US1656810A - Hollow girder for light structures - Google Patents

Description

Jan. 17,1928. 1,656,810

K. ARNSTEIN HOLLOW GIRDER FOR LIGHT STRUCTURES Filed July 23, 1924 INVENTOR MMMW ATTORNEYfi Patented Jan. 17, 1928 UNITED STATES KARL ARNSTEIN, F FRIEDRICHSHAFEN, GERMANY, ASSIGNOR TO IQUFTSOHIFFZBAU ZEPPELIN GESELLSGHAIT MIT BESCHRANKTER HAFTUN G, OI FRIEDRICHSH AFEN,

GERMANY.

HOLLOW GIRDER FOR LIGHT STRUCTURES.

Application filed July 28, 1924, Serial No.

My invention relates to hollow girders for light structures, especially for aircraft. For such girders preferably light metal such as aluminum or its alloys, for example, durati lumin will be used. The simplest shape for hollow girders would be tubes. For light structures such as aircraft such tubes will have to have very thin walls. At the same time the thickness of the walls will have to be uniform all over the circumference and all over the length of every tube. Only under these conditions light structures made up of tubes will be reliable, because with the lower margin of safety in use with aircraft the constructor has to rely on exact and precise members of building. In the manufacture of tubes with very thin walls it is very hard and troublesome to get the precision required for such purposes. This manufacture aifords much waste and thereby is very expensive. My invention does away with all these drawbacks by making up hollow girders out of sheet metal strips. Such thin strips, according to my invention, are cut out so as to form a kind of truss and the edges of the strips and those of the cuts are bent for the purpose of stiffening the memher. The bent longitudinal edges of such strips are riveted together thus forming hollow girders of triangular, rectangular, rombic, pentagonal or other suitable cross section. Every hollow girder need not be made up of as many longitudinal strips as the cross section may show sides, because one strip may also be bent over its total length once or several times so as to form two or more sides oi the polygon of the cross section.

Hollow girders made up according to my invention have the advantage of having a reliable thickness of their walls, because there is no special difliculty in the manufacture of precise light metal strips. Further on, if desirable, different thicknesses 1n the strips making up one girder may be chosen, thereby allowing even better adjustment to possible complicated stresses in the girder. The feature of having overlapping riveted seams along the girder increases its stiffness and its resistance against bending by. axial compression. Hollow girders ac-. cording to my invention are also easily joined to each other or to plates or the like. Thus these girders show the advantages of both 727,848, and in Germany August 11, 1923.

spatial trusses and of closed up hollow girders but avoid their disadvantages.

In the, drawings aifixed to this specification and forming part thereof, my invention is exemplified. Fig. 1 is a cross section of a v girder embodying m invention; Fig. 2 is the corresponding si e view and Fig. 3 is a top view giving two diiferent examples for 1t. Figs. 4 to 12 are cross sections glving as many examples of how my invention may be made use 0 In Fi s. 1 to 3 the girder is made u of four in ividual strips on, a, a an (1. These strips are cut out at b, and the edges of these cuts 6 are bent as shown at c. It may be noted that the openin or cuts 6 are of such shape that the hen s c integrally surround these openings, avoiding any points where the truss-like portions between these openings merge into the flat ortions of the strips without reinforcement. rom the bends. The edges of the strips themselves are bent as shown at e. And the edges of the inner strips are bent a second time as shown at 7. Thus each strip is made to form a real truss in itself and then the four strips constituting a hollow girder according to my invention are riveted together with rivets d. In Figs. 2 and 3 three different examples are given showing how the strips may be cut out.

It will be observed by reference to Fig. 2 that the larger and smaller openings b are so formed that they define pairs of intersecting diagonals, the transverse or diagonal direction'of each of which is indicated by the center or medium line .79. It will also be observed that these center or medium lines p lie between and are approximately equidistant from the adjacent edges of the respective larger and smaller openings. These center lines 79 intersect the neutral axis, indicated at 'r, of the smallest cross-sectional area of the corner portions of the girder; that is, the neutral axis of the cross-section of the corner of the girder at the lines drawn at right angles toward the corner portion of the girder from the extremities of the respective openings nearest such corner. The

itch of the pairs of diagonals is represented y the reference character '1, and it is determined by the distance between intersecting points a of the pairs of diagonals. Having determined these points and lines, it will be clear that the outer intersecting points of the pairs of diagonal center lines p with the neutral axis 1*, determines a distance m which, according to the form of the invention disclosed by Fig. 2, is not less than 0.5 and not more than 0.8 of the pitch of the diagonals. In order that the maximum eiiieiency of the girder, together with minimum weight thereof, may be attained in this particular construction and arrangement of elements, it is necessary that ratio between the distances :1: and y be confined within the limits refe red to.

