Proceedings of the Institution of Mechanical Engineers

The linear induction motor as a planar development of the conventional rotary machine is described and the fundamental differences between it and the conventional machine are discussed.

The effects of the discontinuities which occur in the linear machine, either in the stator as ‘short-stator’ effects or in the ‘translator’ as ‘short-translator’ effects, are discussed. The secondary member of the linear machine is referred to as a ‘translator’ in order to distinguish it from the rotor of the conventional rotary counterpart. The exploitation of the double-sided stator system is also briefly discussed.

A linear induction motor has been constructed as an accelerator specifically for axi-symmetric impact extrusion. Some elements of design employed in the construction, together with a description of the model impact-extrusion machine, are given. The linear induction motor consists of a twin arrangement of double-sided stator systems, side by side, and in the same plane. The kinetic energy possessed by a mass accelerated in guides between the two stator systems is used for impact extrusion and the mass is propelled by the force exerted on a single-plate ‘dual translator’. The linear induction motor functions as a ‘short-translator’ machine.

Experimental results presented show the nature of the accelerated motion of the mass, the force-slip characteristic, and how the overall energy efficiency of the linear induction motor is related to the root mean square phase voltage.

Impact forward extrusions were performed for which \ in and 1 in diameter billets of pure lead and 1/2 in diameter billets of tellurium lead and super-pure aluminium were used. Some evidence is presented to show the limitations of impact extrusion.

The operating conditions to which some castings are subjected are much more severe than they were a quarter of a century ago, and are likely to become more severe in the future. Castings which were acceptable in the past are often considered unsuitable for present-day working and great cost is involved in achieving cast components which can be used in modern equipment. These costs are often incurred in correcting the castings. By changing designs, production methods and inspection and testing techniques the cost of the castings should in the long run be reduced, and the challenge of future conditions will be met.

Precautions taken to ensure ‘clean’ conditions in the first civil nuclear power stations resulted in excessive costs and delays. These precautions are aimed at the elimination of materials which could poison the core, create a maintenance hazard, affect the fuel elements or increase the fire risk in the core.

The present paper reviews the subject in the light of the considerable experience of constructing and running reactors now available, and an attempt is made to assess the importance of the various precautions.

An account is given of a scheme for teaching design-development engineering to undergraduates which has now been in operation since 1960 in the Department of Mechanical Engineering, the University of Birmingham.

The essential feature of this scheme is that selected groups of final year students are engaged on the design of research and/or teaching equipment currently required in the Department. These designs are detailed by second-year students and are subsequently manufactured by them during their vacation employment in industry. The manufactured designs are taken back by them to the University to be developed in the first term of their final year. Following this, the equipment is either fed into the teaching or research activities or re-designed to start on a new cycle. Thus, the students concerned get direct experience of the complete design-production-assembly-development sequence.

A description of the detailed working of the scheme, its organization and the experience gained in running it, is given. A number of completed designs are discussed. A detailed statement of the overall drawing-design teaching system is presented in Appendix I.

The ‘Feilden report’ has drawn attention to the shortcomings of the design tuition received by engineers, and there has been much discussion of what can be done about this in a university course. In this paper are described experiments in teaching design to students taking a sandwich course for the Diploma in Technology at one college. It is believed that an exchange of ideas on this particular aspect of the problem is worthwhile, particularly when thought is being given to the inclusion of design as a subject in examinations of the Institution.

The thermal development of the modern steam and gas turbine over the past two decades has been greatly assisted by a much better understanding of the fluid behaviour as it passes through the machine. This has been brought about by the increasing amount of aerodynamic research and development being carried out on the many components of these turbines.

This paper concentrates on the fixed and moving-blade elements of the large steam turbine, and describes the design and operation of a transonic variable-density wind tunnel for static cascade testing of turbine blading. The importance of Reynolds number and Mach number is emphasized, and the manner in which these parameters influence the blading losses. The origin of the trailing edge shock waves on blades discharging obliquely, and their effect on performance, is discussed in some detail, drawing on both experimental and theoretical techniques. A large proportion of the flow section of long last 1.p. stages is operating in the supersonic region, and possible future blades may have relative discharge tip Mach numbers approaching 20.

