BACKGROUND OF THE INVENTION Broadly, this invention concerns a system for increasing the design lift capability of an airframe either as optional new equipment or as a retrofit. More particularly, the invention involves a system providing additional lift capability on demand through use of lightweight flexible sheet materials.

SUMMARY OF THE INVENTION A lift augmentation system according to the present invention may include a leading edge support that is extendable. Such extendability may permit the lift augmentation system to telescope longitudinally along an existing wing. That extendablity may also permit the lift augmentation system to rotate between a stowed position and a deployed position. The lift augmentation system also includes at least a pair of flexible surface elements carried in part by the leading edge support and which function as aerodynamic surfaces for the lift augmentation system. One of those flexible surface elements at least partially defines the suction surface for the lift augmentation system. Another of those flexible surface elements at least partially defines the pressure surface for the lift augmentation system. To change the lift augmentation area, a deployment system for the lift augmentation system is operable to extend and retract the leading edge support as well as the flexible surface elements. The flexible surface elements may be fabricated from one or more materials. Suitable materials include, for example, fabric-based materials, composite materials, carbon fiber reinforced materials, synthetic polymer sheet materials, woven cloth materials, and materials having laminated surface layers. In some applications, battens may be used to locally stiffen the flexible surface elements. The deployment system may include a spar subsystem for extending and retracting the leading edge support and a fabric control subsystem for deployment and retraction of the flexible surface elements. Suitable fabric control subsystems may include a roller on which the flexible surface elements are wrapped. A suitable conventional motor may control the deployment of the flexible surface elements as the lift augmentation system is extended and recover the flexible surface elements as the lift augmentation system is retracted. Where multiple flexible surface elements are used for the lift augmentation system, multiple rollers may advantageously be used. To secure the flexible surface elements to structural elements of the lift augmentation system, slide systems may be provided on structural members where the slide systems slidably receive corresponding edges of the flexible surface elements. In some applications, a cable and pulley system may be used for the fabric deployment subsystem. Suitable spar deployment subsystems may include various mechanical arrangements. For example, one or more rack and pinion arrangements may be provided with the rack element attached to a spar and the pinion drive attached to a stationary support. Alternatively, a screw-drive system may be used. In a screw drive system, a rotatable threaded member may be attached to a spar while a fixed cooperating element is secured to a stationary support. Or, a fixed threaded member carried by a spar may cooperate with a rotatable cooperating element rotatably carried by the stationary support. Regardless of the mechanical arrangement, the spar deployment subsystem is preferably operable to move the leading edge support between first and second positions, where the first position may be a fully stowed or retracted position and the second position may be a fully extended or partially extended position. Where the lift augmentation system is positioned at the tip of an existing aerodynamic surface, the spar deployment subsystem may telescopically move the spar. Where the lift augmentation system comprises a pivotal system, the first position is typically fully stowed while the second position is typically fully deployed. The lift augmentation system of this invention can be used as a subassembly for original equipment, or as a subassembly for retrofit applications. In either event it can be used with a multiplicity of airframes. Preferably, when used in a wing-tip augmentation scenario, the lift augmentation system increases the nominal wing area in the range of about 15% to about 35%. In the wing-tip augmentation application, the lift augmentation system has a cross-sectional configuration that corresponds to the cross-sectional configuration of the existing wing tip. Furthermore, the leading edge element preferably has a contour conforming to the contour of the existing leading edge so that as the lift augmentation system is deployed and retracted, the leading edge element slidably moves longitudinally with respect to the leading edge of the wing without deleteriously affecting aerodynamics of the existing wing. As desired, the airframe may be manned or unmanned and remotely controlled. Furthermore, the airframe may include any of a variety of propulsion systems including, by way of example, a jet engine, pusher type propellers, pull type propellers, diesel engine, rotary engine, ducted fan engine, a mixed cycle engine, or a mixed combination such as a forward-mounted fuel-burning reciprocating engine in conjunction with an aft-mounted small jet or gas turbine engine.

