The 985th Lecture to be given before the Society, “ The High Temperature Turbo-jet Engine ” by D. G. Ainley, B.Sc, A.M.I.Mech.E., A.F.R.Ae.S., was given at the Institution of Civil Engineers, Great George St., London, S.W.I on 15th March 1956, with Mr. N. E. Rowe, C.B.E., D.I.C., F.C.G.I., F.I.A.S., F.R.Ae.S., in the Chair. Introducing the Lecturer, Mr. Rowe said that Mr. Ainley had been working on gas turbines since 1943 when he joined the gas turbine division of the Royal Aircraft Establishment. He transferred to Power Jets Ltd. and later to the National Gas Turbine Establishment. His early work was associated with the development of axial flow compressors, contraction design and so on; he then transferred to turbine design, became head of the section dealing with turbine and heat transfer problems and for the past five or six years had been chiefly engaged on the cooling of gas turbine blades. Mr. Ainley graduated from the University of London, Queen Mary College, with first class honours. In 1953 he was awarded the George Stephenson Research Prize by the Institution of Mechanical Engineers.

This paper gives an account of the engineering and operational aspects of the introduction and first three years' operation by British European Airways of the first propellerturbine engine to go into airline service—the Rolls-Royce Dart which powers the Vickers Viscount air liner. The origin of this type of gas turbine engine and its chief advantages and disadvantages are considered. The main features and operational characteristics of the Dart engine are detailed. The training, operational handling, flight planning and maintenance aspects of the introduction and operation of the Dart engine in the Viscount are reviewed, and the experience accumulated is summarised. It is noted that apart from all the new ground that has had to be covered and all the associated development, no special problems have been encountered. Considerable advantages in respect of engineering and operational simplification have been demonstrated. Experience indicates that this type of engine has good reliability and long overhaul life characteristics, and confirms its general suitability for medium-speed air transportation. The paper ends with mention of some of the probable trends of propeller-turbine development, and with suggestions for some additional improvements which the author considers would benefit civil operators.

The importance of maintenance of aircraft in airline operations is emphasised by the fact that, in British European Airways at least, 25 to 30 per cent, of the total direct cost of operating an aircraft is absorbed by maintenance costs. This applies fairly generally to all aircraft in B.E.A.'s fleet, and is also applicable to most of the world's airlines: in the U.S. the proportion is slightly lower, which may be due not to relatively lower maintenance costs, but to relatively higher crew costs there.

This investigation is concerned with the stresses in a hollow circular cylinder of constant wall thickness, and closed by flexible plates, also of constant thickness. The cylinder is subjected to the combined action of an internal pressure and an axial force, both of which are statically applied. Although the particular case envisaged is that of a shock absorber, there are other engineering elements to which the analysis is applicable. Any closed circular cylinder of constant wall thickness subjected to an internal pressure is within the category. In a paper, Dr. D. M. A. Leggett investigated the case of an oleopneumatic shock absorber with rigid end plates, and what follows is an extension of his paper. As would be expected, the flexibility of the end plates causes a reduction in the flexural stress.

A solution, in terms of known integrals, is obtained for the motion from rest of a machine, idealised as an undamped linear mass-spring system, when subjected to an exciting force whose frequency varies at a constant rate.

In many installations of modern high speed machinery the running speed of the machine is in excess of the resonant or natural frequency of the system, and consequently starting up or stopping the machine could result in vibrations of large amplitude. The problem of assessing the magnitude and duration of these vibrations is very complicated and has been solved analytically only for the case of a single degree of freedom system excited by an oscillating force whose frequency varies linearly with time. However, even this solution is not easy to evaluate, the integrals involved demanding either graphical construction and numerical integration or summation of series.

The supersonic and subsonic jets are both considered by the method used by Miles for an oscillating aerofoil between wind tunnel walls.

The present problem and that of Miles are special cases of the flow past an oscillating aerofoil between porous walls, and provide a useful check for results in the porous wall problem. It may be assumed that the ratio of the change in pressure across a porous wall to the normal velocity at the wall defines a quantity called the porosity parameter, which is a constant at any particular point on the wall. For the special cases of the porosity parameter being everywhere infinite and zero, the porous wall corresponds to the solid wall and the free jet boundary respectively.

This note is presented as an idea to be criticised rather than as a description of a fully developed experimental technique. There are weaknesses in the method which will prevent it from giving absolutely correct answers, for example, the twist imparted to the boundary layer when a body of revolution is rolled cannot be represented. But some of the major effects can be represented, and the idea may possibly be developed to be of practical significance.

It is standard wind tunnel practice to measure the aerodynamic derivatives CYβ, C1β, Cnβ, CMβ, CLβ and CDβ by having a wind stream of constant direction, and measuring aerodynamic forces and moments on a model aircraft placed at angles of yaw and pitch to the stream.