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Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Committee, Reports and Technical Notes of the U.S. National Advisory Committee for Aeronautics, and publications of other similar research bodies as issued.

14. Peppermint extract is the flavouring extract prepared from oil of peppermint, or from peppermint, or both, and contains not less than 3 per cent. by volume by oil of peppermint.

DURING the past few years the aeroplane has increased in performance to such an extent that normal machines of to‐day have speed, climb, load capacity, economy, and reliability characteristics, combined, only considered possible from individually specialised record making designs of ten years ago. Both airframe and engine are concerned in these gains, and the two now require to be such close partners that apportioning of credit is scarcely possible and research on both components has to proceed in step.

FOR many years the basic design and construction of aircraft has been closely linked with the cooling system employed for the power plant which it is desired to utilise and as a general rule machines have been produced specifically for either liquid‐ or air‐cooled engines. Conversions of liquid‐cooled engined machines to suit an air‐cooled installation and vice versa have been successfully carried out in the past and to‐day there is a tendency for twin‐engined military aircraft to be constructed so that alternative installations may be employed, but the complications necessitated by such a practice provide good reason for producing the airframe to suit one particular engine. The general recognition of this policy has served to emphasise the importance of deciding the type of engine most suitable for the purpose for which the machine is required and has possibly lent weight to the claims submitted by various engine manufacturers. The merits of one variety of engine as opposed to the other is a subject which has from time to time received much attention, but, as the object of this article is to trace the development of liquid‐cooling systems, a brief outline of what is considered parallel advancement in air‐cooled practice may be of interest.

THE protection of aluminium and magnesium and their alloys for service in aircraft has received a considerable amount of attention and much publicity in recent months. An important phase of this work, now being carried on by British, American and Continental designers, is the prevention of corrosion of aircraft fuel tanks, and the information so far available goes to show that not only are the composition and treatment of the metal used of importance, but also that the design of the tank is a factor which must be taken into consideration.

131A Aluminium Alloy Sand or Die Castings (suitable for Pistons, etc.).

PROBABLY the most outstanding in‐dustrial tendency of recent years is the mechanization of production. In quantity production, machines have replaced men.

TO check the suitability of a given strut cross‐section, for a given length and safe concentric working load, is a simple matter provided that a working stress curve or formula is available, but the reverse process of obtaining a suitable cross‐section, for a given length and load is under normal circumstances a tedious trial and error task, unless comprehensive tables of the properties of the required section arc available. The author's method permits a very close first approximation to be obtained, which is frequently sufficiently accurate to enable the required cross‐section to be laid out without further trial.

ALL machines, particularly modern machines, are constructed and operated with the general understanding that they will at some time wear out. Wear is combated in many ways but never more successfully from both scientific and economic points of view than when all the major parts of a machine wear out together. This state of affairs is obviously preferable to having a machine which will never wear out at all; for even if such an article could be made, the cost of its construction and operation would be uneconomical. As is well known, many machines do not wear out before they become obsolete, but again this is rarely either a sound economic or scientific proposition. Not only is loss of capital involved but an inaccurate estimation of operational life is a failure in the application of engineering knowledge. If this outlook can be sustained for machines generally it is certainly vital and of the highest importance for prime movers such as aero engines with which this paper is chiefly concerned. An aero engine today must give definite life for definite cost and in no other branch of engineering are quality and reliability so vital and cost, by reason of its very magnitude, so deeply considered. Hence no one has attempted to construct an aero engine which could be economically scrapped after its first overhaul life and not even the most optimistic manufacturers have devised a non‐wearing, everlasting product. As might be expected, a reasonable compromise is the general rule but it is however a noticeable fact that modern engines are becoming more and more resistant to wear and if anything there is a general tendency to the second alternative referred to above. The term “wear” in the general sense covers a multitude of physical changes and chemical reactions, some of which it is hoped to consider later, but if for a moment this expression is held to embrace the deterioration of highly stressed steel parts from prolonged fatigue, marked recent improvements can be reported. Some years ago it was common to replace certain aero engine parts for no other reason than that they were “time expired”. It was considered in such cases that the parts after a certain life had passed the safe limit of their fatigue resistance, although the parts themselves and the rest of the engine would be in what appeared a perfect condition. Developments over the past few years have made it possible to eliminate such precautions and in most modern engines all parts can be relied upon to maintain a safe margin of fatigue resistance for the useful life of the complete engine. This is an isolated example of how the wearing qualities, or more accurately, the endurance, of engines has been improved and it is of interest to note that these advances in the selection and better use of materials have nearly been equalled by improvements in actual surface wear resistance. It can be safely asserted that bearing combinations are available today which will resist surface wear indefinitely under the heaviest possible conditions of loading, providing the loading is not associated with other factors which cannot as yet be overcome. It is therefore an object of this paper, in addition to considering wear generally, to examine these factors as their interest lies in the obstacles they present to the production of a machine which will approach the ideal of being completely worn out after a given life.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Notes of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.