It is a great honour to be invited to present a survey of the aeronautical research in the Netherlands to this distinguished audience and I wish to express my thanks to the Council of the Royal Aeronautical Society for giving me the opportunity to deliver this lecture. The more I appreciate it in view of the friendship between our two countries, between the Society and its Dutch counterpart and the personal friendship with so many present on this occasion.

It is my intention to give a survey of some of the work performed in the Netherlands in the post-war period and to describe briefly the main installations which are now available or under construction. I hope that I will be able to give you an impression of the scope and the nature of the aeronautical research activities in the Netherlands. These activities are being directed in the first place by the immediate needs of the industry and the aircraft operators; and in the second place by the desire to contribute to the general development of the art, thereby also supporting the exchange of results on an international basis, even more essential than before, considering the rapidly growing importance of aviation in its broadest sense.

Before entering into more technical matters it may be worthwhile to give very briefly an outline of the present organisation of aeronautical research and development in the Netherlands.

The problems involved in the packaging of Service radar equipment are reviewed. Information on shock testing techniques, instrumentation and a design procedure for cushioning are given, together with some examples of current packaging methods used by the Ministry of Supply's Radar Research Establishment, Malvern, Worcs. The paper is based on a lecture given to the Royal Aeronautical Society, Gloucester and Cheltenham Branch in December 1954. Received October 1956.

Some experiments concerned with the wake flows of a number of flat plates of low aspect ratio (Fail, Owen and Eyre) have suggested that for large angles of inclination to the undisturbed stream the wake includes a region of recirculation. The present observations include a detailed study of this region, with particular reference to the wake produced by an equilateral triangular plate, and an attempt is made to explain why the recirculatory flow is found only at angles of incidence greater than 35°. The data includes some wind tunnel measurements of force coefficients, static pressure and mean velocity, and observations of the wake flow made in a smoke tunnel and in a water tunnel.

A Similarity in properties will be demonstrated between the moments and product of inertia of a lamina and the components of plane stress. It is now a well established fact that in two-dimensional stress theory it is advantageous to use certain combinationsof the stress components.

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First, it will be shown that the use of similar combinations of the moments and product of inertia leads to a useful graphical means of obtaining these quantities for awkwardly placed axes and also to some results not normally to be found in the text-books. Secondly, an application to photoelastic analysis is also made.

This Note describes the design and construction of a “ Tilting Test Bed ” for helicopter engines for Alvis Ltd., for which some onerous requirements were laid down (Fig. 1). The most important of these were that:—

1. (i) Readings of engine torque and b.h.p. must be given by a dynamometer, so as to provide accurate data.

2. (ii) The engine, and therefore the complete test plant, must be capable of being tilted, while running, through 120°—from the horizontal to the vertical and 30° beyond.

3. (iii) During the tilting process the engine throttle setting must remain unaffected and the readings of torque, b.h.p., fuel consumption, and so on, continue with unaltered accuracy.

4. (iv) A powerful fan must be incorporated, for cooling certain types of engine not provided with selfcontained fan, and the air-blast must continue unchanged during tilting.

The buckling of skewed plates with clamped edges and under externally applied shear, and skewed plates with simply-supported edges but with both externally applied axial and shear loading have been considered previously. It is the purpose of the present note to consider the buckling of simply-supported rhombic plates under externally applied shear as shown in Fig. 1.

In References (1), (2), Dr. Lachmann develops a method for calculating the growth of the laminar boundary layer over an aerofoil surface with spanwise suction slots placed at intervals along the chord. For this form of control, the laminar flow develops normally from the downstream edge of a slot until it attains the critical Reynolds number (expressed in terms of either the displacement or momentum thickness) at which transition is imminent. The layer then encounters another slot which so thins and stabilises the part not removed by suction, that it is able to continue downstream in the laminar state.

A new feature of the above investigation is the establishment of a second critical Reynolds number which provides an initial condition on the downstream side of a slot. Essentially it defines the minimum value of the displacement or momentum thickness for which, in relation to the local surface roughness, there is no danger of transition due to this form of disturbance.

The method referred to in Dr. Coleman's notes was developed with the collaboration of my colleague Mr. J. B. Edwards of Handley Page Research Department. The purpose was to obtain a rational estimate of suction quantities and suction distribution, linked up with measurements of boundary layer profiles and suction quantities on wind tunnel models, and also to assess the effect of a certain degree of roughness of the order to be expected on actual wings. Existing theoretical methods ignore roughness which, however, is a most important parameter not only in wind tunnel tests, but also in flight at higher values of the unit Reynolds number; surface roughness obviously limits the intensity of suction which can be applied at a spanwise suction strip.

It was intuitively assumed that the removal of fluid by suction was equivalent to cutting off the lower portion of the boundary layer profile at the upstream edge of the suction strip and that a rapid re-adjustment of the boundary layer profile within a short distance took place.