The problems associated with the design of a stopped rotor aircraft are summarised. The decision to attempt to overcome the aerodynamic difficulties by the choice of a rotor blade section which is basically insensitive to atmospheric gusts dictates a largely circular cross section. During the rotor lifting phases of the flight the circular section is constrained to lift by a technique called circulation control by blowing — this technique is described and some results presented. A scale model hingeless rotor has been tested at the National Gas Turbine Establishment. Typical performance figures are presented and their implications discussed. In particular, it is shown that operating rotors at high values of thrust coefficient per blade leads to high induced power factors. Cyclic control of rotor lift is achieved by hub throttling the air to the circulation control slots —a simple mechanism to achieve this result is described. Two possible schemes for a VTOL circulation control stopped rotor transport are discussed and compared.

Much of what I am going to say is opinion and many will find it controversial. It is therefore essential to start off from a firm and incontrovertible basis of fact. By this means it should be possible to narrow down the controversy considerably.

Table I represents the state of aviation in this country in comparison with the USA. These facts are confined to civil aviation since it is the growth of civil aviation that I am talking about.