[1]Patented Sept. 18, 1945 2@384,893 UNITED STATES PATENT. OFFICE 2,384,893 AI[RCRAFT Louis H. Crook, Washington, D. C., assignor to Aerodynamic Research Corpomtion, Washington, D. C., a corporatio at the District of CoIumbia 7 Application February 19, 1942, Serial No. 431,590 19 Claitns. (Cl. 244-73) This invention relates to certain improvements in a passage formed extending through the airfoil in aircraft; and th6 nature and objects of the invention will be readiiy recognized and understood by those skilled in the arts to which it relates, from the following detailed description and ex- 5 planation of the accompanying drawings, illustrating what I at present consider to be the preferred embodiinent or mechanical and aerodynamic expression of my invention from among various other forms, designs, arrangements, con- 10 struction@ and combinations of wbich the invention is capable within the broad spirit and scope thereof. The invention is adapted to and capable of embodiment in aircraft generary of the lighter- 15 than-air types and of the h-eavier-than-air types, as well as to aircraft bf compromise types that embody characteristics of both lighter-than-air and heavier-than-air types w ' ithout being solely or distinctly either of a lighter-than-air type or a 20 heavier-than-air type; and the term "aircraft" Is generally used herein and in the appended claims, unless otfierwise qualified speciflcally or, by surrounding context, in a broad generic sense to include any aircraft to which the principles Of 2r) the invention may be adapted and applied. Airfoils or bodies capable of -developing aerodynamic lift when moved through the air, when of low aspect ratio, that is, when such bodies or airfoils.in plan form approach the square or cir- 30 cular form with the length approximating the width, develop certain definite aerodynamic characteristics of advantage over airfoils of high asspect ratio, that is, over airfoils which have a wl.dth or span several times greater than the 35 length or chord of the airfoil. While the lo* aspect ratio airfoils may have a lower lift coefficient at small angles of attack than high aspect ratio airfoils, yet they present certain advantageous control characteristics as well as in- 40 creased stability botb static and dynamic o-Ver the high asi@ect ratio airfoils. At large angles of attack and large Reynolds ntimbers, the square or circular or round airfoils; that is, low aspect ratio airfoils, have a much greater lift coefficient 45 than any other kn.own type of large aspect ratio airfoils. In ttddition su@h airfoils or bodies of low aspect ratio iend thernselves peculiarly, both structurally and aercdynamically@ to the utilization of prOPul- 50 sion Tneans and methods of what may be aptly termed the thrtigt aiigmentation type, such foi example as propulsion means of the type In which a propeller or other air Impelling and thrust force developingelementL-,mountedandeonflnedwith- 55 or body in the direction of flight of the aircraft for displacement of air rearwardly therethrough from the leading edge or forward portion of the airfoil to -the trailing edge or rear portion of the airfoil. One of the aims of my present invention is tc provide an aircraft adapt&d t(> either the lighterthan-air or heavier-than-air embodying for its primary structure an airfoil orbody of'low aspect ratio in which the aerodynamic efficiencies and advantages of the low aspect r4tio al.-foil are effi-, clently and correctly utilized, and tG provide a system and arrangement of stabilizing surfaces and control surfaces for such design of airfoil or body which are in such aerodynamic cooperation and relationship with such low aspect ratio airfoil designed In accorda'nee with the invention in order to produce by such arrangement a design 6f aircraft that will have a desired degree of stability, both static and dynamic, and which.will be effectively controllable in pitch, roul and yaw under and throughout &U conditioris of flight. With aircraft of lighter-than-air types it bas been well established that the lift of such a craft Is very large in a circular cross section form of airship, and with respect to the adaptations of the principles of my present invention to aircraft of the lighter-than-air types one of the objects of the invention is to advantageously utilize this lift characteristic by the Provision of a design which is based upon and embodies the primary structure or body formed of airfoil section having a low aspect ratio approaching the square or circular form in plan to increase the advantageous lift of the usual dirigible and to obtoin more effective stability and control characteristics which results In increasing, the pay load of a lighter@ than-air craft designed in'accordance with this Invention over the pay