It is my privilege to speak to you to-night on some aspect of the work of testing experimental aircraft, and in order to present my subject to you in as lucid a manner as possible, I am going to ask you to consider that we actually have a machine before us waiting for its first test.

The calculator is a device in slide rule form for assisting in the design and stressing of flat rectangular panels in shear.

In the Incomplete Tension Field theory, the ratio q/qb becomes an important factor, where

q applied shear stress (lb./in.2)

qb shear stress at which panel first buckles (lb./in.2).

This ratio is normally evaluated by use of the formula

qb = KE(t/b)2

where E Young's modulus (lb./in.2)

t thickness of panel (in.)

a length of longer side of panel (in.)

b length of shorter side of panel (in.)

and K depends on the value of b/a and the edge conditions, and is normally obtained from R.Ae.S. Data Sheet 02.03.01.

This method becomes laborious when dealing with large numbers of panels.

By the use of the Calculator, q/qb may be found quickly, with no unnecessary paper work.

The role of meteorology in air operations is becoming increasingly important and an understanding of meteorology is desirable in the consideration of a number of the problems to be faced. The forecasting of winds en route and the use of these forecasts is one such problem, which has been brought into greater prominence by the advent of fast, high-flying aircraft. A great deal of work is being done on upper air winds and it is already clear that curious and significant phenomena sometimes occur. Thus very high winds are sometimes found in belts of limited lateral extent—the so-called “jet stream.” Not only high winds, but high rates of change of wind occur in such regions and they are clearly a potential source of difficulty to the navigator. Apart from the jet stream —a meteorological highlight of recent development—airline operators are also concerned with the problem of route planning.

In the early stages of development of every form of transport, the pioneers have cheerfully undergone great extremes of discomfort and unpleasantness. As the sense of novelty and adventure began to lose its early appeal a slow but insistent demand for greater comfort arose. To-day, there is a growing tendency to take aeronautics as a matter of course, and an increasing demand for those standards of comfort which have become the rule in the older methods of transport.

The two factors that most seriously prejudice one's comfort in aerial transport are probably noise and vibration. The problem of aircraft noise was laid before you last session by Dr. Davies.

The engineer has seldom a good word to say for vibration. In all his schemes it comes to cross him like an ill-tempered fairy godmother. In the days when men designed by eye and worked in tenths of an inch instead of in thousandths, vibration was more of a nuisance than a serious problem. To-day, when factors of safety are being pared to the bone, when weight is regarded with a jealous eye and members are being stressed right up to the limits of their capacity—to-day, vibration is rapidly becoming a definite limiting factor in design, and the problem of vibration in all its varied forms, one of the most pressing that the engineer has to face.

The purpose of this paper is to explain in simple terms the methods employed in, and the principles underlying, the technique of resonance testing and flutter calculations and to place that technique in its proper perspective within the framework of fighter aircraft design. No attempt is made to present original work, or to examine the more advanced aspects of the subject as both of these are considered to be outside the scope of the paper.

The reasons behind the growth in importance of resonance tests and flutter calculations are dealt with first. The technique of ground resonance tests is then given in detail. A few words follow on model resonance tests, the calculation of normal modes, and some aspects of flight resonance tests. The technique of flutter calculations is considered last of all, an attempt being made to give a simple explanation of “ flexure-torsion ” flutter, plus the basic theory of two-freedom flutter leading to the Lagrangian equations. The methods and instruments described in the paper may be regarded as typical, but as the subject is continually evolving they are far from final.

Some present trends in technique are mentioned, together with the difficulties experienced in dealing with the aerodynamic forces in the transonic region. It is essential that these forces be assessed, and the only known method is by experiment.

Throughout the world helicopters are being operated in a variety of roles today and, whereas ten years ago, there was not one type which had got beyond the stage of being an inventor's plaything, several types are now suitable for regular military and civil operations. At present, so far as is known to the author, public transport services using helicopters are confined to charters and scheduled mail services, with the exception of a scheduled passenger service which has been run by the British European Airways Corporation as an operational experiment since June 1950. The factors, both technical and economic, which have so far prevented the large scale introduction of public transport helicopter services, are being progressively overcome and in due course operators will find that manufacturers have made available suitable aircraft. The operators' task will then be to fly these aircraft in a safe and regular manner and give the public the best service possible.