The piloted aircraft provides the supreme example of the highly complex machine performing a precise function in which the control loop is still completed through a human operator. Although both physically and mentally his task has been greatly assisted by the introduction of automatic pilots, auto-stabilisers, power controls, flight directors and the like, he still possesses the ultimate advantage over the machine of being able to use judgment in the face of arbitrarily changing circumstances. Thus, until it is possible in advance to define the required tasks exactly, and to measure the subsequent performance of the system in precise and unambiguous terms, the pilot will be saved from the encroachment of automation.

The performance of the human operator is described by the aptness and speed of his reaction to the pertinent stimuli, in effect his transfer function as an integral element of the overall control loop.

This paper considers some of the special problems of wind tunnel testing which arise in high-lift work. Discussion is confined to current experience in the R.A.E. and N.P.L. low-speed wind tunnels, and refers mainly to tests on blowing over flaps or jet-flaps. Comments are made on suitable size of model, methods of feeding compressed air into models without affecting balance readings, and general test technique. Methods of model construction are not specifically discussed.

So much has been said in the past four or five years of the need for Great Britain to increase the numbers of her trained scientists and engineers, and so much emphasis has been put on training by industry, that the country as a whole is aware, if somewhat vaguely, of the urgency of the present national need. Whether there is a real awareness of the continuing nature of the need, is, however, far less certain; and I make this my apologia for attempting some further discussion of a position which, to engineers at least, is at present patently and painfully obvious. It must be remembered that only a few short years ago, engineering skill was at a discount and the engineer something of a social pariah; moreover, the higher his academic training, the further he was beyond the pale.

A simple exposition, using d'Alembert's principle and methods of virtual work, is given of the properties and applications of the normal modes of vibration of a linear elastic system. The use of the normal modes in problems of free and forced vibration and dynamic loading is discussed with the aid of simple examples, and it is shown that by these methods dynamical problems for any linear system may be solved without the use of the fundamental equations of motion, provided the natural frequencies and modes of the system are known. In most problems the solutions converge rapidly, so that only the first few modes of vibration need be considered, and in these cases the solution may be modified to give further improvement in convergence. Unsatisfactory convergence may be obtained, however, in problems where there is an exciting force of very high frequency, or an impact of short duration. An approximate allowance may be made for damping, provided this is small.

There have recently appeared a number of papers and notes bearing on the merits of turbo-prop vis-a-vis turbo-jet transport aeroplanes, mostly exhibiting specific favour towards one type or the other, but disagreeing among themselves and all based upon investigations which, it is contended here, are incomplete.

The basis used has invariably been a comparison of the relative direct operating costs per unit of weight (i.e. per passenger or per ton) per mile, and the relative earning capacities have not been considered. This, it is believed, is a serious omission which can only lead to a distorted assessment and erroneous conclusions.

The author has been associated with a thorough-going investigation into the relative merits of twin-engined turbo-prop, turbo-jet, and reciproeating-engined aeroplanes, all designed on a strictly comparable basis to do, as far as the performance of suitable available engines would allow, the same job in terms of capacity payload and associated operational stage length, take-off and landing performance and one-engine-inoperative climb performance in given atmospheric and altitude conditions.

While the use of blade lacing wires or shrouding is not altogether common in gas turbine practice, occasions may arise when their use is desirable, and the purpose of this note is t o present a method whereby the vibrational characteristics of a number of blades wired together may be conveniently found.

In the early stages of preliminary design, it is essential to have a method for the comparison of aircraft on an operating cost basis. The standard S.B.A.C. method is too lengthy and, in any case, demands a greater amount of data than is usually available in the early design stages.

The formula presented in this note is an extension to the ones presented by the author in the January 1955 and November 1956 Journals and is more accurate in that it provides for variation in aircraft first cost, type of power plant, speed and range.

It is submitted that the formula gives a reasonable first estimate, suitable for early design comparisons, and that the few parameters required are normally available at the earliest stage of the design.