The object of this paper is to set down an overall picture of the practical aspects of compressor blade vibration. In doing so it is inevitable that a certain content is effectively a repeat of other people's contributions to the subject. The authors make no apology for this and offer the paper as a "state of the art" as practised at Bristol Siddeley Engines Ltd. In bringing together the many relevant issues of this problem, it is hoped that a useful presentation is obtained.

There is little hesitation in indicating the most obvious and important practical aspect of blade vibration as that of the inherent danger of blade failure and it is known that the axial flow compressor is susceptible to complete failure caused by the fatigue of one blade.

The multi-stage axial flow compressor is a highly complex aerodynamic machine with, its early and late stages required to operate over wide ranges of incidence and Mach number conditions. To some extent, of course, use of variable geometry can reduce this to less taxing proportions. The aerodynamic environment of front stages has broad boundaries somewhat wider than those relating to rear stages, while middle blade rows generally operate under sensibly constant conditions. This diminishing “severity” of operation, front, rear to middle stage blading is not unrelated to the incidence of blade vibration problems which shows a similar pattern.

In the context of this paper, the term “large rocket engines” refers to those liquid propellant engines at present being built for use with ballistic missiles. The engineers concerned with their development however, are always hoping that the same units may be used for launching satellites and for the early stages of space flight.

Now it is axiomatic that in such vehicles the take-off thrust should exceed the weight. On the other hand, common propellant combinations only give an impulse of about 240 pound seconds per pound of propellants. Thus it follows that the duration of one stage of powered flight at constant thrust could not exceed 240 seconds, even if the net take-off acceleration were zero and the whole missile consisted of propellants. Allowing for sensible take-off accelerations, and for the weight of structure, engines and payload, a more realistic figure would be 150 seconds. As re-use of the engine system is not usually contemplated, the entire operational life of a large rocket engine is probably less than three minutes.

The purpose of the work was to investigate the effect of the finite width of plate on the elastic-stress distribution due to a central crack in a flat plate loaded in tension.

The range of investigation: (i) Two-dimensional photoelastic tests were carried out on flat-plate specimens. The photoelastic specimens were geometrically similar to the 10 in. wide fatigue specimens used by Frost and Dugdale, with the central crack simulated by a slot bounded by holes of small radii, (ii) A theoretical solution of the problem was derived and compared with the present and other photoelastic results.

It is shown that the effect of the crack-length/plate-width ratio on the elastic-stress concentration at the head of the crack can be expressed by the following formulae:

At its fifth meeting, the Commonwealth Advisory Aeronautical Research Council discussed the need for a better understanding of the operational requirements for aircraft in different parts of the Commonwealth. It therefore asked for papers from the respective countries, bearing in mind particularly the possibilities of V.T.O.L. and S.T.O.L. aircraft.

A survey has been made in Australia. The general impression gained is that within the Australian continent there are no outstanding future operational needs, if the term outstanding is interpreted in the sense of V.T.O.L. or S.T.O.L. or other extraordinary condition of operation. This is not surprising since Australia has, on the whole, excellent conditions for flying; there are no high mountains, very little icing or fog, and the country tends generally to be flat and low. In external operations conditions are not so favourable and certain definite requirements emerge. Theses together with some general observations, have been recorded as of interest to designers. It is clear that simpler forms of V.T.O.L. aircraft than rotary winged types are needed, and this may well indicate a need for more research.

There is no doubt that there is a very definite requirement for V.T.O.L. and S.T.O.L. aircraft in Southern Africa. With the increasing tempo of development of the various territories, South of the Sahara, the need for S.T.O.L. and V.T.O.L. aircraft will increase rapidly. The aim of this paper is to point out a number of the requirements and to draw attention to some of the problems to be overcome, in connection with the application of such aircraft.

Statistical data referring to the areas, population densities and surface transport facilities of some of the African territories South of the Sahara, are given in Table I. As far as transportation facilities reflect the degree of development, it is clear that most of these territories are in a relatively underdeveloped state. In recent years, however, there has been an increasing rate of economic expansion in Africa, and with it a growing need for aircraft facilities. Apart from the usual applications, such as for passenger and freight transportation, there are duties, as follows, which are of special importance in Africa.

In this lecture i want to survey some of the problems of the aerodynamics of re-entry, as they affect either purely earth-bound or space vehicles; and in particular, as they are affected by the trajectory the vehicles are designed to follow, or may find themselves upon due to some error of navigation. This is a self-set task and an ambitious one: but in truth it is an artful one, as it provides an excuse for me to leave the discussion of problems at a stage where their difficulties begin to defeat me.

Some measurements in the R.A.E. Bedford 3 ft. wind tunnel on a typical high tailplane illustrate a Mach number effect on the tailplane rolling moments due to sideslip which has been apparently overlooked previously. Fig. 1(a) shows that the increase in tailplane rolling moment due to sideslip is much larger than the increase in the fin lift curve slope a1F, Fig. 1(b). This extra increase in rolling moment is associated with the increase in the tailplane lift curve slope a1T, Fig. 1(c). In fact the rolling moment on this high tailplane varies roughly as the product of the fin and tailplane lifts, as Fig. 1(d) shows. A qualitative explanation follows.

Consider the idealised high tailplane shown in Fig. 2. At zero geometric incidence and positive sideslip the fin lift will induce positive and negative incidence distributions on the starboard and port sides of the tailplane.

The effect of initial waviness on the wrinkling of faces in sandwich construction is studied. Formulae are derived to determine the failing stress when the faces wrinkle due to failure of the core in tension, compression or shear. The importance of core strength requirements in maintaining surface smoothness is noted. A comparison of theory with experiments is made, and the agreement between the two is found to be reasonably good.

A sandwich construction consists of two thin face layers of high-strength material and a thick core layer of lightweight material. The function of the core is twofold. Firstly, it increases the bending rigidity of the faces and second, it stabilises them so that they will not wrinkle until high stress is reached.