DD-bb and bb-E. Though these elements serve special and peculiar aerodynamic functions, in correct combination and interrelationship with one another, they may. nevertheless, have their proportions modified within certain limits, and, in the cases of Caa, and bb-E, they may be even suppressed to extinction in the visible structure of the wing, without wholly nullifying the advantages I gain from the complete ensemble. The actual presence of all of them, however. in the visible structure, is necessary to ideal functioning.
Because this section is neither thin nor symmetrical (its longitudinal axis being sinusoidal), its action upon an air mass through which it is moved can be most conveniently analyzed and explained by division into two groups of efiectsa first, due
to variations in thickness, and a second, due to deviations from symmetry.
Accordingly, to explain first the effects due to the variations in thickness, Fig. 4 is presented as an equivalent of Fig. 2, except that it is symmetrical with respect to the longitudinal axis, represented by a dotted line in these two illustrations, which are substantially identical except for the straightening out, so to speak, of Fig. l, which therefore eliminates the effects due to the sinusoidal curvature of Fig. 2. In Fig. 4, the purpose of the forward portion Caa is to penetrate or part the air mass, through which the wing moves, to a degree of separation sufficient to allow the wing to pass.
It is necessary to digress here, to explain that, although a pair of concave curves, as shown, is the ideal entering outline for such a penetration form, to produce with a minimum energv expenditure the acceleration to either side of the obstructing air molecules, yet, if such an entering portion be partially or wholly lacking in the actual and visible device, its place will be taken and its function assumed by relatively-inert air, which will pack up against the front of the device and constitute a sort of continuouslyrenewed, invisible extension of the visible structure, which will automatically assume a correct form, and so serve the purpose, of an element which through ignorance or intent may be omitted from the design and construction of the actual device. This is sufficiently shown, for the present purpose, in Figs. 5 and 6, in the first of which the whole, and in the second of which a large portion, of the element C-aa is lacking in the actual structure, shown by the white outline, the banked-up air being indicated by the shaded areas f.
By the movement of Caa, in the direction of. the large arrow J in Fig. 4, and in Figs. 2, 3, 5, 6, 7, and S, the air that it displaces is compressed against the adjacent atmospheric masses, which because of their inertia and indefinite extent do not have time to move away and make room for it. This compression of displaced and adjacent air is propagated through the air in the form of a compression wave, like a sound wave, and, like a sound wave, at the end of the period it possesses, by virtue of-its initial duration and amplitude, it reacts. Moreover, the air having constituted the resistance to the movement of C-aa, in yielding to the power that propels this must absorb the energy of the propulsion, so that it is in this rapidly-dissipating dynamic compression of the air wave that the energy expended momentarily resides. Furthermore, action and reaction being equal and opposite, it follows that, if there were no losses in the operation, the initial reaction of the air wave would return the full measure of energy put into it. Actually, of course, there must be some loss, but the possible efliciency of such a reaction may be at least surmised from some of the well-known facts concerning the closelysimilar waves by which sounds are propagated. A tiny insect hanging on a leaf, for example, a cicada, by thrumming on his wee thoracic drum, so small as to be almost invisible, easily achieves the feat of lifting many millions of tons of air a million times a minute-a performance so amazing that, despite the small magnitude of the movement involved, it could not be accomplished with less than thousands of horsepower, were there only action and no reaction, were the air merely moved and left moved, instead of moved and let move back.
It is the function then of aa DD,Fig. 4, and in Figs. 2, 3, 5, 6, 7, and 8, to receive and utilize the reaction of the air wave produced by Caa, in the same illustrations. To this end, for best results, its length must bear a suitable relation to the period of the air wave, as affected by the length of Caai, and its taper should begin gradually, to conform to the gradual reversal of the air movement, and should thereafter rapidly increase in abruptness, as the reacting wave gains velocity, until there is reached the final phase, of the wave dying out, correspondence with which in the structure is provided by the final reversal and suppression of the taper aaDD, as it blends into DD-bb. The effect of thus having the air, compressed by C-a-a, react against (ra -DD, as indicated by the small arrows 0? cl. Figs. 2 and 4:, is to extrude aaDD from between the impinging air masses with a force theoretically equal and acting in the opposite direction to that originally absorbed in the propulsion of C-aa, but practically minus, of course, whatever loss the device involves from the impossible perfect efficiency of theory.
