IT was an open secret for a considerable time—before the fact became, as it has been now for some months, common knowledge —that the BRISTOL AEROPLANE COMPANY was concerning itself with the development of the helicopter. It is, therefore, with particular interest that we publish this month an article on the performance of rotors by MR TOMS, who is a member of the staff of this firm's helicopter department. It follows an American article, which appeared in Aircraft Engineering last October, on the power requirements of this type of aircraft, from MR AUTRY, of the BOEING AIRCRAFT COMPANY. Our regular readers will, of course, also remember the ‘classic’ series on ‘Rotary Wing Aircraft’ by DR BENNETT, then with the AUTOGIRO COMPANY, and now with the FAIREY AVIATION COMPANY, which originally appeared in our January to August 1940 issues, and the recurrent demand for which necessitated our recently having to make available photostat reprints for those who missed it at the time and now want to make a study of the basic principles of the subject.