In the following paper the writer's aim is to indicate certain possible lines of development and research which his own investigations and preliminary experiments have shown to be at least worthy of serious consideration.

If we review the present state of the art we find the position to be substantially as follows :—From a thermodynamic point of view the performance of the modern aero engine has approached so nearly to the ideal obtainable from the cycle on which it operates that there is little scope for improvement.

It is extremely difficult to obtain reliable data concerning the actual performances of German giant aeroplanes, and it will therefore be better for our purposes to confine ourselves to generalities without the use of actual figures, whose reliability may be open to question.

In the first instance as regards “ speed , ” we find within each of the two “ A ” and “ B ” type designs, that the speed diminishes as the number of motors increases. That is to say, a two-engined “ Type A ” aeroplane will have a greater speed than a four-engined “ Type A2 ” machine, with conditions as regards the horse-power loading and wing loading approximately the same.

Exactly the same rule is distinguishable in the case of the “ Type B ” machines. In the case of the “ Type A ” machines this result is obviously to be expected, firstly, on account of the extra head resistance introduced by an increased number of motors when exposed to the wind ; and secondly, on account of propeller “ interference ” and inefficiency.