I am pleased to have the honour of presenting the 18th Henson and Stringfellow Memorial Lecture. The subject of helicopter modelling is certainly appropriate because of the pioneering experiments that Henson and Stringfellow carried out with steam-powered plane models more than 50 years in advance of the Wright brothers. Although true powered flights were not quite achieved, these models were notable for excellence in overall design, the efficiency of their small steam engines, and their ultimate influence in later developments that culminated in the first successful aeroplane. Although not as well known, models were also extensively employed in the early development of the helicopter and have since become almost indispensable for advancing helicopter technology. The main emphasis of this lecture will be devoted to the diverse ways in which small-scale helicopter models are presently employed in advancing this technology. To best accomplish this objective, I have chosen specific examples of helicopter models to illustrate their versatility and wide range of application. The presentation of these models will also serve a secondary purpose—to demonstrate the advanced level of technology that now exists for producing these sophisticated and fascinating models.

The rolling up of the vortex sheet shed from a finite aspect ratio wing into discrete vortices has been extensively investigated in the past. Most of these investigations have, however, considered wings having an elliptic loading.

The early design charts of Silvertstein et al gave downwash angles for a variety of flapped and unflapped aerofoils by considering the trailing vortex sheet to be composed of discrete line vortices but ignored the rolling up process that takes place.

In recent years much attention has been given to developing new methods of steering tactical missiles. One method of particular importance is known as thrust vector control (TVC) which allows the missile to be steered by vectoring the efflux from the propulsion engine. In the case of engines powered by liquid fuel the normal TVC technique is to swivel the complete combustion chamber. This method is, however, unsuitable for solid propellant motors and so different techniques have been developed. This present paper makes a comparison of different systems of recent origin developed within the UK which are now available for project application.