load possible to a lighterthan-air craft, using the same. volume of buoyant gas but having a body or hull design and shape of a conventional form., WJth respect to the adaptations of the principles of my present invention to aircraft of the lieavier-than-alr types, one of the aims and objectives sought by the invention Is to provide a design of aircraft embodyiiig a primary structure in the form of an airfoil or body having a low aspect ratio that will utilize and make effective the highly advantageous static and dynamic stabiuty characteristics as well. as more favorable control che@racteristics possiblp with an alrfoil or body of low aspect ratio, as well as.to Permit the production of larger size heavler-than-air ersft
[2]2 without encountering dangerous disadvantages due to the control cha.-acteristies, both static and dynamic, that are developed - and encountered with attempted larger sizes of heavier-than-aii craft of conventional designs based upon and embodying airfoils or lift surfaces with high aspect ratios. A further characteristic and a feature of the Invention that is made possible:by the use of a low aspect ratio airfoil or body as the primary structure of the aircraft, resides in the mounting and inclusion of substantially all structlire, mechanisms, and loads b(>th operating and pay, within the confines of the airfoil or bqdy, which being of airfoil section and therefore of generally streamlined form, result in the reduction of the dmg and other disadvantageous characteristics developed from structure and elements located exteriorly of the airfoil or body and in the airflow about the body. The design of an airfoil or body based upon the low aspect ratio form and providing the primary structure for an aircraft in accordante with myinvention, is peculiarly adapted for efficient utilization 6f propulsion rneans and methods of the so-called thrust augmentation types; pressure propulsion, s6 called Jet propulsion or the like, and a further feature of my inventi6n resides in the structural and aer6dynamic asgociation and combination of such propulsion means with the airfoil or body design of the in,ventioni which propulsion means preferiibly embodies a passage extending throagh the airfoil or body of the aircraft in the directi6n of flight, that is along or generally parabel to the longitudinal axis of the craft from the forward or leading edge port@on of the airfoil to @the rear or trailing edge portion thereof, together with rneans for propelling and displacing air rearwardly through said passage to develop a thrust force for propelling the aircraft, with such propulsion means In such c6ordinated relation with the stabilizing and control surfaces 6f the aircraft and. of such/ airfoil or body as to obtain highly effective and advantageous stability and control characteristics as well as maintain more efficient flow 6f air over the airf6il or body to thereby obtain maximum efficiency of performance for the craft. Fkirther important features of the invention relate to the thrust augmentation propulsion means with pae@icular reference to the shape and design of the air displacement passage and of the air Impelling and thrust force developing elements mounted therein, as as to e relationship of the airflow or air displacement through such passage with the low aspect ratio airfoil or body and with the stabilizing and control surface sy@tem and arrangement for the aircraft as provlded, in 'accordance with the teachings: of this invention, all in order to obtain a maximiim thrust force from a minimum of power and an Increased aerodynamic performance for the air6raft. With the foregoing general aims, objects, and results in viewi as well as'certain others that will be readily apparent from the fohowing detailed explanation and description, my invention consists in certain novel features in design and arrangement, and in combination and construction of the various elements maldng up the invention, all as will be more fuuy and particularij referred to and specifiedhereinafter. Referring to the accompanying cirawings in responding parts and elements throughout the several figures thereof; Fig. I is a perspective view of an aircraft embodying the principles and, features of my invention. Ing. 2 is a perspective view, more or less diagrammatic, showing the propulsioii unit of the invention removed from the aircraft and ineluding the air displacement passag the ar10 rangements of propellers therein and the relative mounting ind arrangement,of the flxed horizontal stabilizing surface,at the - t railing or discharge end of the dis@lacement'p'assage. Fig. 3 is a iiew more or less diagrammatic, 15 taken as in vertical longitudinal section through the propulsion unit of Figs.,.l and 2, and particularly showing the action of the airflow