Prototype helicopters at the Bristol Aeroplane Company have been produced and servicing schedules have been made up detailing the maintenance work and inspection that has to be carried out after the following periods : (a) between flights, (b) daily, and (c) after 30, 60, 120 and 240 hours flying.

At the time these schedules were made it was not fully realised that the work would not be carried out exactly in this way.

We now learn that the airline operators are dividing their 30, 60, 120 and 240 hour inspection and maintenance schedules into small parts. One of these parts is added to the routine daily inspection, and so, by the time 240 hours of flying have been completed the whole of the interim schedules have also been completed, without withdrawing the helicopter from service. This system can only be operated providing that all work in the schedules can be split into tasks of less than, say, three hours each; there must, of course, be exceptions as obviously the overhauling of an engine takes longer than three hours.

In preparing this paper it was obvious to the writer, from a perusal of the titles of the other papers arranged for this meeting, that some of the subjects discussed will have been dealt with in some measure by previous speakers, as this paper also deals with the Westland-Sikorsky S-51 helicopter. Where such repetition occurs the writer tenders his apologies.

The Westland Sikorsky helicopter is well known in this country through its commercial activities over the past three years, and more recently its application to the Navy and R.A.F., whilst its American opposite, the Sikorsky S-51, has accumulated many thousands of flying hours to its credit, proving that the design has dependability and adaptability for the many roles of operation it has to meet. A close liaison between the American and British makers ensures the best possible service to all its operators.

The Westland-Sikorsky S-51 inherits to a large degree the same qualities as the American model, and in discussing its maintenance many of the practices used are common to both models.

It will be appreciated that, in this short paper, only brief reference can be made to various aspects of importance to the design and performance of rotary wing aircraft. Nevertheless, it is suggested that these references will serve as a basis for discussion, as well as to emphasise the necessity for more investigational work.

Because of the rapid development in the “science” of rotary wing aircraft, the subject of materials of construction will become increasingly important and most probably difficult as the designers’ demands and desires increase. Today, therefore, any discussion on materials can only be based on current design knowledge and requirements, with indications to the materials which may be considered most suitable for future projects.

Bearing in mind such limitations in scope, together with the fact that a certain amount of choice of material is left to the designer, it is proposed to refer to various aspects of materials and their selection which, in the opinion of the author, warrant the attention of those concerned with the responsibility of design development and research.