Boundary layer theory is the cornerstone of our knowledge of the flow of air and other fluids of small viscosity under circumstances of interest in many engineering applications, especially also in aeronautics. Many complex problems in aerodynamics, as for instance the problem of skin friction, which was theoretically attacked very early by F. W. Lanchester, have been clarified by studying the flow within the boundary layer and its effects on the general flow around the body.

Research work on boundary layers, as started by Prandtl in 1904. was for the first twenty years—up to Prandtl's Wilbur Wright Memorial Lecture to the Royal Aeronautical Society in 1927—almost entirely restricted to Prandtl's Institute at Göttingen. But since about 1930 boundary layer theory has been generally accepted, and in the past thirty years there has been an almost exponential rise of the number of contributors to its further development.

The author tries to trace certain lines, along which this important branch of modern fluid dynamics has developed in the past thirty years. In this connection the following topics are treated to some extent:

1. I. Transition from laminar to turbulent flow.

2. II. Boundary layer control for high lift and low drag of aerofoils.

3. III. Aerodynamic heating at high speed (high Mach numbers).

4. IV. Boundary layer efff cts on swept wings and on rotating bodies.

I. The theoretical investigations of the problem of transition start from Reynolds' and Lord Rayleigh's hypothesis of the instability of laminar flow. After many unsuccessful attempts Tollmien, 1930, finally succeeded in calculating the critical Reynolds number for the boundary layer on a flat plate. More than ten years later Tollmien's stability theory was completely confirmed by very careful experiments of Dryden and his co-workers.

II. After many wind tunnel experiments the investigations of boundary layer control for high lift of aerofoils led to the construction of two aeroplanes with boundary layer suction at the aerodynamische versuchsanstalt gottingen, in 1938, which were quite successful. later on, also, a considerable reduction of the skin friction of aerofoils was obtained with the advent of the laminar flow aerofoil.

III. In flow at high Mach numbers the velocity boundary layer is accompanied by a thermal boundary layer which is caused by frictional heating. The large increase in the temperature of a solid surface in a high speed stream which can be calculated from boundary layer theory only, poses a serious problem to aeronautical engineers (“thermal barrier”).

IV. The aerodynamic characteristics of swept wings and Delta wings are largely governed by the behaviour of their boundary layer. Some of the draw-backs of such wing plan forms can be remedied by boundary layer control, as for instance by a “boundary layer fence.” For turbo-machines the influence of the centrifugal forces on the boundary layer plays an important role for their aerodynamic coefficients.

The Short SC.l is a small delta wing V.T.O. aircraft of about 7,800 lb. all-up weight. Its unusual feature is that it is provided with vertical thrusting engines to enable it to take-off and land vertically and to hover. It can also operate normally as a conventional aircraft.

The nature of the aircraft introduces a number of problems in the design of the landing gear. The first of these is that all wheels must be fully castoring since a vertical landing may take place with a certain amount of drift in any direction. Another complication arises because of the possibility of landing with slight backward drift, it being necessary to move the main wheels aft when the pilot intends to make a vertical landing; if the wheels were left in the required rearward position for conventional take-off the elevator power would be inadequate to lift the nose of the aircraft. The landing gear is therefore provided with simple means for moving the wheels fore and aft by a small amount, to move the position of the main wheels in relation to the centre of gravity.

The first International Agricultural Aviation Conference, held at the College of Aeronautics at Cranfield between the 15th and 18th of September 1959, was well timed to mark one stage in the development of the art of airborne farming—it was the stage when the art ceased to be mainly experimental and became essentially a commercial business.

Intermittently for the past thirty years, in various parts of the world, attempts have been made with varying degrees of economic and practical success to do certain operations connected with farming, forestry or other allied activities. Two main factors within the past decade have served to intensify the interest and activity in the art. One important factor is the general improvement in aircraft, including helicopters, coupled with the very large number of relatively suitable ones which became redundant (and therefore cheap) at the end of the Second World War. The other factor, equal in importance, concerns the development of the science of agricultural chemistry which has given the farmer a new and wide range of fertilisers, selective weed killers and other chemical forms of pest control which are effective in reasonably small bulk.

Sporadic commercial aerial spraying operations have been undertaken in the United Kingdom for more than a decade but only over the past two or three years has it been possible for companies to make a sustained attempt to plan their work in a way which will put operations on a self-supporting annual basis.

Today, the degree to which an operator will plan his work is largely a matter for him to decide; there are few legislated requirements. The law as it stands specifically permits the work of the agricultural operator and leaves him—in the main—to order his affairs as he thinks proper. However, it cannot be long before the incidence of accidents and public anxiety about the effects of drifting chemicals brings about a change in the official attitude towards the Industry. Looking ahead we must expect some form of licensing to be introduced, which will require all operators to meet a standard set by the Ministries of Aviation and Agriculture.

The Soviet Deputy Premier, Mr. Anastas Mikoyan, is reported to have stated recently that Russia has a missile ready to “visit the Sun.“

The Russians have been achieving a notable series of “firsts” in space exploration, and this statement may have led some to speculate on whether they will be the first to reach the Sun.

It is, of course, strictly impossible to talk in terms of hitting or reaching the Sun, as it has no solid surface. Indeed the streams of matter and radiation it emits travel out into space beyond the orbit of our planet. However, for practical purposes the Sun is opaque over a diameter of just under a million miles, and this constitutes a generally agreed boundary for purposes of such a study as this.

Conditions on the bodies that constitute the Solar system are dominated by the Sun, and this alone would justify the continued examination of its behaviour. Additional justification is provided by the fundamental knowledge of matter obtained through observing the Sun and its radiated energy.

The flow through porous screens has been widely studied from both the theoretical and experimental points of view. The most widely used types of screen are the wire mesh and the perforated plate, and the majority of the literature has been concerned with the former. Several attempts have been made to correlate the parameters governing the flow through such screens, i.e. the pressure drop, the flow conditions and the geometry of the mesh.

If a circular plate has a concentric circular hot area, there is a critical temperature for this area at which the plate buckles. This temperature is calculated in this note for the case of a clamped plate supported in such a way that the radial stress in the cold part obeys the inverse square law.