BRIEF DESCRIPTION OF THE DRAWINGS Many objects and advantages of the present invention will be apparent to those skilled in the art when this description is read in conjunction with the attached drawings wherein like reference numerals have been applied to like elements and wherein: FIG. 1 is a schematic perspective view of an airframe having a lift augmentation system according to the present invention; FIG. 2 is a top view of the lift augmentation system in a fully deployed position; FIG. 3 is a front view of the lift augmentation system in a fully deployed position; FIG. 4 is a top view in partial cross section of the lift augmentation system in a fully deployed position; FIG. 5 is an enlarged partial cross-sectional view taken along the line 5-5 of FIG. 4; FIG. 6 is an enlarged partial cross-sectional view taken along the line 6-6 of FIG. 4; FIG. 7 is an enlarged partial cross-sectional view taken along the line 7-7 of FIG. 4; FIG. 8 is an enlarged partial cross-sectional view taken along the line 8-8 of FIG. 4; FIG. 9 is a schematic top view of a lift augmentation system arranged for pivotal deployment; FIG. 10 is a view in partial cross section taken along the line 10-10 of FIG. 9; FIG. 11 is a view in partial cross section taken along the line 11-11 of FIG. 9; FIG. 12 is a view similar to FIG. 9 showing stowed and deployed positions for the leading edge spar; FIG. 13 is a schematic top view of a lift augmentation system having a pair of wing assemblies; FIG. 14 is a schematic front view of the embodiment of FIG. 13; and FIG. 15 is a schematic perspective view of a lift augmentation system mounted for use on an unmanned, unpowered airframe.

DETAILED DESCRIPTION OF THE INVENTION For purposes of this description, the term airframe is intended to be a generic reference to any type of vehicle that can move through a gaseous medium such as air. For example, airframe includes, by way of example and without limitation, airplanes, gliders, lifting bodies, spacecraft during recovery, helicopters, and the like. The airframe may be powered by a propulsion system, or it may be unpowered. Similarly the airframe may be manned, or unmanned, or remotely controlled. Turning to FIG. 1, an airframe comprising a suitable conventional airplane 20 includes a high wing assembly 22 attached to and supported by a fuselage 24. The wing assembly 22 typically has left and right wings, 22α, 22b. Each wing normally is designed to have a nominal wing area. As depicted, the airplane 20 also has a twin-boom tail assembly 26 attached to and supported by the high wing 22. To provide powered flight, the airplane 20 also includes a pair of propulsion units 28, 30. Each propulsion unit 28, 30 may operate on any suitable conventional fuel, including without limitation, gasoline, diesel, and synthetic fuels. Moreover, each propulsion unit may operate on any desired thermodynamic cycle. Furthermore, each propulsion unit may comprise an internal combustion engine, a jet engine, a rotary engine, a mixed cycle engine, or a ducted fan engine. Each propulsion unit may be operably connected to a propeller, or other suitable device for driving the airframe through air. Here, for example, a forward mounted propeller 32 is driven by one of the propulsion units 28, while a ducted fan 34 positioned between the twin booms of the tail assembly 26 is driven by the other one of the propulsion units 30. The propulsion units 28, 30 can operate simultaneously or one at a time. Thus, the ducted fan 34 functions as a pusher-type propeller and could be positioned at the back of the fuselage 24 to attain quieter operation than would occur with a front-mounted pull-type propeller 32. The outboard end of each wing 22α, 22b includes an extendable/retractable wing-tip lift augmentation assembly 40. The wing-tip lift augmentation assemblies 40 are mirror images of one another. Accordingly, it will suffice to describe one of the assemblies 40 as it will be understood that the other has the same features but operates in a reflected way. Each wing tip assembly 40 can be essentially self- contained. As a result, the wing tip assemblies 40 may be offered as a retrofit accessory for an existing aircraft. Alternatively, the wing tip assemblies 40 may be offered by original equipment manufacturers as optional equipment. Each wing-tip assembly 40 is movable between a first, fully retracted position 40' (shown in phantom lines in