US2959384A - Airfoil structure - Google Patents

Description

Nov. s, 1960 J. PAVLECKA 2,959,384

AIRFOIL STRUCTURE Filed Jan. 9, 195s 2 E my( @Y /7 42 INVEN TOR.'

Imm m n United States Patent FIL STRUCTURE John Pavlecka, 8797 Capital, Oak Park 37, Mich.

Filed Jan. 9, 1958, Ser. No. 708,339

20 Claims. (Cl. 244-124) This invention relates to a structure for hollow bodies consisting of a shell of an elongated profile and of internal supporting members, and which is particularly suitable for airfoil bodies such as airplane wings and control surfaces, helicopter rotor blades, etc.

The subject matter of this invention is the same as that of my application Serial No. 265,315 filed on I anuary 7, 1952, which application was abandoned after its allowance, and is related to the subject matter of my following applications: Airfoil Structure, Serial No. 706,229, filed December 26, 1957; Airfoil Structure, Serial No. 749,005, led July 16, 1958.

One object of this invention is to devise a shell type of structure having a smooth exterior and an inaccessible interior, the body of the structure being integrated of a number of panel units each of which is an individual subassembly fabricated with full accessibility, and all the subassemblies are held in rigid yet separable unity by linear keys telescoped into them through one end of the shell.

Another object is a shell structure in which a number of panel units provide jointly both the shell and supporting members therefor, the panel units having stress members such as stringers and spars integral therewith, which members function also as carriers of key-engaging means and of abutment means, and are interlocked by keys of a variable and normally oversize shape sprung into their engaging means and urging them against one anothers abutment means by preloading forces so that they coact as unitary supporting members for the shell.

A further object is a union of two or more panel units in a shell type of structure by means of key-locked and relatively immovably constrained stress members thereon, such locking and constraining duty being performed by a tubular key which is slit or interrupted in its periphery, the key being fitted into congruently interlitted protruding archways on the stress members with an interference by being normally larger than the archways and being resiliently deformed thereby whereby it draws the stress members by their archways into yabutment with one another at confronting faces alongside the archways.

Another object resides in devising a rigid union of three panel units or subassemblies in a structure bearing key-locked stress members, such as stringers or spars or a combination thereof, the three stress members complementing one another at radial planes around a key locking them into unity, the key having a resiliently variable protile and drawing the three members together by Ibeing confined with a change of its profile in them, thereby causing one or more of the members to be wedged inbetween divergent planes on the others.

A still further object is an airfoil or similar shell structure in which a closed profile end panel unit and two side panel units are held together with preloading forces by means of stringers on them interlocked by a resiliently confined key so that they function as a unitary spar, and in which opposedly alined stringers on the side panel units apart Afrom the closed end are interlocked and held forcibly in contact with each other by another such key to provide another spar or spars in the structure.

Another object is an airfoil or similar shell structure in which two side panel units and a movable control unit, such as an aileron, flap, or air brake, are cojoined into rigid unity by a resiliently constricted key in en- `gagement with two opposed stringers on the side panel units and with a third stringer or spar wedged inbetween them, the latter stringer or spar bearing hinge brackets mounting the movable control unit.

A still further object resides in an airfoil or similar structure in which a number of panel units are secured into rigid yet separable unity by means of spanwise stringers or spars, the stringers or spars being in complemental engagement with one another of segments around resiliently contracted linear keys and being locked and constrained together thereby, both the panel units and the stringers or spars thereon being braced by chordwise ribs or bulkheads in their function as cooperating supporting members for the structure.

A comprehensive object is an airfoil or similar structure in which either one or both the leading and the trailing portions constitute individual units or subassemblies, the latter one being either fixed or movable as an aileron, and are each provided with a stringer or spar, and intervening dorsal and ventral panel units are provided with stringers along their vfore and aft edges which stringers bear confronting faces on their inward side and bear angularly parted or divergent faces on their outward side, and the Stringer or spar on the leading and on the trailing panel units bear convergent faces that are wedged inbetween theV divergent faces on the side panel unit stringers and are interlocked therewith by linear keys, the wedged condition resulting from the keys being reduced resiliently in size to exert compacting forces on the stringers or spars and thereby cause Vthem to cohere firmly at their faces.

These and other useful objects are attained through the principle of division of a structure into individual units and their integration in the manner herein disclosed, first with reference generally to all the figures in the drawing which forms apart of this specification, and then with reference to each figure individually.

