The Prime Purpose of this initiative Halford lecture is to speak of the man and his work.

It may seem rather peculiar to preface such a lecture with an obituary but as I wrote one of them with deep feeling in my heart I make no apology for quoting parts of it to start this lecture and later, to expand on those aspects of his rich life which may be of interest.

Before considering the special case of the North Atlantic, I should like to attempt some clarification of the term “Air Traffic Control” (A.T.C.). It is in fact a service for which I.C.A.O. member states have accepted responsibility dedicated primarily to avoidance of air-to-air collision hazards and secondly, to providing an expeditious traffic flow. When traffic is dense these requirements are somewhat incompatible and, of course, safety considerations are paramount; therefore the traffic flow suffers impediment in some form or other. Traffic Controllers provide service by issuing clearances which are subject to pilot acceptance. Pilots can ask for alternative clearances if they deem those offered unacceptable. Although the A.T.C. service clearly shoulders a large measure of responsibility for avoidance of air-to-air collisions, the ultimate responsibility is vested in the pilot-in-command who is authorised to take any action he considers necessary to maintain safe flight.

Ten years ago it seemed that the solid propellant rocket engine could make only a limited contribution to rocketry. Although it was simpler and more compact than its liquid propellant rival it suffered from three serious drawbacks. The nozzle was uncooled and so the burning time had to be short, the entire propellant container was subjected to the full combustion pressure and temperature and therefore the inert weight of the engine was high and, since the specific impulse of solid propellants is in general lower than that of liquid propellants (because solids are partially reacted systems) the engine performance was consequently poor, and finally, no means were available for controlling the magnitude and duration of the rocket thrust. These facts were the foundation of the opinion, still held by some people, that solid propellant engines were only suitable as boosters or short burning time sustainers for small missiles.

In his classic paper, The Expanding Domain of Aeroelasticity, Collar indicated how various types of problems (involving at least two of the three kinds of force—aerodynamic, elastic and inertial), which had hitherto been dealt with in their own “watertight compartments,” were tending to coalesce into a single subject which might be defined as “the dynamics of a deformable aeroplane.” The title of the subject, as Collar pointed out, at once suggests (to the mathematician at least) the formal solution of the problems which it comprises.

In this Note the reheat thrust boost for a turbo-jet engine is shown to depend upon various dimensionless parameters, one of which is engine pressure level. The importance of this ratio is illustrated graphically and it is shown to be most important over the range normally encountered on a test bed. It is shown that a given reheat system would deliver a higher thrust boost on a high pressure level engine than it would on a low pressure level engine. Finally, the pressure level effect on the thrust from an engine having a reheat system fitted but operating with the reheat unlit is discussed.

During the Second World War, a great many rockets were made and used operationally by both sides. By the end of the conflict, a pattern had begun to emerge. For applications where burning times were short and performance unimportant when compared with the need for simplicity, solid propellant rockets were used exclusively. Where control of thrust and the ability to start and stop repeatedly were involved, as in aircraft propulsion, or where performance was vital, as in the V2 ballistic missile, liquid propellants were applied. Since the war, this general pattern has persisted. There has been a progressive improvement in the performance of both types. At the same time, the thrust and total impulse of rockets have risen, until engines producing over one million pounds of thrust are envisaged.