It here requires to be explained that the angle of taper to which aaDD is designed in any case, always must be sufficiently abrupt, or obtuse, to fall within the friction angle, of the air upon such material and quality of surface as may be used. A com mon cause of oor results, in designing socalled streamline struts and bodies, particularly the latter, is to confer upon them so gradual a taper that the friction wholly or partially balances the lateral pressure. A wedge driven into a block of wood, if of a too obtuse angle, will be forced out by the springing together of the wood upon it. If finely tapered, it will hold as positively as though its sides wer parallel.
The function of DD-Jibis thus made plain. It is to extend the length of the section, and therefore the area of the surface, to a degree that would not be attainable were the taper uniform from (66 to 66, or E. For example, in Fig. 7, which represents the body outline of a well-known aeroplane, and in Fig. 8, which reproduces the cross section of one of the most successful aeroplane sustaining surfaces, the tapers shown by the solid lines are too gradual to afford the desirable extrusion effect which, as has been explained, has so vital a bearing upon the energy problem in flight. Commencing, however, as a basis for design, with the major diameter act, Fig. 7, and the maximum thickness cm, Fig. 8, in conjunction with the required lengths (I -E, in both figures, it is evident that uniform or substantially uniform taper must inevitably result in toogradual a taper. The recourse obvious from the foregoing explanation, is to make the taper non-uniform, in which case it may be as shown by the outer pair of dotted lines 99, Fig. 7, and by the upper dotted and lower solid lines g'g, Fig. 8, or as shown by the inner pair of dotted lines hh, Fig. 7, and by the upper solid and lower dotted lines hh, Fig. 8. Of these two alternatives, the objection to continuing the major diameter or maximum thickness nearly to the rear, and there terminating it with an abrupt taper, is that the taper thus secured, even though abrupt enough, is too: far from the points of initial air compression to realize any material ain from the subsequent reaction. So the sc ieme of tapering off from the maximum dimension immediately as well as abruptly, as at Mt, Figs. 7 and 8, and so extending the structure with a portion relatively thin, is the sound engineering solution of what has long proved a baffling problem.
T o reiterate, then, the function of the portion DDZ)Z), Figs. 2, 3, 4, 5, and 6, and ML, Figs. 7 and 8, is to extend the surface of the wing without forfeiting the reaction upon aaDD, Figs. 2, 3, 4, 5, and 6, which is so necessary to balance the energy account initially set up by Uaa, and without which balance progress through the air can be had only with a highly-objectionable even if not a positivelyprohibitive resistance. The fact that the rear of aa-DD does not terminate in a point, and that, therefore, the surface at DD is not infinitely-thin, is an immaterial feature, because reaction of the air wave clear to the longitudinal axis, as represented by the dotted line, would correspond to the previously-mentioned one hundred per cent recovery of the energy input, which, of course, is not realizable in an actual mechanism.
In Fig. 4, the element lib-E is not differentiated from DDZ b. The reason for it will now be explained, in further consideration of Fig. 2.
Returning now to Fig. 2, the first effect of bending or curving the symmetrical structure of Fig. 4 into the unsymmetrical structure of Fig. 2, is to destroy the equality of the reactions on the two sides, so that the sum of the effects on the lower, or concave side, is materially greater than the sum of the effects on the upper, or convex side.
It is evident that an infinitely-thin flat surface could pass edgewise through the air with no edge resistance, and that a very thin flat surface may similarly pass through the air with very little resistance, but an infinitely-thin surface is only a theoretical conception, while an insufficientlythick surface encounters the practical objection that it is not easy to make such a surface adequately stronga problem in aeroplane design which is so ditficult to solve by any quality or disposition of material placed within the plane itself, that it is commonly met by the use of plural superimposed surfaces, connected by a maze of struts and stays, wholly external to the sustaining surfaces proper. It has been shown herein, however, that the provision in a sustaining surface of sufficient thickness to afford considerable strength is not incompatible with low resistance to propulsion, provided the exceedingly-important principle of recovering energy, in the place of that of minimizing its expenditure, be adopted. In an aeroplane wing constructed and designed as herein described, with a stream line front edge, with sustaining areas inclined at a negative angle to the line of travel in the forward portion of the wing and sufficiently near said front edge to receive the effective reaction of the air wave generated thereby, and with other surfaces inclined at a positive an gle to the line of travel but near the rear portion thereof and of course tending to retard progress of the wing, it will be found that the ratio between such negatively inclined propelling areas and positively inclined retarding areas will be of an order which, in combination with the pressures acting against the respective surfaces will give a lift-drift ratio of the total wing not poorer than 50 to 1.
