The purpose of this paper is to give some account of the work on spinning and the progress which has been made since S. B. Gates and L. W. Bryant presented their paper to the Society, which was published in more comprehensive formi by the Aeronautical Research Committee as R, & M. 1001.

Although it is distinctly possible that the aeroplane of the future will be unspinnable it is a fact that the great majority of present day aeroplanes are capable of taking up the spinning motion either inadvertently or by deliberate intent on the part of the pilot. If it were really true that all those aeroplanes which apparently require to be forced into a spin would J ever inadvertently fall into one, a considerable number could be definitely classed as safe by forbidding spinning on such aircraft.

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.

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.