A structure such as an airfoil body has an elongated profile defined by two sides and two closed profile ends, one of which may be occupied by another airfoil'body hinged to the main one, such as an aileron, a flap, a rudder, or an elevator; the interior of both of these bodies is inaccessible for fabrication in consequence of which the prevailing technique is to build in interior members individually and apply pieces of skin to them one at a time by riveting, mostly of the blind kind with one side out of view. According to my principle of subdivision, such a body is constructed of three or more subassemblies, each one complete in itself, and all of them open for fabrication with full accessibility so that resistance welding or adhesive bonding `can be substituted 'for riveting; all such subassemblies are locked together by linear keys so that they form jointly not only the shell of the body but its supporting members aswell; these results are achieved through the use of aparticular division of the components of the body of the structure, and the use of linear keys of a normally oversize profile sprung into place whereby preloading forces are introduced into the interlocked members to lock them together relatively immovably.

The division of such a body is effected along lengthwise or spanwise parting lines located so thatfpreferably three panel units obtain, each of which represents a portion of the shell and of the'interior stress members therein; one such panel unit constitutes one closed chordal extremity of the structure and two others provide portions of its sides or the whole sides of the shell and stress members integral therewith; a fourth panel unit may constitute either a xed other closed chordal extremity of the shell, or a body movably attached to and complementing the side panel units; such a movable unit, as an aileron, elevator, etc., may not only employ the same manner ofattaching it to the side panel Aunits Vas the fixed unit, but its own body may also be integrated of a number of segmental subassemblies.

Each subassembly or panel unit carries on its inner side certain structural members which include stringers or spars at and along panel edges and on some of them also stringers apart from the edges, and ribs or bulkheads extending chordwise between the stringers. The stringers or spars on each panel unit are the carriers of means for obtaining a slidable engagement, jointly with the stringers or spars on the associated unit or units, with linear keys telescoped inbetween them; in this manner the stringers or spars on a closed profile extremity panel unit and on two side panel units, complementally associated with one another at the parting lines and at a location or locations apart from them, are cojoined into unity; the stringers or spars so key-locked as well as the keys themselves embody certain distinctive features that cause them to cooperate as single stress members equivalent to the usual one-piece beams or spars.

One such feature resides in that the stringers or spars are formed with faces along their key-engaging means, which faces assume confronting positions on each two stringers in opposed alinement or in juxtaposition with each other; another feature resides in that when three stringers or spars on three associated panel units are interlocked by one key, two of the stringers have confronting faces thereon along one side of the key and have angmlarly spaced apart faces thereon along the other side of the key; the third Stringer or spar, usually on the chordal extremity panel unit or pivotally attached thereto, has convergent faces thereon alongside of its keyengaging means, and fits inbetween the divergent faces on the two stringers while engaging the same key therewith; the purpose of such confronting opposed faces on the stringers or spars and of such angular confronting faces thereon is to provide abutments of one against the other or others and cause them to block one another relatively immovably while engaging the key; yet another feature resides in constraining the abutted stringers or spars in a rigid and cohesive union by applying preloading forces to the abutted faces thereof; to this end, the key is formed with a tubular resiliently contractible profile, and the key-engaging means on the stringers or spars is made to contain the key in a contracted shape and size and be drawn by forces so produced towards the key; such drawing action results in the stringers or spars abutting each other and being wedged against each other forcibly at their confronting faces. Two opposed stringers so abutted and two opposed stringers with a spar wedged therebetween, buttressed by chordal ribs or bulkheads, not only endow the structure with rigidity but are competent to function as one-piece supporting members therefor.

The hereinabove disclosed structural principles are applicable to a large variety of embodiments of which a number of exemplary ones are shown in the drawing and are described in the following text with reference to the figures therein.

In the drawing:

Fig. l is a profile view of an airplane Wing and its aileron each of which is assembled of three panel units by two linear keys in the case of the wing and one key in the aileron.

Fig. 2 is an exploded view of the components of the wing and of the aileron of Fig. l.

Fig. 3 is a partial sectional view of archways as the key engaging means on stringers and spars pertaining 4 to the wing of Figs. 1 and 2, taken in the plane and direction indicated by arrows 3-3 in Fig. 2.

Fig. 4 is a profile view of a multiple spar wing and of the aileron thereof, each one consisting of three panel units supported as well as held together by key-locked stringers and spars. V

Fig. 5 is a view of the paneliunits pertaining to the wing and to the aileron of Fig. 4, shown in a disassembled State.

Fig. 6 is a prole view of another airfoil body such as a wing or control body with a fixedly attached trailing portion, in which four panel units are key-locked to constitute the body and provide supporting members therein.

Fig. 7 is a view of the structural components which constitute the airfoil body of Fig. 6, shown in a disassembled state.

Fig. 7a is a fragmentary view of a modified spar alternate to the one shown in Fig. 7.

