BACKGROUND ART An idealized airfoil, such as a flat plate of infinite span and a thickness approaching zero, when moving through a gaseous fluid, e. g. , air, at a fixed velocity, and the surface of the airfoil is at a small angle, i. e., the angle-of-attack, relative to the direction of motion, the oncoming flow is separated into a flow of air along the upper surface of the airfoil and a flow of air along the lower surface. This bifurcation of the flow starts in the vicinity of the leading edge of the airfoil, and becomes confluent at the trailing edge of the airfoil.

This Kutta Joukowsky hypothesis is acceptably accurate for the ideal airfoil, provided the angle-of-attack of the airfoil approaches zero. For much larger angles-of- attack, the velocity of the airflow over the upper surface of the airfoil is considerably reduced as the flow of air approaches the trailing edge. The air, therefore, separates from the wing simply because the reduced momentum of the air flow prohibits the flow of air to continue to the trailing edge of the wing and beyond. This flow separation results in loss of wing lift and can cause an aircraft flight safety problems.

Severe causes of wing air flow separation is commonly termed"wing stalling".

Practical airfoils, or wings, do not have infinite spans.

Airfoils of finite wingspan, therefore, when moving through the air at a finite speed and inclined to the direction of motion, i. e. , having a positive angle-of- attack, will be pushing down on the incoming air. The reaction of the affected air is to impose an air pressure on the lower surface of the airfoil and in close proximity to the wingtips to accelerate air upward and around the wingtip edges of the finite span wing. The air moved upwards in the vicinity of the wing tips, as the wing moves forward, forms a rolled-up vortex flow whose axis of formation is nearly parallel to the direction of flight. Because wingtip vortices are known to increase the drag of an airfoil and with it, a reduction in its aerodynamic efficiency, the reduction of wingtip vortices is a subject of continued practical interest. Airfoils moving in a rotational manner are also known to produce vortex flows off the edges of their distal wingtip, or blade tip. Due to the reduction in efficiency produced by blade tip vortices, airfoil shapes, particularly their planforms, are varied in efforts to minimize vortex production. Two or more airfoils rotating about a hub or axis of rotation can be termed a rotor or a propeller with the word propeller applied principally to the rotating propulsor providing forward thrust.

Lifting structures can include the combination of a translational airfoil, a wing, and one or more rotors in close proximity to the trailing edge of the wing. Rotors in close proximity to a wing provide lift augmentation to the wing, drag reduction and stall resistance. If

mounted and articulated, they may provide flap augmentation.

Rotors surrounded or partially surrounded by the surfaces of a wing are known to interact via the vortex flow of their blades with the airflow of the wing. An example of this aerodynamic interaction is the augmentation of the lift of the wing of an aircraft by the interactions of the wing flow with flow of a rotor located in a semi- circular cutout in the rear portion of the wing with the center of rotation of each rotor located on what would otherwise be the trailing edge of the wing.

While the above art provides for enhanced lift and reduction in drag to airfoils, there remains a need for significant basic improvements in the aerodynamic performance of wing-rotor systems, including wing stalling. New technical design architectures for vehicular embodiments and operation are required, including the synergistic combination of a wing, rotor and propeller for increased lift, reduced drag and increased thrust requirements. In particular, when compared to semi-circular cutouts, there is a significant fundamental need to increase the wing area ahead of the cutout so that a larger portion of the wing area from the wing's leading edge to cutout contour, is more favorably influenced by rotor flow. Accordingly, there is a need to move the axis of rotor rotation aft of the wing's original trailing edge thereby increasing the surface' area of the wing ahead of the frontal section of the cutout contour. Further and most significantly, moving the axis of rotation aft of the wing's trailing edge also minimizes and possibly eliminates any potential adverse

effects of rotor inflow on induced wing lift and stall resistance from that portion of the rotor inflow that is located behind the axis of rotation of the rotor.

Each blade of a propeller produces a vortex flow that generally is not considered by those skilled in the art as a contributor to induced lift or induced thrust.

There are geometric techniques, as stated herein, for propellers located in close proximity to wing surfaces that permit propeller blade tip vortices to augment wing lift and provide induced thrust.

DISCLOSURE OF THE INVENTION Disclosed are the methods and means for enhancing lift, reducing drag, and enhancing the pre-stall angle-of- attack of an airfoil illustrated by several apparatus embodiments of the present invention wherein wing-rotor configurations are described that provide aerodynamically enhanced high lift, low-drag, and a resistance to stall.

