When first I was approached to lecture to the Society it was suggested that I might speak to you on “Modern Aircraft Materials.” I did not choose this subject, firstly because I felt it was much too comprehensive to be susceptible of compression within the period of any ordinary paper; and secondly, because the relevant data (in so far as it is known) is enshrined in the official specifications, in the catalogues published by the metal manufacturers, and in a large number of papers presented to this and other learned Societies.

This analytical treatment gives general considerations concerning “ true rolling ” of a rolling body in a circular path : firstly, for constant speed of its centre of gravity, and, secondly, for acceleration of its centre of gravity. From these are derived the relations of the dimensions, as function of the conditions, and the corresponding constructions for both taper roller bearings and ball bearings, which are essential to produce “ true rolling” at constant and variable shaft speeds.

I have been invited to-day to put forward the case for,the compounding of a piston engine with a turbine, and this I propose to do in very general terms.

This is a scheme which we investigated fairly fully, both theoretically and experimentally, some ten years ago, and with which we would have proceeded actively had not the war, and consequent pressure on more immediate problems compelled us, temporarily, to lay it aside.

This paper had not been easy to prepare because any adequate treatment of recent investigations and research would have to pre-suppose in the engineer-reader a whole body of information which it would not be reasonable to suppose he has. Further, the author's pitch had been cleared, for nearly three years ago the Institution of Production Engineers published a paper by him entitled : "A Survey of Selection and Allocation for Engineering Occupations."

After much thought, he decided to deal mostly with some of the fundamental ideas underlying selection, and to offer a bibliography to assist readers who so desire, to gain further knowledge of the underlying facts and theories of Occupational Psychology and of the application of these to investigations which have been carried out in the allied fields of vocational guidance and selection, and to procedures which are being increasingly used.

The photo-elastic method can be used for either of two main purposes:

1. a) As a qualitative design tool to obtain indications of possibly unsuspected sources of stress concentration.

2. (b) As a means of obtaining a complete analysis of a two-dimensional stress problem, i.e., the determination of the separate magnitudes of the principal stresses at any point, as well as the direction of the principal planes relative to some axis of reference.

All that is required for (a) is the stress pattern which becomes visible and can be photographed when a loaded model cut from a sheet of suitable material is placed in a field of circularly polarised light.

The development of the gas turbine is so rapid and the thermo-dynamic ingenuity which is being lavished upon it at the present time is so imaginative and varied that the words “ in its forms ” which appear in the title to this paper can mean as much or as little as you please. Partly because I want to limit the scope of this paper to developments which might be expected to be in service within the next five years, and partly because I am frankly not sufficiently acquainted with the characteristics of many of its more advanced forms, I am going to confine myself to a discussion of the effects upon the speed and economy of commercial aviation of the two simplest and immediate variants of the gas turbine— the simple jet-producing turbine and the simple propeller-driving turbine.

The so-called Preferred or Standard Number Series is neither well-known nor often used in the British Aircraft Industry, perhaps because the series has not been published by the British Standards Institution or any other official body. Its use has much to commend it on the grounds of convenience and standardisation. Just as it is necessary for the international comprehension of science to standardise on basic symbols and terminology, so is it sometimes beneficial that numbers themselves should be widely used in the same manner.

The Series is published in France as the Renard Series, and also by the International Standards Association, using rounded off numbers to suit the metric system. The American Standards Association has published an American Standard differing from the I.S.A. table only in so far as certain values are rounded off to reasonable inch figures; included also is a table of more approximate fractional sizes.

A Stress analysis of screw threads of Whitworth form has been performed.

The critical stress in the threads is a shear stress, and this may be expressed simply in the form:–

where

Smax=shear stress.

f=distribution factor.

= 1.0 when screw and nut are both in tension or compression.

= 2.0 when screw and nut are in tension and compression respectively, unless specially designed for an improved distribution of load.

k = coefficient, depending mainly on fit, but also on pitch of threads, L and D.

<0.8 for close fit.

<0.9 for medium fit.

<1.0 for free fit.

P=axial load.

L=length of engagement.

D=nominal diameter.

By means of a broad survey of the developments in aeroelastic science during the past ten years and of comparable developments in associated fields, in so far as they involve elastic deformation, the present paper attempts to show how the individual subjects concerned are developing strong interconnections. At one time the subjects were for the most part regarded as discrete entities; now they are developing into component parts of an integrated whole —the dynamics of a deformable aeroplane.

It is suggested that in the future it may be necessary to discontinue the present methods of treatment of the component subjects as separate, and to adopt a standard method of attack on the problem treated as a unified whole, especially when adequate computational aids become available. A modified approach, involving an arrangement of the subjects in a frequency spectrum, is also discussed. Some speculations on the elastic provisions which may be necessary in the future are included.

The following investigations were made primarily in order to determine the manner of transmission of concentrated loads from the frames to the skin of a circular fuselage. The usual assumption, that the shear distribution in the skin adjacent to the frame is given by the simple “ beam theory,” was considered to be of doubtful validity, and for some time past the writer had suspected that a critical examination of the problem would show a very considerable variation from the ordinary theory in the immediate vicinity of the loaded frame. The writer's attention was first drawn to the problem by the work of Wignot, Combs and Ensrud in N.A.C.A. Technical Note No. 929, and the present investigations were made because a more fundamental approach to the subject was considered to be desirable.

If the motion of an aircraft is restricted, near the ground, to zero bank, comparatively simple solutions to the resulting equations of motion can be obtained, enabling the response to an applied yawing moment to be calculated rapidly. In this paper the analysis is made for three simple forms of applied yawing moment. From the results obtained in a particular case it is possible to judge the suitability of the fin and rudder design chosen on the basis of maximum sideslip reached. A general curve of overswing, in terms of the aerodynamic derivatives of the aircraft, enables the maximum sideslip to be calculated rapidly in a particular case.

Because of typogiaphical difficulties the symbols ^ have been replaced by ° with v, r and t throughout the paper.

A description of a test made recently in this test rig should prove of interest to those engaged in the design, stressing and structural testing of large aircraft structures, particularly wings, in that it would appear to represent a considerable advance over any previous test of this nature made in this country, and opens up new fields in simplicity and speed of application of the loads. The full load was applied to the wing in this test by one operator in approximately 50 seconds, thus approaching much more nearly than on any previous test made here the conditions which occur in flight.

It was with the greatest pleasure that I accepted the invitation of the Council to deliver the Wilbur Wright Lecture this year. Not that I count myself worthy to follow in the footsteps of the many illustrious men, British and American, who have delivered it in the past, but rather that I feel we are on the verge of discoveries and advances almost as spectacular as that flight of Orville Wright's, forty-three years ago, and that my peculiar experience may enable me to present to you some of the results of recent researches which have led me to the above somewhat prophetic conclusion.

Experience with the installation of guns in aircraft in recent years suggests that there has been little co-operation between gun designers and aircraft designers. This becomes more apparent as gun calibres increase and if satisfactory fighting aircraft are to be produced in the future, closer co-operation between gun designers and aircraft designers will be necessary. In consequence, a brief review of the progress of gun design in recent years, with special reference to its effect on installation, may be of interest.

From 1918 to 1938 the standard guns used in the Royal Air Force were the Lewis gun and Vickers Maxim gun, both Army guns modified for air cooling. The installation of these guns had reached a standard form by 1918 which was adhered to for the best part of 20 years.