British Aviation's best friends—and sometimes, recently, there have appeared to be very few of them— could hardly claim that the image of the industry, both manufacturing and operating, civil and military, has been anything but dismal during the past few years. However bad that image may be, it has been largely brought upon itself by, what an observer on Mars—or in America—might consider has been a carefully co-ordinated series of inept blunders on the part of those running successive Governments, the manufacturing industry, the airlines, the Service requirements, the administrative machine and by the Press and politicians (of all parties) as well. All are to blame—many for making wrong decisions, most for making no decisions at all.

I Have the great honour to give the Fifth Memorial Lecture in tribute to Juan de la Cierva, a great man and pioneer in rotating wing development, whose work was predominantly done in England.

His fundamental practical achievement, resulting from a deep knowledge of aeronautical science, was the demonstration of the fact that a big airscrew with suitable pitch could serve as a lifting surface without the danger of stall which is inherent in fixed-wing aircraft.

Is there a danger of trying to over-simplify the manner in which costs can be reduced? Has the colour grey been deleted from our dictionary, and is everything really black or white? It would seem to me there is a tendency for the technical man to over-rule completely the practical man or vice versa, and maybe there is room for the colour grey to return and be high-lighted in our dictionaries.

A number of subjects come readily to mind where, in my opinion, neither the purely theoretical nor the purely practical approach can achieve the best results, and the only efficient way is a combination of both. Job control and time standards is, I consider, a subject which comes into this category.

The title of this lecture is a little misleading in that the intention is to give broad coverage not only to the handling qualities of the aircraft, but also to some of the general information and lessons derived from the flight-testing, some of the background and some of the supporting work. Attempts will be made to correlate some of the characteristics with shapes that are generally regarded as less radical. Only limited attempts will be made to cross-read to larger applications of the slender delta, not because of absence of cross-read, but because this is an activity which must not be undertaken lightly or ill-advisedly, and is within neither the time-scale nor the scope of this lecture.

Nowhere in the literature of helicopter noise can one find a general understanding; only isolated, inconsistent, and often inadequately documented facts. These could, of course, be reviewed but hardly with profit; it is easier to ask critical questions of nature than of previous investigators.

For fundamental reasons the helicopter in its present state of development is not in fact matched to the bulk, low-cost transport of passengers. But for equally good reasons the phenomena of aerodynamically generated noise now bid fair to banish from inhabited localities all other forms of vertical take-off and landing aircraft so that, if a city-centre to city-centre aircraft transport system is ever to be practicable, it will most probably be based on some metamorphosis of the helicopter.

The main factor contributing to hydroplaning on slick runways is the existence of a squeeze film in the contact area between tyre and surface. The situation may be improved by optimising surface texture so that the asperities break through the water film in a minimum time. Two techniques are described for characterising surface texture: a superposition solution based on viscous channel flow and a dimensionless number approach involving size, spacing and shape factors. The “feel” of a surface is quantitatively obtained, and an outflow meter is described which, by directly measuring the mean hydraulic radius of runways, provides a comparison of their drainage abilities.

This note is concerned with the significance of a “hold period” on thermal fatigue endurances and on the use of a frequency exponent to correlate the results of mechanical fatigue tests at various temperatures.

In their note in the January 1965 Journal (pp. 53-55), Coles and Skinner quite rightly pointed out that residual stresses, set up as the result of plastic yielding in compression during an initial heating period, will undergo redistribution during a subsequent “hold period” at an elevated steady temperature. However, it is important to note that the redistributed stress pattern and the associated creep strains at the conclusion of the “hold period” will depend very much on the nature of the applied loading. For example, the compressive strain and the associated tensile stress set up in the rim of the disc will both fall in magnitude if the disc is not rotating and may reach infinitesimal values if the “hold period” is long enough.

It is commonly stated in the literature on laminar flow control (see, for example, ref. 1) that the important parameter controlling the height of tolerable roughness is the Reynolds number per foot, or unit Reynolds number, Vh; provided this parameter is the same in any two cases (which are closely geometrically similar) then it is assumed that the tolerable roughness height will also be similar. It is the object of the present note to point out that this is true only in very restricted circumstances and that in general the actual physical scale is also of considerable importance, as the following shows.

The Free and damped vibrations of a circular plate with given initial conditions, which is either free or elastically restrained along its outer edge, are discussed using the method developed by Reid and some numerical results are also given.

The vibration of a circular plate has been studied considerably and most of the authors seem to be interested in determining the frequencies of vibration and the nodal patterns. A few investigators have studied the problem of determining the subsequent motion of a thin plate started with some given initial displacement or velocity. Sneddon has attempted this problem, taking into account an approximate boundary condition. Recently Reid has discussed this problem without taking recourse to any approximate boundary condition. He has developed a method of analysis to determine the displacement of a freely vibrating thin circular plate with the given initial conditions, using the norm of the eigen functions.

An analytical solution is given for the one-dimensional distribution of temperature in a web of an idealised multi-cell wing structure when the adiabatic wall temperature variation is assumed to be either an instantaneous or a linear function of time. The maximum temperature difference between skin and web centre is computed for a range of structural geometries and thermal parameters. Thermal stresses are calculated assuming a parabolic temperature distribution in the web.

In the establishment of a fluid circuit's behaviour, it has been shown that the condition of the entry flow into each component of the circuit is of significance. This note indicatesthe problems encountered by a designer using diffusers at the present state of knowledge, and outlines a hopeful method of reducing diffuser pressure losses.

A simplified approximate solution for clamped skewed plates under uniform pressure is presented. Variations in maximum edge and centre moments with skew angle and sides ratio are shown plotted. The convergency of the solution is checked and results compared with the limited available data. Results were verified by an experimental investigation.