The lightweight and compact separate jet lift engine has been with us long enough to have built up an acceptable level of confidence in its abilities, but there have been misgivings over the magnitude of some of the operational problems, in particular those of ground erosion and hot gas reingestion due to the high velocity jet.

The object of this paper is to present a Series of tests which has been made by Rolls-Royce to ascertain the nature of the problems and to put forward some simple solutions. It is not suggested that any of these solutions is unique but merely that they are adequate for our present needs.

Helicopters have reached a state of mechanical reliability today comparable to that of the aeroplane. Rotary wing aircraft have been severely limited performancewise, however, by the fixed wing type of instrumentation commonly used. It has been impossible to operate helicopters throughout their complete flight regime in their normal operational areas during instrument flight conditions. This paper defines the problem, the approach taken by Bell Helicopter Company, the flight test programmes and results, and the future for helicopter instrument flight operations in both populated and remote areas using information sensors and displays designed expressly for VTOL machines.

The success of inter-city transport helicopter operation will depend on the ability to fly between small sites in city centres with good regularity. Any compromise, such as moving the site to the outskirts of the city or only being able to fly in fine weather, will destroy the advantage of the helicopter over other forms of transport. During the past decade there has been considerable progress in the improvement of helicopter flying qualities so that it is now possible to specify equipment which will enable a helicopter pilot to control his machine in all visibilities and most conditions of turbulence. Further developments in ice protection will enable the basic helicopter to be cleared as an airworthy vehicle for all-weather flight. However, there still remains the problem of navigation, which becomes particularly acute for the final instrument approach. Existing equipment, in particular the Decca Navigation System, can probably meet the case for aerial navigation at altitude, but to fly down an approach to low altitudes into a restricted site demands a higher standard of accuracy and reliability than is offered by any currently available equipment. This paper only deals with the blind approach down to a height of the order of 200 ft. above the landing pad. To extend this to blind landing would require an even higher degree of accuracy and reliability, which does not seem to be justified until some actual operational experience of a simpler blind approach system has been gained to establish whether or not there is a real need for blind landing. A blind approach system which will permit a cloud break height of 200 ft. to be followed by a visual approach and landing on ground lighting should offer at least as good a standard of weather regularity as is currently achieved by fixed-wing aircraft.

Scheduled Transport flying has developed continuously and more or less logically over a period of more than thirty years to its present state of regularity. During this time various equipments have been introduced, to help the pilots in their task of flying from A and finding and landing at B in all weathers; and further equipments have been introduced to relieve the pilots of the considerable strain of simultaneously flying the aircraft and using these primary aids.

While many of these equipments have been brought to such a stage of usefulness and reliability as to be regarded as essential to flight safety, they have not encroached on the fundamental safety concept of:

Two pilots.

Adequate “engine out” performance.

Infallible airframe and flying controls.

Fuel reserve for diversion.

Since the first decade of this century aircraft have been equipped with instrumentation to show attitude and direction and to assist navigation and to monitor the performance of the prime mover, if any. Their sophistication has grown with the aircraft but while aerodynamic shapes have apparently simplified over the years, instrument configuration has tended towards complex arrays of electro-mechanical analogues.

Fundamentally, instruments are means of data communication between the systems of the aircraft and the human crew, the latter functioning either as part of a closed loop or, alternatively as the monitor of an automatic control. When functioning as a monitor it must always be considered that the human operator may have to revert with minimum delay and disturbance to the first role, namely that of an active part of the control system. In extreme cases of multiplex automatic systems, such as those intended for Auto-land, there may be a case for denying revertion on the grounds that channel redundancy will reduce the failure rate to an acceptable value, added to the fact that the pilot might in fact be incapable of improving the situation after a certain point in time and space had been reached.

In the “Peak Amplitude” method of resonance testing the total amplitude of vibration is plotted against frequency or (frequency). The method is unreliable for systems which are heavily damped and for systems with close natural frequencies (for both of which a vector plot such as that suggested by Kennedy and Pancu should be used) but for many systems it provides a rough guide to the resonance properties. One of the principal difficulties attending the analysis of the amplitude plots is to find which part of a given peak is due to the resonant mode and which to the off-resonant vibration. In the note a method is described for analysing a peak assuming that:—

• (i) only a single resonant mode is involved

• (ii) the contribution to the amplitude from the off-resonant vibration is constant in the neighbourhood of the peak.

The effect of wall divergence (in excess of the normal value given for compensating the Boundary Layer growth on the tunnel walls), on the simulation of Sonic flows in solid wall wind tunnels is presented in this note which is a condensed version of Ref. 1.

Recently Spreiter showed that flows with free stream Mach number one can be simulated reasonably well in choked solid tunnels. Berndt and Petersohn showed that the thickening of the boundary layer on the walls of solid wall tunnels reduced the interference considerably. Wall divergence θg in excess of the normal one of about one degree (used for Boundary Layer compensation) may lead to favourable conditions for the thickening of the Boundary Layer and this appeared to be an interesting way of reducing the interference.

A recent paper(1) gives details of an investigation on the low endurance fatigue behaviour of an aluminium-zinc-magnesium alloy (D.T.D. 683). It becomes apparent in subsequent discussion that information on another aluminium alloy to B.S. L65C would satisfy a wider practical interest than the former. Although the equipment used for the earlier work was engaged on another project, it was decided that the latter should be halted for a period to enable a brief programme on low endurance fatigue to be conducted on B.S. L65C material which had previously been kindly provided by the Aluminium Development Association.