FIG. 2) and a second position (shown in solid lines in FIG. 2). The second position may be the folly extended position depicted in FIG. 1 or an intermediate position located between the fully extended and fully retracted positions. In this way, as the wing-tip assembly 40 is extended, the area of the associated wing 22α, 22b is increased and the available lift for the airplane 20 increases. A wing-tip assembly 40 may increase the nominal area of the associated wing by as much as about 100%. Preferably, the area increase will be about 50% and most preferably the area increase will be in the range of about 15% to about 35%. Moreover, the wing-tip assembly increases the aspect ratio for the combined original wing and assembly 40, thereby increasing the lift and aerodynamic efficiency of the resulting combination. While the chord of the wings 22α, 226 in FIG. 1 is shown as a constant, the wing-tip assembly 40 can be used with wings that taper in the direction from the fuselage to the wing tip. Regardless of whether the wing is tapered or not, the leading edge of the wing-tip assembly should be essentially collinear with the leading edge of the associated wing. Moreover, the trailing edge of the wing-tip assembly 40 should be essentially parallel to its leading edge, with the chord of the wing-tip assembly 40 being substantially the same length as the chord of the associated wing tip. To further enhance the lift augmentation properties of the wing-tip assembly 40, it may be provided with an upwardly extending fence 42, as well as a downwardly extending fence 44. As desired, the fences 42 on opposite wing tips may have a dihedral angle between them. Likewise, the fences 44 on opposite wing tips may also have a dihedral angle therebetween. These wing-tip fences 42, 44 are effective to reduce the secondary air circulation flow between the bottom or pressure surface of the wing and the top or suction surface of the wing. Reduction of that three-dimensional secondary flow also enhances the lift otherwise available from the wing 22. As will be described more fully below, these wing-tip fences 42, 44 may also function as fairings to conceal apparatus related to extension and retraction of the lift augmentation system 40. Turning now to FIG. 2, the wing-tip lift augmentation assembly 40 includes an extendable leading edge support 50 having a length which exceeds the spacing between the retracted position 40' and the extended position. In this way, the leading edge support 50 can provide additional cantilever support for the lift augmentation system. Preferably the leading edge support 50 includes an edge cuff 52 which may be fabricated from a carbon-fiber-reinforced epoxy matrix or other equivalent material, including laminates. The edge cuff 52 conforms to the leading edge contour of the associated wing 22ZJ and has a length sufficient to give continuity to the leading edge when the lift augmentation system assembly 40 is fully extended. To support the edge cuff 52 and reduce forces resisting its sliding movement, suitably shaped polytetrafluroethylene (Teflon®) pads (not shown), or other suitable material with similar characteristics, may be provided between the leading edge cuff 52 and the upper and lower surfaces of the wing leading edge. The pads can be applied to either the inside of the leading edge cuff 52 or to the external surfaced of the wing. Preferably, the pads are applied to the inside surfaces of the edge cuff 52 to reduce potential disruption of airflow over the wing in normal operation. Those pads also permit the cuff 52 design to support some torsion and bending loads which are applied to the associated wing 22b when the lift augmentation system is deployed. The lift augmentation system 40 also includes at least two flexible surface elements, one surface element 54 is located on the top or suction surface of the lift augmentation system while one other surface element is located on the bottom or pressure surface of the lift augmentation system . Moreover, it is contemplated that two or more surface elements 54, 56 may be used for the suction surface, as well as for the pressure surface of the lift augmentation system 40. The flexible surface elements are preferably fabricated from sheet material that is sufficiently flexible that it can be rolled. The material may be woven or non- woven. The flexible surface elements may also be fabricated from any suitable conventional dimensionally stable synthetic material such as aramid fiber (e.g., Kevlar®), polyester fiber (e.g., Dacron®), ultra high molecular weight polyethylene fibers (e.g., Spectra™), high strength liquid crystal polymer fiber (e.g., Vectran™), nylon, or the like. Furthermore, the material of the flexible surface elements is selected such that it is sufficiently strong that it can withstand, without failure, aerodynamic pressures and forces