US3471107A - Stabilizing the vortices over a thin delta wing - Google Patents

Description

STABILIZING THE VORTICES OVER A THIN DELTA WING ,F'iled Feb. 10, 1967 I Oct. 7,1969 K. 1". ORNBERG 6 Sheets-Sheet l PRIOR ART PRIOR ART 7 K eZZ Tpz'sZ nUmbsrg I STABILIZING THE VOR'I'ICES' OVER A THIN DELTAY'WING'.

Filed Feb. 10, 1967 Oct. 7, 1969 I K; T. bRNBERG I 6 Sheets-Shleet 2 V 'QKABI.

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' STABILIZING THE VORTICES OVER A THIN DELTA WING Filed Feb. 10, 1967 6 Sheets-Sheet 5 3&13.

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STABILIZING THE VORTICES OVER A THIN DELTA WING Filed Feb. 10, 1967 s Sheets-Sheet s :62 FRO RESSVURE souecs United States Patent STABILIZING THE VORTICES OVER A THIN DELTA WING Kjell Torsten Ornberg, Linkoping, Sweden, assignor to Saab Aktibolag, Linkoping, Sweden, a corporation of Sweden Filed Feb. 10, 1967, Ser. No. 615,230

Claims priority, application Sweden, Feb. 11, 1966,

Int. Cl. B64c 3/00, 3/04 US. Cl. 244-41 14 Claims ABSTRACT OF THE DISCLOSURE This invention relates to sharply swept-back wings which produce lift by the generation of vortices over their suction surfaces, and the invention has more particular reference to means on such a wing for counter-acting deflection away from its suction surface of adjacent vortices that are located at the same side of the longitudinal centerline of the wing and have the same direction of rotation.

With a thin, sharply swept-back wing, lift is to a large extent produced byvortices formed over and attached to the upper or suction surface of the wing. The vortices are generated even at low angles of attack as the result of air flow separation at the thin and swept-back leading edges of the wing, and the high suction peaks induced by the vortices upon the surface under them increase the lifting effect of the wing.

With a wing having a true delta planform, with straight leading edges, only one vortex is normally produced at each of the leading edges. It is advantageous, however, to produce two or more vortices at each side of the longitudinal centerline of the wing and this can be accomplished by producing discontinuities in the velocity of the air flow at each leading edge. One expedient for accomplishing this is disclosed in Swedish Patent No. 160,134, and is illustrated in FIGURES 1, 5 and 11 of the accompanying drawings. It consists in providing one or more plates or fences 5 that project downwardly from the pressure surface of the wing 7 near each of its leading edges 8, such plates being located intermediate the wing root 9 and the wing tip 10 and edgewise aligned with the normal direction of flight. Each such plate produces a discontinuity in the normal outwardly directed flow at the pressure surface of the wing, and thereby generates an outboard leading edge vortex 11 which is additional to the inboard vortex 12 that originates near the apex 13 of the wing.

A plurality of vortices is also generated at each leading edge of a wing having a so called broken delta planform, wherein each leading edge has a forward portion which is disposed at one acute angle to the longitudinal centerline of the wing and a rearward portion which is at a diflerent acute angle to said centerline. In such a wing the break between the forward and rearward portions of each leading edge can define either an outward or an inward obtuse angle, the former being illustrated in FIGURE 2 and the latter being illustrated in FIGURE Patented Oct. 7, 1969 3. With either type of broken delta planform, the change of the sweep back angle of the wing at the break 14 and 14 produces a discontinuous change in the increase of the shearing strain of the vortex sheet separating from the leading edge, so that if the change in sweep-back angle at the break is sufficiently large, the vortex sheet can be rolled up into two separate leading edge vortices 11 and 12 at each side of the centerline, as illustrated in FIGURES 2 and 3, instead of only one vortex being formed at each side as in the case of a delta wing having straight leading edges.

A plurality of vortices at each side of the centerline is also produced over the main wing 107 of a canard aircraft, as illustrated in FIGURE 4, wherein a smaller secondary wing 207 is located in front of the main wing in accordance with the principles of US. Patent No, 3,188,- 022. In such a canard aircraft the two leading edge vortices 12' of the forward wing are bound to the two leading edge vortices 11' of the main wing as they pass over the latter.

In each instance where plural vortices are generated at each leading edge by means of one of the above described arrangements, such vortices have the same direction of rotation, as illustrated in FIGURE 5.