The results of experiments on the dynamic free stretch forming of peripherally clamped circular blanks of brass and mild steel subject to an underwater explosive charge are given for use in connection with studies on explosive metal forming. The results are presented in six parts.

part 1: Some results for the effect of hydrostatic head above the charge on the polar deflection suffered by a blank are given and it is shown that for some otherwise fixed sets of parameters, at a depth of about 18 in below the free water surface the polar deflection is greatest. Illustrations of how strain distribution and the plastic work done on a blank vary with hydrostatic head are also given. In particular it is shown that the energy received from an explosive charge by a blank may greatly exceed the fraction expected by reference to the solid angle subtended by the blank at the point charge. With the aid of some blank speed measurements an attempt is made to relate the kinetic energy acquired by the blank to the plastic work done on them.

part 2: The measured maximum speed of deformation over the central portion of blanks is shown to be less than 300 ft/sec (rupture excluded). For some circumstances that two phases of motion exist is incontrovertible, and the mechanism responsible for these, we believe, is as follows. In the first phase the speed is dependent upon stand-off distance and is a consequence of the primary shock wave and subsequent cavitation and diffraction effects that occur as a result of the shock wave impinging on the blank. The second phase (arising only with the larger stand-off distances) occurs some time later and may be accompanied by a greater deformation velocity; it is thought to be due to a water hammer or similar effect.

part 3: An attempt is made to present generalized results for the maximum polar deflection incurred as a function of both charge weight and hydrostatic head.

part 4: This shows how the density of a curtain of air-bubbles, measured by aerator pressure, inserted at the walls of the confining tank reduces the polar deflection or damage a blank may sustain.

part 5: A short empty cardboard cylinder (sealed at each end with a layer of polythene) inserted between the blank and charge leads to increased polar deflection, other things remaining the same.

part 6: Deals with gas-bubble pulsation and generally confirms the Willis formula, namely, that for charges not too near a free water surface or an underwater blank, the period of oscillation is proportional to (charge weight)^1/3 and (the ambient pressure at the charge)^−5/6.

Earlier work on a water-hammer technique for high-rate forming of sheet metal has been extended to include work on deep drawing using lead plugs. A study of the pressure-time history of a deforming blank during its initial movement is reported.

An assessment of the overall efficiency of the process has been made and is found to be about 50 per cent; this is an order of magnitude better than that found with comparable electro-hydraulic and explosive methods.

The effect of certain electrical parameters on the forming of flat circular aluminium sheet specimens clamped at their periphery and formed by means of the underwater spark discharge process as described in a previous paper (40) is extended to cover a number of different materials. Experimental observations on the effect of stand-off distance and material thickness on deformation and deflection are included and the speed of movement during the deflection of specimens of different materials is compared. The variation with polar deflection of strain at a particular radius is presented and the nature of the discharge current is also discussed.

The use of a line explosive charge in the expansion of water-filled brass tubes is investigated, both on a small experimental scale and on a large industrial scale. Results are presented showing how the radial velocity of deforming tubes and the distribution of hoop and axial strain in the deformed product are related. Metallurgical and some other aspects of the process are discussed.

The manner in which the overall energy efficiency of a small linear induction motor, previously used by the authors for impact extrusion, has been increased is described. The improved motor has been used to perform the impact blanking of 1 in and 2 in dia. circular blanks of aluminium, brass, copper, and mild steel in various thicknesses of strip. The energy required to blank when the piercing tool is initially moving at between 9 and 36 ft/s was found to be less than 50 per cent greater than that required for an identical slow-speed operation.

This paper reviews the published literature on the explosive welding of metals and the related subject of pressure welding. The mechanism of explosive welding is closely associated with that of shaped charges with metal linings, so a brief résumé of the theory of such charges is given. It is also noted that fluid waves are sometimes generated at the weld interface in explosively welded joints, and the mechanism of their generation is discussed.

