Fractal geometry provides a method for modelling the scale dependence of fluctuations in atmospheric-turbulence velocity. In this paper the basic concepts are outlined and illustrated by a method of data analysis which, for a fractal process, displays measured probability distributions in scale-invariant form. To a first approximation the data exhibit statistical self-similarity, consistent with the classical theory of Kolmogorov. However, on more detailed analysis, the more intense fluctuations show systematic departures from self-similarity, consistent with recent theoretical estimates of the fractal dimension of the support of turbulence. Implications for aircraft gust response are discussed.

Pseudo-streamwise vortices develop during the transition of a boundary layer from the laminar to the turbulent state. It is suggested that the induced velocities associated with these vortices cause a gross change in the flow, and that the initial uniform flow is no longer tenable. The character of the flow in the boundary layer must change suddenly, and it is believed that this change provides the trigger for flow breakdown to turbulence.

The approach taken by this examination of flight simulation in the RAF in the Second World War reflects the fact that one author is an engineer and the other a psychologist. As a consequence the paper not only attempts to examine the technology that was established to create the training devices but also something of the personalities who created the simulators and the applications to which they were applied.

In the space available it will only be possible to skim the surface of a topic which has been relatively undisturbed for some thirty years. The authors hope is that the paper will stimulate interest and admiration for the dedicated and ingenious innovators who set out to create the devices which enabled the Royal Air Force to learn new skills safely and apply them effectively.

The concept of air propelled vehicles to travel in deserts is reviewed. An analysis of trafficability problems in Egyptian deserts is presented with emphasis on sand surfaces. Theoretical equations are derived for the prediction of acceleration, resistance to motion and range at constant speed of the Aero-Roue and the hovercraft over sand.