The example given in Fig. 4 equals that of Fig. 1 only the edges of strips a and a are not bent to cover the edges of strips a and a twice, thus allowing only one row of rivets in each corner.

Fig. 5 gives the same example as Fig. 4. but the shape of the cross section is rombic instead of rectangular.

Fig. 6 is in shape alike Figs. 1 and 4 but instead of having 4 strips only 2 strips 9' and g. are used, these two being bent rectangular along their longitudinal axis. The two seams where the two strips are riveted together are completely like the four seams in Fig. 1.

The cross section of Fig. 7 is again reetangular in shape. In this example the gir er is made up of two strips 9' and g bent rectangular along their longitudinal axis, in the same way as in Fig. 6, only the edges of the strips are bent differently as shown in h. They form an acute angle and their furthest edges are again bent as shown In ig. 8 gives the cross section of a hollow girder assembled in the same way as that represented in Fig. 7. The only difference is, that the shape of the cross section is rombie instead of being rectangular and thereby affording other angles of the bends as shown. Girders made up in the way shown in Figs. 7 and 8 allow also joining with others in the diagonal line of the cross section by insertion of the joining members between the edges of the strips at h.

Fig. .9 shows a triangular cross section. The two strips i and 2' having been bent at their edges 1n an acute angle is, while the third strip has only a slight bend f at its edges.

In the triangular cross section shown i Fig. 10 onl two strips are made use of, one of them being bent to an acute angle along ts longitudinal axis, the second one Z closmg the girder in the same way as with i in Fig. 11 again shows a rectangular cross section but this time only two pieces are made use of. Strip m has two main longitudinal bends so as to form three sides of the rectangle, the furthest edges bent again in the same way as with all the other strips. Strip m is like i of Fig. 9 or Z of Fig. 10 closing the figure.

In Fig. 12 another example is represented. In this case strip n has three main longitudinal bends and has besides the bends in edges like in the other cases. Strip n is bent in its edges as shown at 0 and riveted to strip it thus constituting a pentagonal hollow girder.-

I want it understood that I do not confine to the examples described or shown in the drawings, as many variations will be obvious to persons skilled in the art.

What I claim is:

1. An articulated hollow girder for light structures such as aircraft comprising a plurality of individual longitudinal trusses formed from thin sheet metal strips; said trusses having apertures, the edges of said apertures being bent inwardly with regard to said hollow girder; the longitudinal edges of one of said trusses being bent so as to overlap the edge of another one of said trusses; the overlapping edges of said trusses being riveted together by longitudinal rows of rivets.

2. An articulated hollow girder for light structures such as aircraft comprising four individual longitudinal trusses formed from thin sheet metal strips; said trusses having apertures, the edges of said apertures being bent inwardly with regard to said hollow girder; the longitudinal edges of two of said trusses having wide inwardly directed bends and narrower second bends at the edges of said first bends, said secondibends again being inwardly directed; the longitudinal edges of the two others of said trusses hav' 'ing narrow inwardly directed bends said wide bands of said first two trusses being riveted to the unbend portions of the edges of said other two trusses.

3. A light weight hollow airship girder having opposite side elements each composed of a strip of sheet metal material provided with openings, each of said elements being stamped to form pairs of intersecting diagonals defined by the adjacent edges of the respective openings, the openings being of substantially continuously curved contour, the distance between the points of intersection of the median lines of a air of diagonals with the neutral axis oi cross-sectional area of one corner portion of the assembled girder being limited between 0.5 and 0.8 of the pitch of said pairs of diagonals.

In testimony whereof I ailix my signature.

KARL ARNSTEIN.

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