Materials science is continually advancing and the aim of this paper is to consider briefly the current state of the art on flexible and rigid materials and methods of selection to assist in the optimisation of material usage in airship construction. Generally the selection of materials for airship construction involves a compromise between the ultimately desirable and the economically attainable. However recent advances in composite material technology have broadened the range and versatility of materials available so that selections can be made which offer the prospect of safe airships with useful payloads at economic costs. It is necessary to consider flexible and rigid materials separately as their function and selection criteria differ substantially.

In recent years the advances in materials technology, coupled with the rising operating costs of conventional aircraft, have led to renewed interest in the airship as a means of fulfilling certain transportation requirements.

This brief paper does not attempt to retell the story of the airship or to try and justify its present day use, this being far better left to the experts in this field, but considers the requirements and considerations to be taken into account when selecting a propulsion device. The propulsion devices considered are limited to open propellers and very low pressure ratio ducted fans.

Hydrogen is the medium of the past and helium is the hope of the future. I do not intend, in this paper to go into the relevant merits of helium over hydrogen and vice versa for its uses in the airship industry, for the obvious reason that most of you here today will be more knowledgeable on this particular aspect than I. What I will try and do in this paper is to give a brief background on the interesting aspects of helium and its unique characteristics.

In considering the subject of this Symposium I was somewhat encouraged by a reminder of my company's first memorandum of association, written back in 1946. It is: to send and receive signals, messages and communications to and from aircraft, dirigibles and all other vehicles propelled in the air. How far-sighted those solicitors and recently demobilised airmen must have been! For although it has been the brief privilege of but very few of my air traffic control colleagues to have worked a non-dirigible a few years ago, I cannot honestly feel certain that they seriously believed that the age of the airship would dawn again. (Or did they?)

The basic information required by the pilot of any airborne machine is the same, regardless of the type of machine and the method it uses to counteract gravitational force. This information falls into two categories: firstly there is the information the pilot needs to ensure the safety of the machine (and of his own neck) when leaving the earth's surface, operating in the alien environment above it, and returning to the surface in an orderly fashion; secondly there is the information the pilot needs in order to turn flying into a useful activity, by being able to navigate safely and economically between defined geographical points.

Into the first category falls all the information relating to the functioning of the machine, to its attitude and motion relative to the earth, and to its speed through the air.

This paper will consider the various types of data links to Remotely Piloted Vehicles. The factors affecting their design will be explained and the important parameters and problems highlighted.

The actual and potential roles for RPVs are well established, whether they be military or civil surveillance, or crop spraying. The information to be transferred between the ground terminal and the RPV or between RPV and RPV will depend largely upon the type of mission. This will impose the biggest constraint on the link design.

In the absence of a criterion for maximum wingtip deflection, the estimation of wing weight is a straightforward technical problem, for conventional planform shapes. Shear force and bending moment are integrated from the wing-tip to the wing root; using the known aerofoil shape, and the maximum allowable stress or strain, the skin thickness is determined at each station, and hence the mass of the entire wing is found.

It is safe to assume constant wing-loading per unit area along the span. If less than this constant value is used near the root, then some of this load must be transferred to stations further outboard; the bending moment at the wing-root is increased, and the skin-thickness and hence the wing weight will also be increased.

The presence of cut-outs in shell structures causes perturbations in the original stress system, so that in the region of the cut-out the local stress level in the sheet may be increased many times. These stress concentrations can be considerably reduced, and in some cases entirely eliminated by the use of a suitably chosen shape of cut-out, and by the use of a suitable reinforcing member around the edge.

The factors which influence the magnitude of these stress concentrations are the shape of the cut-out and the dimensions of the reinforcement. The geometry of the shell itself is generally of only secondary importance, provided that the size of the cut-out is small compared with the radius of curvature of the shell.

Lateral (asymmetric) aerodynamics of aircraft have received comparatively little attention compared with longitudinal (symmetric) aerodynamics of aircraft. Up to the present time, understanding, supported by effective and extensive numerical methods, has been built up on the attached flow past wings, wing-body combinations, etc, in symmetric conditions. It is now a natural progression to assess how far some of the predictive techniques for symmetric conditions can be extended to asymmetric conditions. Some of the surface panel methods have been developed purely for the symmetric case and their extension to an asymmetric flow is not merely a routine matter. As a preliminary step, to build up some experience and understanding of asymmetric flows, it is investigated how the standard vortex lattice model for finite wings might be modified to calculate the rolling moment on a finite wing due to steady sideslip (i.e. Lv, Clβ) at low speeds.

The ability to design components such as drive shafts, propellers and rotor blades to carry combined bending and torsion alternating stresses, which may be out-of-phase is a common requirement in industry. The test data of Nishihara showed that fatigue limits for ductile materials are apparently higher for combined bending and torsion with phase difference than for the conventional in-phase cyclic stressing case. This is true when the out-of-phase fatigue data are stated in terms of the maximum in-phase shear stress amplitudes. However, Little showed that this apparent increase in fatigue strength is very misleading, as when the fatigue limit data are expressed in terms of the true shear stress amplitudes it becomes clear that the fatigue limit actually decreases as the phase difference increases.