my invention relates to a mechanism for supporting and driving a wing flap . more particularly , it relates to a folding truss type flap support / drive mechanism which is adapted to produce a flap movement closely approaching a rectangular fowler motion verses deflection angle progression . many different types of mechanisms for supporting , guiding and driving a trailing edge wing flap have been developed for a variety of aircraft . they include ( 1 ) a simple hinge , ( 2 ) a four - bar upright linkage , ( 3 ) a four - bar overhead linkage , ( 4 ) variable curvature tracks , ( 5 ) circular arc tracks and ( 6 ) a folding beam four - bar linkage . there are one or more obvious deficiencies associated with several of the previously mentioned mechanisms . the simple hinge has a low take - off fowler motion and requires large fairings with high cruise drag . the four - bar upright linkage has deficiencies similar to the simple hinge but to a lesser degree . the four - bar overhead linkage has high actuation forces . the variable curvature tracks have wear problems with roller carriage . the circular arc tracks have low take - off fowler motion . my folding truss mechanism was developed in an effort to minimize the cruise drag associated with flap mechanisms fairings , and at the same time achieve the desirable characteristics of the more effective flap systems now available ( e . g . the system used on the boeing 767 aircraft ). the trailing edge flaps of a high performance aircraft must fulfill two functions . they must provide a high lift to drag ratio take - off configuration and a high lift coefficient landing configuration . a high lift drag ratio for take - off can be accomplished by trailing edge flap positions with high fowler motion ( aft motion , which increases wing projected area ), a single converging slot between flap and spoiler trailing edge , and a small flap deflection angle . the high lift coefficient for landing requires high fowler motion , two relatively narrow converging slots ( for double slotted flap ) and high flap deflection angles . theoretically , the best fowler verses deflection angle progression would be rectangular . this would require two separate mechanisms , one to drive the flap straight aft and another to rotate it . this is not a practical solution . therefore , a single flap mechanism , that approaches the rectangular progression the closest , is the most desirable . my folding truss flap support mechanism is a compound four - bar linkage scheme . it is simple in concept and for a single - slotted flap configuration contains the same number of links and joints as the flap mechanism for the boeing 767 aircraft . all joints are simple pin joints or monoballs , which provide positive structural rigidity and precise positioning control for the mechanism , compared with systems such as curved track roller carriage flap mechanisms . all the links in the support mechanism but one have uni - axial loads , which mean lower structural weight than for mechanisms with links subjected to bending loads . in basic makeup , my folding truss flap support mechanism comprises a drive link which is pivotally attached at its upper end to an upper frame portion of a wing section forward of the flap , e . g . the main wing body , for fore and aft pivotal movement about a first axis . a second pivot axis is established below and aft of the first pivot axis , by a pivotal connection between the lower end of a support link and a fixed frame portion of the wing structure . the upper end of the support link is pivotally attached to both the upper end of a swing link and the after end of a slave link , to form a third pivot axis . a fourth pivot axis is formed at a forward connection of the flap to the lower end of the drive link . a fifth pivot axis is formed where the lower end of the swing link makes a rearward connection to the flap . the drive link , the portion of the flap which extends between the fourth and fifth axis , the swing link , and wing structure form a first four - bar linkage . the support link , the drive link , the wing section structure which interconnects the first and second pivot axis and the slave link form a second four - bar linkage . this linkage provides a moving anchor point for the swing link . the moving anchor point permits the swing link to be relatively short and to move the rear connection to the flap a greater distance aft , through a shallow arc , for maximum fowler motion . the shallow arc is necessary for flap transition control to take - off position . the compound motion of the support link / swing link combination , not only provides the desired shallow arc for the flap carriage rear support , but it also creates an abrupt hook motion near the end of the travel to provide ideal flap position for