If I may I will begin with a few words of explanation and apology. It is always difficult to talk about helicopters to an audience not familiar with their peculiarities and it is doubly difficult to do so in a Memorial Lecture. For, although the helicopter industry has and has had its great men, they are few in number compared to those who made their names in the traditional field and it is not easy to find a direct connection. Indeed it is not unknown for the leaders of the fixed wing industry to be violently opposed to the helicopter in any shape or form. Fortunately I have not been able to discover such antagonism on the part of J. D. North; equally I have been unable to find that he was a supporter of the helicopter. Therefore I cannot begin in the traditional manner of a Memorial Lecturer by showing some sketch or brief excerpt written by him which will illuminate precisely the points it will take me ten pages to say. But I have been made very conscious of North's abilities and hope to pay some respect to him indirectly by laying emphasis on helicopter control.