Experiments are reported on the explosive cladding of mild steel with stainless steel, 70/30 brass, and high-conductivity copper. These have been aimed at establishing the effect of impact angle, weight of charge, and the thickness of the flyer plate on the form of the weld achieved. The mechanical strength of the welded joints has been investigated by shear, tension, and bend tests, and the variation of hardness across the weld interface has also been examined. Results of these various tests are presented and discussed.

It is concluded that explosively cladded material has some advantages over conventionally pressure cladded material. In particular it is probable that the strength of the welded interface is much stronger. With large charges and small angles of impact it is possible for the parent plate to suffer from shock damage which can be clearly seen under a microscope, but it is not known if this is harmful to the mechanical properties. Hardness is increased each side of the interface but a reduced value is measured close to the interface.

This paper describes a number of programmes for digital computers that have been developed by the authors' firm to eliminate many of the tedious hand calculations which are encountered in the preliminary stages of steam-turbine and condenser design.

By their use a considerable amount of the designers' time is saved and fatigue is reduced. These programmes also eliminate mistakes and inaccuracies which may occur in long calculations made by hand.

The programmes described have been chosen as being representative of the range of programmes used in preliminary turbine design and optimization and are as follows:

a programme to enable steam properties to be calculated, based on the formulae given in the Keenan and Keyes Steam Tables;

a programme which can be used to determine the efficiency of small industrial turbines;

a feed-heating programme which will carry out the calculations necessary to determine the preliminary energy balance for a feed-heating cycle;

a detailed energy-balance programme incorporating turbine-efficiency calculations;

a condenser-optimization programme for determination of the ideal parameters to be used in the design of a condenser.

The programmes are arranged so that unskilled operators can run them on the computer without the help of an experienced programmer. Facilities are also made available for writing programmes in a simplified form called ‘autocode’ which can be used by an engineer after the briefest of trainings.

Some programmes are described in considerable detail to assist others who may wish to write a similar programme or to compare them with programmes of their own.

All these programmes have been in regular use for more than three years and have greatly enlarged the scope of investigations which may be carried out in the project stage of the design of a steam-turbine generator and associated power-station equipment.

In the last two decades there has been a progressive increase in the scope of small gas turbine development and application, both in commercial and military fields. Technological advances in the military field have created demands for prime movers able to meet more stringent operational requirements.

An environment now exists in the U.S. Armed Forces conducive to the acceptance and use of small gas turbines that can be adapted to the many specialized applications demanding distinctive physical characteristics.

In 1957, the U.S. Bureau of Naval Weapons entered into a contract with Solar, a Division of International Harvester Company, for the design and development of a small, lightweight, single-shaft gas turbine engine to power a one-man helicopter. Rated at 55 s.h.p. for 100°F ambient conditions, the engine design requirements were based on simplicity of operation and maintenance, low production cost, and a short development time. These factors were considered more important than optimum specific power, fuel consumption and weight. A two-shaft version of this engine was also required to power a one-man flying platform. To facilitate the required low engine airflow, weight and rugged characteristics, a single-stage centrifugal compressor and radial inflow turbine, mounted back to back, were selected. A unique feature of the two-shaft engine was the simple method of achieving two-shaft capability by using the exducer portion of the radial turbine as a power turbine. This design resulted in both engines having the same nominal performance, weight and envelope dimensions, with maximum component interchangeability.

A comprehensive aerodynamic development programme was undertaken to improve component efficiencies and various aspects of this programme are discussed.

Based on favourable results from this programme, the building and development of an uprated engine was undertaken. By incorporating a modified compressor, a 38 per cent increase in s.h.p. and a 6 per cent decrease in specific fuel consumption (s.f.c.) was obtained.