Also described is a wing leading edge air blowing system in conjunction with a trailing edge wing-rotor combination providing means for substantially vertical take-off and landing of air vehicles and substantially precluding the air vehicle from stalling. In addition, wing-rotor-propeller embodiments are described that provide aerodynamically high lift and low-drag and forward thrust for all vehicles including embodiments for air vehicles and watercraft.

The teachings of the present invention illustrate, through example embodiments, the benefits of vortex interaction maximization via less-than-semicircular airfoil cut-outs (i. e. , arcular or arcuate airfoil

trailing edge recesses) while enhancing the vortex amplitude via rotor blade planform design. Additionally, the present invention through example embodiments, illustrates the benefits of vortex interaction maximization using a propeller interposed between two substantially parallel airfoils with at least one airfoil having a plurality of rotors each rotating within a cut- out or recess. Additionally, the present invention, through example embodiments, illustrates the benefits of augmenting wing-rotor assemblies with air blowing devices and thereby enhance the lift augmenting of the wing-rotor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS For a further understanding of the nature and objects of the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein: FIG. 1A is a plan view of a wing illustrating semi- circular and arcular cutout regions; FIG. 1B is a plan view of an example wing having two arcular cutouts of the present invention; FIG. 1C is a plan view of a wing illustrating two rotors, each with their center of rotation aft of the wing's trailing edge and having a portion of the rotor region of rotor rotation coincident with an arcular cutout region; FIG. 1D is a plan view of a wing illustrating two rotors, each with their respective center of rotation and entire region of rotation aft of the wing's trailing edge;

FIG. 2A is a side view of an example rotor orientation of the present invention; FIG. 2B is a side view of an example rotor motor assembly of the present invention; FIG. 3A illustrates a rotor planform with an inverse taper; FIG. 3B illustrates a rotor planform with an inverse taper and swept tips FIG. 4 is a perspective view illustrating the vortex flow emanating from the tips of a rotor or propeller in motion; FIG. 5 is a perspective view of the rotor tip trailing vortex in proximity to the wing ; FIG. 6 is a side view of a wing and rotor illustrating the rotor interface vortex flow within the wing airflow; FIG. 7 is a diagram illustrating the upward velocity induced along the wing by the rotor vortices increasing in the direction of the trailing edge of the wing ; FIG. 8A is a plan view of a wing with arcular cutouts and rotors combined with an air blowing system; FIG. 8B is a perspective view of a wing with a singular arcular cutout and rotor combined with an air blowing system ; FIG. 9 is a cross-sectional view of wing and rotor flows initiated by compressed air blown over the wing surfaces ; FIG. 10 illustrates an example of combinations of rotor and propeller embodiments of the present invention integrated into an aircraft ; FIG. 11 is a perspective view illustrating both propeller and rotor embodiments of the present invention; FIG. 12 is a side view illustrating both propeller and rotor embodiment and resulting induced lift and thrust vectors of the present invention;

FIG. 13 is a perspective view of both rotor and propeller embodiments of the present invention applied to a watercraft ; FIG. 14 is a perspective view of a diagram illustrating the lifting effect produced by rotor vortices; FIG. 15 is a diagram illustrating the magnitudes of lifting pressures on a wing relative to location of vortices ; FIG. 16A illistrates smoke flow over a representative wing-rotor configuration mounted in a wind tunnel for rotor rpm of 0; and FIG. 16B illistrates smoke flow over a representative wing-rotor configuration mounted in a wind tunnel for rotor rpm of 7,500.

BEST MODES FOR CARRYING OUT THE INVENTION FIG. 1A is a plan view of a wing 102 illustrating that, for a given rotor diameter, arcular cutouts 108, as contrasted with semi-circular cutouts 208, result in more wing area 138 ahead of the cutout, or wing recess, that is favorably influenced by rotor flow. Additionally, any potential adverse effects of"rotor inflow"on wing lift and stall resistance from that portion of the rotor flow behind its axis of rotation is significantly reduced or eliminated by the axis of rotation 122 of the several embodiments of the present invention being aft of the original wing trailing edge 106.

FIG. 1B is a plan view of a wing 102 having a leading edge 104 and a trailing edge 106 with arcuate or "arcular"cutouts 108 where the term"arcular"is used to describe arcs of circles the centers of rotation 122 of which are behind the imaginary lines of extension 124 of

trailing edges 106 of the wing 102 and by necessity require less cutout area than semicircular cutouts. That is, the arcular area of a wing in plan view is substantially equivalent to a segment of a circle with the chord being analogous to the trailing edge.

