A TUBULAR FRAME

Abstract: A tubular main frame (2) for an aeroplane, bridge, or pressure vessel, for example, comprises a honeycomb structure with cells (4) thereof distributed round the periphery of the frame and along the frame, the cells each being at least pentagonal, preferably largely hexagonal.

Description: ■E -TϋBULftR FRAME This invention relates to a tubular frame. The honeycomb is well known in the natural environment and its advantage in strength: eight ratio is well documented. The strength:weight ratio factor is an ongoing problem in the aeroplane and aerospace industries. The greatest percentage of commercial aeroplane structural weight is that of the main airframe structure and skin structure combined so it is in that area that an improvement is sought. The type of commercial aeroplane fuselage structures in use at present is mainly frame and stringer covered by a skin. Another fundamental problem in an aeroplane structure is that of metal fatigue caused mainly by compound fluctuations leading to weakening, cracking, or even total failure. According to the present invention, there is provided a tubular frame comprising a honeycomb structure with cells thereof distributed round the periphery of the frame and distributed along the frame, said cells each being of at least five-sided form. Owing to the invention, the tubular frame can be of greater strength than if comprised of a honeycomb structure consisting of rectangular cells. The present frame has superior axial, torsional and lateral stiffness, so as to make a more rigid structure whereby the factors that cause metal fatigue can be reduced. It is possible to re-locate some of the loadings and look at the design criteria from a different aspect by introducing the present stronger, more rigid structure of a configuration better suited to perform its function and a better method of manufacture. The present invention is applicable to airframes, bridge structures, pressure vessels, model aircraft, coffer dams, ship hulls, tubular reinforcing, packaging, columns and beams, axles and pre-fabricated buildings. In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in whic :- Figure 1 is an end view of an aeroplane fuselage including a circular-cylindrical honeycomb structure. Figure 2 is a fragmentary side view of the fuselage with skin removed. Figure 3 is a fragmentary top plan view of the fuselage with skin removed, Figure 4 is an inner end view of an alternative version of a cell of the fuselage, Figure 5 is a side view of a straight, corrugated member of a plurality of identical members from which a honeycomb structure similar to that of Figure 1 can be made. Figure 6 is a view similar to Figure 2, but of another version of the honeycomb structure. Figure 7 is a side view of a curved, corrugated member of a plurality of identical members from which the honeycomb structure of Figure 6 can be made. Figure 8 is an inner end view of a cell of a plurality of identical cells from which the honeycomb structure of Figure 6 can be made. Figure 9 is a developed perspective view of a further version of the honeycomb structure. Figure 10 is an inner end view of a cell of the honeycomb structure of Figure 9, Figure 11 is a developed plan view of a yet further version of the honeycomb structure, Figure 12 is a fragmentary end view of a honeycomb structure of elongated cross-section, and Figure 13 is a view similar to Figure 7 of a curved, corrugated member for use in a honeycomb structure which tapers internally and externally. Referring to Figures 1 to 3, an aeroplane fuselage 1 includes a circular-cylindrical tubular frame 2 externally covered by a skin 3. The frame 2 consists of a circular- cylindrical honeycomb structure consisting of hexagonal cells 4 distributed round the periphery of the frame 2 and distributed along the frame 2. Opposite sides 4a of each of the cells 4 lie in axial planes of the frame 2. The four other sides 4b of each cell, namely those which extend obliquely about the periphery of the frame 2, have each surface thereof radial to the tubular frame 2 and so are helical. The honeycomb structure is assembled from a p l urality of individual cells 4, all of which are arcuate as viewed longitudinally of the frame 2, attached face-to-face to each other. Each individual cell 4 may be made by suitable bending of a strip with its ends then welded together, or by casting. The cells 4 may be attached to each other by means of hollow and/or solid rivets and/or by a bonding material, for example glue. Extending along the top of the frame 2 is a spine 5 in the form of two