Such adjacent corotating vortices bring about substantial improvements in stability and efliciency of an aircraft so long as they remain attached to the wing. However, at high angles of attack they can interfere with one another, to the point where the mutual interchange of energy between adjacent vortices increases beyond a certain value, whereupon they tend to roll up onto each other and start to rotate around a common axis, as illustrated in FIGURE 6. When this happens, the outboard one 11 of the vortices thus rolled up is deflected away from the suction surface of the Wing, with the result that the wing loses a part of its lift. Concomitantly its center of lift is displaced, with consequent disturbances 1 to trim in pitch and/ or roll.

The general object of the present invention is to provide a simple but effective means for preventing such interference between adjacent corotating leading edge vortices at each side of the centerline of a thin, sharply sweptback delta wing, to thereby prevent the above-mentioned undesirable loss of lift and disturbances to pitch and roll trim.

Another object of this invention is to provide a thin, sharply swept-back wing having smooth curves of lift coeflicient vs. angle of attack and moment coefficient vs. angle of attack through a substantially large range of angles of attack.

It is also an object of this invention to provide simple and effective means cooperating with a thin, sharply sweptback wing for insuring that each of a plurality of vortices generated at each side of the centerline of the wing will remain effectively bound to the suction surface of the wing through a substantially large range of angles of attack, rather than being deflected upwardly from the suction surface by mutual interference.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims.

The accompanying drawings illustrate one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIGURE 1 is a plan view of a thin delta wing, seen from above, having plates or fences as hereinabove described for generating a plurality of leading edge vortices, the vortices thus generated being shown diagrammatically;

FIGURE 2 is a view similar to FIGURE 1 but showing an outwardly broken delta wing and the vortices that obtain over its suction surface;

FIGURE 3 is a view similar to FIGURE 1 but illustrating an inwardly broken delta wing and the vortices that obtain over its suction surface;

FIGURE 4 is a top plan view of a delta wing canard aircraft embodying the principles of Patent No. 3,188,022, the vortices generated by the wing arrangement being illustrated diagrammatically;

FIGURE 5 is a diagrammatic sectional view through a thin delt wing, taken on a plane normal to the longitudinal centerline of the wing, illustrating a system of pairs of corotating vortices over its suction surface when the wing is at a low angle of attack and indicating the relative forces acting upon such vortices by reason of their mutual interference;

FIGURE 6 is a view similar to FIGURE 5 but illustrating a condition, such as occurs at high angles of attack, wherein mutual interference between adjacent corotating vortices has caused them to roll up on one another and to rotate about a common axis;

FIGURE 7 is a view corresponding to FIGURE 5 but showing the conditions that exist over a wing embodying the present invention at low angles of attack;

FIGURE 8 is a view corresponding to FIGURE 6 but showing the conditions that exist over a wing embodying the present invention at high angles of attack;

FIGURE 9 is a diagram comparing performance characteristics of a heretofore conventional inwardly broken delta wing with those of a similar wing embodying the principles of this invention;

FIGURE 10 is a diagram similar to that of FIGURE 9 but wherein rolling moment coeflicient is plotted against sideslip at subcritical and super-critical angles of attack;

FIGURE 11 is a side perspective view of an aircraft having an inwardly broken delta wing embodying the principles of this invention, the vortices over the suction surface of the wing being illustrated diagrammatically;

FIGURE 12 is a fragmentary vertical sectional view taken on a plane extending spanwise along the wing of the aircraft shown in FIGURE 11;

FIGURE 13 is a more or less diagrammatic perspective view of a delta wing canard aircraft embodying the principles of this invention;

FIGURE 14 is a sectional view taken on the plane of the line 14-14 in FIGURE 13;

FIGURE 15 is a view similar to FIGURE 12 but illustrating another modified embodiment of the invention;

FIGURE 16 is a sectional view taken on the plane of the line 1616 in FIGURE 15; and

FIGURES 17-19 are views similar to FIGURE 16 but respectively illustrating other modified embodiments of the invention.

Referring now to the accompanying drawings, the numeral 7 designates generally a thin, sharply swept-back wing, so arranged, according to any of the above-described known expedients, that two or more laterally adjacent vortices 11 and 12 that rotate in the same direction are formed over the upper or suction surface 15 of the wing at each side of its longitudinal centerline.

