During the last fifty years much experimental and theoretical work has been carried out on the subject of the failure of struts, i.e., rods under axial compression. Most of this work has been devoted to the case of struts pin-jointed at both ends and only a small part examined the behaviour of rigidly encastred struts. From these investigations we know that in case of very slender struts the critical load for rigid encastrement is the fourfold of that for pin-jointed ends. This difference becomes less with decreasing slenderness of the strut, but even for slenderness ratios usually attained in aircraft framework it is considerable, if high tensile steel is used. In actual framework, compression members being more or less rigidly joined to nodes which may twist elastically, they represent a case between both forementioned extremes and may best be regarded as elastically encastred. Since according to above statements the load which may be sustained by a strut obviously depends a great deal upon end constraint, it is of great importance for design purposes to determine exactly the effect of elastic encastrement.

When the Royal Aeronautical Society did me the honour several weeks ago of asking me to give a lecture on sound-proofing of aircraft, I hoped to be able to prepare a formal paper and read it to you. I did not realise at that time, however, that my temporary duties as consulting engineer to the civil aircraft division of the French Air Ministry would take practically all my time. So I arrived in London with only the scantiest notes and shall be obliged to talk more or less extemporaneously on the broader subject of comfort in air travel. I hope that I may have the opportunity to supplement this lecture by a more elaborate paper at a later time.

The theory of the aerofoil has now been studied to such an extent that, from this province, it is hardly possible to expect further material improvement in its aerodynamical qualities : profiles differing but little from an inverse of a parabola (Joukovski profile) would appear to be the theoretical ideal. Subsequent important progress in that respect may be sought only in another direction, viz., in the application of a series of supplementary contrivances having a marked influence on the properties of the flow around the aerofoil. Here we are referring to such devices as the sucking away of the boundary layer (Absaugeflügel), or the insertion of appliances on the aerofoil itself. Nevertheless, up to the present, only one of the very earliest attempts in this direction, namely, the slotted wing, has developed sufficiently to be in any way widely adopted in contemporary aircraft construction.

The modern internal combustion engine, particularly the power unit developed for aircraft propulsion, provides a subject of great metallurgical interest and speculation.

The requirements of the aero engine designer for greater engine power while retaining a low weight/power ratio has inspired research into fuels of improved characteristics, and on the metallurgical side into materials of superior properties to those previously available.

In the design of a fan drive regard should be had to possible critical or resonant speeds which may result in failure of the system. It is not sufficient to arrange for the ordinary whirling speed to be well above the maximum running speed. In whirling the forced vibration arises from static or dynamic unbalance of fan and/or its shaft and the frequency of the forced vibration is the frequency of revolution of the fan shaft. Other important forced vibrations may however be set up.

The authors review the capabilities of the typical modern airplane for high-altitude operation and present the restrictions of the power plant of the modern airplane which prevent it from delivering its normal output at high altitudes. The paper also discusses the improvements in the aerodynamic characteristics of the airplane as well as changes in the power-plant design and the progress achieved in cruising operation at high altitudes within the limitations imposed by passenger comfort and safety. The authors evaluate further possible gains which may result from an extension of this trend, and examine the engineering problems involved in both the airplane and the engine.