A somewhat similar, exceedingly-important, and heretofore wholly-unrecognized (except as hereinafter noted) principle applies with equal force to the problem of economizing the energy used for sustention, as will next be disclosed.
First, though, so great is the present confusion on this subject, and so far are the laws of efficient flight from being understood, it is desirable to point out that the mere sustention of a weight, at any given height, without any further lifting. is not a proposition for which any scientific theory demands an expenditure of energy. A weight on a pedestal, or suspended by a cord, is permanently in equilibrium. And, to prove that air. lighter than the weight, may take the place of the pedestal or cord, it is sufficient to point out that a weight upon a piston, which is sustained by air in a vertical cylinder, is also in permanent equilibrium, and may be slid or rotated upon the surface of the air with no energy expenditure except to overcome its friction upon the air, and against the walls of the cylinder, its sup port at the given level being a phenomenon wholly apart from any matter of power input.
This static condition, of support upon confined air, by the use of a piston and cylinder, is by the use of a wing capable of extension to a dynamic condition, in which, without any expenditure of energy except to overcome a minute departure from theoretically-perfect efficiency, a weight is supported upon unconfined air. Indeed, to refer back to the matter of the masses of air moved by an insect producing a sound wave, it is in a remarkably-related manner that the wing of a bird, perhaps not by moving millions of tons of air in a millionth of a sec- 0nd, but certainly by moving not less than many thousands of pounds of air a minute, derives from this reacting air mass propulsion of his body volumes through it, and sustention of his weight within it, with a marvelous economy of energy.
To return again from the general to the particular, the type of wing section illustrated in Fig. 2 is the means of accomplishing the equivalent of the bird result. To explain the reasons for the peculiar curvature, it has first to be understood that air meeting the front edge of the wing has impressed upon it a rising trend, due to the tendency of the burdened air beneath the surface to spread against the surrounding atmosphere in advance of the surface, as well as in other directions, so that it naturally seeks to force its way up past the forward edge of the wing. The downwardly-inclined front edge of the wing therefore enters air which, relatively considered, is in motion parallel to the inclination of the wing edge, so that it encounters it normally to the angle of its inclination.
The air which meets the wing is thus divided into two portions, that which is passed under by the wing and that which is passed over by the wing.
To consider first the air that the wing passes under, this, not being banked up against a zone of compressed air, such as prevails beneath the wing because of the load borne by the wing, has a lower initial pressure than that f the air beneath the wing. It does have impressed upon it, however. the degree of compression due to the inclination of the top surface C-a to the longitudinal axis Cc, this compression reaching its maximum at a, above the surface. From this point, because of the reversal in curvature, back nearly to the axis at D, the air reacts, so that the work done upon it by C a e, of the wing section, is returned to a e D, if these triangular areas be regarded for the moment as work diagrams.
Beneath the wing there occurs a similar action and reaction, the air compressed from C to a returning by its reaction the substantial equivalent of the work of compression, against a-D, the triangular areas 0 a e and a e D bearing the same relationships to each other as prevail in the similar case above the wing. There are the differences, however, that the air beneath the wing, during both the compression and the consequent reaction, is above atmospheric pressure to a degree perceptibly higher than the increases above atmospheric pressure which prevail in the air above the wing; and that, because of the negative angle to the line of wing movement, the air pressures above the front of the wing oppose its forward movement, while the air pressures beneath the front of the wing conduce tn the forward movement.
It is here pertinent to emphasize the fact that the quantitative values of the pressures involved in these operations, with even the heaviest-laden bird wings, are exceedingly small, reaching maxima of about atmosl phere, or about ounce, per square inch.
3 Curves plotted from bird wing sizes and loadings, however, indicate. that there is a law. governing increase of loading with increase of size, wherefrom a wing may be expected to carry at least three pounds per square foot per linear foot of chord. In this connection, it is well to note that the common fashion of expressing these pressures, in the English system of weights and measures, in pounds per square foot instead of per square inch, seems to induce in many careless minds a sort of psychological tendency to overestimate their magnitude.
Returning again to the air the wing passes under, between D and Z) the reaction continues until the pressure falls practically to atmospheric, or probably even slightly below this in the neighborhood of b, at which point the compression wave again reverses its movement, from Z) to E, as in accordance with well-known laws it tends to die away in a succession of diminishing oscillations, in the absence of any force to renew the impulse.
