Rubber is an indispensable material for the German industry. The yearly consumption is at present about 100,000 tons. For thirty years the German chemical industry has studied the problem of synthetic rubber for engineering purposes, but it has only been in the last few years that the difficulties have been successfully overcome.

The superposition of the flexural instability of the plane form of a cantilever wing in its own plane, over that of the torsional elastic equilibrium, gives rise to a special phenomenon of mixed instability which has been translated analytically by Prof. C. Minelli into the problem of determining the first positive characteristic value of a certain system of two ordinary, linear and homogeneous equations, in two unknown functions, with given limiting conditions. The methods of calculation, both analytical and numerical, for the solution of this problem are described. The results confirm the intuitive inferences according to which, other conditions being equal, the backward displacement of the elastic axis worsens conditions by lowering the critical speed.

To-day all altitudes up to, and including, the stratosphere are within the scope of aviation. The engines must therefore be provided with highly developed superchargers so as to obtain high performance even at these altitudes. The single or multi-stage superchargers necessary to accomplish this become an integral part of the engine and exercise a distinct influence on its general construction.

In many types of engine the supercharger is built on to the accessory drive end, that is the rear of the engine, so that the supercharger shaft lies co-axially or parallel with the crankshaft.

The article deals with the calculation of plane frames each bar of which is able to withstand flexion perpendicularly to the main plane. After having shown that the stress corresponding to the loads parallel to that plane is independent of the stress corresponding to the perpendicular loads, the author develops for this latter a method of resolution based on Cross’ principle. Fictitious supports are added to each knot and then successively removed, till the structure reaches the true form corresponding to the loading. A very important improvement of the original method—formerly not applied to a three-dimensional construction— consists in the use of adjustments, that is appropriate movements of parts of the structure as a whole.

The method proved to have many advantages: Difficulties independent of the degree of redundancy, no loss of accuracy between the beginning and the end of calculations, large number of verifications in the course of resolution, reliability of the results, easy understanding of the successive steps, possibility of simultaneous work for many contributors, and relative shortness of the amount of work required.

Laminated materials incorporating plastics seem to be especially well suited lor highly stressed aircraft components, by reason of their good strength properties. Paper, fabric and wood veneers treated with plastics on a phenolic basis were tested with regard to their strength, especially in bending, shear, absorbed energy in impact bending, notching strength and in their resistance against moisture. Further, the behaviour of compressed plastics was studied at different temperatures under static and dynamic loads. A part of the research was extended to pure phenol resin and to thermoplastics based on methacrylate and polyvinylchloride. The bonding properties of laminated compressed plastics were established. Concluding, some experiments relating to the practical manufacture of aeroplane components are communicated.

The following remarks refer to the fundamental conditions which have to be considered for the use of rubber for the mounting of engines. It is thought essential that aircraft firms should ask for information with regard to rubber components they intend to use at an early stage of the design so that faulty applications of such parts can be prevented. Figures for the permissible loads and hints for the design of rubber components are given, with special reference to the use of Buna. Some constructional features are discussed as an explanation of the advice tendered to the designer.