at and over the leading -and tralung edges of the aircraft body and through the propulsi @on unit 2o displacement passage and the propellers therein as well as over the fix6d and - movable stabili7.ing surfaces at the intake and discharge ends of the displacement passage. Mg. 4 is a front view in elevation of the for25 ward or leading edge portion of a primary body forming, low asp6ct ratio airfoil in accordance Nvitlj. my invention, showing the approximate relative proportions of one form of central and vdrtically elliptical c6ne-like intake opening or 30 entrance to the thrust augmentation passage or chamber in the airfoil Fig. @5 is a front view in elevation similar to Fig: 4 showing a modifi@d form of low aspect ratio airfoil having a lateral cross section cam35 ber or contour designed for lateral stability; the same design and form of central and vertically elliptical cone-like intake or forwa@rd entrance to the thrust augmentation passage through the airfoil being sh6wn in relative proportions to the d,) airfoil, as the intake or forward entrance shown in Mg. 4, Mg. 6 is a spanwise cross sectional view through the symmetrical type of body forming airfoil of Mg. 4 taken in a verti6al plane approximately 45 midway of the 16ading and trailing 'edges and showing the decreased 6r reduced diameter of the thrust augmentation passage in the airfoil at such location. Flg. 7 is a spanwise cross s6etional view through Co the laterally cambered primary. body forming airfoil of Mg@ 5 taken in a vertical plane approximately midway between the leading and trailing edges and showing the reduced diameter of the thrust augmentation passage at such loca55 tion in the airfoil@ F@g. 8 is a more or less diagrammatic view in vertical cross section taken chordwise through an airfoil section having a substantially flat lower surface and ia cambered upper surface, with a go design and arrangement of thrust augmentation passage or chambers extending chordw,.se therethrough from the leading edge to @ the trailing edge of the airfoil in accordance with the principles of my invention. 65 Fqg. 9 is a more or less diagrammaticview in vertical cross secti6n chordwise of an airfoil section having a substantially flat and uncambered upper surface with a cambered lower or undersurface for increasing longitudinal stability 70' of the airfoil, showing an arrangement and formation 6f the thrust augmentation passage through an airfoil of such design and contour. Flg. 10 is a m6re or less diagrammatical view siinilar to Figs. 8 and 9 but sh6wing a symmetriwhich similar reference charpeters refer to cor- 75 cal airfoil having a cambered upper surface and
[3]2,384,893 ,t cambered lower or undersurface, with the tlirust augmentation passage through the airfoil formed by the forward and rear cone-like chambers more or less schematically illustrated, and having the negative and Positive pressure art-ows applied along the walls or surfaces of the passage to irldicate the pressure conditions through the passage. ;Figs. 11, 12, 13 and 14, are more or less dia,grammatic outline views in top plan showing typical plan form shapes of low aspect @ratio airfoils, particularly adapted to embody the prinei-oles and features of my present invention. In accordance with the principles of my invention an aircraft, whetber of the lighteithanair or of the heavier-than-air types, referring now to the acec)mpanying drawings, basically embodies a wing airfoil or body A that is of low aspect ratio and which forms and provides the primary structure for the aircraft. This primary structure forming a low aspect ratio wing or body A, due to the aspect ratio tbereof, inherently possesses and is endowed with the advantageous cha,racteristies both aerodynamically and structurally resulting from airfoils or wings of the low aspect ratio forin. While an aircraft of th6 in-@ vention may he of either the l ighter-than-air or the heavier-than-air type, the example oi aircraft of the invention disclo,.zed in the accompanying' drawings may be.taken to be of the heavier-thanair type. With the basically inherent aerodynamic ancl control advgntages of low aspect ratio airfoils or wings, I have developed by the present invention a design and form of airfoii or wing that r,rovides the primary structure or body for tle ah-craft and which wing forming primary structure efficiently utilizes sucli advantages and increased efficiency of results, by employing low aspeclu ratios of a range of the order of approximately from I to 1.27. with a thickness factor for the airfoil or wing that wiii vary; in accordance with whether the airfoii or wing is to form the priniary,structure for a lighter-than-air craft or a heavier-than-air craft, and which thickneSS factor will also in either case vary in accordance with