In giving this paper, my aim is to give an outline of the practical aspects of flight tests performed with a Bo. 105 helicopter, in the speed range of 100 kt to 220 kt, rather than to dwell on theoretical explanations for the results obtained, which have been dealt with in Refs. 1 and 2. In a short paper of this nature it is not possible to deal in detail with all aspects of such a test programme, so I have selected some results which I hope will be of interest. A number of similar investigations have of course been performed with other helicopters during the past, albeit not with this type of main rotor system, and to those who are familiar with these flight programmes I must apologise for not bringing any startling new discoveries.