It is to be noted that, to the extent that the pressure upon the top of the wing surface is above atmospheric, between D and Z), this pressure must act to impel the wing in the normal direction of its travel, and that, to the extent that the pressure may be below atmospheric between Z) and E, this must also contribute to the forward movement.
Instead of being permitted t die out, as in the case of the air wave above the wing,
the compression wave which reacts between a-D, under the wing, has impressed upon it a renewed impulse as the surface DZ comes into play. This new impulse slightly increases the pressure at first, but, inasmuch as the curve of Db falls short of conforming to the curve of acceleration of the rebounding air, which comes nearer to taking the course represented by the dotted line 2', Fig. 2, there results finally a relatively-low pressure, possibly below atmospheric, in the neighborhood of Z). Below Z), however, reversal again takes place, so that somewhere before E the pressure on the underside of the wing is again positiveabove atmosphere.
It is evident, of course, that positive pressure acting against the more forward area of that portion of the wing under side between D and b can exert little propelling or retarding effect, whereas any negative pressure just in advance of Z), or any positive pressure between E and 5, must in both cases contribute to the propelling forces.
As nearly as it has been possible to determine, in experiments I have conducted, the sum of the retarding pressures on the top of the wing between C and D, and possibly at some point between Z) and E, plus the retarding pressure on the underside between D and b, and of any vacuum that may exist above the surface just in advance of 5, or beneath the surface just to the rear of Z), is such as to exceed in only the very slightest degree the sum of the propelling pressures on the top of the surface between D and b, and under the surface between C and D, and Z) and E, plus such vacuum as may exist between Z) and E above the surface, or just in advance of Z) beneath the surface, so that in so far as propulsion is concerned the system is very nearly in balance, and requires only the very smallest amount of energy to move it in the direction of the large arrow J, Fig. 2.
Contrary to the condition with respect to propulsion, in so far as the condition of sustention is concerned, the system is not in balance, the magnitude of the effects that tend to lift the surface up being greater than the magnitude of the effects that tend to draw it down, so that the imposition of weight upon the wing is necessary to establish it in balance upon a horizontal course, and to prevent it from climbing when the requisite small amount of energy is applied to effect its forward movement at a suitable speed.
Even at very high speeds the amount of energy thus necessary for propulsion is very small, in proportion to the load carried, because of the various balancing and compen sating reactions which have been shown to be involved, so that in flight the loaded wing slides along upon a level of air much as though it were moving through a vacuum, upon a frictionless level surface.
It is a fact that the portion of the wing surface between Z) and E might be built rigid, to a given curvature, but it is difficult to secure sufficient stiffness in combination with proper thinness, except with undesirably heavy materials, in addition to which it is aerodynamically advantageous to have this rear portion of the wing flexible and elastic, because in this case the curvature undergoes a certain amount of automatic adjustment to meet variations in flying conditions, due to upward and downward steering movements and to changes in speed. This portion of the wing, moreover, may be much curtailed, or even suppressed altogether, without wholly losing the valuable effects secured by the other features of my invention, so that though its incorporation is highlydesirable it is not absolutely-essential.
It remains to be explained that the cross section illustrated in Fig. 2 is not suitable for the portions of a wing near the tip, be-
I cause here the free escape of the air around the tip relieves the tendency to build up a pressure beneath. and so suppresses the rising current in front, which furnishes the reason for the downturned front edge. Consequently, it is desirable not alone to flatten, shorten, and thin out the wing sections towards the wing tip, but also to raise the front edge to an increasing degree as the tip is approached. As the extreme tip is approac ed, the thickness and curvature both substantially disappear, leaving only the increased inclination as adefinite feature.
Concerning the exact proportions of the different elements involved in my wing design, these are subject to a certain amount of modification to conform to changes in wing size and speed, and are susceptible of additional modification without seriously impairing their functioning, so the actual proportions most desirable are best determined by trial and experiment in each given case-at least until more data has accumulated on wing design than exists at present.
In further explanation of the principles involved in the action of my wing section, should the preceding description seem in any respects inadequate, its ope-ration may be likened to that of the system illustrated in Fig. 9. This is schematic, however, not actual, being intended to indicate the application of a principle rat-her than the construction of a device.
