(Above) TEST TO DESTRUCTION - It can be seen that although the stringers on this Dove wing have fractured (between ribs 6 & 7) the bond is still intact. Finally, we are able to give, by courtesy of the de Havilland Aircraft Co., Ltd., photographs of the full-scale tests on the wing of the Dove. It will be seen from these photographs that "top hat" stringers are used, and it is de Havilland's experience, based upon a large number of unpublished panel tests, that panels with Reduxed "top hat" stringers will develop shear stresses up to 125 per cent. of those developed by exactly similar panels with riveted and spot-welded joints. The results of the full-scale test fully support this conclusion. The appearance of the wing under load is quite different from that of one of riveted construction. In the latter case the buckles all run through the areas of stress concentration, i.e., the rivet holes. In the case of the bonded wing it will be seen that the skin is held firmly along the whole length and the whole width of the stringers. Such a construction is, of course, much stronger than one in which the skin is perforated like a sieve and in which the load is taken on a large number of small areas surrounding the perforations. The wing was subjected to the following series of loadings:- No. of cycles Load cycle (1) 1,200 0 to 2 g. (2) 500 0 to 2.45 g (3) 5 0 to 3.4 g (4) 10,000 0 to 1.5 g (5) 5 0 to 3.86 g (6) 5 0 to 4.37 g (7) Destruction test by static loading to 5.5 g, which is 108% of the design load.
After more than 11,500 stress cycles the wing was in perfect condition, and failure did not occur until after the fully factored load had been passed by an appreciable margin. The failure was an impressive demonstration of the strength and reliability of Redux bonding, because even where the wing skin fractured, only one stringer parted from the skin for a very short length. There can be no doubt whatever that had a conventional riveted structure been tested in a similar way, either the rivet heads would have come off or they might have pulled through the skin. Other Advantages of Redux An improvement in strength is not the only result of using Redux. The skin of the Dove, for example, is in striking contrast to that of most other aircraft because it is so clean. On high-speed aircraft this will become of greater importance in the future. The other advantage is saving in cost. Aircraft riveting is quite an expensive business and Redux is already effecting appreciable economies in aircraft production. In the case of the Dove, Messrs. de Havillands use a large press and sets of stringers are bonded to fuselage and wing skins in sizes up to about 4 ft. by 12 ft. It must be made clear that all the attachments required are made in one operation. When riveting is used it is necessary to jig drill each hole in the stringer and skin as a separate operation, and to countersink each hole in the skin before the actual riveting is carried out. This discussion has mainly dealt with the attaching of stiffeners to skins. There are, however, many other uses for Redux. It is used for constructing the floor of the Vickers-Armstrongs "Viking." In this case a comparatively thin plywood floor is reinforced by top hat stringers. The rolled light alloy sections are first of all bonded to 1 mm. Veneers. Even in a small 6-ft. by 3-ft. press it is possible to bond about 180 ft. in one hour. The veneered sections are then cold glued to the plywood. The floor is then free from any rivet or boltheads and is also strong for its weight. Bonding also makes it possible to attach local reinforcements either to metal or to wood. Good examples of this are to be found in the folding wing attachments of the "Hornet" and the "Mosquito." SIMPLIFIED SPAR CONSTRUCTION - On the left is shown the large box spar assembly on the Mosquito, which makes an interesting comparison with the smaller unit of the Hornet, on the right, with Redux bonding.
DETAIL COMPONENTS - Built up from sheets of Alclad, this provides an example of "Reduxed " local reinforcement. Future Developments There is no doubt whatever that the main difficulty in the development of Redux-bonded structures is its application to doubly curved surfaces. Hitherto flat and singly curved surfaces have caused little difficulty, but at present it is necessary to make up form tools to bond doubly curved panels. At present no other method has been evolved for applying the heat and pressure necessary for bonding. Such tools can, of course, be castings, but even so they tend to be expensive in relation to the numbers of aircraft produced.
After more than 11,500 stress cycles the wing was in perfect condition, and failure did not occur until after the fully factored load had been passed by an appreciable margin. The failure was an impressive demonstration of the strength and reliability of Redux bonding, because even where the wing skin fractured, only one stringer parted from the skin for a very short length. There can be no doubt whatever that had a conventional riveted structure been tested in a similar way, either the rivet heads would have come off or they might have pulled through the skin. Other Advantages of Redux An improvement in strength is not the only result of using Redux. The skin of the Dove, for example, is in striking contrast to that of most other aircraft because it is so clean. On high-speed aircraft this will become of greater importance in the future. The other advantage is saving in cost. Aircraft riveting is quite an expensive business and Redux is already effecting appreciable economies in aircraft production. In the case of the Dove, Messrs. de Havillands use a large press and sets of stringers are bonded to fuselage and wing skins in sizes up to about 4 ft. by 12 ft. It must be made clear that all the attachments required are made in one operation. When riveting is used it is necessary to jig drill each hole in the stringer and skin as a separate operation, and to countersink each hole in the skin before the actual riveting is carried out. This discussion has mainly dealt with the attaching of stiffeners to skins. There are, however, many other uses for Redux. It is used for constructing the floor of the Vickers-Armstrongs "Viking." In this case a comparatively thin plywood floor is reinforced by top hat stringers. The rolled light alloy sections are first of all bonded to 1 mm. Veneers. Even in a small 6-ft. by 3-ft. press it is possible to bond about 180 ft. in one hour. The veneered sections are then cold glued to the plywood. The floor is then free from any rivet or boltheads and is also strong for its weight. Bonding also makes it possible to attach local reinforcements either to metal or to wood. Good examples of this are to be found in the folding wing attachments of the "Hornet" and the "Mosquito." SIMPLIFIED SPAR CONSTRUCTION - On the left is shown the large box spar assembly on the Mosquito, which makes an interesting comparison with the smaller unit of the Hornet, on the right, with Redux bonding.
DETAIL COMPONENTS - Built up from sheets of Alclad, this provides an example of "Reduxed " local reinforcement. Future Developments There is no doubt whatever that the main difficulty in the development of Redux-bonded structures is its application to doubly curved surfaces. Hitherto flat and singly curved surfaces have caused little difficulty, but at present it is necessary to make up form tools to bond doubly curved panels. At present no other method has been evolved for applying the heat and pressure necessary for bonding. Such tools can, of course, be castings, but even so they tend to be expensive in relation to the numbers of aircraft produced.
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