Accordingly, a portion of the rotor travel 126 is within the region of the arcular cutout or arcuate recess 108.

Rotors 120 whose axes of rotation 122 are behind and in line 166 substantially equidistant from or otherwise substantially parallel with the original trailing edge of the wing 106 and substantially coincident with the axis for the arcular cutouts 108 are illustrated in FIG. 1C.

An alternative wing planform 151 illustrated by FIG. 1D has rotors 220 whose axes of rotation 122 are behind the trailing edge of the wing 106 to the extent that no portion of the sweep of each rotor crosses the trailing edge 106 of wing 151.

FIG. 2A is a side view at a cross-section 180 of FIG. 1C illustrating a preferred embodiment of the present invention including: each rotor 120 installed in a plane inclined relative to each of the cutouts 108; the center of rotation 122 of each rotor located aft 135 of the nominal trailing edge extension line 124 of the wing 102; the height of vertical boundary 228 of each cutout 108 of sufficient size to permit tips of the blades 219 of rotors 120 to be below the upper boundary 230 of the cutout 108 and above lower boundary 232 of the cutout 108; and where the leading tips of blades 219 of the rotors 120 are in close proximity to the boundary of cutout 108 and the trailing tips of the blades 279 may be in or out of the plane of the wing 285. The rotor in this example is inclined at an angle 290. This angle of

inclination 290, measured from the plane of the wing 285 in this example to the plane of rotor rotation 226, is variable and in alternative embodiments subject to servo- based adjustment as part of an example mounting assembly illustrated in FIG. 2B. FIG. 2B illustrates in example the propulsion unit 288 is mounted to the wing 102 via a support unit 286 that is rigidly attached to the lower surface of the wing 102. The rotor 120 is attached to the shaft 290 of the propulsion unit 288. Embodiments of the propulsion unit 288 include a gasoline engine, an electric motor and a hydraulic motor. For each of these example embodiments, the propulsion unit 288 is rigidly attached to the wing by the support unit 286. In several embodiments, the rotor angle of inclination 290 is fixed and part of a rigid mounting assembly 286, as illustrated in FIG. 2B. This mounting configuration for rotors 120 as well as propellers is well understood from the prior art. In several embodiments of the present invention, the rotor angle of inclination 290 is adjustable so that the plane of the blades 226 is inclinable to the plane of the wing 285 or to an angle out of the plane of the wing 102.

For all flight conditions of practical use and for all adjustments in inclination 290 whether fixed, manually adjusted or adjusted as part of a servo system and for each rotor, the leading tips of the rotor blades 219 are continually below the upper edge of each arcular cutout 108 and above the lower edge of each cutout 232. In alternative embodiments where the craft is propelled principally with propellers, mechanical drive linkages are made to drive the rotors 120 parasitically off the propeller motor and accordingly, separate propulsion units are not used. In alternative embodiments the rotors have variable pitch where the local angle-of-attack of

each blade is adjustable. In addition, the drive shafts may be disengaged in the event of drive power failure, allowing the rotors 120 to be feathered.

The preferred planform shapes of rotors are illustrated in FIGS. 3A and 3B. The preferred planform taper ratio is inverse; that is, the length of the chord at the tip of a blade is greater than the chord lengths at distances from the axis of rotation less than the tip chord distance.

The planform shapes of inverse taper ratio are preferred due to their vortex creation properties. FIG. 3A illustrates a rotor 310 with linearly increasing chord length as the distance from the axis of rotation increases. FIG. 3B illustrates a rotor 320 with linearly increasing chord length as the distance from the axis of rotation increases combined with linearly swept tips at each end.