Fig. 8 is a view of the underside of one of the side panel units and of the trailing end unit of Figs. 6, 7 and 7a, taken in Fig. 7 in the plane and direction indicated by arrows 8-8 therein, and showing the spacing of keyengaging archways on the stringers and spar therein.

Fig. 9 is a profile view of an airfoil structure such as a helicopter rotor blade, the shell and the stress members of which consist of three subassemblies interlocked into unity by a single linear key.

Fig. 10 is a view of the individual components of the blade of Fig. 9 shown in a disassembled relationship.

The wing and the aileron structures of Figs. 1 and 2 embody the same principles of construction and assembly in that each one includes three panel units which jointly form both its shell and internal stress members, and are held in unity in an identical manner; moreover, the aileron is attached to the wing in substantially the same manner as its leading end unit; this unit includes a panel 2 the edges of which extend spanwise on opposite sides of the wing, and between them the panel is continuous around the wing leading portion; in edge-to-edge alinement with this panel at two parting lines is a dorsal panel 1 and a ventral panel 3, both of which terminate with spanwise edges at the aileron. Besides the panel 2 the leading unit includes a Stringer 10 which is based on the marginal portions of its opposite sides and intervenes between them, in which respect it represents a spar; this spar and the panel 2 form jointly a cellular member in the interior of which is disposed a number of chordal bulkheads 11 abutted against the spar webs. The construction of the dorsal and of the ventral panel units 1 and 3 is the same in that each one has two stringers, 4 and 5 on the former and 6 and 7 on the latter, based on its inner face at and along its spanwise edges, and a number of chordwise ribs such as 8 and 9, respectively, extending between the stringers and abutting them.

The profile of the side panel unit fore stringers 4 and 6, both substantially alike, includes attaching flanges 12 and 13, dual walls i4 and 1S standing thereon, shoulders 16 and 17 supported each on one of the Walls and connected with each other by a series of longitudinal archways 18 to which the faces on the shoulders are directed radially. The aft stringers 5 and '7 on the same respective panels have a prole analogous to that of the fore stringers 4 and 6, except in that their respective walls 19 and 20 support archways 21 and 26 directly in a radial position thereto without any shoulders, while their other walls, such as 22, support the archways `through the medium of shoulders 23 and 24., respectively. The fore Stringer archways 1S and 25 and the aft Stringer archways 23 and 24 are interrupted by lengthwise clearance spaces, and are staggered into complemental positions as shown in Fig. 3; when assembled into the structure, the archways on each pair of opposedly alined stringers 4 6 and 5 7 interfit congruently with one another and their respective shoulders 17 and 27, and 23 and 24, fall into confronting positions of each other, while their respective annessi shoulders 16 and 28, and walls 19 and 20, assume radially divergent directions.

Both the leading panel unit 2 and the trailing unit as represented by the movable aileron, are secured to the side panel units 1 and 3 by means of spars; the spar 10 in the leading panel unit 2 has a profile defined by attaching anges 29 and 30 based on the opposite inner faces of the panel unit, lateral walls 31 and 32 projecting therefrom convergently and bearing a set of archways 33. The spar 34 for mounting the Iaileron has a profile including lateral shoulders 35 and 36 in radially convergent directions and connected by archways 37; as shown in Fig. 3, these archways have a length substantially equal to that of the archways 21 and 26 on the associated stringways on each of the stringers and on the spar 34 are nominally twice as long as the archways so that both stringers and the spar interiit with one another into a coaxial alinement of their archways; the length and the spacing of the archways on the two associa-ted fore stringers and spar 46-10 in the leading end of the wing are the same as on the stringers and spar shown in Fig. 3.

In the assembled wing, the fore stringers and spar 4-6-10 and the aft stringers and spar 5-7-34 intert congruently with each other and are interlocked in that relationship by linear keys 38 and 39, respectively; the stringers and spars so interlocked confront each other with their shoulders and walls and thereby block each other relatively immovablly; moreover, the keys 38 and 39 are oversize in their free shape and are split lengthwise so that when sprung into their place in the stringers and spars they exert distending force on the archways confining them and thereby draw the stringers and spars together; under this tension the stringers and the spar in each union abut each other forcibly at their shoulders and walls and, furthermore, because of the convergent walls on the spars and 34, these members are wedged inbetween the respective divergent stringers; such abutted and wedged unions in the wing of Fig. 1 function as single rigid stress members or main spars for the wing.