to which the lift augmentation system will be subjected during flight operations. Material having carbon fiber reinforcement is also suitable for these flexible surface elements. Such carbon fiber reinforcement may be used as a component of a fabric-based material. The material may comprise a film of synthetic polymer sheet material, or a composite material. For example, a composite material may comprise a cloth woven with aramid, polyester, and/or carbon fibers and including laminated surface layers such as a polyester film (e.g., Mylar®) for strength and stretch resistance and an outer layer of PVF film (e.g., Tedlar) or PVDR (e.g., Kynar) for ultraviolet protection. A deployment system is provided to extend and retract the lift augmentation system relative to the wing tip and to extend and retract the flexible surface elements, thereby changing the augmentation area. The deployment system includes a spar subsystem for extending and retracting one or more spars and a fabric control subsystem for deploying and retracting flexible surface elements. To support the lift augmentation system 40 relative to the wing or airframe, a leading edge spar 60 (see FIG. 4) may be attached to a bulkhead 62 at the tip of a wing. Preferably , the leading edge spar 60 is mounted so that is can move longitudinally with respect to itself as the lift augmentation system 40 moves between its first and second positions. To provide the required structural support, the leading edge spar 60 may also be supported by other structures in the existing wing. A mid-chord spar 64 may also be provided for support of the lift augmentation system. The mid-chord spar 64 would also be longitudinally slidable with respect to itself as the lift augmentation system 40 moves between its first and second positions. A suitable conventional actuator 66, such as a DC motor, may be provided for at least one of the spars 62, 64. Preferably an actuator 66 is provided for each spar to reduce binding during deployment and retraction. Mechanically, the lift force exerted on the wing tip assembly may be reacted by the suitable conventional frictionless bearings (not shown) that guide the associated spars 60, 74 during extension and retraction. The outboard bearing generates a downwardly directed reaction force while the inboard bearing generates an upwardly directed reaction force, the bearing reaction forces generating a force couple that reacts at least part of the moment exerted by the lift force on the end of the corresponding wing 22. One end of each flexible surface element 54, 56 is attached to the bulkhead 62 to secure it and provide a substantially continuous aerodynamic surface for the associated wing. The other end of each flexible surface element 54, 56 is preferably attached to a fabric control subsystem for regulating the deployment and/or retraction of the flexible surface elements. The fabric control subsystem may include, for example, one or more corresponding rollers carried at the end of the lift augmentation system within the fairings provided by the lift enhancement devices 42, 44. The flexible surface element collection/deployment rollers may be carried on a single shaft and operated by a suitable conventional actuator 68, such as a DC motor, which is also located within the fairings provided by the lift enhancement devices 42, 44. For example, the actuator 68 may include a gear (see FIG. 5) which meshes with a gear 70 at the end of the roller shaft. Thus, as the actuator 68 operates, it can control the rate at which the flexible surface elements 54, 56 are deployed or retracted. Moreover, the actuator 68 provides a mechanical detent to rotationally fix the collection/deployment rollers so that the quantity of the flexible surface deployed can be controlled. The roller assembly (see FIG. 4) carried at the outboard end of the wing tip assembly 40 furls and deploys the flexible surface material. More particularly, the flexible surface element 56 (see FIG. 7) may be furled on a forward roller assembly 72 and the aft surface element 56 may be furled on a corresponding aft roller assembly (not shown). To simplify operation, the upper surface element 54 may be positioned above a corresponding lower surface element 54'. The upper and lower surface elements 54, 54' are simultaneously deployed and furled from the roller assembly 72 by wrapping them simultaneously around the roller assembly 72 during furling and by simultaneously paying them out from the roller assembly 72 during deployment. Various actuating mechanisms may be contemplated for the spar deployment subsystem to deploy the wing-tip lift augmentation system assembly 40 relative to an existing wing. For example, one suitable actuating mechanism may include a suitable conventional gear rack 70 (see FIG. 6) attached to or integral with the leading edge spar 60. The gear rack 70 cooperates