landing . my folding truss mechanism can be adapted to a variety of flap configurations . these include a single - slotted flap , a double slotted flap ( main / aft ) and a double slotted flap ( vane / main ). the support can be provided by an underneath flap support mechanism or by a varied end support flap mechanism . my folding truss mechanism can be located underneath the flap in a very compact envelope , and requires an enclosure fairing smaller than that of a track flap ( boeing 757 flap , for example ). or , it can be located at the ends of the individual flap panels and contained within the contour of the wing trailing edge , requiring no flap mechanism fairings . the flap actuation hinge moments and power requirements are low for my folding truss mechanism and the air loads on the flap always tend to move it in a stowing direction , which is a desirable failsafe characteristic for the flap in the event of actuation failure . fig1 is a sectional view of a wing showing a single slotted flap and my folding truss mechanism in a stowed position ; fig2 is a view like fig1 but showing the flap and the truss mechanism in a take - off configuration ; fig3 is a view like fig1 and 2 , but showing the flap and the truss mechanism in a landing configuration ; fig4 is a view like fig1 - 3 of a fixed vane main flap and a folding truss mechanism in a stowed position ; fig5 is a view like fig1 - 4 , of the mechanism shown in fig4 in a take - off configuration ; and fig6 is a view like fig1 - 5 , of the mechanism shown in fig4 and 5 , in a landing configuration ; fig7 is a view like fig1 - 6 , but of a double - slotted flap and a folding truss mechanism in a stowed position ; fig8 is a view like fig1 - 7 of the mechanism shown by fig7 in a take - off configuration ; fig9 is a view like fig1 - 8 , of the mechanism shown by fig7 and 8 , in a landing configuration ; and fig1 is a graph of fowler motion verses flap angle , comparing the fowler verse deflection angle progression of the folding truss mechanism of the present invention with a tracked flap , a hinged flap , and the theoretically best motion . as previously mentioned , the best fowler verses deflection angle progression would be rectangular . this is shown in fig1 . fig1 also shows that the folding truss flap support mechanism of the present invention accomplishes this task better than many presently used flap mechanisms . the versatility of the folding truss flap mechanism of the present invention is evident from the number of flap configurations which can be achieved . fig1 - 3 show an embodiment of the folding truss mechanism of the present invention as a part of a single - slotted flap , with underneath support . the basic mechanism comprises two four - bar linkages coupled together in a manner which produces a compound motion of the flap rear support point . the first or primary four - bar linkage , herein the &# 34 ; overhead &# 34 ; linkage , comprises a drive link 10 which is pivotally attached to fixed structure 12 ( it is grounded ) for pivotal movement about a pivotal axis 14 . fixed structure 12 may be a bracket on the wing rear spar 13 . at its opposite the drive link 10 is pivotally attached to a forward end of a flap carriage link 16 , for pivotal movement about a pivot axis 18 . flap carriage link 16 is connected to and supports the flap 20 . the primary linkage also includes a swing link 22 which is pivotally attached at one of its ends to the flap carriage link 16 , for pivotal movement about a pivot axis 24 . link 22 is pivotally attached at its opposite end to the second four - bar linkage . the second four - bar linkage provides a moving anchor point for the swing link 22 . it comprises an upright support link 26 . link 26 is attached to the fixed structure ( it is grounded ) through a support beam 28 , a slave link 30 and drive link 10 . a short support link 29 connects the forward end of beam 28 to the forward wing section . the pivotal connection between the upper end of drive link 10 and fixed frame structure 12 is herein referred to as the &# 34 ; first &# 34 ; pivot axis . the &# 34 ; second &# 34 ; pivot axis is formed where the lower end of the support link 26 is connected to the beam 28 . the &# 34 ; third &# 34 ; pivot axis is formed where the upper ends of the support link 26 and the swing link 22 are connected to the aft end of the slave link 30 . the &# 34 ; fourth &# 34 ; pivot axis is established where the lower end of the drive link 10 is connected to the flap member . a &# 34 ; fifth &# 34 ; pivot axis is established where the lower end of the swing link makes a rear connection to the flap member . a &# 34 ; sixth &# 34 ; pivot axis is established where the forward end of the slave link 30 is attached to the drive link 10 . the six pivot axes are the basic axes of the