The wing aft spar 34 mounts on the reverse side of its shoulders 35 and 36 a number of brackets such as 40 to which the movable aileron or flap is hinged; the structure of this body corresponds to that of the wing, and consists of three panel units 41, 42 and 43 which constitute jointly its shell as well as interior stress members; these members include a spar 44, stringers 45 and 46, and ribs 47, 48 and 49 buttressing them on the respective panel units, The opposed stringers 45--46 on the side panel units confront each other at shoulders such as 50 on the aft side of a row of interrupted archways on them, and on the fore side thereof are parted from each other between divergent shoulders such as 51. The leading panel unit spar 44 has convergent shoulders 52 thereon supporting its archways, which shoulders become wedged inbetween the stringers divergent ones as the two stringers and the spar jointly engage with their archways a normally oversize key of a tubular split cross-section with the same results as in the unions in the wing; at the trailing aileron end screws 54er other equivalent means is employed to join the panel units 42 and 43 to a feather edge. For connecting the aileron or iiap pivotally to the wing, the leading panel unit ribs 47 are hinged to the wing bracket-and-spar subassemblly 40-34.

The structure of the wing and that of its aileron or flap of Figs. 4 and 5 is distinguished by the same features as the ones in the preceding figures, the exceptions being certain modified Stringer and spar profiles, and the use of two opposed stringers in a central location for additional strength. The wing shell and its stress members are again composed of three panel units 55, 56 and 57 which are provided with respective complementally grouped spar and stringers 58, 59 and 60 at the leading prole end, and apart from it the dorsal and the ventral panel units 56 and 57 are provided with stringers op- 6 posedly alined in two pairs 61--62 and 63-64, the latter pair of which is associated with a spar 65 for supporting and pivotally mounting the yaileron or flap.

The spar 58 in the leading panel unit 55, and the bulkhead 66 abutting it are analogous to those in the wing of Figs. l and 2, the spar again having the characteristic convergent walls 67 and 68 with archways 69 thereon; its companion Stringer 59 on the dorsal panel unit 56 resembles it in that it has convergent walls 70 and 71 to provide its abutting faces, and archways 72 on them. The other Stringer 60 on the ventral panel unit 57 conforms closely to its counterpart 6 on the panel unit 3 of Figs. 1 and 2, except in that its shoulders 73 and 74 astride archways 75 are coplanar and in a forwardly in clined position. When assembled, the stringers 59-60 Iare face-to-face at their respective wall 71 and shoulder 74, while their other wall and shoulder, 70 and 73, provide divergent faces inbetween which the spar convergent walls 67 and 68 are drawn as the three sets of archways 69-72-75 are interfitted and interlocked by a key 76 of ia resiliently contracted profile.

Stringers 61-62 jointly constitute a central spar in the wing; both are `of the same species, differing only in height; their profile includes archways 77, two shoulders 78 therealong, lateral walls 79, and flanges 80; the two stringers become abutted Shoulder-against-shoulder as a key 81 of a resiliently reduced girth is telescoped into them; the taller Stringer 62 is buttressed by chordal ribs 82 and 83 which tie it with the stringers 60 and 64 located at the panel unit edges. The dorsal panel unit 56, because of predominant compressive stresses in it, is reinforced by spanwise stiifeners 84.

The Stringer -and spar trio 63-64-65 which holds the wing trailing end in unity as well as secures the aileron to it, is made up of certain types employed in this and in the preceding wing assemblies; the Stringer 63 is identical with the Stringer 61 on the same panel unit, and the Stringer 64 is of the same type as the Stringer 5 of Figs. 1 and 2 in that its inclined wall 85 and shoulder 86 provide its abutment faces; the profile of the spar 65 is related to that of the spar 34 of Figs. 1 and 2 with convergent shoulders 87 and 88 astride a series of archways; it has a number of brackets such as 89 secured to it for mounting the aileron pivotally. When assembled, the opposed stringers 63-64 abut each other with their inward shoulders 86 and 90 while their respective wall and shoulder 85 and 91 form a divergent open Sector into which is wedged the spar 65 with its shoulders 87 and 88 as it engages a resiliently conned key 92 jointly with them.

The aileron or ap in this wing assembly also makes use of the three-unit construction, the panel units 93, 94 and 95 being held together with preloading forces through the instrumentality of respective stringers and spar 96, 97 and 98, and a resiliently contracted key 99. However, in contrast to the aileron configuration of Figs. l and 2 the trailing portion of the shell and the stress members therein are provided in this case by a Single panel unit 95, while the leading shell portion and the stress members therein are constituted by the dorsal and the ventral panel units 93 and 94. The spar 98 in the trailing panel unit 95, similarly as all the spars in the wing structures herein disclosed, is characterized by convergent walls astride its key-engaging means, represented in all the embodiments by interrupted protruding archways. The stringers 96 and 97, both of a similar profile, on the leading panel units 93 and 94, respectively, are analogous to the Stringer 64 on the ventral panel unit 57 in the wing in that their abutment faces are provided by a shoulder and an inclined wall. The same wedged condition of the end panel unit spar 98 between the abutted stringers 964497 obtains as in the preceding such cases herein disclosed, due to the use of a tubular key 99 sprung into its place by resiliently deforming its profile.

