The aircraft maintenance function is a vital element of airline operations. The achievement and sustaining of the airworthiness standard throughout the life of an aircraft is its prime concern and responsibility. There are many approaches one may take in describing the maintenance function, no one of which is complete in itself, but when considered collectively as a reference framework, can provide a comprehensive insight into the rather complex and dynamic process involved.

The generally steadily rising costs of labour and material, together with lagging or level fare structures, are demanding even greater gains in productivity and utilisation of resources to maintain profit margins and adequate returns on investments. The productivity gains made possible by introduction of jet aircraft are being exhausted and new ways must be found to achieve lower operating costs. At the outset I think it might be reasonable to ask ourselves the simple question “Why aircraft maintenance?” From an airline corporate or operating viewpoint it certainly conflicts with the objectives of attaining low operating costs, low material inventory levels, high utilisation of aircraft. I have stated on several occasions that “we are the trouble department—and when we have no trouble we are really in trouble”.

Considerable interest is currently evident in the potentialities of large airships as a means of transporting freight; studies are proceeding at various levels in a number of countries, the two most serious projects in the UK being those under respective development by Cargo Airships Limited and by Airfloat Transport Limited.

Although most proposals concur in envisaging a very large helium-filled vessel cruising at 80 to 110 kt (148-185 km/h) and carrying payloads of up to 500 tons (508 000 kg) there is significant diversity of approach in the selection of fields of application for the airship, and in the establishment of the appropriate design parameters.

This paper, therefore, seeks to indicate some areas of the overall transport spectrum which might be expected to favour airship operation, and discusses some of the problems associated with different modes of operation.

Particular reference will be made to the Airfloat Transport project, which is a vessel with a gas capacity of 30 million ft3 (849 510 m3) intended for the carriage of large indivisible loads over moderate distances.

The Islander is extremely simple and has had few aerodynamic problems; the exception was a persistent elevator “buzz” in some aircraft which was annoying more than it was serious and the cause of which was never satisfactorily established, despite an investigation that took six to seven months and which included wind tunnel testing and elaborate flight instrumentation. It was eventually reduced to an acceptable level by improved detail engineering.

The NACA 23012 section that we use is not a popular section nowadays despite having a good CL max, low CMO and low CDO. Its main drawback is the abrupt stall it can give to a wing. The usual cure for this is to provide generous washout. We chose to confine our washout to the wing tip and, as no dihedral was necessary apart from the tips, we achieved a very simple rectangular box structure with no joints—both a stressman's and a production engineer's dream. It is not often that you can please them both.

The sonic boom from an aircraft in level supersonic flight has been studied extensively. What is perhaps not so well known is the effect of a curved flight path in causing a local focus of shock-waves, and accentuated boom, and more particularly the production of a zone of silence, or rather “no boom” in other localities closer to the centre of curvature of the curved flight path than the M=1 radius. A steady shock wave pattern cannot rotate at a subsonic speed. It remains to be determined whether the necessary aircraft flight paths can be tolerated by both passengers and aircraft.

The subject is not new, and was theoretically predicted by Bryan and Lamb in 1921, and verified experimentally by the present author in 1938, for the case of propellers or airscrews. Figure 1 shows the effect of progressively tightening the radius of turn of the aircraft.

Taxiing induced vibrations in large aircraft due to runway unevenness have been recognised as a significant factor in causing metal fatigue damage and dynamic stressing in airframes, as well as crew and passenger discomfort. The purpose of this paper is to develop a method of analysing random vibrations of a flexible aircraft, taking account of non-linearities in the oleo-pneumatic undercarriage in the form of orifice damping and Coulomb friction. The analysis assumes that the random input to both main undercarriage legs is identical, therefore it only considers symmetrical wing modes in the general deformation of the airframe.

The application of matrix displacement methods to elastic problems leads to an array of simultaneous equations, of the form:

in which K is non-singular. This, when inverted, enables the component deflections u to be determined for any specified loading f. The deformed shape of the system is thus obtained in terms of displacement of the nodes and the latter are used to derive the stress within each element. The stress solution thus lacks precision, since it is not clear as to what point within the element the calculated stress refers. There will be a number of such elements connected to any given node and generally, the computed stress is different within each.

The majority of current prediction procedures for turbulent flows employ models of turbulent momentum transfer which calculate an effective viscosity for μeff such that for a boundary-layer flow the shear stress, τ, is given by:

A number of recent experimental investigations (ref. 1-3 for example) have found, however, that in strongly asymmetric turbulent flows, τ is finite where the mean velocity gradient is zero—and vice versa. These phenomena, which are evidently not describable in terms of an effective viscosity hypothesis, point the need for a more complete description of turbulent motion.

A number of theoretical methods concerning the flow about jet flapped wings have been developed for predicting the increase of lift due to super-circulation around an aerofoil, but only a few of those methods have been concerned with a jet flapped wing with ground effect.

The main purpose of this paper is to introduce a simple approximate representation of the flow around a jet flapped aerofoil in the case when the jet hits the ground. Hence, it is assumed that the existence of a stationary vortex is neglected and the wake fully develops from the leading edge. It is also assumed that the jet is replaced with a suitable distribution of sinks along the jet axis, to represent the effect of jet entrainment. When the aerofoil is in very close proximity to the ground, it may be assumed that the jet impinges on the ground before the mixing layer finally emerges in the centre of the jet.

To the majority of an aircraft manufacturer's technical staff the words “Flight Test” conjure up a vision of a ramshackle collection of seedy looking huts on the far side of the company's airfield, which itself may be 20 to 30 miles away from the main organisation. Within these huts dwell a small band of dedicated enthusiasts who apparently are willing to subjugate most of their waking hours and personal lives to performing their function in spite of the machinations of their two greatest enemies—aircraft unserviceability and the weather. While starting work at 08.30 hrs. (if not earlier) their working day always seems to reach its climax about one hour before sunset, irrespective of the time of year, and goes on for long after the last test aircraft has landed. However, they are a fortunate few, in that they have the privilege and responsibility of working with the company's end product in its functional form, an experience that today is denied to, or at least is remote from, the large majority of design and manufacturing staff.

In university research on the flow through turbo-machines it is often necessary to produce blades which can be manufactured in a small workshop at relatively low cost. As part of a project to investigate the development of the annulus wall boundary layers in a compressor, a set of rotor blades were designed and manufactured for the large rotating cascade wind tunnel at Cambridge University. The apparatus is shown in outline in Fig. 1 and a detailed description of this wind tunnel has been given by Oxford. The air passes through the research rotor and then through the auxiliary fan and throttle. The combination of a variable speed research rotor with variable speed and pitch on the auxiliary fan and variable throttle leads to a highly versatile apparatus with a wide range of operation. An important feature of this apparatus is the sixteen channel pressure transfer device which allows pressures measured on the rotating blade to be transmitted out to a stationary multi-tub manometer.