mechanism . the particular order followed in the numbering of these axes is arbitrary . line 33 is a reference line for use in comparing the change in position of the flap 20 as it is moved from or to its stowed position to or from its take - off or landing positions . as the drive link 10 rotates in a counterclockwise direction , it moves the flap carriage link 16 aft . simultaneously , the drive link 10 moves the slave link 30 aft , as part of the second four - bar linkage . the moving anchor point , formed by a pivot joint 31 between the slave link 30 and the support link 26 , permits the relatively short swing link 22 to move the flap carriage rear support a much greater distance aft , through a shallow arc , for maximum fowler motion . the shallow arc is necessary for flap transition control to take - off position . the compound motion of the support link / swing link combination , not only provides the desired shallow arc for the flap carriage rear support , but it also creates an abrupt hook motion ( indicated by line 35 in fig1 ) near the end of the travel to provide ideal flap position for landing . the shallow arc motion of the flap carriage rear support is similar to that which could be achieved with a very long aft link in a single overhead four - bar linkage flap support scheme . a principle advantage of my folding truss mechanism is that it can achieve a desired motion , similar to other mechanisms requiring much greater stowage space . the mechanism drive scheme shown , is a rotary actuator 32 connected to the drive link 10 through an actuator arm 34 and a push rod 36 . arm 34 is pivotally connected to rod 36 for pivotal movement about a pivot axis 38 . the opposite end of rod 36 is pivotally attached to both the drive link 10 and the slave link 30 , for pivotal movement about a common pivot axis 40 . other drive schemes are also possible , including direct rotary actuation of the drive link 10 , linear hydraulic actuator or ball screw actuator drives . the flap 20 , as shown , is attached to the flap carriage fitting by spherical joint connected flap hanger links 42 , 44 at three of the four flap support locations . one of the forward flap attachments is a single mono - ball joint for stability . the hangers 42 , 44 would accommodate conical or skewed cylindrical flap motion as well as structural deflections . the hangers 42 , 44 could be eliminated if spherical joints were used at several locations in a mechanism to provide limited lateral compliance and angular adjustment of certain links . the upper joint of the drive link 10 is a rigid pin joint for reacting side loads . the flap mechanism fairing consists of a fixed forward segment 46 and a movable aft segment 48 . the movable part 48 of the fairing is connected to the flap carriage fitting by a fairing slave link 50 , which moves the fairing away from the flap 20 during deployment to clear the moving mechanism . this flap fairing 46 , 48 is proportionally smaller than that for any other flap mechanism with similar motion . the flap deployment sequence begins with an initial nose down motion as the drive link 10 moves the flap 20 aft . the flap 20 then begins to rotate in a nose up direction until it reaches the take - off position , with flap deflection at ten degrees ( 10 °), as shown in fig2 . the fowler motion at the take - off position is approximately 68 . 5 % of the fowler motion at maximum flap deflection . the maximum flap deflection is thirty - six degrees ( 36 °), as shown in fig3 at which point the fowler motion is 56 . 3 % of the flap chord and 15 . 3 % of the wing chord . the flap chord is 27 . 3 % of wing chord . the slot developed between the flap 20 and the trailing edge of the spoiler 52 is approximately 1 . 56 % of flap chord for take - off and 1 . 7 % for landing . of course , these numerical values are for the specific embodiment that is illustrated in fig1 - 3 . in other embodiments , the values most likely would be different . the flap configuration shown in fig1 - 3 is based on an existing wing trailing edge geometry , and does not reflect the maximum capability of this mechanism scheme . the flap mechanism scheme just described could also be adapted to incorporate an aft flap with an actuation mechanism similar to the main flap . this would result in a double slotted flap configuration which would have much better performance characteristics than the single slotted configuration . referring to fig4 - 6 , the third embodiment involves the flap control mechanism of this invention adapted to a fixed vane / main flap . it is a modification of the single slotted flap with underneath support ( fig1 - 3 ). the fixed vane / main flap configuration poses additional requirements on the flap deployment mechanism not encountered with the single slotted flap . the