The rate of ice accretion on an aircraft depends upon meteorological factors and aircraft characteristics. There are on the one hand atmospheric pressure and temperature; water content; droplet size; electrostatic conditions. On the other hand, there is the collection efficiency made up of aircraft component design characteristics such as size; shape; material; surface finish. Finally, there are aircraft flight variables such as speed; attitude; skin temperature; vibratory state.

Meteorologists are able to define potential icing intensity if they can forecast the ambient factors mentioned. The intensity may be defined as light, moderate, or severe, or by some such broad adjective, with reference to a hypothetical collector. Similarly, the air-worthiness authority, e.g. the Air Registration Board, must be satisfied that an aircraft can be operated safely in the appropriate meteorological conditions. Therefore the probable association of each meteorological factor with the others needs to be known.

Before reading my paper I wish to express my thanks to the President and Council of the Society, and my great appreciation of the privilege accorded to me of speaking before this expert gathering.

My ambitions with regard to the subject of this paper were originally very farreaching, but I soon realised that it would be impossible to cover the enormous field falling under the heading of “ rotating wings,” and at the same time to advance sufficiently into detail to escape the criticism that this was merely a new collection of facts, already known and very general in terms, and therefore possibly only of interest to students of the history of aviation.

This paper focuses on depth trajectory tracking control for a Remotely Operated Vehicle (ROV) with dead-zone nonlinearity and saturation nonlinearity of thruster; an adaptive sliding mode control method based on neural network is proposed. Through the analysis of dead-zone nonlinearity and saturation nonlinearity of thruster, the depth trajectory tracking control system model of a ROV which uses thruster control signals as system input has been established. According to the principle of sliding mode control, an adaptive sliding mode depth trajectory tracking controller is built by using three-layer feed-forward neural network for online identification of unknown items. The selection method and update laws of the control parameters are also given. The uniform ultimate boundedness of trajectory tracking error is analysed by Lyapunov theorem. Finally, the effectiveness of the proposed method is illustrated by simulations.

It is suggested that a convenient way of presenting the results of fatigue tests in which two different stress amplitudes are applied alternately is to plot log N against log (n 1/n) where N is the total cycles to failure and (n 1/n) is the fraction of cycles run at the high stress.With these co-ordinates, a simple geometrical construction gives a safe design method for the two-stress level system using only the conventional S-N curve and the value of (n 1/n) expected to be encountered in service. If N 1 and N 2 are the lives at the high and low stresses as read from the S-N curve, one point may be plotted at (log N1, 0) since this represents the programme when all cycles are at the high stress. On the assumption, shown to be justified, that less than one cycle of high stress per 10,000 total cycles would not significantly affect the life at the low stress, a second point is plotted at (log N2, 4). The straight line joining these two points is always found to predict safe values of N for any value of (n 1/n).This conclusion is checked against a wide range of experimental results taken from six different sources in the literature covering rotating-bending and push-pull tests, ferrous and non-ferrous metals, any order of stressing and length of programme cycle from 50 up to 5 million. This last feature means that the length of the programme cycle in service need not be known. All that is required is the proportion in which the two stress amplitudes are mixed. The average value of the ratio (experimental life/predicted life) for the data examined is 1·8, the extreme values being 1 and 56. By plotting in three dimensions an equation is also developed for the three-stress level spectrum and a suggestion is made for an extension of the method to multiple stress levels.

The structural problems of metal aircraft design largely centre round the difficulty of making efficient compression members. This difficulty is accentuated when loads are small in relation to the size of the structure. For example, the diameter of an aeroplane fuselage cannot usually be less than the height of a man, which results in such small forces at the surface of the shell that the lightest practicable beam is quite disproportionate to its strength.

As a measure of load in relation to size, it is convenient to use a quantity that we suggest may be called the “ structure loading.” This quantity, due to H. Wagner (8), is simply the square root of the applied load divided by a characteristic dimension (such as the length) of the member.