It is not possible to go fully into all the aspects of this problem in the time at my disposal. I am accordingly confining myself to a discussion of the feasibility of operating heavier-than-air craft in fog with reference to the instrumental equipment required. The meteorological aspects were dealt with in a paper by Captain Entwistle two years ago.

In order to obtain a correct perspective on the problems of flying in fog it is necessary to realise that many cases of impaired visibility, which would not normally be regarded as fogs, may seriously increase the risks of flying. This reduction of visibility may be caused by fog proper or by haze, drizzle, rain, snow or dust. The problem I wish to consider then is that of flying, navigating and landing when the visibility is such, that flight would be impossible or unduly dangerous without special equipment.

The subject I haveto talk about this evening is one on which many previous papers have been read before this Society, so I am afraid I must ask you not to expect much original material from me. Practically the whole of the material I have gathered together is the result of practical experience, and from this point of view I hope it will prove interesting.

During recent years considerable development has been done and good progress made with both the design and operation of big flying boats.Also, the Schneider Cup races have caused a considerable amount of research work to be done on the development of twin float seaplanes, particularly with regard to taking off the water at very high speeds and also to the air resistance of the floats.

In the last year we have seen the advent of the Dornier Do.X the largest flying boat yet constructed, whose total flying weight approximates to 50 tons.

Rubber is an indispensable material for the German industry. The yearly consumption is at present about 100,000 tons. For thirty years the German chemical industry has studied the problem of synthetic rubber for engineering purposes, but it has only been in the last few years that the difficulties have been successfully overcome.

In the design of structural frames it is often the practice to assume the joints to be pinned, or hinged, and to calculate the forces in the members on this assumption; actually, the joints are made with considerable rigidity. The following are the results of an analytical and experimental investigation into the stresses in a rigid-jointed space frame and of the magnitude of the errors due to the assumption oi pinned joints.

The whole process of designing an aero engine, from the original concept to the production of the first of the type, called a prototype, normally takes abouttwo years.

The prototype design may originate from proposals put forward by the engine maker from specifications for military aircraft engines, issued in the United Kingdom by the Ministry of Supply, or from the Aircraft Industry.

It is not usual for engines to be designed specifically for civil aviation requirements. More often they are adaptations of military engines de-rated to increase their reliability, and to extend the overhaul period. With the growth of civil transport and the development of guided missiles, it is possible that this state of affairs may be reversed and engines for civil aircraft may become more important than those for Service use. At the present time, it is difficult to foresee a potential civil or private aircraft engine market that would justify the cost of designing and developing a small jet engine on that score alone.

My first reaction to being asked to speak on this subject was that it is the user and not the producer of model data whose views we want to hear, and I am glad to say that Mr. Ellis has agreed to co-ordinate with me, so that I have some inside knowledge to draw on, if I venture to say what a designer does.

I wish in the main, however, to take the title in rather a different way, and to discuss in what sense model tests can be expected to give results useful to the designer.