For mounting the aileron or ilap on the wing, collars such `as 100, with lugs thereon are included at intervals 7 inbetween the intertted stringer and spar archways on the'key 99, and are secured immovably to the key by pins orbolts `101; the lugs are attached pivotally to the bracketand-spar unit 89-65 in the wing.

The airfoil body of Figs. 6 and 7 consists of four panel units of which 102, 103 and 104 provide' the leading portions, the dorsal and the ventral side, respectively, and unit.105 complements them asa fixed trailing portion; obviously, a movable control unit such as an aileron, elevator, etc., can be substituted for the xed one and secured to the main body in the same manner. Two linear keys 106 and 107 of an oversize open profile in their free condition interlock the units 102, 103 and 104 into a rigid assembly; for this purpose two stringers 103 and 109 run on and along the opposite marginal faces of the panel unit 102; each of thesestringers is formed with two angularly related faces, one on a shoulder 110 and the other on a lateral wall 111, and with lengthwise interrupted archways between them. Bulkheads 113 abutting these stringers give the panel unit its shape and transfer loads thereon to and into the stringers.

The dorsal panel unit 103 comprises two stringers 114 and 115 of a profile analogous to that of the leading panel unit stringers 108 and 109; a number of ribs such as 116 extend chordwise between the stringers as integral parts of the panel unit. The components of the ventral panel unit 104 include a Stringer 117 at and along the aft edge of a profile similar to that of its counterpart 115 on the dorsal panel unit, and a spar 11S at Iand along the fore edge; this spar, in addition to being a carrier of instrumentalities for cojoining the three panel units 102, 103 and 104 into a. wedged relationship lat both the dorsal and ventral sides, functions also jointly with the stringers on the panel units and with the interlocking keys which cause the wedged relationship, as the main spar in this structure.

The spar 118 may `be either a single-web beam as shown in Fig. 7, or a box beam shown in Fig. 7a as 11Sa, the essential features, i.e., two sets of archways 119 and 120, shoulders 121 and 122 astride one set, and shoulders 123 and 124 astride the other, being the same in either case; chordal ribs such as 125 extend between the spar 118 and the aft stringer 117 to complete the panel unit 104 as a rigid subassembly.

The shoulders 121 and 122 on the spar 118have divergent directions matching the convergent faces on the associated Stringer 109 on the panel unit 102; when the archways 120 between them are intertted with those on the Stringer 109, and with a split and normally oversize tubular key 107 in them, forces are exerted by it that urge the spar and Stringer into a wedged contact with each other at their angular shoulders. The shoulders 123 and 124 at the upper extremity of the spar 118 have the distinguishing convergent directions as on the spars in the preceding embodiments; in the assembly, the stringers 108 and `114 abut each other at the dorsal parting line with their faces 111 and the shoulders 123-124 on the spar 118 become wedged inbetween their divergent shoulders 110- 126 as the resiliently confined key 106 draws them together.

The same wedging action takes effect at the juncture of the fixed trailing panel unit 105 with the side units 103 and `104 as spar 128 on the former unit, with convergent lateral walls thereon, is drawn and constrained relatively immovably inbetween divergently related walls on the opposed stringers 115- 117 on the latter units in the presence of a resiliently constricted split tubular key 129 in the respective archways 130-131--132 intertitted with each other congruently according, for instance, to the arrangement shown in Fig. 8; the archways are all of equal length and the clearance spaces between them are double their length, in which respect this arrangement is similar to that of Fig. 3.

Another embodiment of the principleof integrating a structure of panel subassemblies by interlocking them and causing them toabut and be wedged against one another, is illustrated in Figs. 9 and 10; in this case an airfoil such as a helicopter rotor blade is assembled of three panel units which occupy complemental sectors around a linear key. Two panel units, 133 and 134, jointly provide thc closed leading and trailing portions as well as the ventral side of the airfoil shell and the inner stress members therein, and the third unit 135 forms a segment of the dorsal side. The panel units have stringers or spars 136, 137 and 138, respectively, thereon and chordwise bulkheads 139, 140 and 141 bracing them; all of the stringers or spars have their attaching angcs at and along the panel unit edges; on two of them, 133 and 134, these edges are on opposite sides and the stringers 136 and 137 thereon are substantially of the same profile which includes an upright wall 142 at one edge and another wall 143 projecting in an inclined direction away from the opposite edge, and both walls are connected by archways 144. The stringer 138 on the dorsal panel unit 135 is dened by convergent lateral walls and 146 connected by archways 147. In the assembled airfoil, the stringere 136- 137 are abutted with each other at their upright walls 142 on one side of a key 148 at the ventral parting line, and their inclined walls 143 are parted divergently on the other key side; inbetween the latter walls is drawn the Stringer 138 and its panel unit 135; as the key 143 interlocks the archways of the three stringers, it induces preloading forces at their confronting walls by the springiness of its material and by its cross-sectional configuration; its cross-section is open on two diametrally opposite sides, and is of an oversize free girth, similarly as in the keys in the preceding embodiments herein disclosed.