Rotor Tip Vortex FIG. 4 is an illustration of a helical system of rotor vortex lines. FIG. 5 illustrates a sector of the rotor- wing configuration 500 operating at a forward speed Vo 510. A major portion of the rotor shaft 290 horsepower is expended to overcome that part of the fluid resistance to the rotating blades 120 that is dependent upon blade lift. This energy, expended to the fluid, produces and maintains a vortex system 504 that trails the motion of the rotating blades 120. In a simplified sense, the tip vortex 504 of the trailing vortex system, illustrated in FIG. 5, produces a significant increase to the circulatory flow around the wing 102. The increase in circulatory flow around the wing is to increase the aerodynamic efficiency of the wing, i. e. , to increase

lift, reduce drag, and increase stall resistance. The favorable contribution of the trailing vortex system 504 of the rotor tip 219 is, by far, the largest contributor to the aerodynamic efficiency of the wing 102. Based upon this new aerodynamic discovery, the aerodynamic efficiency of the wing-rotor system is improved and that improvement in embodiments of the wing-rotor assemblies of the present invention is determinable to a great extent by a method of calculating the contribution of the vortex flow of the rotor to the aerodynamic characteristics of the wing 102, including stalling, and thereby permits the selection of the appropriate properties of arcular cutouts 108, and the inverse taper rotor blade planform 310,320 for maximum aerodynamic efficiency.

Interface Vortex Wake FIG. 6 is an illustration of the interface vortex wake 610. This significant flow phenomenon of the wing-rotor combination that must be understood to be used as part of the method of configuring the wing-rotor embodiments, is the mechanism of the interface vortex wake 610 that in a simplified sense represents a"free surface"fluid boundary between the flow along the lower surface of the wing 606 and the rotor wake flow 610.

To this point in the disclosure of the application of the principles by way of the embodiment's of the presentation, the direction of vortex circulation is assumed to be consistent with that required for the rotor 120 providing lifting thrust. The following is the disclosure of the effect of the interface vortex wake 610 on the

aerodynamics of the wing for the wing angle-of-attack assumed to be zero, i. e. , practicably negligible.

The vortices of the interface vortex wake 610 can be considered as identical mechanisms by which momentum can be transmitted in a fluid. In the several embodiments of the present invention, the vortices of the interface vortex wake 610, by inducing upward directed velocities along the surface of the wing 102, impart fluid momentum to the wing. FIG. 7 illustrates in a diagram that this imparting of fluid momentum to the wing 102, per unit of time, results in a lift force 710 acting on the wing 102.

Indications of the magnitudes of the induced lifting pressure distribution and induced lift force are obtained from FIGS. 6 and 7, respectively. Now the fluid mass that imparts, or otherwise induces momentum to the wing 102 also induces kinetic-energy to the wing 102. The kinetic energy induced on the wing 102 provides an induced aerodynamic thrust force 740 acting on the wing 102 of a magnitude such that the product of this force and the forward velocity of the wing. Vo, the rate of doing work, is equal to the magnitude of the kinetic energy induced on the wing 102 per unit of time.

The aerodynamic forces induced on the wing 102 by the action of the"interface"vortices are enhanced by the conventional"vector"method. Referring to the diagram of FIG. 7, the"upwardly"directed velocities (i. e. , up wash velocity) 730 induced along the wing by the action of the vortices 610 results in an effective local increase in wing angle-of-attack 750. Since the local resultant aerodynamic forces must be at right angles to the local stream velocity 760, the force vector must be rotated

ahead of the lift vector by an amount necessary to be orthogonal to the local stream velocity 760. The component of this resultant vector 770 parallel to the stream direction must, therefore, be a"thrust"vector 740, and not generally a drag vector.

If one contrasts the aerodynamic forces induced on a wing 102 by vortex action with the aerodynamic forces "imposed"on an isolated wing by a fluid reaction, i. e., wing at angle-of-attack, in the latter case a drag force occurs, plus the tendency for flow separation along the upper surface that leads to stalling instead of a favorable thrust force that exists for the wing-rotor configuration combined with flow attachment along the upper surface even at high angles-of-attack. This aerodynamic anti-stall phenomenon, is a new and significant discovery, due principally to the rotor vortex flow, and in particular the tip flow.

Air Blowing System FIG. 8A illustrates, in plan view, an air blowing system for a wing-rotor configuration with the jets 801 placed aft of the leading edge 104 of the wing 102. In some embodiments, the jets 802 are mounted conformal to the wing surface. FIG. 8B is a perspective view depiction of this air blowing system 801. The combination of this air blowing system 801 and the wing-rotor system permits substantially vertical take off and landing (VTOL).

Mechanically generated air flows along the upper and lower surfaces of the wing 102 from leading edge 104 to trailing edge 106 is provided through leading edge slots 802. FIG. 9 is a cross-sectional view taken at 805 of FIGS. 8A and 8B illustrating the compressed air blowing

embodiment having a blower 910 working to enhance the beneficial effects of the wing-rotor configuration. The increased airflow works to amplify the effects of the interface vortices 610 resulting in enhanced lift and forward thrust at airspeed with air blowing augmentation.

