I was delighted and honoured to have been invited to give this lecture on the technical aspects of the Schneider Trophy and the world speed record attempts. Great Britain and Italy were the main contenders in the final and most exciting phase of the contest. As the Macchi aircraft were the most successful defenders of the Italian colours and, being myself the successor to Dr. Mario Castoldi, designer of the famous Macchi racers for the Schneider Trophy, I was very pleased to accept the kind invitation of the Society to give this lecture, especially in consideration of the fact that, as far as Macchi contribution is concerned, it was possible for me to collect first hand information directly from the people who actively collaborated with the racing effort.

The words “space station” mean many things to many people. In fact, a very wide range of craft have been studied under this name over the years. The range of such studies has included large rotating craft providing an artificial gravity environment and accommodating hundreds of people (the type envisaged by Arthur Clarke in his book, 2001: A Space Odyssey) and small two or three-man craft designed for mission durations of 30 days. The one thing that all these programmes have in common is that they emphasise the use of spacecraft for the conduct of meaningful and beneficial investigations using the vantage point or the environmental features of space. In addition, they have involved the presence of man as a means of providing more effective conduct of the assigned tasks. This approach differs somewhat from activities that are strongly aimed at specific and demanding mission accomplishments, missions which place great emphasis on reliable and safe operation of the flight hardware and the demonstration of new operational techniques. Nevertheless, past programmes such as Mercury, Gemini, and Apollo have included many of the basic space station ideas.

Many engineering problems are unsuitable for either pure digital or pure analogue computation. An example is provided by the helicopter. Owing to the size of the problem, a digital solution takes too long, and far more equipment is required than is generally available on analogue computers. In addition, there is the difficulty of including important non-linear effects.

A hybrid computer is a combined digital and analogue computer and can be used to advantage in these circumstances. I shall mainly be concerned with the integration difficulties which arise when applying this form of computation to helicopter simulations. The concepts developed are not restricted to the helicopter problem and an integration technique will be explained which has wide application in the study of other engineering systems.

The usual method of determining the static pressure distribution about a model under test often relies on guessing the required positions of the static holes before the form of the distribution is known, and subsequently adding further holes to the model where particular interest may arise. This technique can clearly prove both tedious and expensive.

Therefore interest lies in the accuracy of representation of static pressure obtained from a static tube lying on the model surface.

In Figs. 1 and 2 are shown two cantilevers, one acted on by a force which maintains its direction as the cantilever deflects, and the other acted on by a follower force which remains tangential to the end of the cantilever. It can be shown, by a simple demonstration, that a follower force is non-conservative (see Bolotin), and therefore has the capability, if it exceeds a certain critical magnitude, of causing oscillatory instability. Thus, the follower force system in Fig. 2 can become unstable in the oscillatory sense while the Euler Strut in Fig. 1, being a conservative system, can become only “statically” unstable, i.e. with the strut diverging monotonically from its equilibrium position. The follower force system can, of course, also become statically unstable. The overall stability of this system has been examined by Bolotin and Beck. Herrmann and Bungay have investigated the stability of a system that combined the main characteristics of the two above in any chosen proportion.

The appearance of the Kármán vortex street in the wake of bluff bodies has been well-known for sixty years. But the simple question of whether it appears also in the wakes of two cylinders in tandem at the same speed range, seems to have been unanswered as yet. The main reason for this is presumably the lack of practical interest. The only exception was in the early years of aviation in the era of biplanes. The use of streamlined or cylindrical struts was common and stimulated the investigations of Panell et al 1915, Wong & Yu 1917, Frazer & Simmons 1917, Biermann & Herrnstein 1933, and others.

Aircraft have been used for survey and pest control for over 50 years, the business expanding from the early days of mostly converted military training aircraft to the present when agricultural aircraft are accepted as specialised aircraft designed for their specific jobs in their own right.

It is with some trepidation that I face an audience with so large a combined technical knowledge and experience of agricultural aviation. When one considers the relationship between the agricultural contractor using aircraft for his work and the farmer, it is clear to me, that we, as the end users, play a relatively small part, all be it a vital one, in the total operation. An operation which clearly requires a high degree of technical skill, exacting safety standards and a high degree of accuracy; backed by high capital investment, sound salesmanship and strict management control.

When I first became interested in the field of agricultural aviation, I thought I had better find someone who had a thorough knowledge, backed up by a great amount of practical experience; so I sought the help of Ron Amsden, who, I am sure, most of you will have heard of. This was about four years ago.

Sometime during last summer, I was asked by Ron Amsden if I would be interested in attending a get-together of interested people on the subject of agricultural aviation and its problems. I had little idea then, that I should be called upon to give my views to such a distinguished gathering of experts. However, in my short experience of agricultural flying, I have gained some useful experience as a pilot and also a good understanding of the problems that arise out of this work.