I claim:

1. In a panel, three structural units forming complemental portions of the structure, a stress member based on the surface of each of said units coextensively with the stress members on the other two units, a linear key interposed between said stress members, said stress members occupying three adjoining sectors around said key and having faces in confronting positions of one another at said sectors and by and between said faces bearing means for engaging said key slidably jointly with one another, at least two of said sectors and stress member faces thereat being convergent toward said key and confronting divergent faces on the stress members occupying adjoining sectors, and means as a part of the profile of said key in cooperation with said stress members keyengaging means for subjecting said stress members to tensile forces and causing them to abut against one another at said confronting faces thereof for relatively irnmobility of said panel units.

2. In a structure, components and their relationships as set forth in claim 1, said key-engaging means on said stress members residing in protruding lengthwise interrupted archways intertted congruently with one another, and said key profile being tubular and being interrupted on at least one side thereof and being confined resiliently in said archways in a contracted size.

3. In a structure, three panel units meeting one another at two lengthwise parting lines to form a closed profile end and side portions of a shell, a linear key in said shell coextensive with said parting lines intermediate thereof, three stress members based one on each of said panel units at and along said parting lines and therefrom reaching to said key and bearing substantially radial faces therealong in confronting positions of one another at three complemental sectors around said key, and means borne by said stress members for engaging said key slidably jointly with one another, said key being oversize and effecting resiliently a change from the free size thereof to the size of said stress member engaging means and thereby subjecting said engaging means and said stress members bearing the same to forces causing said stress members to abut one another at said confronting faces thereon.

4. Ina structure, components and their relationships 9 as set forth in claim 3, one of said stress members having walls based on the opposite sides of the panel unit forming said shell closed end and bearing said faces on said walls, two others of said stress members having each dual walls based on one of the panel units forming said shell side portions, said two stress members bearing said faces on one of said dual walls thereof in confronting positions with said closed panel unit stress member faces and having shoulders borne on the other of said dual walls thereof away from said closed shell end and providing said faces thereon in confronting positions of each other.

5. In a structure, two panel units forming opposite portions of a shell, stringers extending on said panel units in opposition to each other, a linear key interposed between said stringers, said stringers bearing means for slidably engaging said key jointly with each other and having faces in confronting positions of each other along one side of said key and having faces parted divergently from each other along the other key side, a spar having convergent faces thereon and by and between said faces bearing means in engagement of said key slidably jointly with said stringers engaging means and being in confronting positions of said convergent faces thereof with said stringers divergent faces, and means embodied in said key for exerting tensile forces on said stringer and spar engaging means and thereby drawing said stringers into abutment with each other at said confronting faces thereof and drawing said spar to be wedged inbetween said stringers divergent faces.

6. In a structure, two panel units forming portions of one side of a shell and meeting each other at a lengthwise parting line therein, stringers extending on said panel units at and along said parting line, a linear key interposed between said stringers at a distance from said parting line, said stringers bearing means for slidably engaging said key jointly with each other and having faces in confronting positions of each other in a location between said parting line and said key, said stringers having other faces parted divergently from each other along the side of said key away from said panel units, a spar having convergent faces thereon and by and between said faces bearing means for slidably engaging said key jointly with said stringers engaging means and being in confronting positions of said convergent faces thereof with said stringers divergent faces, and means embodied in said key fo-r exerting tensile forces on said Stringer and spar engaging means and thereby drawing said stringers and said panel units thereof into abutment with each other at said confronting faces thereof at said parting line and drawing said spar to be wedged inbetween said stringers divergent faces.

7. In a structure, three panel units forming an airfoil shell divided at three spanwise parting lines, two of said parting lines extending between all three of said panel units on one shell side and one parting line extending between two of said panel units on the other shell side, stringers based one on each of said panel units at and along the respective parting lines thereof, a linear key interposed between said stringers in said shell, each of said stringers bearing faces convergent with each other in a location between the panel unit thereof and said key and in confronting positions of the faces on the other two stringers, by and between said faces said stringers bearing means for engaging said key slidably jointly with one another, and means embodied in said key for exerting tensile forces on said stringers through said engaging means thereof and thereby drawing said stringers into abutment with each other at said confronting faces thereof and holding said panel units cohesively at said parting lines therein.