with a corresponding actuator 66 (see FIG. 4) to extend and retract the assembly 40 relative to the wing by longitudinally translating the leading edge spar 60. Another suitable mechanism would be a rotary screw and conforming threaded collar. Here, the screw may be attached to either the leading edge spar or the existing wing structure and the conforming collar may be attached to the other of the leading edge spar or the existing wing structure. Either the screw or to conforming collar may be rotated to advance and retract the leading edge spar relative to the existing wing. While the accompanying figure depict the leading edge spar as a single element, it is contemplated that the leading edge spar may also be a sectional system where shorter sections telescopically are received by other sections so that the overall length of the leading edge spar can be reduced. In such an arrangement, the spar deployment subsystem can telescopically move the leading edge between first and second positions as described. Furthermore, the leading edge spar may be telescopically received in a conforming sleeve which can be mounted to an existing aircraft structure to simplify retrofit applications. To facilitate proper tracking of the surface elements during retraction and deployment, each flexible surface element may include fore and aft protrusions, e.g., 80, 82 (see FIGs. 6 and 8), that are received in correspondingly shaped channels e.g., 84, 86, provided in the front and mid-chord spars 60, 64, respectively. More particularly, the upper flexible surface element 54 has a protrusion 80 (see FIG. 6) supported close to the upper edge of the leading edge spar 60 and another protrusion 82 (see FIG. 8) supported close to the upper edge of the spar 64. Similarly, the lower flexible surface element has a protrusion 80' (see FIG. 6) supported close to the bottom edge of the leading edge spar 60 and another protrusion 82' supported close to the bottom edge of the spar 64. The other flexible surface elements 56, 56' have a protrusion 83, 83', respectively, at the forward edge (in the direction of airflow over the lift augmentation system) but not at the rear edge. The protrusion 83 of the upper flexible surface element 56 is located at the upper edge of the spar 64 while the protrusion 83' of the flexible surface element 56' is located at the lower edge of the spar 64. The rear edges (see FIG. 4) of the aft flexible surface elements 56, 56' are connected to hold them together during use. In some applications, it may also be desirable to shape those rear edges by providing a concave curvature facing the downstream direction for flutter control or compensation. Those protrusions 80, 80', 82, 82', 83, 83' and the associated channels are analogous to the bolt rope used in sails and the corresponding spar channels provided to receive them. As seen in FIG. 7, the end portion 90, 90' of each channel 84, 84' may be faired or smoothed to provide a gradual entry for the edge of the flexible member thereby reducing the likelihood of damage to the flexible members 54, 54' from sharp edges. With this arrangement the flexible surface elements can be securely carried by at least one spar in such a way that smooth airflow over the spar-surface element interface is maintained. Another embodiment of the lift augmentation system according to this specification is depicted in FIG. 9. In this embodiment, the deployment system includes a spar deployment subsystem that pivotally extends and retracts the leading edge spar while the fabric control subsystem extends and retracts flexible surface elements along the leading edge spar. For example, in this embodiment, the lift augmentation system 40 includes an extendable leading edge spar that can be moved about a vertical axis through a pivot 100 in a plane. The extendable leading edge spar 102 is positioned at the forward edge of the lift augmentation system 40. A wing-tip assembly 104 may be pivotally connected to the outboard end of the leading edge spar 102 and defines the outboard end of the lift augmentation system 40. To provide lift augmentation, a flexible surface element 106 extends rearwardly from the leading edge spar 102. When fully deployed, the flexible surface element 106 also extends from the fabric control subsystem which may include a roller assembly 108 attached to an airframe to the wing-tip assembly 104 at the end of the spar 102. The flexible surface may be fabricated from the same materials described above in connection with the wing-tip mounted embodiment of the lift augmentation system. This embodiment of the lift augmentation system may increase the lift area of an airframe by more than 100%. In some applications, this embodiment of the lift augmentation system may prove the entire lifting surface for an airframe. The roller assembly 108 may be rotated by a suitable conventional