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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. This has the great advantage of permitting the use of simple spur gearing, but suffers from the disadvantage that in passing through both intake and delivery section, the working fluid is subjected to several right‐angled changes in direction. In the case of the Rolls‐Royce Merlin for example, with air intakes on either side, there are 2 × 2 right‐angled bends before the inlet to the impellor is reached and two more at the delivery side. Such bends naturally involve losses in supercharging which should definitely be avoided. Hence in Germany in the two liquid‐cooled inline types the Jumo 211 (Fig. 1) and Mercedes‐Benz DB600 (Fig. 2) the supercharger shaft is built square to the engine crankshaft and the supercharger located at the side of the transmission casing, so that a single right‐angled bend suffices to change the direction of flow of intake air from that of flight and lead it axially to the impellor. If, at the same time, care is taken in nacelle design to ensure an undisturbed flow of air to the intake duct, then the total static head of flight may be utilized in supercharging the engine, resulting in an increased altitude rating. The proportion of this increase due to full utilization of the flight static head is shown in Fig. 3. For example, at a speed of 600 km.p.h. (373 m.p.h.) its value is about 1,400 m. (4,600 ft.)

The distributions of mean velocity U in the turbulent How of a fluid flowing under pressure through a straight pipe of annular cross‐section is calculated on the basis of the similarity theory of turbulence, assuming that the mean motion is steady and symmetrical about the axis of the pipe. Both the T and the M theories arc employed. Remembering that the dU/dr changes its sign at the position of maximum mean velocity, the annular region is divided into two regions, i.e., the inner and the outer, and these two regions are treated separately.

IN these notes I have attempted to describe the main features of longitudinal stability and control in the simplest possible terms, omitting the mathematical apparatus which makes this subject so formidable to those who are not constantly using it. Designers are certainly justified in complaining that most analyses of this subject contain, so to speak, so much XYZ that the ABC of the matter (if indeed there is one) is successfully hidden from them. In making a drastic attempt to return to ABC it must be realised that such a statement can be neither strictly accurate nor complete. Something will be gained, however, if it helps some designers to be clearer about what they are supposed to be doing in this part of their task, and why. The XYZ of the subject is, of course, indispensable to the working out of any particular problem of design A classified list of some useful recent British reports will be found in the Appendix.

In connexion with the series of articles on rotary‐wing aircraft by Dr. Bennett which concluded last month, our attention was called to this paper by Professor von Kármán. Although it is now to some extent of historical interest only, it did not at the time of its appearance receive the attention it deserved and we believe that this translation will be of interest to those concerned with the subject

Scholars have identified various uses of Facebook by activists and social movements in political activism and beyond. They overlooked, however, the possibility that social movements may take advantage of certain capabilities provided by social media platforms, while neglecting others, thereby creating differences in patterns of use between movements. The purpose of this paper is to investigate these differences and to assess the role of the lived experience of activists and supporters in shaping them.

This study compared two protests in Israel with respect to activists’ use of social media, the class profile of participants and the leadership’s demands and their resonance among various social groups. Each case was analyzed by combining thematic and quantitative analysis of online data from Facebook pages and of offline data from various sources.

The two protests exhibited distinctively different patterns of use of the capabilities provided by Facebook. These differences are associated with the lived experience of protest participants and of the individuals the movement leadership sought to mobilize.

This study is the first to show that successful public policy protests can exhibit distinctive use patterns of social media for political activism. It also identifies lived experience as an important factor in shaping these patterns.