8. In a structure, three panel units forming an airfoil shell, one of said panel units providing a closed profile extremity of said shell and meeting the other two panel units at spanwise parting lines on the sides of said shell, a first pair of opposedly alined stringers extending one Stringer on each of said side panel units at and along said parting lines, another pair of opposedly alined stringers extending one Stringer on each of said side panel units at the other shell profile extremity, a spar based on the inner sides of said closed extremity panel unit at and along said parting lines coextensively with said first pair of stringers, linear keys interposed o-ne between said spar and said first pair of stringers and another one between said other pair stringers, said spar and first pair stringers and said other pair stringers bearing means for engaging said keys slidably and bearing faces in confronting positions of one another along said keys, and means embodied as a part of the profile of said keys for exerting forces on said spar and Stringer engaging means and thereby drawing said spar and said first pair stringers together and drawing said other pair stringers together and causing them to abut one another at said confronting faces thereof.

9. In a structure, components and their relationships as set forth in claim 8, a third pair of opposedly alined stringers extending one Stringer on each of said side panel units intermediate said iirst and other pairs, chordal ribs integral with at least one of said side panel units extending between and abutting the stringers of said three pairs on said unit, a linear key interposed between said stringers of said third pair, said stringers bearing means for engaging said key slidably and bearing faces lin confronting positions of each other along said key, and means embodied as a part of the profile of said key for exerting forces on said Stringer engaging means and thereby drawing them together and causing them to abut at said confronting faces thereof.

10. In a structure, two panel units forming each one side of an airfoil shell, another panel unit forming a closed airfoil extremity of said shell and meeting said side panel units at two spanwise parting lines on the shell sides, a structural unit complementing said shell at the other airfoil extremity, a first pair of opposed stringers extending one Stringer on each of said side panel units at and along said parting lines, another pair of opposed stringers extending one Stringer on each of said side panel units at and along said other -airfoil extremity, linear keys interposed one between said stringers in each pair, said stringers in each pair having confronting faces along one key side and having divergently parted faces along the key other side, two spars having convergent faces thereon, one of said spars being based on and intervening between the opposite inner sides of said closed extremity panel unit at and along said parting lines and with said convergent faces thereof confronting said iirst pair Stringer divergent faces, the other one of said spars bearing means for mounting said structural unit complementally to said shell and with said convergent faces thereof confronting said other pair Stringer divergent faces, said spars and stringers confronting one.

another bearing means for engaging said respective keys slidably, and means embodied in the profile of said keys for exerting forces on said stringers to cause them to abut each other at said confronting faces thereof and to cause each of said spars to be wedged inbetween said stringers divergently parted faces.

1l. In a structure, components and their relationships as set forth in claim 10, said structural unit complementing said shell at said other airfoil extremity being another panel unit and meeting said side panel units at spanwise parting lines on the shell sides, said other one of said spars being based on and intervening between the opposite inner sides of said complemental panel unit at and lalong said parting lines.

l2. In a structure, components and their relationships as set forth in claim 10, said structural unit complementing said shell at said other airfoil extremity being a pivotally movable body, said other one of said spars bearing hinge brackets on the reverse side of said convergent faces thereof and mounting said movable body pivotally thereon.

13. In a structure, two panel units forming each one side of an airfoil shell, another panel unit forming one closed airfoil extremity of said shell and meeting said side panel units at two spanwise parting lines on the shell sides, a structural unit complementing said shell at the other airfoil extremity thereof, two stringers extending side-by-side one on each of said panel units at and along one of said parting lines, a stringer and a spar extending side-by-side each on one of said panel units at and along the other one of said parting lines, two opposed stringers extending one on each of said side panels at and along said other airfoil extremity, linear keys interposed one between said stringers side-by-side, another one between said stringer and spar side-by-side and a third one between said opposed stringers, said stringers side-by-side and said stringer and spar side-byside having confronting faces in a location between said panel units and said keys, said opposed stringers having confronting faces lalong one key side, said stringers sideby-side and said opposed stringers having divergently parted faces on the other key side away from said confronting faces thereof, said spar intervening between said stringers on said side panel units and bearing convergent faces and confronting said divergent faces on said sideby-side stringers therewith, another spar extending in said shell and bearing means for mounting said structural unit in said other airfoil extremity and having convergent faces and confronting said opposed stringers divergent faces therewith, said spars and stringers confronting one another bearing means for engaging said respective keys slidably, and means embodied in the profile of said keys for exerting forces on said stringers to cause them to abut each other at said confronting faces thereof Iand to cause each of said spars to be wedged in between said stringers divergently parted fac.

