Traffic growth and the replacement of the older, less efficient and noisier aircraft—60% of Western World capacity may be regarded as in this category—provide the opportunity for applying new technologies to subsonic commercial transports. Reduction of operating cost continues to provide the major incentive, though increasing emphasis is being placed on low fuel consumption and low noise.In this paper, the term ‘advanced technology’ is taken to embrace significant engineering advances which are not commonplace on aircraft flying today. In general, it is wrong to think of such advances as new inventions. Almost without exception they have evolved over the years, with few quantum jumps. There are, of course, exceptions to this and a recent example as regards engine development might be the introduction of high bypass ratio engines in the late 1960s, which brought about a 25% improvement in specific fuel consumption. However, even this major step could be regarded as an evolutionary development from engines of bypass ratio about 1·0, which themselves had conferred significant gains relative to the straight turbo-jet engines of the late 1950s.
The thermo-mechanical effects of firing induce very considerable stresses on the internal surface of the gun barrels. Consequently, micro-cracks appear very soon in the life of the tube. So it is important to control the propagation of these cracks. For more than 10 years, modeling has been used by Giat-Industries to understand and to control this phenomenon. This paper focuses on the study of short crack propagation kinetics during firings. Two-dimensional modeling taking into consideration the residual stresses from a hydraulic autofrettage and the thermo-mechanical stresses due to the successive firings is presented. The cyclic plastic behavior of the material is taken into consideration. This makes it possible to observe the effect of loss of the residual stresses at the surface due to the firings. Cracks of increasing length are introduced in the model to calculate the stress intensity factor. An innovative point is the modeling of the contact between the crack lips in order to take into account the effect of crack closing during cooling. Indeed the effective stress intensity factor range is calculated using this model for numerous crack lengths. A classic Paris law is then used to predict the crack propagation kinetics. Sensitivity analysis has been carried out using this model; in particular, the effect of autofrettage on crack propagation is analyzed as well as the effect of the use of lower-strength steels.
SummaryThe effects of distortion on the longitudinal stability of swept wing aircraft at high speeds (sub-critical Mach numbers) are considered on a quasi-static basis. The method is based on the theory of Gates and Lyon but involves some extension of this theory.The treatment of wing distortion is considered in some detail and the effects of built-in twist and camber and wing weight are included, using the so-called superposition method. The application of the analysis of Lyon and Ripley for investigating fuselage, tail and control circuit distortion is suggested, but means of modifying and simplifying this procedure where desirable are put forward.The analysis is illustrated by means of a simple example of a swept wing fighter aircraft for which wing, fuselage and tail distortion effects are considered, and the results are discussed with reference to the individual and combined distortion effects, as well as the effect of compressibility.
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