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This paper presents a preliminary analysis of the effects of kinetic healing at supersonic speeds on the torsional and flexural stiffnesses of thin solid wings. The main investigation is based on the small deflexion theory, but the scope of the analysis for torsion is extended to cover the effects of large deformations.

IN an earlier article dealing with the general aspects of clastic distortion phenomena, which appeared in an issue of Aeronautics, mention was made of the various factors which tend either to promote, or to damp out and eliminate the onset of the aerodynamic inertia elastic vibration phenomena known as flutter, and it was pointed out that in this respect the provision of an adequate measure of rigidity, both as regards to twisting and flexure of the wing or tail surface structure is one of the most effective safeguards against the occurrence of torsional‐flexural flutter.

IN Parts I, II and III of this series we have discussed the physical nature of divergence, control reversal and various forms of flutter, and have seen how these phenomena can be predicted by theory. The flutter problem is so complicated, however, that the aircraft designer needs the assistance of certain guiding principles; otherwise he may find when the aircraft is ready to fly that the flutter calculations which are just completed show that drastic modifications to the aircraft are necessary. These principles form the basis of this concluding part of the series and have two main objects: first to avoid large changes in design on flutter grounds and secondly to obtain a high efficiency from the flutter calculations.

THE primary duties of an aircraft design team are to design an aircraft capable of meeting a certain specification of performance and manoeuvrability with suitable flying qualities, and to ensure that it will be strong enough to withstand any aerodynamic loads it may suffer in flight. It will be found that the aircraft when built is not a rigid structure, but this in itself is not important. We are all familiar with the flexing of an aircraft's wings when struck by a sharp gust of wind in flight, but as long as the wings are strong enough no harm is done. On the contrary, in a passenger aircraft the flexibility of the wings in bending will have a favourable effect, as it will cushion the passengers to some extent from the suddenness of the gust. Flexibility of the structure, however, is not always beneficial and it often introduces new difficulties in the designer's problems. These difficulties arise when the deformation of the aircraft structure introduces additional aerodynamic forces of appreciable magnitude. The additional forces will themselves cause deformation of the structure which may introduce still further aerodynamic forces, and so on. It is interactions of this type between elastic and aerodynamic forces which lead to the oscillatory phenomenon of flutter, and to the non‐oscillatory phenomena of divergence and reversal of control. The study of these three aero‐elastic problems becomes more important as aircraft speeds increase, because increase of design speeds leads to more slender aircraft with thinner wings, and therefore to relatively greater flexibility of the structure. The dangers, in fact, are such that the designers of a modern high‐performance aircraft have to spend considerable effort on the prediction of aero‐elastic effects in order that suitable safeguards can be included in the design. By far the greatest part of this effort is spent on flutter, which will be discussed in Parts II, III and IV of this series, but any of the three problems may force the designers to increase the structural stiffness of parts of the aircraft. The wing skin thickness on a modern aircraft, for example, is nearly always designed by consideration either of aileron reversal or wing flutter. Divergence is usually less important but as it is the simplest of the three phenomena to treat analytically, we shall study it first.

This paper aims to obtain the further and overall generation about the static characteristics of the structure for the better application of the structure.

Through nonlinear finite element simulation, serials of comparative analyses are performed on this structure and other three assumed structures, which illustrate the effect of the main part of the structure on the structural static properties. Meanwhile, adopting the first order method, spatial cable force optimization makes the structural mechanic more rational.

Under same level stress, this three‐main‐truss and three‐cable‐plane bridge could save almost 38.8 percent vertical chords materials consumption at least. In contrast, this bridge has a lower lateral torsional stiffness, considering the key to raise the lateral and torsional stiffness is enhancing axial stiffness of plane bracing, the suitable plane bracing members area is twice as the original area. After rational optimization, the cable tension ratio between the mid‐cable plane and the two side‐cable planes ranges from 1.09 to 1.14.

The work in this paper of the comparative analysis could give other engineers a way to a deep analysis method for the structural analysis, especially in civil engineering. The conclusions would provide other designers some applied advice.

The Concept of Stability and Types of Instability THE term stable or unstable is applied to a body or system in accordance with the nature of the ultimate consequence of applying a disturbance. If the body or system is at rest and in equilibrium in a certain configuration, that configuration is said to be completely stable if the system ultimately comes to rest in the same configuration after the imposition of any disturbance. Frequently interest is confined to small disturbances; the term small is vague but must be interpreted as meaning that the motions of disturbance (or deviations) are so bounded that they can be described by linear differential equations. When this is so, the investigation of the stability becomes relatively easy and the actual magnitudes of the initial disturbances are not required in the discussion of the stability. The same concept of stability for small disturbances can obviously be applied to any steady motion and indeed to any regular motion. The criterion for stability is that the deviations from the basic motion consequent upon a small disturbance shall ultimately become vanishingly small.

An ideal method for predicting the fatigue life of spherical thrust elastomeric bearings has not been reported, thus far. This paper aims to present a method for predicting the fatigue life of laminated rubber spherical thrust elastomeric bearings.

First, the mechanical properties of standard rubber samples were tested; the axial stiffness, cocking stiffness, torsional stiffness and fatigue life of several full-size spherical thrust elastomeric bearings were tested. Then, the stiffness results were calculated using the neo-Hookean, Mooney–Rivlin and Yoeh models. Using a modified Mooney–Rivlin constitutive model, this paper proposes an improved method for fatigue life prediction, which considers the laminated characteristics of a spherical thrust elastomeric bearing and loads of multiple multi-axle conditions.

The Mooney–Rivlin model could accurately describe the stiffness characteristics of the spherical thrust elastomeric bearings. A comparative analysis of experimental results shows that the model can effectively predict the life of a spherical thrust elastomeric bearing within its range of use and the prediction error is within 20%.

The fatigue parameters of elastomeric bearings under multiaxial loads were fitted and corrected using experimental data and an accurate and effective multiaxial fatigue-life prediction expression was obtained. Finally, the software was redeveloped to improve the flexibility and efficiency of modeling and calculation.

VIOLENT oscillations of particular parts of an aeroplane structure have been observed and studied since early days. The theory of wing oscillations is, however, rather more modern and was initiated, it is believed, by A. G. von Baumhauer and C. Koning, who presented a paper at the International Air Congress in 1923. Since that year the subject has been much developed both abroad and in this country. The literature has grown rapidly, and a detailed notice of the papers cannot here be attempted.

THIS paper seeks to draw from current research work on flutter and related problems results of general design significance ; and, avoiding mathematics, endeavours to set these results out in relation to past and present problems.

IN Part I wc saw how structural flexibility could introduce aerodynamic forces which might eventually lead to instability, or to the complete nullification of a desired aerodynamic effect. The phenomenon of flutter presents another problem in stability, but in this case an oscillatory instability is threatened. It must be realized at the outset that flutter is no mere resonance phenomenon such as the bad vibrations a motor‐car may exhibit at a particular engine speed. Flutter is a vibration in which energy is extracted from the airstrcam to help build up the amplitude, and a catastrophic failure can easily occur within a second of the start of the flutter.