Self excited vibrations of helicopters on the ground have been the cause of several accidents It is, therefore, essential that the means of ensuring freedom from such phenomena should receive serious attention

The theory of R P COLEMAN, is briefly reviewed and compared with results obtained from model rotor tests This comparison affords general confirmation of the theoretical results

The theory of a rotor on idealised supports is applied to a single rotor helicopter of known hub impedance Then experimental methods for determining this impedance are described

Finally, the influence of Ground Resonance on undercarriage design is reviewed The influence of shock absorber struts and tyres on the coupled rigid body modes of the helicopter is discussed and three undercarriage schemes representing alternative approaches to ground resonance elimination are examined It is found that, with respect to ground resonance, the most advantageous system for land based operations is one in which all the helicopter-undercarriage modes have very low frequencies

An Appendix indicates the application of the theory to a twin rotor helicopter of any configuration

In the first part of the paper a brief review is made of major items for research in the helicopter field, the subjects touched on including rotor aerodynamics, stability and control, evaluation of configurations, vibrations and fatigue, and operational aspects An outline is given, in the section on stability and control, of work being done at A & A E E in connection with the assessment of the longitudinal handling characteristics of helicopters The second part of the paper contains an account of recent work at A & A E E on the low speed and take-off performance of a helicopter An empirical method of low speed performance estimation is described, and the variation with wind speed of the ground effect on a rotor is discussed theoretically and on the basis of experimental results A theoretical analysis of the forward take-off motion of a helicopter is briefly presented, and the final section is concerned with the performance of a multi-engine helicopter in the event of failure of one engine, with particular reference to the possibility of safe operation from the type of site proposed for civil use