Probably the most important factor in the choice of a small gas turbine for military applications is its ability to develop more power, per unit weight and volume, than other engine types. In general, the specific weight of reciprocating engines, in the same power class as the subject gas turbine, average about 10–15 lb/hp with specific volumes ranging from 0.220 to 0.30 fr³/hp, compared to values of 0.53 lb/hp and 0.027 ft³/hp for the turbine.

Over 20 different variations of this engine have been produced for such diverse applications as small aircraft and boat prime movers, aircraft and helicopter auxiliary power plants, mobile generator sets, and ‘winterization’ kits for U.S. Army field service.

Intensive efforts are being made by companies on both sides of the Atlantic to develop the small gas turbine for a variety of applications. It seems reasonable to predict that these efforts will ultimately lead to the development of units with improved performance and lower initial cost.

A simple method is presented for calculating the strength of pressure pulses transmitted through pipes with area changes or in simple branch systems. The method is based on the assumption of one-dimensional flow, otherwise the exact gas relations are employed. A number of examples of typical practical configurations were investigated both theoretically and experimentally and the results compared. With the exception of one or two cases where three-dimensional effects predominate, the agreement between the theory and the measurements was very satisfactory. The application of the theory to flow problems in internal combustion engines is discussed in some detail.

Job evaluation is a technique which seeks to provide a logical basis for the setting of comparative pay rates. The methods used originated in America over 35 years ago and most job evaluation plans are adaptations of the three original ones described in this paper. A new technique has been evolved in Britain recently which is very akin to job evaluation but far more sophisticated in its approach. As far as is known, this technique has only been tried in a limited way at one firm so that only a brief mention is made of it, despite its obvious interest.

Like a lot of other modern management techniques, job evaluation can do more harm than good unless human nature is taken into account. A man still wants to be regarded as a unique individual and so resents any attempt to fit him into a cold scientific pattern.

Success in job evaluation, therefore, depends largely on the personalities of those responsible and on the creation of mutual trust between management and men.

A description is given of an apparatus for carrying out tension tests under hydrostatic pressures of 60 ton/in² or more. The results of an investigation of the effect of hydrostatic pressure on the tensile properties of a number of metals are given. It was found necessary to protect cast materials with a rubber sleeve. The fracture strain increased with hydrostatic pressure, but this increase was not linear but varied with the crystal structure of the metal. In zinc and Mazak a sudden transition from brittle to completely ductile behaviour occurred at a critical pressure; this was probably due to a flat stress/strain curve.

It was found in tension tests under pressure that specimens could deform and neck in a characteristic tensile manner, even though all the stresses were compressive. Fracture also could occur when the axial stress was compressive.

It was found that the present results on tension, and previous results in torsion on cast iron, conformed either to a criterion that fracture occurred when the largest tensile stress reached a critical value which decreased as the volumetric compressive stress increased, or to a maximum deviatoric stress criterion, the critical value increasing with volumetric stress.

A theory has been developed based on the accepted heat transfer theories of Fishenden, Saunders, Weise and others, together with the results of the author's experiments. From this theory it is possible to evolve a design sheet which can be used to predict ambient temperatures within cabinets for predetermined areas of ventilation. Hence, design curves of temperature, in relation to areas of ventilation, can be obtained for specific cabinets and methods of cooling. From these curves, it should be possible to select the method of ventilation and the optimum cooling area and hence ensure that the maximum tolerable ambient temperature in which the components are required to operate shall not be exceeded.

The effects on the hottest component, when the methods of ventilation are altered, the ventilating area is varied and the main heat source is progressively raised, are studied. The results of these experiments and the comparisons between predicted and observed ambient temperatures are discussed. Recommendations for positioning components within cabinets for maximum cooling effects are made.

The Pendulum process is a new incremental rolling method for producing thin metal strip from thick plate. This is done in a single step, bypassing a sequence of conventional and often unproductive operations, such as process coiling, storing, annealing or cleaning. Rolling is carried out generally without preheating.

The forces in the reduction zone are largely controllable and comparatively hard alloys can be rolled without overloading the equipment.

