The title of Prototype Testing is taken here to refer to the flight tests carried out on a new aircraft by its constructor. It embraces a wide field of subjects and in a short paper, it cannot be covered in any way comprehensively. I propose therefore to deal mainly with very general aspects of the subject.

The paper does not attempt to embrace out of the ordinary types with special problems peculiar to themselves—an extreme example of which is probably the Brabazon I. Most of my experience on this subject has been concerned with small aircraft, many of them single-seaters, and consequently some of my statements may apply more particularly to this type of aircraft, although many will probably apply equally to other types of aircraft.