In 1962 the passenger fatal accident rate was less than one passenger fatality per 100 million passenger miles. This is a figure which can be used to demonstrate the safety of flying relative to other forms of transport.

I am not going to discuss the merits of the criterion of “passenger miles.” Whatever one says about it the rate achieved last year does demonstrate a notable improvement on the pioneer days of aviation when the airline passenger achieved a reputation of daring by accepting the risks then present.

The take-off manoeuvre is described in outline and the safety requirements applicable to this phase of flight are briefly reviewed.

A more detailed inspection of the take-off manoeuvre reveals some of the difficulties which confront the pilot and indicates the type of additional information with which he should be provided.

Means of providing such information and the problem of measuring the necessary quantities are discussed and this leads to a description of the range of equipment currently being developed and under consideration by Smiths Aviation Division.

This includes: —

• (i) A ground run indicator

• (ii) A ground run predictor

• (iii) A pitch rate indicator

• (iv) A take-off director.

Finally, some thoughts are presented on the subject of instrument displays and the problem of incorporating the required additional information into existing flight systems.

Certain criteria are desirable to measure the adequacy of handling qualities, performance, guidance, and perhaps wholly external things like noise, associated with an aircraft on its final approach. These criteria should be quantitative so as to enable the designer and operator to predict or lay down suitable limits to the operation, to compare one aircraft with another, and to make good use of operating experience.

A review is made of recent research in the United States relating to runway slipperiness and to slush-drag or fluid-drag effects on aircraft ground performance. The formation of fluid spray and its drag effects on aircraft are traced from spray origin at the intersection of the tyre and runway to impingement on the aircraft over the complete aircraft ground-velocity range. Six manifestations of tyre hydroplaning are presented and discussed: fluid-drag peak, tyre spin-down, loss of aircraft directional stability, loss of aircraft braking traction, suppression of bow wave, and progressive detachment of the tyre footprint from the fluid-covered runway surface as ground speed is increased. A convenient formula for estimating tyre-hydroplaning speed is indicated to be

where Vp=hydroplaning speed, knots

p=tyre-inflation pressure, lb/sq in.

Comparison with available experimental data is shown. The effects of fluid viscosity and density on runway slipperiness are discussed. The effects of some runway-surface textures, tyre-tread patterns, and aircraft landing-gear wheel arrangements on slipperiness are described. The paper also includes indications of areas of interest that need further study.

The designer's task is always to choose the best compromise to meet the various conflicting requirements put upon him. This task is eased when these requirements and ways of meeting them are expressed precisely in numbers, which is so in most performance work, but rarely true of safety or reliability.

In these latter areas the feedback of operational information shows when a problem exists and how important it is. For existing aircraft a solution must often be sought by ad hoc tests before the results of fundamental research are available.

In the past ten years or so a number of changes have taken place in aircraft which have progressively reduced the potential tyre life and tend therefore to increase the operational cost. We now see that the latest aircraft have developed to such a stage that there is a certain hazard in stopping them on wet or slush covered runways. To ease this situation, further changes are recommended to the tyres, likely still further to reduce tyre life.

In the art of brake design, many of the difficulties which existed in the past have now been overcome, and this is due largely to the wealth of experience obtained over a wide range of energy absorption rates and heat sink temperatures. Much of this experience has been obtained on brake test machines on which the essential aircraft braking conditions can be reasonably simulated on the complete assembly of wheel, tyre and brake.

Investigations by one of the authors in connection with the design of a fan for a blower type of wind tunnel showed that regular and repeatable dust patterns occurred on the blades of a one-quarter scale model fan of 18 inches diameter. Dust was deposited on the fan blades along the leading-edge and on the suction surface over an area thought to be the turbulent region of the boundary layer. The introduction of isolated protuberances on the dust free area of a blade gave rise to turbulence wedges in which dust was also deposited and this was interpreted as confirmation of the coincidence of the dust deposits with regions of turbulent boundary-layer flow. These deposits showed the existence of a considerable extent of laminar flow on the suction surface of each blade close to the root, a region where high lift coefficients would be expected with associated adverse pressure gradients. Two-dimensional wind tunnel experiments were made to confirm the interpretation of the observed dust patterns by comparison with the smoke filament and volatile liquid methods of flow visualisation and these are reported in Reference 2.

It is well-known that, at large distances from the flight path, the waveform of the sonic bang from an aircraft, without lift at any rate, has the characteristic N-wave shape, as illustrated in Fig. 1. When we depict a waveform such as this we are stating what would occur at large distances in the absence of viscosity and other diffusive effects, such as turbulence. We know, of course, that in reality, because of these effects, the bow and stern shocks will be “softened”, i.e. the pressure jumps associated with them will not be instantaneous, but will have a finite, but small, “rise time”. However, this is not the matter under discussion. The essential feature of the N-wave illustrated in Fig. 1 is that the pressure jumps associated with the bow and stern shocks are equal, and that the positive and negative phases are of equal duration. The arguments for the waveform to take up this shape at large distances are put in a classical paper by Whitham.

The notched fatigue strength of the aluminium alloy HE 15, under stress conditions similar to those occurring in aircraft structures, is greater when the material is naturally aged than when it is fully heat-treated. This is attributed to the lower proof stress of the naturally aged material, which enables the high stresses in regions of stress concentration to relax more readily. However, no further improvement was obtained by re-solution-treating the alloy to reduce the proof stress further.

We have followed with considerable interest the two recent technical notes that have appeared in the Journal on aquaplaning (Mr. Gadd, p. 189, March 1963 and Mr. Gray, p. 302, May 1963). May we take this opportunity of drawing to your attention some work on this topic which has been carried out in the Civil Engineering Department of the University of Melbourne in co-operation with the Department of Civil Aviation, Commonwealth of Australia?