The operation of scheduled night flying presents two tasks to aviation:—

• (1) The technical task of taking off from and landing on an aerodrome.

• (2) The operation of the flight from one aerodrome to the other.

The first task presents no completely new problem, as sufficient experience was gained during the war. All that was necessary was to provide facilities which guaranteed regular traffic.

The second task was purely one of navigation. It had to be solved in accordance with the strict demands of maximum safety and maximum regularity of the service. The only means of navigation then available, the compass, was not sufficient for these requirements, and at night it was not possible to count on keeping on the course by observing objects on the ground.

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.

Air transport has now become so important a factor in the life of the community that preventive medicine must seriously take into account the new problems that inevitably have arisen. Increased speed of transport brings about more frequent contact with rapidly increasing numbers of those of other communities as well as of their own.

The amount of information on the effect of accelerations on human beings is scanty and somewhat rudimentary with the single exception of observations made on aeroplanes. Aircraft in general have to be built to certain factors of safety so as to keep the total flying weight as small as possible, and for this reason accelerometers have been carried to measure the resultant forces experienced in flight. In this way a measure has been obtained of the forces likewise impressed on the human pilot directing the craft. The practice of flying has gradually developed by the careful training of the pilots so that undue stress is not placed on the aircraft structure and as a corollary this has been made possible by the pilot using his physical sensations to limit the violence of any aerobatic manœuvre. But the practice in this respect differs in various countries and so an attempt is here made to collate what information exists on the effect of accelerations on the human body and to consider whether the stresses experienced in flight can be increased with safety. It is, however, realised that the subject is a very open one and that the experimental data are very scanty.

In a recent article on supercharging, various practical conditions are given which place limits on the degree of supercharging possible with aero engines. Some time ago the writer was shown the results obtained with a supercharged engine and, although the performance was very creditable up to an altitude of 12,000 feet, above this altitude there was a remarkable decrease in power, this decrease being so considerable that it could not be readily accounted for. Various modifications were made in an attempt to improve the engine's performance at the higher altitudes, but without success, and it was only after a new type of carburettor had been fitted that improved results were obtained.

The control of an aeroplane is effected through the medium of three distinct sets of control surfaces known as the elevators, ailerons, and rudder, these surfaces being so disposed with reference to the centre of gravity of the machine as to be capable of producing rotation about three mutually perpendicular axes passing through this point, and called the lateral, longitudinal, and normal axes respectively. Thus, the elevators cause a rotation about the lateral axis of the machine, the resulting motion being known as pitching, the ailerons a rotation about the longitudinal axis, producing rolling, and the rudder rotation about the normal axis, producing yawing.

In this paper the author does not propose to deal with any particular form or type of engine or fuel-injection system, but to discuss some of the problems which are encountered when engaged on the development of a high-speed compression-ignition engine.

The main problems to be solved consist in devising suitable means for utilising to the fullest possible extent the oxygen available within the cylinder and for avoiding the production of smoke and noise and, in so far as it is connected with combustion conditions, smell.

Most engineers have a sound working knowledge of the handling of materials of different kinds, and of their properties, and make use of these wellknown properties. If, however, the engineer attempts to explain any of these properties he frequently finds that his training has not equipped him with an acceptable explanation.

In recent years much work has been done towards explaining these properties, but this work is dealt with in the specialist works of chemists, physicists and metallurgists, and is usually not easily available for the engineer, involving as it does a great deal of reading and investigation.

A noticeable peculiarity in the flight of a certain number of birds is the way their wing-tip feathers separate, both in flapping and in gliding flight. So wide do the gaps between the feathers become, at times, that the outer parts of the wings take on the appearance of hands with their fingers spread out. One's first thought about the matter is that there is probably nothing in it; that the feathers separate simply because they are feathers, and, as such, cannot help themselves; but, on investigation, this turns out to be one of the most interesting of the many aspects of the flight of birds; interesting, not only because it brings to light the infinite care and cunning that have been bestowed on the construction of their wings, but also because it demonstrates the possibility of applying some of the lessons that birds can teach us, to the design of flying machines—gliders in particular. When considering such questions we should always humbly remember that birds are the outcome of the law of the survival of the fittest through countless ages of flying, while we have been at it only for about thirty years.

There has been a great advancement in recent years in the technique and production of suitable fuels for both aircraft and automobile engines and the author hopes that a few notes on the fuel problem with particular reference to aircraft work may be of help to those engaged on aero engine design and operation.

In the author's opinion it is somewhat surprising that, with the information and data at present available on the subject of fuels, greater use is not made of this when considering the design and operation of an aero engine.

One of the most recent and important branches of aeronautics is aerial survey. During the last seven or eight years great improvements have taken place which have developed it into a science of its own. Several aerial survey companies are now operating in various parts of the world, and the untiring and persistent manner in which these pioneers have succeeded in overcoming difficulties has been crowned with success, as it is now accepted by most governing powers as a useful, economical and quick method of surveying.

It was a great revelation to me to read Lieut.-Comdr. Graham's study of the “Safety Devices on Wings of Birds,” reprinted in the Journal of the Aeronautical Society of January, 1932. I had always believed that the gaps formed by the tip feathers on a bird's wing were not strictly comparable to slots, because from a superficial observation of birds’ wings, it appeared that the slots were running in the wrong direction, namely, from the top to the lower surface of the wing. Lieut.-Comdr. Graham's outstanding contribution is his discovery of the reason for the emargination of the web of the slot forming wing tip feathers. There can be no doubt that this arrangement is aerodynamically equivalent to a multi-slotted wing.

If I wish to know the load which a structure will support without yielding or breaking, or its deflection under some load, I usually make calculations embodying numbers representing certain properties of the materials used, determined by some simple experiments. Sometimes the mathematics may be exceedingly difficult, or even intractable; or the mathematical solution may be achieved only at the expense of assumptions whose validity seems to need confirmation. I may then experiment with my structure, full scale; but it may be large and costly and I may wish to know the answer before I venture to build it. I may make a small scale model and experiment with that.