Until recently an aeroplane undercarriage has generally been called upon to serve two purposes only :—

To absorb the energy due to the vertical velocity of the aircraft when landing;

To enable the aircraft to be flown off from, and manoeuvred over, ground which may be very rough or very soft.

To these requirements are now added a third :—

To absorb the energy due to the horizontal velocity of the aircraft by means of wheel brakes.

These three duties must be carried out with the minimum possible weight and head resistance, for the undercarriage must be as self-effacing in flight as it is all-important on the ground.

The problems connected with wheel brakes are very specialised in themselves and have a particular interest at the present time. For this reason it was decided to deal with them first, and later to turn to the more general aspects of undercarriage development.

Fire control has two phases, prevention and cure. Of these the first is obviously the most important, but equally obviously serious attention must be given to the second.

Great advances have been made towards the minimising of the fire hazard as it affects aircraft. Previously inflammable components have been replaced by ones of metal; tanks have been made much less prone to disintegrate in a crash, and the press has provided us with a non-inflammable fuel.

It is not my intention to-night, however, to deal with this aspect of the case; it has received a great deal of attention and is constantly before you as aircraft designers. I propose to elaborate the subject of curing those cases we are unable to prevent.

The subject of fire extinction has been curiously neglected scientifically. Recently, one must admit, some attention has been bestowed upon it, but attention of rather a haphazard nature.

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.