The ingoing material is forced by feed rolls into a gap formed by converging paths of the work rolls which are moved backwards and forwards. The work rolls are freely rotatable, each being supported by two rows of backing rollers. The rolls are rotated solely by frictional contact with the strip and must remain loaded during the whole cycle. Deformation takes place during both strokes of the cycle. The limitations of the method are discussed and some results reported.

The basic feature of the paper is the development of the exact characteristic equation for a feedheating train composed of a number of cascaded heater groups in which each heater is taken to be of a rather general type. With the aid of this equation a systematic computational procedure may be devised which permits the variation of the train performance resulting from changes in the heater characteristics to be exactly and easily determined. A differential method, suitable for most practical analyses, and based on a series expansion of the characteristic equation, is also presented in some detail. The relation of the content of the paper to the ultimate objective of estimating variations in cycle heat rate resulting from changes in feedheating train performance is discussed in Appendix III.

Appendix II contains an example of a complete feedheating calculation and compares the results of exact analyses of variations with those obtained by the differential method.

The successful operation of high-pressure steam generating plant depends on many factors, one of which is the maintenance of a high standard of purity in the feed water. Contamination of the feed water by ingress of hardness salts from condenser tube failures is therefore serious. Early in the operational life of the three 120 MW units at Kincardine it was found that aluminium brass was an unsuitable alloy for the condenser tubes: corrosion was widespread and tube failures were a regular occurrence. The investigations made to determine the cause of failure and to provide a more suitable alloy for tube replacement are described. However, it was impractical to retube the condensers completely. Aluminium brass tubes which have given satisfactory service are generally found to have protective films rich in iron oxides. The condenser tubes at Kincardine did not have an iron oxide film nor did the cooling water contain any appreciable iron. Ferrous sulphate was added to the cooling water to provide iron and the effects and cost of conditioning are described.

The design of oil engines for strength and stiffness has, in recent years, become much more stringent than before the 1939–45 war. This is due to the need to meet more competitive market conditions by increasing power/weight ratio without incurring mechanical unreliability. Many engine components are inherently most difficult to analyse by theoretical approaches. The adoption of model techniques for experimental stress analysis can show great savings in cost compared with the use of prototype full-scale testing for proving mechanical strength. The advantages of model techniques for prediction of stresses due to mechanical loading are discussed in the paper, and some applications, using plastic, rubber, cardboard and aluminium models are described together with a full account of the experimental techniques, results and limitations.

The Council present their Report on the work and progress of the Institution during 1964 for the information of the members at the one hundred and eighteenth Annual Meeting

An analysis is made of the viscous power losses in a liquid-filled pipe under oscillatory compressible flow conditions, particular attention being paid to Shell Tellus 27 oil in a 7/8 in diameter pipe, 80 ft long.

Using an effective friction coefficient to take into account oscillating flow, the efficiency and the power-carrying capacity of the pipe are calculated for four discrete values of resistive output load. It is shown that if the load is not equal to the characteristic impedance of the pipe, then the efficiency is reduced and the power capacity depends upon the frequency of operation of the pipeline. A mismatched load should be resistive with the pipe preferably tuned to the quarter wavelength frequency supplied from a constant pressure generator. Relative power output increases under these conditions are achieved at the expense of efficiency and increased pipe pressure.

Agreement between theory and experiment for the load conditions considered is good.

The chemical techniques adopted in the pre- and post-commissioning phases at West Thurrock power station are described. Apart from the detailed account of the chemical cleaning operations, types of cleaning processes, acids and strengths, sampling arrangements, circulation rates and method of final inspection are also considered. Mention is made of the desirability of sections of the plant arriving on site in a clean sealed state. The cleaning methods bring about a rapid reduction in boiler water silica so that full load can be achieved quickly.

A new technique, involving nitrogen sealing, to reduce metal pick-up during start-ups has been evolved, whilst the early control of both feed and boiler water conditions is stressed and an optimum hydrazine level determined.