actuator 110, such as a DC motor. The roller assembly 108 is operable to furl or roll up the flexible surface element 106 when it is retracted to a stowed position and can control or brake the deployment of the flexible surface element as it is deployed to the position depicted in FIG. 9. As with the first embodiment, at least a pair of flexible surface elements 106, 107 (see FIG. 10) are provided, one 106 being on the top or suction surface, and the other 107 being on the bottom or pressure surface of the lift augmentation system. The leading edge spar 102 has a cross-sectional shape that is smoothly rounded and that functions as the leading portion of an airfoil. At the back of the leading edge spar 102 a pair of brackets 112, 114 are provided to support the corresponding forward edge of the associated flexible element 106, 107. To this end, the brackets 112, 114 may, for example, be fashioned by an extrusion process. Regardless of how the brackets 112, 114 are fabricated, each bracket includes a corresponding channel 116, 118 to receive and hold an enlarged edge 120, 122 of the associated flexible member 106, 107. Each bracket 112, 114 also includes a plurality of bearing races 130, 132, 134, 136. The bearing races 132, 138 oppose one another, as do bearing races 134, 136. Moreover, the bearing races 130, 132, 134, 136 circumscribe the channel 116. Thus, when viewed in cross section, the brackets 112, 114 define a rearwardly projecting finger extending from a position adjacent to the upper and lower surfaces, respectively, of the leading edge spar 102. As illustrated (see FIG. 9), the flexible surface elements 106 may taper from the root of the wing at the pivot 100 to the tip of the wing at the plate 104. So that the entire flexible surface elements 106, 107 can be retracted, the roller assembly 108 has a length sufficient to wrap the widest part of the flexible surface element 106. Preferably, the upper and lower flexible surface elements 106, 107 are joined at the trailing edge 150, or within a distance of about 10% of the chord length of the lift augmentation system cross section. That connection helps the flexible surfaces 106, 107 retain an airfoil shape in cross section and helps reduce the possibility of separation between the suction and pressure surfaces at the trailing edge. If desired, the upper and lower flexible surface elements 106, 107 may have one or more battens 152. The battens 152 can be spaced at intervals along the leading edge spar 102. When used, the battens 152 help stiffen the flexible surface elements and help preserve an airfoil shape. As an alternative, vertically extending fabric webs may be provided at intervals along the spar 102 to regulate the spacing between the upper and lower surface elements 106, 107. Such fabric webs may be a substantially continuous cross-section of the desired airfoil shape, or material strips spaced chordwise and attached to both the upper and lower surface elements 106, 107. To exend the flexible surface elements 106, 107 to the deployed position, a headboard 154 (see FIG. 9) is attached to the outboard end of both surface elements 106, 107. The headboard 154 securely clamps the ends of the surface elements 106, 107 together (see FIG. 11). In addition, the headboard 154 includes a plurality of linear reduced friction bearings 160, 162, 164, 166, 168, 170, 172, 174 that cooperate with the bearing races 132, 134, 136, 138 (see FIG. 10) provided on each of the brackets 112, 114. Those bearings allow low friction sliding to occur between the headboard 154 (see FIG. 11) and the leading edge spar 102. Moreover, the bearings are arranged in the headboard 154 so that a longitudinal axis 180 of the headboard 154 defines a fixed angle with a chord 182 of the lift augmentation system. For these purposes, the chord is taken as a line through the forwardmost point of the leading edge spar 102 and the trailing edge of the flexible surface elements 106, 107. With this arrangement, the headboard 154 also fixes the angle of attack for wing-tip of the lift augmentation system system. This embodiment of the lift augmentation system is also movable between a first position (see FIG. 12) and a second position. Here, the first position is fully retracted (shown in phantom lines). In the second position, the leading edge spar 102 is fully extended and is generally perpendicular to the axis of the roller assembly 108. To rotate the leading edge spar from the retracted position 102' to the extended position, a cable-and-pulley arrangement may be used. For example, one end of a flexible deployment cable 190 may be attached to the leading edge spar 102 inboard of the outboard end of the spar 102. Preferably, the cable-to-spar connection is located at about the middle of the distance between the pivot 100 and the outboard end of the spar 102. The deployment cable 190 