The usefulness of boundary-layer control (B.L.C.) at the knee of a trailing-edge flap, over the wing nose close to the leading-edge or at the knee of a leading-edge flap is first noted. Various methods of providing B.L.C. are outlined, comprising slot blowing, slot suction, area suction, inclined air-jets, and specially-designed aerofoil shapes. The aerodynamic aspects of slot blowing over trailing-edge flaps and the wing nose are then examined in detail and both slot suction and area suction are also considered. The associated practical design features required for good performance are discussed and some flight-handling implications are mentioned.

This interesting discussion ranged over the whole known field from that of near space with meteorological, communications, navigation and astronomical satellites, from prestige flights and satellites with military applications to interplanetary space with all the added difficulties arising from radiation and other engineering problems; landings and bases were mentioned as regards the planets. The desirability of this country having its own space problem, in addition to co-operation with other countries in Europe, was touched upon. The discussion was opened by Mr. R. H. Francis and Dr. W. F. Hilton, the former concentrating mainly on the instrumental rôles and the latter on the irreplaceability of man in certain aspects of space development.

A semi-empirical method is given, together with systematic data sufficient for estimating the maximum lift characteristics of wings at Mach numbers below 0·6. The method gives the effect of sweep, aspect ratio, taper ratio, camber, leading-edge radius, maximum-thickness position and Reynolds number. The accuracy is good for most wings at full-scale Reynolds numbers, but deteriorates for wings with trailing-edge angles greater than about 12° (which for conventional sections correspond with thickness/chord ratios about 0·140), and for heavily cambered sections.

Throughout the years that rotorcraft have been on the British Register of Civil Aircraft, the single reciprocating engined, single main rotor helicopter has been the predominant representative of this particular family of aircraft. These helicopters were certificated to the British Civil Airworthiness Requirements (BCAR), Section G, “Rotorcraft,” issued in January 1954, which was written in terms of such helicopters.

During the past few years there have been significant changes in rotorcraft design—the turbine engine has been introduced and the multi-engined type has become a reality.

Basic changes in the design trends of any type of aircraft must inevitably involve a re-appraisal of the appropriate requirements by the responsible airworthiness authority. The BCAR are subjected to a constant process of refinement and revision and, as a result of the development of new types, the Air Registration Board has been considering the airworthiness implications and preparing amendments to most parts of Section G, but I wish to discuss only Flight Requirements which are in the main contained in one Sub-Section of Section G—Sub-Section G2. From the recent revisions I have extracted only the significant changes, although there are still problem areas I would like to put on record.

Incidence and sideslip must be measured accurately in aircraft performance and stability tests. A convenient method is to install wind vanes on a nose boom. When only one sideslip and one incidence vane are fitted, mutual interference occurs, and the vanes do not indicate the true flow direction. This interference can be 0·5° at 0° incidence at subsonic and supersonic speeds. Thus a symmetric configuration of vanes is essential for accurate measurements of incidence and sideslip.

A cruciform arrangement of four wind vanes was fitted around the nose boom Pitot head of the Fairey Delta 2 supersonic research aircraft. The effect of the Pitot boom on the vane sensitivity was determined by a calibration of the aircraft vanes on a duplicate Pitot-static head in the R.A.E. Bedford 3 ft wind tunnel.

The effects of the fuselage and the wing upwash are only present at subsonic speeds and can be estimated.

References 1 and 2 discuss the shock position in over-expanded nozzles, and in particular the transition from nozzle flow characterised by a normal shock in the nozzle to nozzle flow characterised by oblique shocks and separation from the wall. As is well known, the shock position and pressure distribution for unseparated overexpanded flow can be adequately explained using one-dimensional fluid mechanics. Ref. 2, while suggesting a criterion for transition to separated flow, maintains that the separation point is not predictable. The criterion suggested by ref. 2 is that whenever the pressure ratio p2/p0, associated with expansion to the nozzle exit plane followed by normal shock compression at the exit Mach number exceeds the nozzle pressure ratio pb/p0, separated flow will occur. Based on this criterion and the double valuedness of the p2/p0 locus, it is argued that at a nozzle pressure ratio of 0·624, a continuous increase of nozzle exit to throat area ratio will provide for transition from unseparated normal shock flow to separated flow and back to unseparated normal shock flow.