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

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