The importance of reliable airworthiness criteria is stressed in an introductory paragraph Practice in aeroplane design is reviewed briefly, noting particularly the current tendency to permit increasingly severe fatigue loads The principal loads on the elements of a helicopter are enumerated, and consideration of their repetitive nature leads to an extended discussion of fatigue failure and methods of correlating fatigue loads Suggestions are offered for a rationale of provisional strength requirements and the amendments desirable following the establishment of additional data The need in this connection for extensive V-g and blade stress records taken in operation is emphasised

Many people in Great Britain are now confident that helicopters will shortly be in general use for a variety of commercial purposes Some of these anticipated functions are not new to air transport undertakings—certain feeder-line services within the British Isles, for example, may well be operated by helicopters—but the fundamental ability of the helicopter to take-off and land in confined spaces gives it an additional scope in circumstances which preclude the use of fixed-wing aircraft

LADIES AND GENTLEMEN,—A number of you may not know our lecturer of this afternoon and I am glad to be able to tell you something of his past experience by way of an introduction

Mr SHAPIRO has had several years of engineering experience and his first aircraft appointment was in France working on the design of gyroscopic instruments, which post was rudely terminated by happenings in 1940 He came to this country and joined Power Jets, working on jet propulsion and then had a further period on aircraft instruments design This was followed by work on electric assister units for aircraft before he joined the Cierva Autogiro Company in 1943 as Senior Technical Officer

Mr SHAPIRO is a Founder Member of our Association, an A F R Ae S and holds an engineering diploma of the Federal Polytechnic in Zurich

LADIES AND GENTLEMEN,

Before calling on the first lecturer this afternoon, I would like to take this opportunity, on behalf of the Helicopter Association, of thanking the President and Council of the Royal Aeronautical Society for their courtesy, in inviting us to share to-day’s proceedings The idea of a full day’s discussion on helicopters originated with the R Ae S, but it can hardly be a coincidence that all those invited to read papers are members—I should say Founder Members—of the Helicopter Association, three of them being Council Members and one an ex-Council Member You are no doubt all aware that the Helicopter Association is of comparatively recent formation and owes a big debt of gratitude to the Royal Aeronautical Society, and other bodies for all the help and guidance they have given in the three years since the Association was incorporated

The success of the helicopter today is primarily the result of a background of rotary-wing experience covering many years of research into the problems of the gyroplane This simple form of rotorcraft, proposed by JUAN DE LA CIERVA, was developed to a stage at which vertical take-off and landing were normal maneouvres and were no longer exclusive features of the helicopter Only the ability to hover remained as the unique advantage of the power-operated rotor—an advantage for which a heavy penalty had to be paid The general problems of the helicopter for civil use are concerned mainly with an alleviation of the penalty that hovering has incurred

LADIES AND GENTLEMEN,—As you know, this is the first lecture of our 1948 49 Session—a series which I am sure you will find both interesting and instructive It is also the first time we have been privileged to use this room for our Meetings and our thanks are due to the President and Council of the Royal Aeronautical Society for granting us this facility

Our lecturer today has chosen a subject which is becoming of very great importance now that Helicopters are being used in a definite operational sense Mr USHER IS peculiarly well suited to talk to us on “Navigational Aids to the Helicopter” as he is qualified as a R A F Advanced Specialist Navigator, and has some experience of Helicopter Pilotage He is a Fellow of the Royal Meteorological Society and an Associate of the R Ae Society and, needless to say, a Member of our Association and also holds the Bachelor of Science Degree and Diploma of Education—both of London

The technical problems confronting the helicopter designer are very clearly enumerated in Captain LIPTROT’s paper, and Wing Commander BRIE has drawn attention to a number of considerations of importance to the operator

With some of these problems I have dealt in an earlier paper, and in order to avoid repetition I propose to leave out from this discussion points which have already been raised

Rotating-wing aircraft in forward flight are subject to vibrations for reasons which are fundamental and we must not therefore expect the elimination of these symptoms but only their reduction to generally tolerable proportions We need, therefore, more accurate methods of recording and analysing vibrations in helicopters in terms of component frequencies and amplitudes, and in addition we must have generally agreed standards for comfort, i e, limiting vibration levels as a yardstick both to makers and users of these aircraft

As my contribution to this afternoon’s proceedings, it is my task to give you a brief account of the Cierva “Air Horse” This machine has the distinction of being the world’s largest helicopter undergoing flight testing

Following the recent S B A C exhibition at Farnborough, I have heard many kind and unkind expressions of expert and inexpert opinion, but the lowest common denominator seems to be that it is an “astounding contraption” Faced with this challenge, my purpose this afternoon is somewhat apologetic, namely, to show that it is neither astounding nor a contraption In fact, we, in the Cierva Autogiro Company, have persuaded ourselves that God decreed three rotor helicopters All others are merely attempts by men to cheat His divine laws

The “Air Horse” design arose primarily as an answer to the demand for large loads It was realized that difficulties in helicopter construction increased in proportion to rotor diameter and nothing was therefore more natural than to increase the number of rotors