vane 54 must be carefully extracted from the cove 56 and in addition it must seal against the spoiler trailing edge when in the take - off position ( fig5 ). this type of motion is very difficult to accomplish with available linkage type flap mechanisms . a track type mechanism and a simple hinge are , at present , the only other ways to accomplish the required motion for a fixed vane / main flap . in fig4 - 6 prime numbers have been used for the parts which correspond to the parts of the above described mechanism shown by fig1 - 3 . in this embodiment , the support beam 28 &# 39 ; includes an upper portion which is pivotally connected to a bracket 60 which is connected to the rear spar 13 &# 39 ;. the upper portion of beam 28 also supports the rotary actuator 32 &# 39 ; which , in this embodiment , is directly attached to the drive link 10 &# 39 ;. the vane 54 is attached to flap 20 &# 39 ; by a forwardly projecting connector strut 62 . fig7 - 9 show a double slotted embodiment . it incorporates a pair of folding truss actuation mechanisms of the type described for each flap . each mechanism is connected to an end of its flap element . the mechanisms are enclosed entirely within the wing contour , as shown in fig7 . this scheme incorporates an aft flap 64 for maximum flap effectiveness in the smallest possible package . the main flap mechanism arrangement is essentially the same as that described for the single slotted flap , with minor geometry changes . the flap carriage fitting is eliminated and the main flap 66 is attached directly to the drive link 10 &# 34 ; and the swing link 22 &# 39 ;. the swing link 22 &# 39 ; has an extension 68 for actuating the aft flap 64 by means of a slave link 70 . the aft flap mechanism is functionally like the main flap mechanism except that the aft support link 72 has an additional lug for supporting the aft flap support link 74 . the primary difference between the main flap and aft flap linkage is that the aft flap is driven through the aft support link 72 rather than the forward support link . the aft flap also has a different relative position for take - off than the main flap , as shown in fig8 . there is no gap between main and aft flaps 66 , 64 in the take - off position but a maximum gap 76 for landing , as shown in fig9 . the combined fowler motion of main and aft flap in the take - off position is greater than that of the single slotted flap shown with underneath support . in this embodiment , the rotary actuator 32 &# 39 ;, the first pivot joint 14 &# 34 ;, and the second pivot joint 27 &# 34 ; are supported on a beam member 78 which is connected at its forward end to the wing rear spar 13 &# 34 ;. even though swing link 22 &# 39 ; includes the extension 68 , the location at which it is pivotally attached to the main flap 66 may be considered to be the lower end of the swing link 22 &# 34 ;. in other words , swing link 22 &# 34 ; is that portion of the member which interconnects pivot axes 31 &# 34 ; and 34 &# 34 ;. referring to fig9 the forward end of slave link 70 is pivotally attached to the lower end of extension 68 for pivotal movement about a pivot axis 80 . the rear end of slave link 70 is pivotally attached to support link 72 for pivotal movement about a pivot axis 82 . link 72 is pivotally mounted onto a support portion of main flap 66 for pivotal movement about a pivot axis 84 . link 74 is pivotally attached at its lower end to the aft flap 64 , for pivotal movement about an axis 86 . at its opposite end it is pivotally attached to the support link 72 for pivotal movement about axis 88 . as has been shown , the folding truss mechanism of this invention is adaptable for a variety of trailing edge flap configurations . it has been shown and described in combination with single slotted flaps , main / aft double slotted flaps both with buried or underneath support schemes , and fixed vane / main double slotted flaps with underneath support . high fowler motion for take - off position can be achieved with this type of flap mechanism ( two to four times that of existing hinged flaps or track flaps ). the mechanism can be designed to accommodate both scewed cylindrical or conical flap motion . all joints are simple pivots designed for minimum wear . the mechanism is designed so that aerodynamic loads on the flaps create stowing hinge moments , for a failsafe design . hinge moments are relatively low compared with other , similar , concepts . the principle advantage of this flap support mechanism is its compact size , requiring small fairings for underneath flap support schemes and no fairings for the bearing support schemes . the payoff would be lower cruise drag for airplanes equipped with trailing edge flaps supported by a folding truss mechanism constructed in accordance with the present invention .