the size of the airfoil or wing. The thicklness of the airfoil or wing is ftirther controlled by the size of the intake and exit cones forming the air displarement passage being he@reinafter fully described and explained. As illustrative of the possible range' of airfoil or wing thickness relative to the fore and aft l(@ngth or chord of the airfoil or wing, I now consider that such thickness factor should be within the range of an order of approximately 12 % to 30 % of the length or chord of the airfoil or wing. By utilizing a low aspect ratio for the airfoil or wing in the range of the order of approximately 1 to i.27, I have designed an airfoil or wing, such as t,@e airfoil or wfng A -(>f Flg. 1, that approximates or approaches the square or .circijlar plan form, which I have found to be @,hc, form in which the advantageous aerodynamic and contr(>l characteristics are developed in their highest degrees. While the preferred ranges of aspect ratio of 1 to '@.27 are considered to giv6 the most efficient results, I do not wish to limit my invention to this exact range in every instance because of the varying conditions that will be encountered in specific aerodynamic or strue- ' tural designs to obtain a certain specific performance to meet particular requirements for which such a design may have been developed, and to meet which an aspect ratio outside of the preferred range may be utilized while still essentially taking 'advantage of the principles of the invention hereof. The -wing or body A having a low aspect ratio to give it a plan form approximating or approaching the square or circular plan, and a thickness within the ranges of the ord6r hereinbefore reierred to, is of airfoil section @aving a relatively thick forward or leading edge portion 10 10 with the Upper and lower surfaces cambe'red to Join reekrwardly in the trailing edge portion I I of cone@iderably less thicknc@ss than the leading edge portion 10 of the wing. Preferably with the heavie r-than-air,,form of wing or body A the 15 camber of the lower surface of the wing is grester than the camber of the upper surface, although it is not intended or desired to limit the airfoils or wings of my invention in every instance to such relative upper and lower surface cambers. 20 The wing or body A of the design and form of my invention thus provides an interior space -within which to locate and house substantially all structure and mechanisms, as well as all loa.ds, with the exception of external control and stab25 ilizing sutfaces, so that a craft is provided having minimum drag and rriaterially increased performance relative to pay load requirements. Preferably, with the heavier-than-air type of craft for which the wing or body A forms a pri30 mary stnicture of the present example, the center of gravity of the craft is located at a low point on the wing or body A along the longitudinal or fore and aft axis and approximately at a point 30% of the chord or fore and aft length of the 3.3 wing from the leading edge thereof. - The low aspec ratio wing or body A forming, as above described. the primary structure'of the aircrdft, be it of the heavier-thanair type as in the example of the accompanying drawings, or 6f the 4@) lighter-than-air type, may be made Of any suitable material or materials and in accordance with any desired or known type of construction suitable to the needs of the particuleir design of aircraft, and th6 speciflcdonstruction or particular ma45 terials employed form no part of my present invention. . The wing or body A which @ioims the primary structure for the aircraft has certain inherent stability characteristics, but I have established that-a wing forming an aircraft body and having the aspect ratio and thickness factors of my design, can be effectively stabilized in roll by an arrangement of vertical stabil.izing fins such as shown.in Flg. I and which arrangement includes the vertical stabilizing fins 12 of considerable area, relative to the wing A, extending upwardly from the upper surface of the' wing at opposite sides and adjacent the opposite ends, respectively, of, the wing A at the forward or leading edge porG,) tion theregf; and similar spaced vertical stgbilizing surfaces 14 (see Mg. 3) depending or extending downwardly from the'lower surfaces of the -wing or body A at opposite sides of the wing, respectively, and preferably In the same vertical plane as the stabilizing flns 12 thereabove By this arrangement of vertical stabilizing flns effective stability in roll is obtained for the aircroft and thiseffectiveness is 'particularly inereasedby the arrangl@ment and aerodynamic cooperao tion of thesestabilizing flns with the arrangement of yaw or directional stabilizing fins or surfaces I S. The arrangement of directionai stabilizing fins .15 of the present example consists of tmfo of such 75 fins located in pilrallel spaced relation spaced
