When invited to give this lecture in a building overlooking London's river, my thoughts wandered back to many pleasant hours spent in watching Nature's graceful handiwork—the common seagull, so lamiliar to those of us who still have “time to stand and stare” in these hustling days of speed arid yet more speed. Wheeling with arched pinions and webbed feet retracted backwards into auxiliary tail organs, these effortless soarers are a vision of to-morrow. What aeronautical engineer, released for a moment from the narrow confines of the drawing board and the workshop, could wish for more profitable day-dreaming than a quiet half-hour spent on London Bridge (shall we say?), admiring the cunning perfection of natural flight? And who could wish for better inspiration for the subject of this paper than a glimpse now and again at Nature's own elegant solution of the undercarriage problem?

With the growing popularity of the stressed skin or monocoque fuselage it is thought that the following notes may be of interest. There are many advantages in using stressed skin construction, but one reason against it in the past has been the difficulty in accurately calculating the strength of such structures. Sufficient information has now been accumulated, however, mainly from American sources, to enable the designer to obtain a fair idea of the strength of stressed skin structures, although the stresses occurring under any system of loads cannot be calculated at present with the same certainty as for the conventional braced structure. In the braced frame fuselage the loads are taken by struts and tie rods in tension and compression, but in the stressed skin fuselage they are taken as bending and shear loads in the skin. Once the ultimate tension and compression stresses are known for the material used, the strength of the struts and tie-rods for any system of braced structures is easily calculated. In the stressed skin structure, however, the ultimate stresses for the material are never realised over the whole structure, as failure invariably occurs through local buckling of the skin. The question is further complicated by the fact that the stress at which local failure will occur in sections built of thin plate varies with the design of the section, and two sections having the same area and same moment of inertia would not necessarily develop the same stress in bending.

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.