Referring to Fig. 9, F-G is an inclined plane, moving horizontally in the direction of the arrow J. It is sustained upon the rollers j, each of which is to be regarded as possessing a definite mass, and all of which are normally supported at the level K K, by the springs 70, which rest upon the surface P P. The strength of the springs 1;, however, is such that they can permanently support only the weight of the rollers, so that were F G to cease its lateral progress it would sink down to P P, just as a skater will, if he stop, break through thin ice which will support him if he keep moving. But, when maintained in movement against the resistance L, the inertia of the rollers added to the opposition of the springs sustains F G by the vertical component M of the parallel ogram of forces Z m n 0. Vere the matter dismissed here, the whole phenomenon would be akin to the ordinary sustension, in present artificial flight by means of an inclined plane, whereby a lift, which is a very moderate multiple of the drift to use terms which have established meanings in flight engineering, as has been mentioned hereinbetoreis secured at the expense of the continued output of a great deal of energy.
The addition of G H to F Gr radically supplant-s this condition. The rollers that have sustained F G through being thrust down by its movement, now react from the thrust of their springs, after they pass the point G, and produce an upward thrust 0 against G H, which is added to the thrust M against F G, and which is theoretically equal to the energy expended through F G in forcing them down. Moreover, besides thus doubling the original lift, by adding that beneath G H to that beneath F G, the horizontal component of the lift 0 is in the direction N. The opposition of L is thus balanced by the thrust of N, the parallelogram of forces p g r .9 being equal and opposite to the parallelogram of forces Z on n 0, so that now the phenomenon has become one of sustension by a dynamic balance of forces in a moving system, which theoretically calls for no input of energy to continue it in perpetual motion, and which in practice, like the generality of perpetual-motion schemes, demands for its continuous operation only such input of energy as is necessary to overcome the frictional and other internal losses of the system, which in the particular case under consideration can be reduced to remarkably small amounts, as is conclusively proved by demonstrable facts concerning the efficiency of bird flight. In the actual case of a gliding wing with- 1n a mass of air, as contrasted with the explanatory scheme of inclined planes, rollers, and springs which has just been outlined, the place of the inertia of the rollers and that of the elasticity of the springs are both taken by the ponderable and elastic molecules of the air relatively adjacent to the wing, while the place of the base P P against which the springs abut, in the case of Fig. 9, is in the case of the wing in the air taken by the inertia of the air more remotely adjacent to the wing.
To a certain degree, and with limitations, to seek still farther for analogies to this remarkable phenomenon, of wing action, which has no really-close counterpart in any other phenomenon of matter and motion, the action of a pneumatic tire presents a few points of comparison of possible usefulness. For this seemingly simple device, which within a few years has revolutionized land transportation, is far more than a. spring or cushioning device, being recognized by the engineers who understand it to consist of a means for absorbing road inequalities and obstacles by the expenditure of energy, the energy thus expended being subsequently recovered, to an all but perfect efficiency, by the elastic reaction of air as it smooths out of the flexible envelope which confines, in leaving it the resisting irregularities which distort it.
Farther this analogy cannot be pursued, it being distinctly a transition from a lower to a. higher order of engineering, to progress from the support and transport of a vehicle upon the confined air of a tire, to its support and transport upon the unconfined air of the atmosphere.
In conclusion, to refer to F 10, this drawing is introduced to indicate that, to a balanced system like F G H, Figs, 9 and 10, there may be added a theoretically-indefinite series of similar systems, such as H Q ac, (Mb 7) R, and R S T, Fig. 10, which by the logical substitution, for the sharp angles G H Q, of the curves (m Z) R S T (action at infinitely-abrupt angles requiring infinitely-great force and being thereforeimpossible), becomes a sinusoidal curve, to the configuration of which a wing must conform, and which the pulsations of the air waves follow.
For practical reasons, hereinbefore made clear, a practical wing section is best made to include only relatively short portions of such a curve, as indicated from C to E, Fig. 10, ca D, and Z), in this illustration, referring to the same parts that are designated by the same letters in others of the illustrations, but it is to be noted that the path of travel through the air which is defined by the air pulsations induced by a wing consists of such a sinusoidal curve indefinitely extended.
To recapitulate the objects of my invention, the reduction in the power necessary for flight is attained by features now fully explained.
The same features explain the increase in the radius of flight.
That the permissible loading, per unit of area, of my wing may without detriment to efliciency be higher than customary loadings of aeroplanes, is indicated by my theories and has been proved by test.
Heavier loading and thicker sustaining surfaces, in combination, allow strength to be increased by reducing the extent to which structural material must be distributed and by improving its arrangement to resist stresses.
