An internal combustion engine divides the heat energy obtained from its fuel into three fairly equal parts. About one-third of the energy becomes useful work; rather more than one-third escapes into the atmosphere in the exhaust gases : and rather less than one-third gives its heat to the cylinders and pistons. As its name implies, an air-cooled engine is one in which the cylinders are cooled directly by air. While the engin.e can and does part with a small amount of its heat by radiation, the bulk of the heat is carried away by air moving more or less rapidly over the surface of the cylinders and cylinder head, which are provided with fins in order to increase the surface in contact with the air. As the loss of heat is nearly proportional to the velocity of the cooling air the faster the aeroplane goes the better will a given engine be cooled; consequently, on a high-speed aeroplane it would be permissible to reduce the area of the cylinders in contact with the air; that is to say, we might save weight by reducing the size and number of fins or, alternatively, the velocity of air over the cylinders need not be equal to the speed of the aeroplane.

The work which forms the subject matter of this paper relates to a device for reducing the air resistance of an air-cooled radial engine. It can be added to the engine without completely enclosing the cylinders, either singly or collectively, in streamline casings of the conventional type, which usually render the engine inaccessible.

Three years ago I had the pleasure of speaking before the Royal Aeronautical Society, and I feel highly honoured that I have again been requested to say a few words about the German commercial air services. From this request I draw the conclusion that Great Britain is as much as ever interested in the progress of German commercial flying. The essential basis of good relationship between the nations, namely, that in order to understand each other they must know each other, applies also to the realm of commercial aviation. The present developments in commercial flying demand that the nations interested shall work with one another and not against one another. This, however, will only be possible if there is a mutual understanding and knowledge of air activities on both sides.

The spin is a mode of motion of which we know very little. The general public are inclined to look upon it as necessarily dangerous, but this we do know it is not. It is only in rare circumstances and under fortunately rare conditions that danger arises. Nevertheless there is ample warrant for its study, and for that study to be treated as one of high importance. New conditions of aeroplane operation are continually arising, the very increase of speed itself would ensure an entry into regions never before penetrated. Hence it is ever necessary to seek for remedies even before serious difficulty has arisen; this anticipating action always seems to me to be absolutely essential, and I am comforted by support in this view from no less an authority than Francis Bacon, who, in his essay “ On Innovations,” wrote: “ Time is the greatest innovator; and if time in course alters things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?”

In the following article an attempt has been made to present the characteristics of a sail by considering it as an aerofoil, the “ lift ” and “ drag ” being replaced by two forces mutually at right-angles in a horizontal plane, one force corresponding to the drag, acting in the same direction as the relative wind. It appears that skill in the art of sailing could be reduced, apart from other considerations, to ability to set the sail in the required position determined by its aerodynamic characteristics.

In my little book, An Approach to Winged Flight, published in 1928, I advanced the view that the flight of all human gliders might fairly be regarded as a winged flight with locked wings.

I suppose that if the wings were unlocked they would flap upwards and the aviator would come down; but that if they could be unlocked and yet restrained by springs so strong that, until any other force were applied, they would retain their horizorital position, then it seemed credible that their movement would be under the control of the aviator and that, as soon as he knew how to exercise that control to his own advantage, he would actually be flying.