Helicopters have several advantages over conventional fixed-wing aircraft, but so far as future operation on a wide scale is concerned, one of the most important may well be that they can be operated successfully in or near to city centres. Their acceptability to the general population depends principally on the effects of noise produced by them but no national or international standards exist at present which specify the maximum noise levels and /or the number of movements permissible for city-centre operation. There are many regulations pertaining to aircraft noise near to airports and to various noise sources in cities but none of these can be directly applied to helicopters.

The problem has been considered by the Committee on the Planning of Helicopter Stations in the London Area, which was set up by the Minister of Aviation in 1959, and whose report was published in 1961, the Wilson Committee on the Problem of Noise who reported in 1963 (Cmnd 2056), in the United States, particularly by Messrs Bolt, Beranek and Newman and also many others. It is not possible to review the literature in this short paper which gives some account of the practical work and considerations concerning the use of helicopters in London with which the author has been associated.

I would begin by asking whether cost benefit analysis has any place in this symposium. It is not directly concerned with finance although one could say that it is a technique for deciding whether a thing is worth the money or, if there is more than one thing, which thing is best value for money. But we need not bring money in at all. The real object is to decide whether a thing, or which thing, is in the best interests of the community.

As such it is a proper prelude to an investment and deserves a place in the symposium.

Flying is now an acceptably safe form of transport. This is obviously so because if it were not so people would not fly. Nevertheless it is a remarkable thing to be able to say. Consider for a moment what it means in terms of engineeering achievement. If you were to start from scratch to design a safe transport system would you for example

1. 1. Design a vehicle with such a light structure and such minimal factors of safety.

2. 2. Make it so that it cannot stop in a fog but has a minimum speed of over 100 mph.

3. 3. Make it so that it can cross oceans and mountain ranges but cannot stop until it gets to the other side.

4. 4. Make it reliant on complex electronic and electro mechanical devices for navigation, collision avoidance and even for control.

5. 5. Use a fuel which, according to type, has a flash point little above and sometimes actually below atmospheric temperature and which is carried in very large quantities.

One could go on listing such absurdities but these are sufficient to establish that, by all the rules, flying has no right to be safe. The fact, however, is different. Flying is many times safer than travelling by road and is, by any reasonable criterion, one of the safest of all the available modes of travel.

In pondering on a subject for this, the fifteenth, memorial lecture, I hoped to find something that might reflect the spirit of Frederick William Lanchester's work. But first of all, I tried to learn a little more of the man himself: his history and the design of events that agitated his enquiring mind. Most of what I discovered only emphasised my own unworthiness to contribute to his memory. For I am a member of Imperial College, and it was from that Institution that Lanchester left, disenchanted, in his third year without taking his degree. Worse still, I hold the Zaharoff Chair of Aviation; in one of my distinguished predecessors, Lanchester was later to discover a fierce opponent to his theory of the lifting wing and to his equally remarkable vortex theory of the propeller. It was only in another sphere, that of the Aeronautical Research Council, that I was able to establish a happy bond between us.

When delivering a Memorial lecture it is customary to open with a tribute to the one who is remembered. But the substance of my lecture is the rotor which Cierva evolved 50 years ago and I hope to sufficiently recognise his contribution during the delivery. Therefore with your permission I will content myself now with marking my deep appreciation of the honour done me by your invitation.

An informed layman reading past papers on rotors and rotorcraft would form the impression that each achievement was only a fleeting gain. The autogyro was to give way to the helicopter, the helicopter to the compound helicopter and the compound to the convertible rotorcraft. The rotor itself, it was argued, is ideal for hovering but hopelessly inefficient in forward flight. Hence the haste to get back to wings, a tendency much increased when fixed wing designers discovered how to use small, heavily loaded, rotors. But such is the lure of the rotor that even its detractors saw the case for its use in landing and take-off.