[4]equidistant from the longitudinal axis of the wing or body, A at the rear or tr@iling portion thereof. The stabilizing fins 15 extend substantially from the trailing edge of the wing A forwardly a distance over the upper surface of the wing and decrease in thickness forwardly until they substantially nierge into the upper surface of wing A. These stabilizing fins 15 are located in planes spaced a'distance inwardly from the vertical planes in which the roll stabilizing flns 12 are located, but these yaw or directional stabilizing fins are not limited or confined to any particular shape or form The inherent longitudinal or pitch sta-bility of the low aspect ratio wing or body A is rendered more effective by the provision of a fixed horizontal stabilizing surface or surfaces, wwch in the specifle examples of the design of aircraft of Flg. 1, comprise a rear horizontal stabilizing surface 16 and a forward stabilizing surface 17. The rear fixed horizontal stabilizing,surface 16 In this instance happens to be mounted in the trailing portion of the wing A in a space or openIng therein at the trailing portion of an air displacement passage which extends longitudinally through the wing -and with the trailing edge of the stabilizer 16 substantially ali@ned with the trailing edge of the flxed trailing portion I I of wing A. Stabilizer 16 is of a relatively thick airfoil section as clearly illustrated in Mg. 3 of the drawings. The forward stabilizing surface 17 is mounted in the forward or leading edge portion of the wing Al and'in this instance, within a space in leading edge portion I 0 which forins the intake or inlet opening for the air displacement passage through the airfoil. Attention is directed to the fact that the locations and positions of the aforesaid stabilizing and control surfaces, both flxed and movable and whether vertical or horizontal, are not limited tO the locations and positions as shown by fuli lines in Mgs. 1, 2 and 3, but such stabilizing and/or control surfaces.may be positioned at other locations or may be mounted and arranged for d'ISplacement liorizontally and vertically to adjusted positions, as indicated for example in dotted lin6s In Mg. 3, in order to take advantage of particular aerodynamic flow conditions due to overall shapes, cambers and aspect ratio that may be employed in any particular design adaptations of the invention. Similarly the invention is not limited tQ the particular angles of attack sh(>wn or ind'lcated for these' various stabilizing and/or control surfaces in the example illustrated by the accompanying drawings. The control of the aircraft formed by the w'mg A with th6 stabilizing surfaces as hereinbefore dei3cribed, is ac6omplished through the medium of movable control surfaces for obtaining control in Pitch roll and yaw. The pitch control for the aircr@it is obtained in this instance from a series, referring now to Mg. 1 of the drawings, of three (3) horizontal control surfaces 18, 18 and I 9, with the two outer control surfaces I 8 at opposite ends of the Intermediate and centrally IGeated control surface I 9. Thege three surfaces are mounted for vertical angular displacement relative to the wing A, and any suitable or desired pilot control Mechanism (not shown,) is provided lor simultaneously angularly deflocting the contr@l surfaces 18, 18 and 19 in the same direction t stablish pitching "e' moments acting gn the wiiyg-A in a desired direction for pitch control, or said surfaces may . be deflected or dis,,Placed to establish moments acting in any other desired direction for control in roU 2,384,893 and/or in yaw. It is to be noted that the intermediate control surface 19 is pivotally mounted to and along the traiung edge of the horizontal stabilizing surface 16 in rearward continuation of such surface. to complete the airfoil section thereof. If desired the intermediate c6ntrol surface 19 may be actuated independently of the opposite outer control surfaces 18 to function as the sole longitudina I I or pitch control surface for the 10 aircraft, with the function of the outer control surfaces 18 as pitch control surfaces being eliminated. The roll i@ontrol of the aircraft formed by the wing or body A is in the particular example here 15 giveni obtained by differential actuation of the opposite outer control surfaces 18 to vertically angularly cleflect these surfaces simultaneously in opposite directions in order to develop roll moment@ acting on the aircraft in the desired direc20 tion. Any of the known or suitable mechanisms may be provided by which the surfaces 18 are differentially actuated while these surfaces are operable for pitch control, the arrangement of operating mechanism