metal strips attached to the sides 4a of some of the uppermost cells 4 and intersecting others of the uppermost cells 4. Extending horizontally across the interior of the frame 2 is a partition, in this case a platform 6. The platform 6 is also of honeycomb structure, as illustrated diagrammatically in Figure 3, and is simply attached to sides 4a of cells 4 at an appropriate height by suitably angled brackets 7. The platform 6 is centrally suspended from the spine 5 by way of a double trellis 8. The spine 5 also absorbs some of the landing loads of the aeroplane and the other main loadings can be attached thereto. Each cell 4 shown in Figures 1 and 2 is fully open at both of its inner and outer ends. However, if required, one or both of the inner and outer ends of each cell 4 may be at least partially closed. A cell 4 having a partially closed outer end is illustrated in Figure 4, where the outer end is partially closed by an end wall 9 having an inner periphery in the form of a circle which is arcuate as viewed longitudinally of the frame 2. In the event that the cells 4 are closed at their outer ends, the skin 3 may be dispensed with. Although the platform 6 is shown supported from a single spine 5, it may be supported from a plurality of parallel spines spaced apart circumferentially of the frame 2 by at least one half-cell. Instead of the honeycomb structure being assembled from individual cells 4 attached to each other, the frame 2 may be assembled from a plurality of corrugated members extending generally longitudinally of the frame 2 and each identical to the member 10 shown in Figure 5. The member 10 may be made by suitable bending from straight strip or by casting. It includes straight sections 10a alternating with helical sections 10b. These define part-cells, i.e. half-cells 4c so that, when these identical members have their sections 10a attached together face-to-face, the cells 4 are provided. Referring to Figures 6 and 7, in this version of the honeycomb structure, the hexagonal cells 4 each have two opposite sides 4d lying in radial planes of the tubular frame 2, these sides 4d having their radially inner and outer edges curvedly co-axial with the frame 2. The other four sides 4e of each cell 4 are helical. The honeycomb structure may be assembled from a plurality of curved, corrugated members 11 which may each be circular or semi-circular as viewed longitudinally of the frame 2 and may be made by bending of strip material or by casting. The member 11 consists of curved sections lid lying in radial planes and alternating with helical sections lie. The member 11 thus provides a plurality of half-cells 4c so that, when the corrugated members are interconnected by attaching the sections lid face-to-face, the cells 4 are formed. Again, if desired, the honeycomb structure of Figure 6 may be assembled by attaching together face-to-face a plurality of individual cells each as shown in Figure 8 and having the sides 4d and 4e. It is not necessary that the cells of the honeycomb structure, whether of the frame 2 or of the partition 6, should be identical to each other. They may have the same number of sides as each other but be different in shape, or they may have differing numbers of sides. A honeycomb structure having such mixed cell structure is shown in Figure 9, where the hexagonal cells 4 interfit with hexagonal cells 4' of different shape, which interfit with pentagonal cells 4''. It will be noted that the pentagonal cells 4'' are of such form that each pair of those cells 4'' is of hexagonal outline. The honeycomb structure shown in Figure 9 may be used in the planar form shown, or in a tubular form in which the parallel sides 4f of the cells 4, 4' and 4'' extend preferably either longitudinally of the tube or circumferentially of the tube. The honeycomb structure of Figure 9 is particularly useful in circumstances when a spine is to be inserted between the face-to-face sides 4g of the cells 4''. Again, the honeycomb structure of Figure 9 can be made either by attaching corrugated members face-to-face, or by attaching individual cells face-to-face. Figure 10 illustrates an individual cell 4*' in which the sides 4f are to extend circumferentially of a tubular honeycomb structure, the straight side 4g is to extend longitudinally of the structure and the helical sides 4h are to extend obliquely. The sides 4g may be oblique to the sides 4f, so that the row of sides 4g is of a zig-zag form rather than straight. If desired, to give a good strength:weight ratio, the sides 4a, 4b, and 4d to 4h may have apertures therethrough. Figure 11 