First, it is necessary to define productivity and the way it is measured. Productivity is a ratio of an output to an input; it is, therefore, somewhat analogous to the engineering concept of efficiency but unfortunately without the accompanying rigour of definition of input and output in energy terms. In productivity measurement, the output can be in value terms, in weight or volume or number, while the input can be numbers of men, man hours, wages or capital or some combination of these. These points are illustrated in Fig. 1, but in this paper I will be concentrating mainly on value outputs and manpower and labour cost inputs. A fuller account of the subject is contained in Ref. 1.

A successful project outcome requires that the ‘right’ product, (from an overall ‘performance’ viewpoint), should be available when the market place needs it, for a price it is prepared to pay.

To satisfy ‘performance’ requirements, (in the widest sense), the task is broken down into manageable elements, and requirements/specifications are formulated. As the design/development proceeds, progress towards achievement is monitored, with eventual verification through ground and flight testing. On ‘timescale’, we develop inter-locking ‘line of balance’ programmes covering all manufacture inputs, such that the effects on total programme achievement of local gains or shortfalls can be seen.

If the comparisons on productivity made by Mr. Harvey for the United Kingdom and other countries are accepted the question to be considered is why there should be any difference.

In particular I would like to identify some of the reasons for making comparisons with a principal competitor — the USA industry.

While the comments made reflect experience on airframe manufacture there is little doubt that the situation is no different in the rest of the aerospace industry or for that matter the UK engineering industry in general.

Two philosophies for the attitude control of space vehicles with flexible appendages have appeared in the literature, these are:

1. (i) control of the rigid centre body to lie within some bounded region while the flexural vibrations are allowed to behave in an uncontrolled manner;

2. (ii) control of all plant states to some finite value as time tends to infinity.

The former method does not require flexural information and therefore avoids the on-board computational burden associated with state estimation, or the cost of additional instrumentation. However, attitude degradation has been observed and reported indicating a clear need to compensate for structural vibrations.

In the places in the UK where these things are discussed, there is a reconsideration of the pros and cons of the two axes systems commonly used for aircraft dynamic calculations.

The first of these is a system fixed in the body and moving therefore with it: this system is referred to as ‘body axes’ and is used by the ‘stability and control’ specialists for assessing rigid aircraft behaviour.

The second is a fixed inertial frame fixed in the earth and is used by the flutter specialists for assessing a variety of behaviours of the flexible aircraft. It is the purpose of this paper to point out the very simple correspondence between these two systems in the case of small perturbations from an equilibrium position of the rigid aircraft flying straight and level. The first section presents unpublished work from the Vickers Aircraft Company’s files done in 1952 which is confined to the symmetric motion at constant speed (i.e. with the phugoid suppressed).

It has long been accepted within the aircraft industry and others, that the number of man-hours needed to produce successive units or batches of units decreases. This effect is called ‘learning’; and a plot of the man-hours required per unit set against the production number is called a ‘learning curve’. Similarly a plot of unit cost (at constant economic conditions) against production number is also called a learning curve, since cost is related to the number of man-hours required.

When the production costs of future aircraft are estimated, learning has to be simulated. This is generally done using curves chosen from a standard family of ‘learning curves’ generated by a simple parametric equation; a curve is chosen on the basis that it is the best-fit by the standard equation to the out-turn data from previous similar projects.

It has been pointed out by a number of investigators that aerofoils with blunt trailing edges have many advantages, both structural and aerodynamic, at transonic and supersonic speeds. However, a profile with a blunt trailing edge unfortunately creates a high base drag at subsonic speeds and this could result in the total drag being considerably higher than that for a profile with a sharp trailing edge. This base drag arises due to the periodic vortex shedding from the blunt base which causes low pressures in the wake thus creating the base drag.

In order to reduce the base drag of a blunt trailing edge at subsonic speeds, this periodic vortex shedding must be suppressed. This has been achieved by various methods — a splitter plate behind the base, the base bleed, base cavities — and these have shown varying degrees of drag reduction.