At low angles of attack the mutual interference between the two vortices 11 and 12 imposes forces upon them that are in the directions and of the relative magnitudes denoted by the vector arrows 16 and 17 in FIG- URE 5. Thus the outboard vortex 11 tends to be deflected upwardly away from the suction surface 15 of the Wing by its interaction with the inboard vortex 12, while the latter tends to be deflected downwardly. So long as the angle of attack of the wing does not exceed a limiting value m the interference between the vortices 11 and 12 does not reach a critical value and they remain attached to the upper surface of the wing, in substantially the condition diagrammatically illustrated in FIGURE 5.

However, if the angle of attack is increased to a higher value m the interference between the vortices reaches the point at which the condition illustrated in FIGURE 6 obtains, with the vortices rolling up on one another and rotating about a common axis. The outboard vortex 11 is thus deflected upwardly away from the suction surface of the wing, with the result that there is a substantial loss of lift. concomitantly there is also likely to be a displacement of the center of lift that produces changes in the pitching and/or rolling moments.

According to the present invention, means are provided on such a wing for introducing between a pair of laterally adjacent corotating vortices a vortex which rotates in the opposite direction from them and which thus cooperates with them in a manner somewhat analogous to the meshing of a train of gears. The oppositely rotating vortex reinforces and stabilizes the corotating vortices at opposite sides of it, and, in a manner of speaking, holds them in check by preventing their deflection away from the suction surface of the wing.

FIGURES 7 and 8 illustrate the effect of introducing such an oppositely rotating vortex 18 between a pair of corotating vortices 11 and 12 at each side of the centerline of a delta wing. Specifically, FIGURE 7 illustrates the vortex system over the suction surface 15 of a wing embodying the present invention at angles of attack corresponding to and below the above-mentioned value a and is thus to be compared with FIGURE 5; while FIG- URE 8 illustrates the vortex system over the same wing at 0: and should therefore be compared with FIGURE 6. It will be observed that the oppositely rotating vortex 18 imposes a downwardly directed force upon the outboard vortex 11 and an upwardly directed force upon the inboard vortex 12; and that simultaneously the corotating vortices operate upon the oppositely rotating vortex to impose upon it forces which tend to maintain it. Note that the system persists at high angles of attack.

Several expedients are available for producing such a counterrotating vortex between adjacent corotating vortices, comprising, in each case, means on the wing located laterally intermediate the cores of the corotating vortices, and preferably located near the leading edge of the wing, for producing a discontinuity in the air flow over the suction surface of the wing whereby a vortex is generated that has a direction of rotation opposite to that of the corotating vortices.

One such expedient is shown in FIGURE 11, which illustrates an aircraft having a wing 7 of inwardly broken delta planform and which is provided with plates or fences 5 that project downwardly from its pressure surface in accordance with the teachings of Swedish Patent No. 160,134 to generate over the suction surface 15 of the wing, at each side of its longitudinal centerline, a plurality of outboard vortices 111, 211, 311 and 411 that all rotate in the same direction. The wing also generates an inboard vortex 12 which rotates in the direction of the outboard vortices and which has its origin at the apex of the wing. The outboard vortex 111 originates at the break 14' in the leading edge of the wing, while the other outboard vortices 211, 311 and 411 originate at the respective plates 5, which thus break up into four smaller corotating vortices what would otherwise be one large outboard vortex, and thereby improve the wing tip flow at transonic speeds.

To prevent the smaller vortices from being disturbed by the large laterally innermost vortex 12 at low speeds and high angles of attack, the wing is provided, at each side of its centerline, with a vortex generating means comprising an upright triangular wall or plate 20 having its apex positioned inboard of the break in the leading edge of the wing and substantially opposite the same laterally, and extending rearwardly along the suction surface of the wing directly adjacent to the inboard vortex 12, in the outward flow which is induced by the latter at high angles of attack. The rearwardly and upwardly inclined free edge of this plate produces a vortex 18 that lies outwardly adjacent to the inboard vortex 12 and the energy for production of the vortex 18 is derived from the inboard vortex 12 so that the inboard vortex 12 is somewhat weakened as it moves rearwardly and cannot exert a disturbing influence upon the outer small vortices 111, 211, 311 and 411, the positions and lift of which are decisive of the stability and control characteristics of the aircraft.