shows a honeycomb structure made solely of the somewhat pear-shaped hexagonal cells 4 ' . It is sometimes desirable that the tubular frame should be of an elongated circular form in cross-section, i.e. with two semi-circular sections 2' joined by straight sections 2'', as diagrammatically illustrated in Figure 12, in which case some of the cells 4 would have planar inner and outer end surfaces, others would have curved inner and outer end surfaces, whilst yet others would each have inner and outer end surfaces each of which is half planar and half curved. The tubular frame 2 may be such as to taper longitudinally. Figure 13 illustrates one corrugated member 11' of a plurality of corrugated members which taper in series both internally and externally to provide a tubular frame 2 tapering both internally and externally. The member 11' has curved sections ll'd lying in radial planes and alternating with spiral sections 11'e. The tubular frame 2 may be of other shapes, for example oval or elliptical in cross-section. To create an enclosure, the tubular frame 2 is closed at both ends by walls, for example geodetic walls. The suspension arrangement shown in Figures 1 to 3 is particularly applicable to circumstances where an internal platform is required, for example in passenger aeroplanes or bridges. The frames 2 described with reference to the drawings are particularly advantageous in the construction of main frames such as those of aircraft, bridges and pressure vessels, by being relatively more isotropic and better able to withstand the internal and external pressure fluctuations than, for example, a frame-and-stringer construction. In particular, in comparison with a rectangular cell structure, the hexagonal cell structure for the same weight is much stiffer in torsion and under vertical loading and its most highly stressed portions are significantly less highly stressed.

Claims: £L&IMS 1. A tubular frame comprising a honeycomb structure with cells thereof distributed round the periphery of the frame and distributed along the frame, said cells each being of at least five-sided form. 2. A frame according to claim 1, wherein opposite sides of each of said cells lie in axial planes of said frame. 3. A frame according to claim 1, wherein opposite sides of each of said cells lie in radial planes of said frame. 4. A frame according to any preceding claim, wherein said structure is made from a plurality of corrugated members each providing a plurality of part-cells and attached face-to-face to each other. 5. A frame according to any one of claims 1 to 3, wherein said structure is made from a plurality of cells, at least some of which are arcuate as viewed longitudinally of said frame, attached face-to-face to each other. 6. A frame according to claim 5, wherein at least some of said cells each have an at least partially closed end. 7. A frame according to claim 5 or 6, wherein each at least partially closed end is the outer end of its cell. 8. A frame according to any preceding claim. and continuously curved peripherally, said cells being correspondingly curved. 9. A frame according to any one of claims 1 to 7, and having its periphery of a form with opposite curved sections joined by opposite straight sections, the cells in said curved sections being correspondingly curved and the cells in said straight sections being straight. 10. A frame according to any preceding claim, wherein at least some of said cells are pentagonal of such form that each pair of those pentagonal cells is of hexagonal outline. 11. A frame according to any preceding claim and of a tapering form at its inside and its outside. 12. A frame according to any preceding claim and including a reinforcing spine extending longitudinally of said frame and in said structure. 13. A frame according to any preceding claim and having a partition extending longitudinally through the volume encircled by said structure. 14. A frame according to claim 13, wherein said partition is another honeycomb structure. 15. A frame according to claim 13 or 14 as appended to claim 12, and having suspension elements suspending said partition from said spine. 16. A frame according to any preceding claim and constituting a main frame of an aeroplane fuselage. 17. A frame according to any one of claims 1 to 15 and constituting a main frame of a cofferdam. 18. A frame according to any one of claims 1 to 15 an d constituting a main frame of a bridge.

Inventors: HOLDEN LAURENCE, HOLDEN, LAURENCE
Applicants: HOLDEN LAURENCE, HOLDEN, LAURENCE
Application year: 1997
Main classification: E04B1
IPC codes: B64C1, E04B1