14. In -a structure, a number of panel units forming portions of a shell, stringers extending on said panel units and therefrom reaching towards each other and bearing each a Set of lengthwise interrupted archways coaxiallywith the other stringers archways, faces borne on said stringers astride said archways thereof, said faces on at least one of said stringers being convergent with each other and confronting divergent faces on the other of said stringers, and a linear key having a normally oversize cross-section and being resiliently deformable, said key being sprung into engagement with said stringers archways and interlocking said stringers and panel units thereof relatively immovably by drawing said stringers into abutment at said confronting faces thereof.

15. In a structure, an airfoil shell having a complemental shell hinged pivotally thereto, two stringers extending each spanwise on one of the sides of said airfoil shell in opposition to each other, a spar coextensive with said stringers on the side thereof toward said complemental shell, hinge brackets mounted on said spar and therefrom projecting toward said complemental shell and having said shell hinged thereto, a linear key interposed between said stringers and said spar, said stringers and said spar bearing means for cojoint slidable engagement of said key, and faces borne on said stringers and on said spar in confronting positions of one another, said stringers and said spar being held by said engagement thereof with said key in abutment at said confronting faces thereof.

16. In a structure, a shell having an elongated profile, a panel forming one closed profile extremity of said shell, two other panels meeting said extremity panel at parting lines and forming the shell opposite sides, stringers eX- tending one on each of said side panels in opposition to each other and having walls based on said panels at and along said parting lines, a spar extending on said extremity panel and having walls based on the opposite sides of said panel in confronting positions of said stringers walls, on said walls thereof said stringers and said spar bearing lengthwise interrupted archways andhaving said archways intertted congruently with one another, and a linear key in a slidable engagement with said interfitted archways, said stringers and said spar confronting walls being convergent in the direction toward said key and being held in abutment with each other by said key engagement with said archways on said walls.

17. In a structure, a shell having an elongated profile, a panel forming one closed profile extremity of said shell, two other panels meeting said extremity panel at parting lines and forming the shell opposite sides, a linear key extending in said shell between said side panels proximately to said parting lines, stringers extending one on each of said side panels at and along said parting lines and reaching to said key and bearing shoulders therealong opposed to each other on the side away from said shell closed extremity, on the side of said key at said extremity said stringers bearing shoulders divergently parted from each other, a spar extending on said extremity panel and having walls reaching convergently toward said key between said stringers divergent shoulders, and means borne on said stringers and on said spar for cojoint slidable engagement with said key, said spar being wedged inbetween said stringers divergent shoulders and said stringers being abutted against eachother at said opposed shoulders thereof by said cojoint engagement with said key for relative immobility of said shell panels.

18. In a structure, two panels forming portions of a shell, a linear key extending in a distanced relationship to said panels, stringers based one on each of said panels reaching to said key and bearing means for engaging said key slidably in conjunction with each other, faces borne on each of said stringers substantially radially to said key, said faces on both stringers confronting each other along one side of said key and being divergent from each other along the other key side, a structural member extending along said stringers divergent faces and bearing means for engaging said key slidably in conjunction with said stringers, and convergent faces borne on said structural member in confronting positions of said stringers divergent faces, said stringers and said structural member being held in abutment with each -other at said confronting faces thereof by said key in said engaging means thereof.

19. In a structure, three panel units forming two sides and one closed profile extremity of an airfoil shell, three stress members extending one on each of said panel units Ain said shell at said extremity thereof, two of said stress members being in opposition to each other and the third one being in a lateral relationship therewith, two stress members extending in opposition to each other one on each of said panel units at the other shell extremity, a spar subject to external loading extending in a lateral relationship to said two stress members in said other shell extremity, linear keys interposed one between said three ystress members and another one between said two stress members and spar, means on said stress members and yon said spar engaging said respective keys slidably, and faces on said three stress members and faces on said .two stress members and on said spar along said keys, said 'three stress members and said two stress members and spar being held in abutment with each other at said confronting faces thereof by said key in said engaging means thereof.

20. In a structure, components and their relationships as set forth in claim 19, and chordal ribs extending on each one of said panel units between said stress members in opposition at said closed profile extremity and at said other extremity of said shell, said ribs abutting said stress members of each panel unit and transferring loads imposed thereon and on said spar into said stress members.

References Cited in the tile of this patent UNITED STATES PATENTS 1,988,085 Orlando Jan. 15, 1935 2,432,396 Earhart Dec. 9, 1947 2,644,553 Cushman July`7, 1953

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