The plate or vortex generating means 20 is arranged to be retracted at high speeds so that the stability of the aircraft is not disturbed by its shock system, particularly at transonic speeds. As illustrated in FIGURE 12, the plate can have a pivote dconnection 21 to the wing structure, with the pivot axis of the plate extending along its lower edge, at its junction with the suction surface 15 of the wing. In this case the plate is swingable flatwise between an operative position in which it projects above the suction surface of the wing and a retracted position in which its outboard surface lies flush with the suction surface of the wing. The plate can be actuated to one or the other of these positions as by means of a link 23 rigidly connected to the plate and pivotally connected to generally conventional hydraulic mechanism 24 or the like.

FIGURE 13 illustrates a generally similar vortex generating arrangement embodied in a canard aircraft having a straight delta main wing 107 and auxiliary wing 207, and wherein the auxiliary wing generates an inboard vortex 12 over the main wing at each side of its longitudinal centerline. A vortex generating plate 20' is located on the main wing at each side of its longitudinal centerline, each such plate being located about midway between the apex of the main wing and its trailing edge, and inboard from the leading edge a distance such as to be outwardly adjacent to the inboard vortex 12. In this instance the plate 20 has a pivotal connection 21 with the wing structure at its apex or front angle, as illustrated in FIGURE 14, so as to be swingable edgewise between an extended operative position, projecting upwardly from the suction surface of the wing, and a retracted position in which its upper edge lies flush with the suction surface of the wing. Again, suitable hydraulic mechanism 24 provides for actuation of the plate between its extended and retracted positions.

FIGURE 15 illustrates another form of means for producing a vortex which is located between a pair of adjacent corotating vortices, and which rotates in the direction opposite to theirs and cooperates with them to bind the vortex system to the suction surface of the wing. In this case the Wing is provided with at least one slot 26 at each side of its longitudinal centerline, elongated in the direction parallel to said centerline. Preferably, however, there are additional slots 26', as shown, chordwise aligned behind the front slot 26. Each slot opens through the wing from its pressure side to its suction side. The generally upright wall surfaces 27 and 28 which define each slot converge upwardly so as to accelerate the air that flows upwardly through the slot in response to the pressure differential between the opposite surfaces of the wing. The outboard one 28 of these two wall surfaces makes a substantially sharp angled junction with the suction surface 15 of the wing, as at 29, to provide a vortex generating separation of air flow. The junction of the inboard slot defining wall 27 with the suction surface of the wing is smoothly rounded, as at 30, so as to substantially prevent the formation of a vortex at the inboard edge of the slot. The spanwise location of the slots 26 and 26 is adjacent to the inboard vortex.

As illustrated in FIGURE 17, each of the slots 26 and 26' can be closed, if desired, by means of edgewise slidable cover plates 32 and 33 which are substantially flush, respectively, with the pressure and suction surfaces of the wing, and which can be operated by any suitable mechanism (not shown). Closure of these cover plates serves the same purpose as retraction of the upright triangular plates in the first described embodiments of the invention, that is, it renders the vortex generating means inoperative for purposes of high speed flight.

Alternatively, as illutrated in FIGURE 18, cover plates 32' and 33 can be arranged to swing fla-twise outwardly, from positions in which they close the slot 26 to operative positions in which they project outwardly from the suction and pressure surfaces, respectively, and are aligned with the direction of flight. In that event the lower plate 32, when extended, serves to increase the flow through the slot by deflecting upwardly the strong outward flow of air that exists under the pressure side of the wing, especially at high values of angle of attack a; While the upper plate serves as a vortex generating means operating similarly to the plate 20 in the first described embodiment of the invention.

Instead of air from the pressure side of the wing being forced through a slot, air from a suitable pressurized source thereof within the aircraft can be directed through a duct 34 communicated with a slot 126 that opens to the suction surface of the wing, as illustrated in FIG- URE 19. In this case the strongly energized air which is emitted from the slot 126 produces and intensifies the velocity discontinuities in the flow over the suction surface of the wing and thereby produces and intensifies the counterrotating vortex 18.

FIGURE 9 illustrates the improvement in the curves of lift coeflicient C and pitching moment coeflicient C in a wing having inwardly broken leading edges, of the type shown in FIGURE 3 and embodying the present invention, as compared with the same characteristics of an identical prior wing not incorporating counterrotating vortex generating means.