passes around a pulley 192 mounted to the housing 194 and then goes into the housing 194 where it is wound on a suitable conventional winding mechanism (not shown). As the deployment cable 190 is wound in, the leading edge spar 102 rotates about the pivot 100 from the first position 102' to the fully deployed position. The deployment system also includes a second cable, the luff-tensioning cable 200. One end of the luff-tensioning cable 200 is attached to the headboard 154. The luff-tensioning cable then passes around a pulley 202 carried at the downstream end of the wing-tip assembly 104, and around another pulley 204 carried at the end of the leading edge spar 102. The luff-tensioning cable 200 then passes internally through the leading edge spar 102 to the housing 194 where a suitable conventional cable winder (not shown) is provided. After the leading edge spar 102 has been extended, the luff-tensioning cable 200 is wound in. Initially the headboard 154 is held in its stowed position. As the luff-tensioning cable tightens, the wing-tip assembly 104 rotates about its pivot 206 from the stowed position 104' where it is in substantial longitudinally alignment with the leading edge spar 102 to its deployed position where it extends rearwardly from the leading edge spar 102. Preferably the outboard surface of the wing-tip assembly 104 and the forward most edge of the leading edge spar 102 are substantially perpendicular at full deployment. Continued winding of the luff-tensioning cable 200 causes the headboard 154 to be drawn outwardly along the leading edge spar 102 until the flexible surface elements 106, 107 are fully deployed (see FIG. 9). As the headboard 154 moves along the leading edge spar 102, the linear bearings move along the brackets 112, 114 (see FIG. 11) and the enlarged edges 120, 122 of the flexible surface elements 106, 107 are pulled longitudinally through the corresponding slots 116, 118. With final tensioning of the cable 200, the trailing edge 150 (see Fig. 10) of the flexible surface elements 106, 107 is held in proper spatial relation to the leading edge spar 102 so that the desired airfoil shape of the lift augmentation system cross section is attained. The flexible surface elements 106, 107 can be retracted by easing tension on the cable 200 and actuating the roller 108 to wind in the elements 106, 107. Moreover, to retract the leading edge spar, aerodynamic drag can be used to swing the spar about its pivot 100 when tension on the cable 190 is eased. It will be appreciated by those skilled in the art that it would also be possible to use hydraulic actuators for the spar deployment subsystem so that the leading edge spars can be retracted with a powered and controlled system. This second embodiment of the lift augmentation system is well-suited for use with an airframe having short stubby wings or no wings. For example, a helicopter with no wings may be provided with a lift augmentation system of this pivotally deployed embodiment. One lift augmentation system would be mounted on each side of the helicopter with the stowed position having the leading edge spar against the helicopter fuselage. When deployed the lift augmentation system extends laterally outwardly from the helicopter body or fuselage. A mirror image lift augmentation system is provided on the other side of the helicopter. These lift augmentation systems are lightweight and can be used to facilitate quiet operation of the helicopter. More particularly, with the wings deployed, the helicopter can operate in an autorotation mode to reduce noise from the main rotor while the flexible wings provide a glider-like operability. In this application, the lift augmentation system provides substantially the entire lifting surface area for the helicopter - except for the main rotor blades. The second embodiment of the lift augmentation system may also be used for an independently mountable wing assembly for use with structures or airframes that have not been designed with wings and for which some gliding capability is desired. Examples of such structures are lifting bodies, air-dropped cargo containers and the like. For these applications, the lift augmentation system provides the entire lifting surface area for the airframe. For such applications, wing assembly 220 comprising a pair of lift augmentation systems symmetrically arranged with respect to one another (see FIG. 13) can be used. The leading edge spars 102, 102" of the wing assembly 220 rotate between the retracted positions 102', and 102'", respectively, as discussed above. Deployment of the flexible surface elements 106, 106' may be coordinated. For example, the roller assemblies 108, 108' may have gears 210, 212, respectively, that are engaged with one another to ensure that the deployment and tensioning of the two sides of the wing assembly 220 are symmetrical. If