In this paper the results are given of an experimental investigation into the flow development and the surface pressures in an unsteady shock boundary layer interaction at Mach numbers of 1.3 and 1.5. The experiment is one in which a naturally grown turbulent boundary layer on the tunnel walls is disturbed by a normal shock wave spanning the test section of the tunnel. The shock wave is oscillated by a periodic pressure disturbance in the tunnel diffuser far downstream of the interaction. Both instantaneous (spatially averaged) and time averaged results for the surface pressures are presented. These results are used to study the flow development and phase changes through the interaction over a frequency range from 34 to 167 Hz. This frequency range was chosen to cover the range of parameters likely to occur in conditions corresponding to stall flutter in the compressor fans of large bypass engines.

This study details the design of an automatic control system for a sailplane in towed flight, the principal objective of which is control the relative position of the tow-aircraft and glider, since a large vertical distance is expected to drive unstable motions of the whole system. The synthesis of the control system is based on an approximated model for the constrained sailplane. The controlled motion of the sailplane is simulated by a general dynamic model of the three bodies, namely the two aircraft and the rope. Significant numerical results are presented and discussed in order to determine the effectiveness of the stability augmentation.

An adaptive method for the computation of steady, viscous compressible flows over a wide range of Reynolds and Mach numbers is presented. The method is based on a well-proven scheme for the solution of the compressible Reynolds-averaged Navier-Stokes equations and employs the flexible AMR-grid structure for the adaptation of discretisation to the computed flow. The basic numerical scheme and the grid structure are reviewed and the sensors employed for the detection of the main flow phenomena are presented. Special attention is given to several flows computed with the adaptive method. The numerical results are partially compared to experimental data and generally a good agreement is observed. It is also recognised that, with the present adaptive method, flow features can be computed with high resolution using greatly reduced computing power. At this time, the method is limited to the simulation of two-dimensional flows, with the extension to three space dimensions currently under development.

A major structural problem in the air transport industry is the very small profit margin i.e. 2-3% over a long period, e.g. 1970-1990. But the industry has to make heavy investment (12-15% of yearly turnover) on a regular basis in market growth and fleet renewal.

As airline cash flow is often insufficient they have to raise equity (limited returns in view of the low profit margins) and inevitably suffer from chronic debt. This is all the more expensive as an airline is often short of capital and made worse when interest rates are high (as is currently the case in France).

The current financial situation was caused by an unprecedented overcapacity crisis, in a time of economic stagnation. This has shown no sign of improvement since the Gulf conflict, and is all the more crucial today because it comes at a time when the air transport industry in general, and Air France in particular, are taking delivery of a large number of new aircraft.

This paper examines a specific case, Air France. This will enable some overall conclusions to be drawn, thereby making an effective contribution to restoring this sector to a sound economic balance in the medium term.

The problem does not just concern airlines. The aircraft financing sector is beginning to feel the effects of the crisis. They might do well to draw the necessary conclusions from this study. Also, one must not forget the aircraft manufacturers, who without doubt still have to face the bulk of the crisis ahead.