being the usual one in which 25 the control surfaces IO are differentially operable in any position to which these surfaces have been simultaneous]Y mjved in the same direction for pitch control. Dirmtional or yaw control of the aircraft of the 30 form of Mg. 1 is obtained by vertical rudders 20 which are pivotally mounted along the trailing edges of the vertical stabilizing surfaces 15, as will he clear by reference to Mgs. 1 and 3. Any suitable pilot operated control mechanism is provided 35 for simultaneously angularly deflecting the surfaces 20 horizdntally in the same direction in 6rder to establish yawing moments acting in the desired direction for controlling the aircraft. A combination of the yaw control surface or surfaces 20 40 with the pitch control surface or surfaces I 8 may be used for additional maneuvers or i-efinements Of control in the pilot control and flight operation of the aircraft. An aircraft, formed @by the low aspect r4tio, 45 relatively thick section wing or body designed in accord@Lnce'with my invention is particularly adapted for the use of thrustaugmentation means and methods for the propulsion of the aircraft, and my invention includes as features thereof the !-)( provision of an efficient form or type of thrust augmentation propulsion means and of the design, arrangement and mounting of such means i@q aerodynamic and structurai association and coordination with the low aspect ratio wing or body 55 and its arrangement of stabilizing and control surfaces@ As an example of one mechanical and aerodynamic embodiment of such a propulsion means, I have shown the w'mg A of the aircraft of Mg. 1 of the drawings as having a passage P extend'mg longitudina ly through the wing A from the leading edge thereof to the rear or trailing Portion of the airfoil. The liading edge portion of airfoil A has a central part of the leading edge IO cut away inwardly to provide the inlet space 65 or intake mouth of the passage, P, while the central trailing portion of the airfoil A is cut away between the vertical stabilizing flns 15 to provide the space of cpening 21 thrgugh the airfoil which forms the space into which the passage P opens 70 and discharges. The stabilizing fln 16 is located I in and extends substantially across and forwardly through this space 21 with the controi surface 19 thereby subjected to the discharge air flow. Stabilizing surface 17 at the leading edge portion 75 of airfoil A is located in and extending across the
[5]2,384,893 space 22 which is formed In the leading edge portion IO of the airfoil and wwch provides the intake for the forward end of passage P. Referring now particularly to Flig. 3 of the drawings, the shape and form of the passage P in 5 accordance with the principles of the invention is clea,rly shown. The forward or inlet end portion of the passage P decreases rearwardly in diameter to provide restricted or reduced sectional area 23 which Is located spaced rearwardly a distance 10 from the inlet 22 for the passage. The passage P then gradually and symmetrically increa-@es in diameter and cross sectional area rearwardly to the rear discharge end of the passage at the space 2 i in the trailing portion of the wing A. Thus air 15 flowing or discharging rearwardly through passage P passes through the constricted or reduced area portion 22 of the passage and flows with increased velocity from such constriction into the rearwardly extended and expanding portion of 20 the passage P. In the present example propellers 24 and 25 are mounted in the forward portion of the passage P for discharging air rearwardly through the passage from the forw@Lrd or leading edge of the 25 wing A rearwardly to the outlet 6nd of the passage where the air is discharged rearwardly into the,space 21 over and across the stabilizing surface 16 and the control surface 19. The propeller 24 is located at the forward inlet end of passage 30 P and has a diameter 5ubstantially that of the intemal diameter of the inlet end of the passage but with operating clearance and is suitably mounted for ' rotation al>out an axis @oincident with the longitudinal axis of the passage. This 35 propeller 24 is suitably d.esigned for the air velocity and air movements required at its location for efficient operation. The propeller 25. is mounted witldn the passage P just to the rear of the constricted or smallest cross sectional area 40 23 of the passage P and this propeller 25 is differently designed from the propeller 24 in order to take care of and 6fifteiently meet the conditions encountered as a result of the increased velocity air movement at such position in the passage P. 45 The propeller 25 is of a diameter substantially that of the internal diameter of the passage at the location of the propeller 25, but with sufficient