WING-ROTOR-PROPELLER CONFIGURATIONS Operating propellers similar to rotors produce"tip" trailing vortex flows as explained in the section below.

FIG. 10 is an illustration of an example aircraft 1005 equipped with a wing-rotor-propeller system 1010. The example embodiment of the present invention, as configured in this illustration, is designed to maximize the contributions of the rotor and propeller vortex flows to induced aerodynamic wing lift and induced aerodynamic wing thrust. This configuration lends itself to an alternative embodiment that includes an air-blowing means such as a compressed gas generator in combination with starboard side and port side vents or jets located on the top side and on the bottom side of the wing containing the air-blowing device. FIG. 11 is an isometric view of the wing-rotor-propeller configuration of FIG. 10 and is also an illustration of the trailing edge flows. The propeller 1110 is interposed between a first win 1130 and a second wing 1120. The propeller 1110 being substantially perpendicular to the second wing 1120 and first wing 1130 and proximate to the trailing edge of the second wing 1121 and the leading edge of the first wing 1131 causes vortices 1111 from the propeller blade tips 1112 to induce lift on both lifting surfaces. The rotor 1160 placed at the trailing edge 1132 of the first wing 1130 produces blade tip vortices 1163 that in turn induce lift on the first wing 1130. FIG. 12 is a depiction of

the induced aerodynamic force acting on the wings of the aircraft and the associated pressure fields. The propeller 1110 produces a forward thrust 1115 and its vortices 1111 induce a lift 1125 on the second wing 1120 and a lift 1135 on the first wing 1130. The rotor 1160 produces an upward thrust 1165 and its vortices 1161 produce lift 1136 on the first wing 1130. Two regions of high pressure are created: one aft of the propeller and below the first wing 1170 and one below the rotor 1172.

Watercraft embodiments use wing-rotor assemblies and wing-rotor propeller assemblies separately and in combination preferably positioned at the mid-body and at the aft portions of watercraft. Where the assemblies are mid-body and substantially outboard, the assemblies are preferably used in pairs. Where the assemblies are at the aft portion, they are used in pairs or. as a single assembly. A watercraft embodiment of the present invention is illustrated in FIG. 13. In this example, a wing-rotor configuration pair is used mid-body 1320 with an elevated aft section using a wing-rotor-propeller configuration 1340. In this example, the lifting surfaces have arcular cutouts 108 leading rotors. Alternative embodiments of the watercraft have an aft section with a wing-rotor configuration without mid-body wing-rotor configurations while other embodiments include mid-body wing-rotor assembly pairs.

AERODYNAMICS OF WING-ROTOR AND WING-ROTOR-PROPELLER The wing-rotor systems and also wing-rotor-propeller systems are synergistic combinations of a wing 102, rotor 120, and a propeller that have higher aerodynamic efficiencies in forward flight than either an isolated

wing, e. g. , a conventional aircraft, or an isolated<BR> rotor, e. g. , a helicopter, or an isolated wing-propeller combination.

Two-Dimensional Wing, Line Vortex Flow A fluid vortex line is characterized by fluid rotating in a circular fashion 1410 in planes normal to the vortex line 1420, as illustrated in FIG. 14. The velocity and momentum of the rotating fluid is upwards ahead of the vortex line 1420 since the direction of the fluid is upwards. Behind the vortex line 1430, the momentum of the fluid is downwards. A thin flat surface (like a wing 102) inserted into the fluid a small distance ahead and in the same plane as the vortex line 1420 will receive the maximum upwardly-directed momentum of the rotating fluid.

If the wing 102 and vortex line are both moving at the same velocity, for example, a value of the magnitude of the velocity vector, Vo 510, then the upwardly directed momentum of the rotating fluid will be communicated to fresh masses of air moving over the wing. Per unit of time, this momentum will cause a distribution of"lifting pressure"1440 to act on the wing. The integration of this pressure distribution yields a lifting force, 710, acting on the wing as illustrated in FIG. 7.

FIG. 15 is an illustration of the distribution of lifting pressure, AP, per unit of Vor'that is induced on the wing by the fluid action of an infinite line vortex for several chord-wise locations of the line vortex.

Accordingly, the ordinate scale is hP/vOr'1510.

The effect of an element of vorticity, rut 1520, at a point on the pressure distribution of a two-dimensional airfoil has been calculated and presented in the FIG. 15.

