This is the fifth occasion on which I have had the honour to address our Society and the third time I have chosen to discuss the same subject: “The stalling of aeroplanes.” I should apologise for thus harping upon a single string were it not that no subject could be more appropriate to an address in memory of Wilbur Wright, and were it not that until the stall is thoroughly understood and its attendant dangers pushed out of the way, aviation will not be free to play the great rôle which it is undoubtedly destined to play in the civilisation of the world.

In an interesting paper on the meteorology of India read before the Society in 1925, Sir Gilbert Walker gave a comprehensive account of the main elements of climate which affect the industrial and social well-being of the country, and dealt with the great question of seasonal weather forecasting, on which he has become the chief authority. I propose to-day to take up some of the newer means of dealing with Indian problems, and to add the consideration of a fresh item, the safeguarding of international aviation.

Referring to Fig. 1, let xOy be the plane of rotation of a rigid rod AOA' consisting of a series of pairs of masses symmetrically disposed about O. Thus at a distance r on either side of O are masses mr. Let AOA' rotate with uniform angular velocity Ω, about the axis Oz and let the plane xOy simultaneously rotate about the axis Ox, supposed fixed in space, with constant angular velocity w. Let ρ be the perpendicular distance mrMr of mr to the axis Ox.

The method generally used in England for calculating the aerodynamic characteristics of wings is that suggested by Glauert (1), in which the circulation across the span of the wing is represented by a Fourier series. On account of the form of the series, certain difficulties arise which make the calculation very tedious when more than about four points along the semi-span are considered.

The idea of navigating a certain type of sailing boat of mine by an autogyro instead of an ordinary sail has long been a desire of mine, in that I always have considered sailors to be very out of date as to rigs.

In conversation with J. Weir this question arose, whereupon he said that he had within his organisation of the Autogyro Company an engineer named O. Reder who had the same desire. We, therefore, got in touch and although the time was very short got out a rig and installed it upon a very small onedesign class, well-known in the Solent, namely, the Redwing. These boats are about one ton, and the rules governing their racing are that the hulls are standard and that any rig can be used, but that the sail area must not exceed 200 sq. ft.

“ The last thing I purposed to speak of, is, Those several Qualities of Timber or of Trunks, by which they are fitted for Mechanical Use.…. The Visible Causes whereof are observable. Partly in the Structure of the several Parts; sc. the Insertions, Sap-Vessels and Aer-Vessels; as to the Number, Size or Position of any of them. And partly, in the Nature of the Parts; I mean such as is manifest to sense. According to our clear and distinct observing of all which Causes, we may understand, Wherefore any Wood is made use of for any certain purpose. And also, wherein fitly to apply it to further Use.”

Snow falls in a great variety of forms, depending on a large number of conditions affecting the crystallisation of the moisture in the atmosphere. The forms may even vary from place to place or from time to time in one storm.

The character of snow as a medium for transportation depends not only on the form of its constituent crystals, but on the nature of the ground on which they fall, the depth of the total covering, the previous history of the underlying layers, and of course on the history of the last fall and the atmospheric temperature of the moment. Considering the characteristics for the purpose of aircraft operation, it is sufficient to make the broad classifications shown in Table I (page 504).

Many “figures of merit” for the comparison of aircraft have been advanced at various times, but in those cases where the basis of comparison has been logical no consideration has been given to first cost, while in those cases where money cost is included, serious objections can be raised to the value of the comparison made.

The accompanying Report No. B.A. 1083 of the Royal Aircraft Establishment demonstrates generally that a moving body or rider plane can be associated with a fixed body or plane for altering the aerodynamic properties of the combination for various useful purposes, and in particular, that rotating cambered rider planes, when associated with the front edge of a fixed wing of standard section (see Fig. 11) “are definitely advantageous” in improving the gliding conditions, and that “by increasing the size of the rotors relatively to the size of the wings, this superiority is increased.”

Previous experiments at the N.P.L. with various types of wings fitted alternately—with optimum wing-tip slots and with rotors—have shown that rotors can give about the same degree of lateral stability as tip slots, but over a much wider angular range. Other experiments with better rotors than used at the N.P.L. have shown that a more powerful stabilising effect over a wider annular range is to be obtained with rotors than with slots.

I. In recent years a systematic research has been made into the methods available for determining the stresses in three dimensional braced frameworks, and in particular into frameworks of the type represented by the hull of a rigid airship. Much of the research has been of a generalised character, intended to act as a useful guide to the designer rather than to deal with any particular problem of loading with which he may be confronted; attention has therefore been largely (though not entirely) concentrated on the stresses in a fully braced parallel tubular structure such as is shown in Fig. I, in which the wire bracing or “ tension ” members are initially strained so as to be capable of carrying compression,— the slackening off of wires, which will of course take place before failure, being considered subsequently by the “ device of the separate panel.”

When the Council invited me to read a paper before the Society they suggested as the subject, “ The Use of Steel in Aircraft.” After some consideration, I came to the conclusion that there was not very much new and interesting to say on the use of steel in structures, but that there was a good deal to say concerning the use of light alloys in special constructions. Not that I claim that what I have to say is new, but the particular use of light alloy sheet to be described certainly merits more consideration than it has so far received in England. It is not to be inferred that I think that the use of steel is likely to decline rapidly, on the contrary, I am of the opinion that it will always be widely used. Everyone seriously, engaged in the technical side of the industry knows that steel of various grades has been used in aircraft from the beginning of aviation amd has been the subject of intensive studies during the last fifteen years. It was obvious from the first that if high stresses could be realised with fair uniformity in the finished structural members—say 35 tons per sq. inch or higher—more economical use of steel on a weight-strength basis could be made than of any other material. However that may be, I shall only touch on steel and its uses in construction at one or two points in the course of the lecture.

Prior to 1914 there was no night flying proper, as we know it to-day, and therefore, so far as I am aware, there was no night lighting. I must except, of course, the night flying exhibitions which were given at Hendon in this country and at a few places abroad.

Three great drawbacks of modern aeroplanes, from a safety point of view, are their tendency to stall, their high landing speed, and their low gliding angle.

The use of wing-tip slots for preventing lateral instability is well known, but they do not materially reduce the landing speed. Moreover, they cannot be used along the whole span without making the wing unstable. The best length of wing-tip slot for securing stability and maintaining the lift coefficient is about 40 per cent, of the semi-span.