opera,ting clearance for the propeller which 50 mounted for rotation about an axis coincide with the longitudinal axis of the passage P. . The air displacement passage P in accordance with my invention is so designed and arranged that the forward Portion or section therebf pro55 vides a cone-like portion 30 decreasing in diameter rearwardly from its forward inlet end, to its discharge end at 23, and a rear cone-like section or portion 31 that -increases in diameter rearwardly from its inlet end at 23 to its discharge end in the cpace 21. The design is such, refer- 0 ring now ParticularlY to F'ig. 10 of the drawiilgs, that the forward section 30 of the passage P has substantial suction or negative pressures established therein and acting on.the walls thereof as Q5 indicated by the arrows in Fig. 10, while the rear cone-iike section or portion 31 of the passage P has substantial positive pressures established therein and acting on the wall theregf as indicated by the arrows applied to that section in Mg. 10. In other words the design and armn.ae-I 70 ment of the passage P is such that the lowest possible pressures wiU be established in and aiong the forward cone-like section 30 and the highest possibie'pressures will be established in and &long the rear cone-Bke section or portion 31 of 75 the passage P, so that the components of the pressures Integrate in a forward direction to substantially increase the thrust at low and medium speeds of the aircraft. Preferably with a wing or body of other than of symmetrical airfoil section, that is a wing having aii airfoil section with a grealtr camber at one side thereof than at the o@her as in the examples of Figs. 8 and 9, the cone-like forward and rear sections 30 and 31 of the air displacement passage are arranged in an angular relationship to each other in the directiori of that surface of the wing of greatest camber. For example, in Fig. 8 is diagiammatically shown a wing having an airfoil section with the upper surface of greater camber than the lower surface of the wing, and in accordance with the invention the forward and rear sections 30 and 31 of passage P are directed upwardly in angular relation to each other to join at the point 23 of smalfest diameter which forms the restricted passage between the forward and rear sections of the displacement passage. Similarly, in Fig. 9 where a wing is sliown having its lower surface of greater camber than its upper surface, the forward and rear sections 30 and 31 are inclined downwardly in angular relationship to each other to meet at the restricted passage 23. Whereas, in ng. 10, and in the examples of Figs. 1 to 3, where the wing is of symmetrical section, the forward and rear seetions 30 and 31 forming the passage P are preferably in axial alignnient. A further factor and a characteristic of the air displacement passage of the thrust augmentation meam of my inv4@ntion resides in the design of the forward intake or inlet end 22 of the air displacement @iassage P and this factor is particularly iuustrated in Figs. 4 and 5 of the accomi3anying drawings. In accordance with this factor, the forward inlet or intake en6 of the passage P.is formed by a vertically elliptical or elongated opening 32 formed through a leading edge portion of the wing A and of a width approximately equal to the diameter of the forward inlet end of the section 30 of the air displacement passage P, but with the opening preferably slightly decreasing in width toward its upper and lower ends. The height or vertical length of this opening or intake 32 is preferably of the order of 80% of the depth or thickness of the wing, although the invention is not limited or restricted to this exact percentage as the same maY be varied to meet the conditions of each design adaptation. By the arrangement of the passage P formed and shaped as described and with the propellers 24 and 25 of the design and character and lo-, cated in the passage as specified, a highly efficient thrust force developing means is provided for propening the aircraft with the thrust developed from the propellers 23 and 24 substantially augmented over the thrust'possible to such propellers when mounted externally of the craft in free air. In operation the propellers. 2.4 and 25 draw air into the forward end of the passage P from the air mass at the leading edge of the wing or body A: and force and impel this air in a column rearwardly through passage P to the rear discharge en(,, thereof. It is to be noted that this column ng displaced rearwardly through pasof aii- bei sage P has a substantial stabilizing effect upon the aircraft formed by the wing A when in flight. The thrust augmentation mlearis and method of my invention as herein disclosed has the further important advantage.of increasing the efficiency
