The lightweight and compact separate jet lift engine has been with us long enough to have built up an acceptable level of confidence in its abilities, but there have been misgivings over the magnitude of some of the operational problems, in particular those of ground erosion and hot gas reingestion due to the high velocity jet.

The object of this paper is to present a Series of tests which has been made by Rolls-Royce to ascertain the nature of the problems and to put forward some simple solutions. It is not suggested that any of these solutions is unique but merely that they are adequate for our present needs.