In the diagram, the symbol,, denotes the x-position of a wake vortex of strength rt where t is measured from the mid-point of the airfoil and is positive in the aft direction.

It is seen from the diagram that a wake vortex located one-half of a chord length, or more, behind the wing trailing edge induces a pressure distribution that is similar to the well-known distribution produced by a small angle-of-attack, while a vortex located very close to the airfoil induces a much stronger pressure distribution over the chord, with a definite peak 1560 near the trailing edge, in the example where t has a value of 1.1.

In maximizing this effect in the several embodiments of the present invention, the vortex lines 166 are substantially parallel to a wing trailing edge 106 so as to induce large lifting pressures along the wing, provided the vortex circulation is in the same direction as the wing circulation with the vortex line located substantially in the plane of the wing or below the plane of the wing while proximate to the trailing edge of the wing 106. In the arcuate recesses herein described, the relationships disclosed provide for methods of augmenting thrust, reducing drag and enhancing the effective pre- stall angle-of-attack of airfoils by placing the axis of rotation of each rotor aft of what would otherwise be the trailing edge of a nominal airfoil, and more precisely

locating the axis of rotation to achieve the desired scaled lifting pressure.

Rotor-Propeller Flows If one reviews in detail the flow pattern in the immediate area of the tips of a rotating blade, it becomes evident that flow conditions can be very different from those near the tip of an airfoil moving in translatory motion. In particular, the"tip effect"is far stronger for a rotating blade than for a wing moving in a translatory manner. Helical vortex lines of large strength (circulation) emanate from the tips of the rotating blades as illustrated in FIG. 4. These"strong" vortex lines are brought about by the relatively large amount of kinetic energy communicated to the fluid by the rotor or propeller when generating lift or thrust.

Some measure of the relative strengths of an isolated wing trailing vortex system compared to a rotor or propeller trailing vortex systems can be determined by calculating the circulation of each of these systems for a constant span loading condition. It should be recalled that circulation, r, is a numerical measure of the capability of a vortex to put into circulating motion around the vortex a mass of air at some velocity.

Continuing the description of the circulation, R represents the rotor or propeller radius in linear units of feet; C represent the wing chord in linear units of feet ; Vi represent the rotor or propeller inflow velocity , in linear velocity units of feet-per-second (fps); T represent rotor or propeller thrust, in force units of pounds (lbsf) ; and VT represent the tangential velocity at

rotor or propeller tip, in linear velocity units of fps.

Equations for calculating Vi and VT are: where p represents air density and Where fis frequency units of revolutions-per-minute (rpm).

Using classical equations for calculating ra and rp, we derive the following equation for the ratio of these circulations: Although equation [3] is based on simplified assumptions, numerical values of the ratio rp/ra obtained from the equation are practical approximations to the actual ratios. This equation yields values of rp greater than ra for a wide range of compatible rotor and wing geometries, rotor or propeller revolutions per minute and flight velocities.

Additional Aerodynamic Features For wing-rotor configurations identified herein the significant increases in wing lift and thrust induced on

the wing by the trailing vortex flows of rotors represent a major improvement in the aerodynamic performance of lifting systems. Additional distinct and significant aerodynamic improvements include the airflow attachment along the upper surface of a wing and inducement of the vortex flap effect.

The airstream and boundary layer flow along the upper surface of the wing that is in front of the rotor will remain attached to the surface of the wing for a range of high angles-of-attack because of the wing surface <BR> <BR> dp o<BR> favorable chord-wise pressure gradient, i. e., j,<BR> du produced by the low pressure field of the rotor above the plane of the rotor. FIG. 16A and FIG. 16B present flow over a wind tunnel model of a wing/rotor configuration in a 45 fps, flow, 1610, at angle-of-attack of 18 degrees, 1630, and rotor rpm = 0, 1620, and 7500 rpm, 1621. FIG.

16B, illustrates that for rpm of 0,1620, the upper surface air flow 1660 is separated. For rotor rpm = 7500, 1621, the upper surface flow 1670 is attached and descends through the rotor boundary.

The vortex flap is defined herein as the frontal portion of the vortex surface of the rotor slipstream that decelerates and deflects the oncoming flow along and below the lower surface of the wing from leading edge to trailing edge. This favorable aerodynamic effect increases the lift of the wing and also by inducing an velocity flow along the wing chord as illustrated in FIG. 7, provides an aerodynamic thrust force to the wing.