The energy that is suddenly released when a structure fails under load usually presents one of the minor problems in strength testing technique. Care has to be taken to ensure that the strain energy in the structure does not do further damage after primary failure and so obscure the location of the original weakness; and the possibility of risks to personnel must not be overlooked. As a general rule, however, aircraft structures fail in strength tests without untoward effects. Most of the strain energy within the structure is absorbed internally or dissipated in loading gear and anchorages, and the most noticeable effect is the noise and vibration which is produced.

The True Balance of a man's worth cannot be struck by a knowledge, however full, of only one of his activities.

I do not propose to confine myself to Cayley's aeronautical activities in this paper, for that would be to do much less than justice to a man whose interests, when known and understood, can only add to the stature of a great Yorkshireman and a great Englishman, one, to quote William Cobbett, “of the resident native gentry, attached to the soil, known to every farmer and labourer from their childhood, frequently mixing with them in those pursuits where all artificial distinctions are lost, practising hospitality without ceremony, from habit and not on calculation.”

Sir Walter Raleigh, in his introduction to the History of the War in the Air (1914-1918), referred to Cayley as one who “amused his leisure with science.” Raleigh was not aware and, indeed, very few who know something of Cayley's aeronautical work are aware, of how active was the interest Cayley took in scientific and engineering matters during his long life. I hope in this paper to add something to Cayley's stature, great as it is, in this respect.

1. (a)Introductory.—The paper deals with experiments carried out in the engineering laboratories of the University of Manchester on a Crossley solid-injection oil engine in which small quantities of hydrogen or coal gas were introduced along with the air supply to the engine.

2. (b)Range of Investigation.—Three series of trials were run with hydrogen, each at a different load, namely, 53·4, 39·4, and; 24·4 b.h.p. The maximum amount of hydrogen used was slightly more than 3 per cent. by volume of the air supply, corresponding, at the lightest load, to some 14 per cent, by weight of the oil fuel supply.

   Three corresponding series of trials were run using coal gas in place of hydrogen, the maximum volume of gas employed being 5 per cent. of the air supply. At the lightest load this corresponds to approximately 2·4 times the weight of fuel oil used.

3. (c)Conclusions.—Such quantities of hydrogen or coal gas can be used satisfactorily in the type of engine considered. No trouble was experienced due to pre-ignition or other causes, and the engine appeared to run more sweetly when gas was being used.

   When running at constant load and speed, the admission of small quantities of gas appears to cause combustion to take place at a slower rate, giving a lower maximum pressure and more burning down the expansion stroke. The thermal efficiency is in consequence slightly reduced, while the heat-losses to exhaust are increased.

In a recently published book, The Aerodynamics of Propulsion, by Küchemann and Weber, there is included a brief discussion of heat flow in an air-air heat exchanger. The treatment given rests on an assumption which appears to be generally accepted, but which seems to the present writer to be physically unsatisfactory and to yield at least one misleading result. It is the purpose of the present note to show that a solution of the heat transfer equations can be obtained using an alternative assumption which seems physically more acceptable.

In this paper an attempt is made to analyse the overall gains that have been obtained in aerodynamic cleanness in the past, to review the overall performance improvement that can be expected in the immediate future from increased cleanness along orthodox lines, and to survey critically certain more advanced concepts aimed at giving still lower drag coefficients and better performance characteristics.

An occasional glance into the past is often of interest. The following notes refer to an event which was one of the principal landmarks in the history of aeronautics, and which attracted much interest abroad, especially in France. It is hardly necessary to remind the reader that the Aeronautical Society of Great Britain subsequently referred to, is now the Royal Aeronautical Society.

The year 1868 was a year of mark in aeronautics, for it was then that the Aeronautical Society of Great Britain held the first Aero Exhibition in the Crystal Palace.

Metal adhesives have been known to the Aircraft Industry for at least ten years, the Chrysler Cycle Weld process being among the earliest. Since then metal-to-metal bonding has been the subject of many papers, but no member of a firm of aircraft constructors is known to have lectured on the subject.

It is hoped, therefore, that this paper may prove a useful contribution to the workshop aspects of the method. The fundamentals of adhesion will be avoided and only brief reference will be made to the strengths of structures assembled by that means; those are matters for the physicist and aircraft designer.