the application requires that the lift augmentation system s of the wing assembly 220 have a swept-back configuration, that configuration is readily accomplished by arranging the angle between the axes of the roller assemblies 108, 108' at twice the desired sweep angle for the leading edge spars 102, 102". To support the spars 102, 102" in a high- wing position, each lift augmentation system may have a vertical strut 222, 224 which carries the associated pivot 100, 100'. In addition, spar-support struts 230, 232 may be provided extending between the associated leading edge spar 102, 102' and the bottom of the struts 230, 232. With this arrangement, the spars 102, 102' can be constrained to move in a plane to which the pivot axis is perpendicular. Turning to FIG. 15, an air-droppable container 250 is shown having a rectangular prismatic shape. Any other suitable conventional shape is also contemplated including, for example, circularly cylindrical, prisms with semicircular, trapezoidal, or triangular cross sections. If desired, a fairing may be attached to the forward end of the container 250. Similarly, if desired, a fairing or directional control structure 252 may be attached to the back end of the container 250 to provide vertical and horizontal stabilization surfaces. To increase the lateral range of the container during an air-drop, a flexible- wing lift augmentation system 220 is attached to the top of the container 250. To some extent, the wing system 220 converts the container 250 to a glide vehicle. The lift augmentation system is stowed in a pod 254 at the time the container starts dropping and is deployed to the position shown by remotely controlled apparatus. The struts 230, 232 support the wing 220 both laterally and longitudinally with respect to the container 250. To that end, suitable support struts and elevatable arms are provided, some of which can be located within fairings around the pod 254 and its vertically extending portions. Those support struts and arms may be further operable to adjust the elevation of the front and rear portions of the pod 254 so that the angle of attack for the wing 220 can also be controlled and/or adjusted. The wing assembly 220 may be positioned generally at the center of the container 250. The lift augmentation system of this invention provides substantial advantages. For example, testing of the lift augmentation system has confirmed a substantial reduction in ground run can be attained - on the order of 40% « and that a significant reduction in take-off speed can also be achieved - on the order of 32% in certain applications. Flight test simulations also indicate that the takeoff distance to cleas a 50-foot obstacle can also be materially reduced - on the order of 40%. Landing performance with the lift augmentation system has even more improved metrics than take-off. Similar controlled descent performance capabilities of the top-mounted lift augmentation system in a pod make it a competitive candidate for application to space re-entry or to airdrop cargo operations. The pod-mounted lift augmentation system offers a small, compact unit for easy handling and shipping yet provides wing area for lift and autonomous descent control for accurate placement on target. Other advantages for the "wing-tip lift augmentation system" include realization of significant gains in wingspan and aspect ratio, thereby efficiently improving the lift to drag relation. In the retracted mode, the wing-tip lift augmentation system provides a short, low aspect ratio and low drag profile which configures an aircraft for speed. Conversely, when deployed, the wing extensions increase the aspect ratio to optimize high lift and slow flight in a "loiter" mode. The extended configuration is advantageous for short field operations and long endurance applications. Importantly, the wing-tip lift augmentation system provides the opportunity for in-flight deployment at reduced power for slow, long endurance loiter capability or transitions between loiter and higher speed operational modes. Further advantages of the lift augmentation system are that the system is not airframe platform dependent and that the speeds in the retracted configuration are better than the rotary wing craft. For military applications, the lift augmentation has the further advantages of near-silent operation with the concomitant tactical potential. It will thus be apparent that a new lift augmentation system has been described above. Moreover, it will be apparent to those skilled in the art that numerous modifications, variations, substitutions, and equivalents exist for various features of the invention. Accordingly, it is expressly intended that all such modifications, variations, substitutions, and equivalents that fall within the spirit and scope of the invention, as defined by the appended claims, be embraced thereby.