The principle of the ram-jet or athodyd has been understood for a number of years. It has been applied in many ways, the most prominent being the flying bomb and, rather less spectacularly, the ducted radiator. The principle is to. convert the velocity energy of a high speed air stream to pressure energy by means of a suitable duct, to apply heat energy to the compressed air, and then to expand this heated air in the form of a high velocity jet. The advantage of such a mechanism is an increase in thrust given by the product of the mass flow of air, and the difference in velocities between entry and exit; the disadvantages are, the necessity to project the duct at high forward speed before any thrust is obtained and, except at very high speeds indeed, the low thermal efficiency.

The energy that is suddenly released when a structure fails under load usually presents one of the minor problems in strength testing technique. Care has to be taken to ensure that the strain energy in the structure does not do further damage after primary failure and so obscure the location of the original weakness; and the possibility of risks to personnel must not be overlooked. As a general rule, however, aircraft structures fail in strength tests without untoward effects. Most of the strain energy within the structure is absorbed internally or dissipated in loading gear and anchorages, and the most noticeable effect is the noise and vibration which is produced.

Designers and technicians pay a great deal of attention to the development of jointing methods for use in the construction of aircraft. A satisfactory method should be neat, economical in labour, flexible in application, and capable of yielding consistent results with a low weight penalty.

Electrical resistance welding meets the above requirements and it is with this process that I shall deal.

In systems for transmitting control motion there may be two shafts set in any relative position, each carrying a lever arm, and the ends of the lever arms may be connected by a link having ball ends. In general, the range of working movement for such a system is somewhat limited and the relationship between the angular movements of the two shafts is non-linear.

Although for some purposes it may suffice to mock-up the system and determine the motion experimentally, for other purposes analytical treatment may be required. The general solution given below is readily applied to particular cases, which may be simpler.