The exercise of carrying out jet V/STOL operations in any given combination of weather and site conditions is clearly open to theoretical analysis and relatively simple solution, along the existing lines of conventional autoland. With present knowledge automatic operation of a jet V/STOL aircraft would not be a very great task, providing that things such as cost, reliability, space, weight, ground equipment, in fact the overall economics of the operation were not allowed to intrude into the problem. But this is not reasonable, the advantages of automatic operation must be weighed against the cost.

Tests of the first experimental VTOL aircraft using tiltable wings and propellers indicated that practical operational aircraft are possible and can operate with a high degree of effectiveness.

The flight tests accomplished up to the present time with the second generation tilt-propeller and tilt-rotor aircraft are discussed and analysed. The XC-142 and the CL-84 tilt-wing aircraft have been performing well throughout their projected flight envelope and good pilot ratings have been obtained with each in hover, transition, and the normal cruise mode. The X-19 tandem wing tilt propeller was flown only up to 100 knots and was lost due to a structural failure in one nacelle. Although the operation of the aircraft had been satisfactory up to this point, this programme was terminated due to shortage of funds.

A study of the various VTOL aircraft configurations operating at low radius of action indicates that the tilt wing/ tilt propeller type are the most cost-effective as long as speed is an important parameter in the operating mission. There are missions where speed is of secondary importance, and therefore, the helicopter will continue to be one of the most effective VTOL for these missions.

Since the tilt-wing /tilt-rotor aircraft tend to be only slightly higher in cost than the helicopter and with development the complexity and maintainability will be reduced to acceptable levels, it is anticipated that further work will be done in the development of these vehicles, and successful and useful machines will be built in the future.

Every control system employs some computing elements and it is customary to designate systems after the type of computing predominantly used in them. Thus, we have hydromechanical systems, pneumatic systems, fluidic systems, analogue electric systems, and so on. Traditionally, as described by Watson, the aircraft gas turbine has used hydromechanical control (see Fig. 1). The diagram does not depict any particular engine component but illustrates some of the principles used in a variety of present-day systems. A mixture of bellows, springs, cams, orifices, etc, compute according to their particular arrangement; frequently the fuel itself is used as the computing medium. Essentially such systems compute continuously using physical representations of the measured parameters. They are, therefore, of analogue form.

Now that the British Services are becoming drawn inexorably into the business of helicopter armament, the attitudes of individuals are widely diverse; some are appalled; some are eager; others mutter evasively “Can't we leave this sort of thing to the professionals?” Number me among the enthusiasts.

My aim this afternoon is simply to air the current problems relevant to helicopter armament in support of British Army operations—in the hope that members of this Society will later come up with clever ideas to solve them.

When side force is produced by the injection of a secondary gas into the supersonic region of an axi-symmetric nozzle, the body shape of the obstruction caused by the secondary flow induces a cone-shaped separation region upstream of the port. From the apex of the cone a conical shock front is developed. Part of the total side force produced is due to the excess static pressure acting on the nozzle wall in

(a) the separated region, and in

(b) the wall area lying between the separated region and the trace of the shock on the nozzle wall.

In such a field the static pressure is not uniform downstream of the shock but varies from point to point on the nozzle wall areas in question. This aspect of axi-symmetric flow makes attempts to correlate theoretical and experimental work difficult. It was considered that basic information about the important parameters, which influence side force, could best be obtained in experiments with two-dimensional nozzles. Here the circular secondary port is replaced by a rectangular port, the separation zone is wedge-shaped, the shock has a plane front, and in theory, the static pressure is uniform between the port and the point at which the boundary layer separates.

As a result of the failure of parts of the airframe on several types of aircraft having high intensity acoustic environments, the military and civil certification authorities are requiring assurances that new designs have adequate strength to resist the acoustic loads. In most cases failures have been detected early enough to prevent serious impairment of the aircraft's structural strength. In some cases this has led to unsatisfactory maintenance and inspection requirements and there is also the possibility of more serious failures arising from the extension of undetected damage. The purpose of this paper is to review the test data available and to present a design procedure for structures in the region of high noise levels. As it is impractical to apply the full theoretical treatment in design because of computational complexity, an approximation is presented and the predicted results are compared with the experimental values.