Modern developments in forging equipment and techniques are combining to make the dimensional accuracy and surface quality of forged stock comparable with that of rolled products. The output of a conventional press forge, employed on the cogging of alloy steels, is comparatively modest, being of the order of 10 000 tons/annum, as compared with a rolling mill installation which has a capacity in the range 500 000 to 1 000 000 tons/annum. It follows that, for production requirements between these two extremes, a high productivity cogging forge unit costing substantially less than a cogging mill should prove to be a worthwhile investment for many alloy steel producers.

This paper contains an account of a design study of a forging machine with an output of 50 000 tons/annum capable of cogging alloy steel ingots down to billets or bars. The performance is based on current industrial requirements and the design concept calls for a machine in which the forging and manipulative functions are fully integrated and controlled. To achieve this, new features in press design and manipulative equipment have been evolved.

It is concluded that a specialized high productivity cogging unit is a practical and economic proposition for the range and quality of steels considered.

Increasing train speeds and the use of multiple pantographs have emphasized some of the problems of ensuring good current collection from the light overhead contact system used for railway electrification at 25 kV in Britain and overseas. The development, in Britain, of instrumentation and test methods is described, and the problems which arise as a result of ‘hard spots' and resonance effects are referred to.

Experimental investigation has shown that greatly improved current collection can be obtained, by suitable modifications, even at speeds exceeding 100 mile/h, and under features such as bridges with minimum clearance. The main principle employed, which has been called ‘stiffness grading’, is to ensure a smooth transition of stiffness, or compliance of the overhead contact system through such features. These are, of necessity, considerably stiffer than normal open route equipment because of the strictly limited electrical clearances. The result is achieved primarily by modifications to the geometry of the equipment.

It has been shown that such modifications can reduce appreciably the tendency of the system to build up oscillations of large amplitude, particularly in sequences of spans of approximately equal lengths. This tendency is much more marked where multiple pantographs are used, especially at certain spacings. Such phenomena can be remedied even more effectively by introduction of damping into the system and this can be achieved more conveniently by use of viscous dampers on the pantograph rather than on the overhead contact system. Appendix I describes recent test results which show that modified simple catenary equipment may be suitable for British Railways‡ requirements if a smooth pantograph trajectory is ensured by suitable control of contact wire profile. This can be achieved by the use of mid-span sag. It will give an appreciable reduction of cost.

Conditions of instability are known to occur in railway overhead current collecting systems during the passage of trains at high speeds. They are manifested as oscillations in the vertical plane of such amplitude as to prevent continuous mechanical contact of the static equipment and the moving collector, thereby causing undesirable interruptions in the supply of electric traction current. An introduction and a brief historical survey precede a short study of the methods of theoretical analysis. It is shown that the completely theoretical approach breaks down because of its complexity, and that simulation by means of an electronic analogue is a way of overcoming the complications. The analogues of the overhead equipment and the collector are treated in detail, as is the task of combining the two under the criteria for their interaction. The simulation is still under development but it is possible to give evidence of the method's potential success. A comprehensive list of references gives details of the world-wide sources of present information from full-scale railway systems.

An exploratory investigation into the vertical displacement of catenary contact systems under load, a problem usually regarded as mathematically intractable, has been carried out using relaxation methods. Solutions for typical simple, stitched, and compound catenary systems under static loading are presented and compared. Solutions for the simple catenary system under conditions of dynamic loading are also given for train speeds of 30, 60, and 90 mile/h, and, by treating the problem without including the effect of friction, as yet unknown, it is shown that this factor alone prevents severe oscillation of the system above about 62 mile/h. The method of calculation adopted is intended to serve as a basis for the more rapid solution of such problems by electronic computer.

Analysis is made of a closed-loop system that contains a hydraulic relay. It is shown that the ramp response of a system with an error signal, velocity feed-forward, and velocity feedback, may be expressed as a rapidly convergent infinite series whose terms may each be determined as the response of a linear system in the presence of a forcing function. Inclusion of a small number of terms in the series is sufficient to provide excellent prediction of the error signal. Similar analysis and results are presented for the system subject to a Coulomb load.