The solid line 40 represents C plotted against a for the prior wing, and it will be observed that lift coefiicient increases substantially steadily with increasing angle of attack on until a critical angle of attack a is attained. With further increase in angle of attack beyond m the value of C remains constant, at best, until the wing reaches a supercritical angle of attack 01 after which C increases sharply with further increasing angle of attack. Similarly the C curve 41 for the prior wing (solid line) has a sharp deflection, corresponding to a severe disturbance of the pitching moment, through the range of angles of attack between a and a With a wing having means for generating counterrotating vortices according to the present invention, the curves of C and C will correspond to the broken lines 40' and 41, respectively, through the range of angles of attack from or; through and beyond a and will thus vary at a substantially steady rate through the entire useful range of angles of attack. From the FIGURE 9 curves it will be apparent that the invention eliminates the possibility of sudden loss of lift and abrupt change of trim in pitch that occurred with prior broken delta wings when their angle of attack was increased beyond the critical valve a FIGURE 10 illustrates, on the basis of a comparison similar to that of FIGURE 9, the improvement in roll characteristics brought about by the present invention. The solid lines 43 and 44 in FIGURE 10 represent rolling moment coeificient C as a function of the angle of side slip 13 for a prior inwardly broken delta wing, at a subcritical angle of attack a and a supercritical angle of attack a respectively. The broken lines 43' and 44 represent the same respective characteristics of a similar wing but embodying the present invention. It will be observed that at the subcritical angle of attack m the curves 43 and 43 substantially coincide. When the angle of attack is increased to a however, the prior wing exhibits marked variation of C with increasing ,8, as iridicated by curve 44, owing to the asymmetric vortex deflection due to side wash. By contrast, as designated by the broken line 44', the wing of this invention has a curve of C vs. ,8 at the angle of attack 04 which is as smooth and stable as its curve for the same characteristic at the low angle of attack value a From the foregoing description taken with the accornpanying drawings it will be apparent that this invention provides simple and effective means on a thin swept-back wing for preventing or minimizing deflection away from its suction surface of adjacent vortices that are located at the same side of the longitudinal centerline of the wing and have the same direction of rotation, to thereby bring about marked improvement of the performance and stability characteristics of the wing at high angles of attack.

What is claimed as my invention is:

1. The method of generating lift by producing vortices over the suction surface of a sharply swept-back Wing which is symmetrical to a longitudinal centerline and which is .moved forwardly through the air, which method is characterized by:

(A) over the suction surface of the wing at each side of the centerline generating a pair of spanwise spaced apart vortices that rotate in the same direction; and

(B) between each such pair of vortices generating a vortex having the opposite direction of rotation and which thus meshingly cooperates with the vortices of said pair to reinforce and stabilize them and maintain them bound to the suction surface of the wing.

2. In the method of generating lift which comprises moving forwardly through the air a sharply swept-back wing that is symmetrical with respect to a longitudinal centerline, and generating over the suction surface of the wing at each side of the centerline a plurality of vortices that rotate in the same direction and have their cores normally spaced apart spanwise:

generating an oppositely rotating vortex between each pair of adjacent vortices that rotate in the same direction, to meshingly cooperate with said pair of vortices for reinforcing and stabilizing them and maintaining them bound to the suction surface of the wing.

3. The .method of generating lift by moving forwardly through the air a sharply swept back Wing that is syrnmetrical with respect to a longitudinal centerline, characterized by:

generating over the suction surface of the wing at each side of the centerline a plurality of vortices having their cores spaced apart spanwise and each of which rotates in the direction of rotation opposite to that of its spanwise adjacent vortices so that the several vortices at each side of the centerline meshingly cooperate to reinforce and stabilize one another and remain bound to the suction surface of the wing.

4. In combination with an aircraft having a thin, sharply swept-back wing and means for producing a pair of spanwise adjacent leading edge vortices over the suction surface of said Wing at each side of its longitudinal centerline, both of which vortices rotate in the same direction:

means at each side of the centerline for generating a third vortex, said third vortex generating means being (a) located a substantial distance forwardly of the trailing edge of the wing and spanwise intermediate the vortices of said pair thereof, and

(b) arranged to produce between the vortices of said pair thereof a vortex having the opposite direction of rotation and which meshingly cooperates with said pair of vortices to stabilize them and bind them to the suction surface of 6. The wing of claim 5, further characterized by:

said surface defining means comprising a plate normally projecting upwardly from thesuction surface of the wing, said upper edge thereof being rearwardly and upwardly inclined.

