If I may I will begin with a few words of explanation and apology. It is always difficult to talk about helicopters to an audience not familiar with their peculiarities and it is doubly difficult to do so in a Memorial Lecture. For, although the helicopter industry has and has had its great men, they are few in number compared to those who made their names in the traditional field and it is not easy to find a direct connection. Indeed it is not unknown for the leaders of the fixed wing industry to be violently opposed to the helicopter in any shape or form. Fortunately I have not been able to discover such antagonism on the part of J. D. North; equally I have been unable to find that he was a supporter of the helicopter. Therefore I cannot begin in the traditional manner of a Memorial Lecturer by showing some sketch or brief excerpt written by him which will illuminate precisely the points it will take me ten pages to say. But I have been made very conscious of North's abilities and hope to pay some respect to him indirectly by laying emphasis on helicopter control.

I would like to begin by suggesting a small but important correction to the title of this Symposium. We must not refer to “the UK”, which infers the islands and surrounding coastal waters, but to the entire area for which the United Kingdom has search and rescue responsibilities.

The ICAO Convention, to which we were signatories in Chicago 1947, laid down that “Contracting States, separately or jointly, shall delineate Search and Rescue Areas for which they will be responsible, and establish one Rescue Co-ordination Centre in each”.

This Agreement went on to recommend that the areas might extend beyond national boundaries, by agreement with neighbouring States, and, as the Search and Rescue Services were to operate in close conjunction with the Air Traffic Services, there would be mutual operational advantages in having the Flight Information Regions and Search and Rescue Areas co-extensive.

The very nature of Naval flying and carrier operations in the maritime environment has always given rise to a requirement for an efficient rescue facility during both peace and war. When safety at sea was solely dependent on surface units it was perhaps natural that a faster aerial vehicle with some form of rescue capability would eventually arrive and as we now know the ubiquitous helicopter became that vehicle.

The military requirement to save people from the sea has been with the Navy for a very long time and that lonely feeling of being by oneself in the water has raised many a heartfelt cry.

Helicopter SAR was conceived in the Royal Navy with the advent of the S51 Dragonfly in 1951. This was the first service helicopter to have a winch. During the time that helicopters were proving their worth in Korea we formed 705 Squadron at Lee-on-Solent with the primary task of developing the SAR role. Initially none of the equipment was standardised and improvisation was the keyword.

HM Coastguard's main function is the co-ordination of all civil marine search and rescue operations around the coast of the United Kingdom—the area limits corresponding to those set out in the ICAO SAR Plan. To achieve this task the coastguards are so disposed around our coast, on a 24 hour watchkeeping basis, to best receive the distress information and vector the appropriate rescue facility to the scene. There are 550 regular coastguards maintaining 150 regular stations (see map) backed up by over 7000 auxiliary coastguards and 214 auxiliary stations. All regular Coastguard Stations maintain watch on MF and VHF marine distress frequencies, are netted in to their local 999 emergency telephone system and are interconnected by VHF radio and telephone. All Rescue HQs and some strategically placed constantly manned stations are addtionally connected to the PO Telex system with direct lines to their adjacent PO Coast Radio Stations. CG Auxiliary stations, provided with VHF radio and telephone facilities, are only manned at times of casualty risk.

It is naturally a great privilege to have been asked to give the 20th Henson and Stringfellow Memorial Lecture here at the Yeovil branch, within a few miles of the place where Henson and Stringfellow worked together and performed some of their historic experiments.

It is perhaps equally natural that, Yeovil having become the home of rotary wing VTOL in the UK and my own Company having pioneered high speed wing VTOL that I should have been asked to make some aspect of VTOL the subject of my paper.

When the Magnus effects are completely absent the oscillatory motion of a dirigible body is said to be plane-yawing. Such bodies are stabilised by attaching fins or control vanes at their rear ends. Initial choice of the fin-size is made, depending on a static stability condition: JM < O, where JM is the normalised overturning aerodynamic moment coefficient. A proper fin-size requirement should normally be found from an appropriate dynamic stability condition. Under the very severe aerodynamic restriction stipulated above, one would expect, if the static stability condition is liberally satisfied by attaching over calibre fins, perhaps dynamic stability requirements could be met. This, however, may considerably reduce the ballistic range of the body. One would, therefore, need some sort of an upper majorant for JM consistent with the dynamic stability of the body and this should be a function of the other associated aerodynamic forces. In the present note a suitable majorant function for JM has been worked out. For this purpose, the aerodynamic coefficients are assumed to be slowly ranging functions of the path length as is usually stipulated. The stability problem has been solved using certain known results in the oscillation theory of differential equations.