The Chairman, in opening the meeting, said that the first part of the Paper would be presented by Mr J D Sibley, who for the past 10 years had been Chief Aerodynamicist at the Helicopter Division, Bristol Aircraft Ltd, Weston-Super-Mare Mr Sibley would discuss the aerodynamic aspects The second part, relating to the dynamical aspects, would be presented by Mr C H Jones, who had been Dynamics Engineer at the Helicopter Division, Bristol Aircraft Ltd, since 1955 Afterwards there would be a short film

The paper discusses a number of aerodynamic aspects which have appeared during the development of the Bristol Helicopters I have deliberately avoided excessive comparisons of the advantages and disadvantages of tandem helicopters versus the single main rotor helicopters, as this subject has been covered by numerous authors

The subject matter covers information on performance, control and stability, which has been obtained in the course of development work on Bristol Tandem Helicopters Some of this information is directly applicable to other types of helicopter

The CHAIRMAN, in opening the meeting, said he had much pleasure in introducing tonight's lecturer Mr Webb had been in the aviation field for 29 years In 1930, he joined the Air Ministry and in the pre-war years he worked at the Royal Aircraft Establishment in the Departments of Airworthiness and Aerodynamics At the beginning of the war, he was appointed Resident Technical Officer, firstly at Armstrong Whitworths and later at the Bristol Aeroplane Company It was during this period that he became associated with the helicopter work when the Bristol Company started to develop helicopters in 1944 He remained there until 1950 and during that time he was responsible to the Ministry of Supply for the early development of the Sycamore and the Bristol tandem rotor types

The President of the Royal Aeronautical Society (Sir Arnold Hall) invited Professor J A J Bennett (Chairman, Lecture Committee, of the Helicopter Association of Great Britain) to introduce the Lecturer

Professor J A J Bennett said that this was a very important occasion, both for the Royal Aeronautical Society and for the Helicopter Association of Great Britain Tonight, they were to hear about the development of an aircraft which was certainly not an aeroplane, and it was certainly not a helicopter according to present-day definitions To accept the F A I nomenclature, it was in an intermediate class, the so-called “Convertiplane” category As, however, there was neither a Convertiplane Association of Great Britain nor yet a Convertiplane Section of the Royal Aeronautical Society, it was appropriate that the two societies should get together and discuss the project

The CHAIRMAN, in opening the meeting, said that it was a privilege to introduce Lt -Col MEAD, who tonight would give us a soldier's viewpoint on helicopters It would be agreed that this was rather a red-letter occasion It had been very difficult to get the Army, except in little private corners, to say very much No doubt Colonel Mead would say that the views he expressed were purely personal opinions, as he had to do, but from his antecedents it was obvious that he knew what he was talking about

The Chairman, in opening the meeting, said that after all the comment in the Press in the last few days concerning the noise of helicopters flying over London and in view of the possibility of further comment in the immediate future because of the existence now of a heliport in London, it was opportune that the Association should be having a lecture this evening on “Helicopter Noise Suppression” from one of its members, Mr H B Irving, who was a leading authority on the subject

The Chairman, in opening the meeting, said that the development of rotating wing aircraft in France had been well supported by military contracts ever since Liore et Olivier had taken a licence from Cierva to manufacture Autogiros The French version of the C 30 Autogiro with the Salmson engine, was given extensive military trials, so much so that on one occasion it had been a surprise to him to see as many as fifty of these machines in operation at an Army airfield in France The development of the helicopter had been undertaken with similar intensity and quite a number of successful types—a whole family of helicopters, in fact—had emerged

An analysis is made of the free and forced oscillations of a single degree of freedom system damped by a multi-step friction damper It is shown that in free oscillation the decay is similar to that obtained with viscous damping, but in this case the frequency increases as the friction increases

In forced oscillation the exact solution is little different from that obtained using an equivalent viscous damper if the ratio (natural frequency/forcing frequency) is less than 1 37 For higher values the mass will remain at rest during some part of the cycle if the friction is large enough, when the above ratio is 3, 5, 7, etc, “stops” occur, however small the friction The variation of phase angle is unusual, under certain conditions the displacement leads the exciting force

On the basis of the results a criterion for the use of the equivalent viscous damper in ground resonance calculations is suggested

The Chairman, in opening the meeting, said he was very glad indeed to see so many members present at the first meeting of the new Session, especially as, some of them had, no doubt, been up half the previous night watching the television programme (to hear the election results)

It was a pleasure to welcome tonight’s lecturer, Mr Newberry, who, since 1951, had been in charge of the rotorcraft work within the Directorate of Engine Research and Development at the Ministry of Supply Mr Newbery had obtained his B Sc degree in 1932 at London University with first-class honours in mechanical and civil engineering and his subsequent career included working in the Airworthiness Department at the Royal Aircraft Establishment and as Resident Technical Officer at de Havilland’s, Stag Lane Since 1942, he had been at Ministry headquarters, where he was responsible particularly for transmissions With his long experience of mechanical systems and in establishing requirements for both rotors and propellers, Mr Newbery was an authority on the subject of his lecture— “The Programme of Development Testing for a Helicopter”

The Association is pleased to announce that the prize of £50 for the 1958 Cierva Essay Competition has been awarded to Mr E R Kendall

Mr Kendall, who is 25 years of age, is a Project Aerodynamicist with the Helicopter Division of Saunders-Roe Ltd He served his apprenticeship with that Company and in 1955 was nominated by the S B A C for a two year course at the College of Aeronautics, where he specialised in helicopter aerodynamics For his exceptional ability in technical study whilst at the College, he received the 1957 Alan Marsh Memorial Award which enabled him to take a short course of helicopter piloting instruction at Air Service Training He is an Associate Member of the Association