It may be stated definitely that installation as a whole has shown little progress as compared with the development of either the aircraft structure or engine, and that to-day the installation of the engine in a machine presents a wide field for sound engineering design and improvement. On the other hand, failure in some part of the installation is the most prolific cause of forced landings. Statistics taken over a considerable period have shown that of the proportion of forced landings resulting from engine stoppage, seven out of eight are due, not to any actual defect in the engine itself, but to some trivial breakdown in the installation.

Apart, too, from the question of reliability and safety, installation development provides room for considerable economy, not only as regards its actual upkeep and repair, but also from its effect on the easy (or otherwise) removal of the engine from the aircraft for overhaul and replacement purposes.

The high performance engine, whether military or commercial, is essentially the light one.

The motor which made flying possible was an internal combustion engine, and the basic reason of its success was the direct use of an easily volatile fuel of high heat value, namely, petrol.

The first engine developed to use this fuel was that of Daimler, and all motor-car, boat and aviation engines have sprung from this engine.

In order to more readily have in mind our problem, we can with advantage briefly run through the main aero engines so far constructed with the progressive results of tests.

The engine of Gottlieb Daimler is illustrated by Slide No. I. It had automatic inlet valves and exhaust governing, the latter being a point to be noted.

The next slide shows the engine of the Wright Brothers. This engine weighed 8.75 lbs. per B.H.P. inclusive; the most successful engine of to-day weighs under 3 lbs. inclusive.