An analytical and experimental investigation into the chatter behaviour of a horizontal milling machine is described in this paper. The experimental results were used to check the basic assumptions involved in the analysis.

The machine structure and the cutting force characteristics of the workpiece material were initially tested separately. The vibration behaviour during machining was then investigated for a range of machining conditions. These included different values of cutter speed, workpiece width, depth of cut and number of cutter teeth, different directions of cutter rotation, and plain and climb milling. The results are presented in the form of stability charts, describing conditions when chatter was present or absent.

Chatter was found to be of the regenerative type, occurring in bands of cutter speed. For all conditions tested, the machining stability defined by the envelope of the chatter bands improved as cutting speed was reduced.

The dependence of the chatter bands on cutter speed, the chatter frequency, and the qualitative changes in the chatter-free machining capacity were predicted successfully at all but low speeds. Quantitatively, the chatter-free machining capacity was predicted to be slightly less than half that found by experiment.

The conventional assumptions for dynamic cutting force characteristics were shown to be in error. More accurate assumptions based on recent fundamental work only partly explained experimental observations, indicating that an additional, and as yet unstudied, dynamic force component exists.

The investigation was a continuation of previous work involving the measurement of strains in the vicinity of forged rings of the type used to connect cylindrical ducts to large spherical shells. On two such rings of different shape strains were measured for the following loading conditions: internal hydraulic pressure in the vessel; axial loads applied to the nozzles; bending moments applied to the nozzles. Results for these two designs of ring, and two designs previously reported, have been compared.

An approximate method of assessing elastic stresses (in such rings) due to the effect of axial loads and bending moments has been found reasonably reliable as a design method.

A method previously found to give reliable predictions for the effect of internal pressure gave, for the two specimens considered here, lower estimates of maximum stress than the experimental maxima.

Aircraft accident investigation is here treated as a problem in detection, calling for observation and deduction, and sometimes for scientific experiments to test tentative explanations. After consideration of preliminaries, such as the discovery and retrieval of the wreckage and its reconstruction as a jig-saw puzzle, most of the principal methods for ascertaining the cause of an accident are described under separate heads. It is shown how the different lines of investigation may proceed more or less simultaneously, and may substantiate each other. They include the analysis of fractures and the study of scratches, marks and indentations. Disruption of mechanical and electrical components is considered and also the evidence of eye-witnesses. Consideration is also given to methods that can be used even when no wreckage is available.

The treatment is essentially practical as it proceeds from one specific example to another, with several photographs taken from actual cases. The paper concludes with a few remarks on modern trends, which do not appear likely to upset any of the basic principles here described.

The problems and aims of Naval engineering have remained remarkably constant during the last 30 years, but requirements dictated by military developments have had an increasing effect not only upon machinery design, but also upon the design of the ship as a whole. The manner and conditions in which our ships must be operated have also changed considerably during this period, calling for additional equipment to make living conditions more tolerable. These changes have required not only the solution of complex design and development problems, but also the development of high standards of manufacture and installation, and the development of efficient organizations for maintenance and spare gear. It is safe to say that the demands made on Naval machinery will become even more exacting, and we can never afford to relax our efforts in striving for perfection in the engineering of our machinery designs.

The mode of production of carbon monoxide and of oxides of nitrogen and those aspects of combustion which control the formation of these gases in a diesel engine are examined.

It is deduced that carbon monoxide production is principally a function of engine maintenance; on the other hand, there is an inherent characteristic for the production of oxides of nitrogen which can be ascribed to each engine design with the engine in standard trim.

The characteristic oxides of nitrogen production for various engine designs will be compared and those aspects of design and operation which control this characteristic will be considered.

In this paper it is shown how principles which are fundamental to external aerodynamics have been applied to study the internal aerodynamics of turbo-machines.

Mention is made of aerofoil cascade, radial equilibrium, and actuator disc theories. Results are also presented of a number of supporting experimental investigations.