7. The wing of claim 6 further characterized by:

means mounting said plate for retraction to an inoperative position in which it is disposed flush with adjacent portions of the suction surface of the wing.

8. The wing of claim 5, further characterized by:

(A) said surface defining means comprising one wall of a slot in the wing which opens to its suction surface, said upper edge thereof being defined by a sharply angled junction of said wall with the suction surface; and

(B) further characterized by means in the wing for expelling from said slot air at a pressure higher than that which obtains above its adjacent portion of the suction surface of the wing.

'9. The wing of claim 8, further characterized by:

said means for expelling air from said slot comprising means communicating said slot with an opening in the pressure surface of the wing.

10. The wing of claim 5, further characterized by:

(A) said surface defining means comprising (1) one wall of a slot in the wing which opens to its suction surface and (2) a plate having a surface normally coplanar with said slot wall and projecting above the suction surface, said upper edge being defined by the upper edge of said plate;

(B) further characterized by means in the wing for expelling from said slot air at a pressure higher than that which obtains above its adjacent portion of the suction surface of the wing; and

(C) means mounting said plate for flatwise swinging motion to a position in which it substantially closes said slot and lies substantially flush with the suction surface of the wing.

11. The wing of claim 10 wherein said slot also opens to the pressure surface of the wing, further characterized by:

a second plate mounted for flatwise swinging motion between an extended position in which said second plate is coplanar with said slot wall and projects downwardly from the pressure surface of the wing, and a retracted position wherein said second plate closes the opening of the slot to the pressure surface of the wing and lies substantially flush with said surface.

12. In combination with an aircraft having a thin sharply swept-back wing with a so-called double-delta planform wherein the leading edge of the wing at each side of the longitudinal centerline thereof has a forward portion which is disposed at one acute angle to said longitudinal centerline and a rearward portion which is at a different acute angle to said centerline and wherein the angular difference between the sweep-back of the two portions is of such magnitude that there are produced at each side of the centerline a pair of concentrated leading edge vortices on the wing that rotate in the same direction:

means at each side of the centerline for generating a third vortex, said third vortex generating means being (a) located a substantial distance forwardly of the trailing edge of the wing and spanwise intermediate the vortices of said pair thereof, and

(b) arranged to produce between the vortices of said pair thereof a vortex having the opposite direction of rotation and which meshingly cooperates with said pair of vortices to stabilize them and bind them to the suction surface of the wing.

13. In combination with a canard aircraft having a main wing with leading edges-sharply swept back and a 9 10 thin profile so that a concentrated leading edge vortex centerline of the wing into at least one pair of vortices tends to form over the upper surface of the wing at each that rotate in the same direction: side of said centerline, and a vortex producing secondary means at each side of the centerline for generating a wing located in front of and above the main wing but third vortex, said third vortex generating means being sufficiently close to it both longitudinally and vertically (a) located a substantial distance forwardly of so that the vortices produced by the secondary wing are the trailing edge of the wing and spanwise interbound to the main wing when passing over the suction mediate the vortices of said pair thereof, and surface of the latter and form, together with the vortices (b) arranged to produce between the vortices of produced on the main wing, a pair of vortices at each said pair thereof a vortex having the opposite side of the centerline that rotate in the same direction: direction of rotation and which meshingly comeans at each side of the centerline for generating a operates with said pair of vortices to stabilize third vortex, said third vortex generating means them and bind them to the suction surface of being the wing.

(a) located a substantial distance forwardly of the References Cited trailing edge Of the main wing and spanwise UNITED STATES PATENTS giltgrmedlate the vortices of said pair thereof, 2,125,738 8/1938 Rose (b) arranged to produce between the vortices of Zlmmerman 244' 40 said pair thereof a vortex having the opposite Kerker et 244 42 direction of rotation and which meshingly co- 3188022 6/1965 Omberg' 3,237,892 3/1966 Elliot et a1. 244-42 X operates with said pair of vortices to stabilize them and bind them to the suction surface of FOREIGN PATENTS the wing. 595,877 4/1960 Canada. 14. In combination with an aircraft having a thin 890,418 2/1962 Great Britain. sharply swept-back wing, and means at the leading edges of the wing for dividing the leading edge vortex that nor- MILTON BUCHLER Pnmary Exammer mally tends to form at each side of the longitudinal JEFFREY L. FORMAN, Assistant Examiner

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