My wing improves the stability of a flying machine, because with it the shift of the center of pressure, with change of angle, is found to be almost suppressed, the slight movement that does remain being, moreover, in the directions to prevent longitudinal upsets instead of in the directions to facilitate them. Thus, when the front of the wing rises, and the machine therefore stalls, the pressure shift is rearward, so that the front of the machine drops, while, when the machine starts to dive, the pressure shift is forward, so that the rear of the machine drops. lVith aeroplanes these shifts are greater in amount and opposite in direction, so that they have proved one of the most fruitful sources of accidents.
Concerning height of flight, it is even now well recognized that the most elficient machines fly highest.
Concerning speed variabil ity, an aeroplane at a contsant angle of incidence can only climb, rather than progress faster, if the propelling power be increased, and must descend, to maintain its speed, if the propelling power be decreased. A wing, on the contrary, having no angle of incidence, speeds up with more power and slows down with less power, throughout a far greater speed range than is commonly obtained with aeroplanes, even when the angle of in cidence is varied.
From the standpoints of simplifying and cheapening the structure,the significances of thickness provided in relatively-liberal proportions, with positive aerodynamic advantage, instead of reluctantly tolerated in insuflicient degree, from structural necessity, are obvious to any one familiar with the elements of flight engineering.
Durable metal members, light and strong as well as replaceable, are a matter of course in a structure possessing sufiicient thickness to allow girder depth, the excessive use of wood in present aeroplanes being an objectionable necessity mainly dicated by their thinness.
The acceleration of manufacture is another obvious deduction from the features herein described, which tend to place flyingmachine design on a sound engineering basis, as contrasted with the present prevalence of hit-and-miss practice, the current quest for extreme lightness, and the ill-advised demand for enormous power.
I am aware that certain principles herein involved have been more or less widely applied in the design of struts, stays, and body forms, but none of these are sustaining surfaces.
I am also aware that aeroplanes have been built and flown with thick sustaining surfaces, and wit-h recurved and flexible rear edges, but without exception in the history of the prior art, and in present aeroplane practice, these have lacked the essential features of relatively-great thickness confined to the extreme forward portion, restricted to areas not too near to the wing tips, and otherwise suitably-placed, and with the tapering rear of the thick portion sufficiently-abrupt to fall within, the friction angle, and with the curvatures of proper character, suitably-interrelated, and correctly-combined with the other necessary elements to produce the results I attain. I do specifically recognize one partial exception, however, in that the Montgomery machines embodied, and the Montgomery patent, U. S. No. 831,173, describes and claims, certain features or wing design which, in so far as they involve questions of curvature and of power required, are fundamentally correct to the extent that they are therein developed, and which are involved in my invention, and which, therefore, though they fail to incorporate the important modifications entailed by the introduction of suitable thickness and of the desirable upturned rear edge, necessarily take precedence over my invention, relegating this application to the status of an improvement patent based upon the Montgomery invention.
Having thus fully described my invention, what I claim as new, and desire to protect b Letters Patent, is-
1. A .ying machine. wing, comprising rearwardly diverging penetration surfaces for displacing air masses, forwardly located reaction surfaces converging rearwardly from said penetration surfaces at an included angle which falls within the friction angle of the reactive thrust of said air masses, and a relatively thin rearward extension.
2. A flying machine wing, comprising rearwardly diverging penetration surfaces for displacing air masses, reaction surfaces immediately in rear of said penetration surfaces and converging rearwardly therefrom at an included angle which falls within the friction angle of the reactive thrust of the air masses, and a relatively thin rearward extension constructed to afford retarding surfaces; the surfaces of said wing being formed to produce a substantial balance of propulsive streamline reaction against retarding head resistance, and of propulsive sustention against retarding sustention.
3. In a flying machine, a sustaining wing arched from front to rear in its central portion, with a progressive upturning of its front edge toward the tips, and a thickened portion of streamline cross-section adjacent its front edge.
4t. A flying machine wing arched from front to rear, and having at its front edge a thickened portion of stream-line crosssection, the declination of the front edge and the thickness of the thickened portion both progressively diminishing toward the tips of the wing.
5. In a flying machine, a sustaining wing having a downturned and relatively thick front edge of streamline cross-section merging rearwardly into a relatively thin and sinuous extension, the upper and under surfaces of the wing conforming respectively to the dissimilar compression waves generated above and below the wing by the passage of the flying machine through air.