Many people still think that if the engine of an aeroplane should stop while the machine was in mid-air, a terrible disaster would happen.All petrol engines may be described as fickle in their behaviour, and so complicated is their structure that the best of them are given to stopping without any warning.Aeroplane engines are far superior in horse-power to those fitted to motorcars, and consequently their structure is more intricate.But if an airman's engine suddenly stopped there would be no reason whatever why he should tumble down head first and break his neck.Strange to say, too, the higher he was flying the safer he would be.
All machines have what is called a GLIDING ANGLE.When the designer plans his machine he considers the distribution of the weight or the engine, pilot and passengers, of the petrol, aeronautical instruments, and planes, so that the aeroplane is built in such a manner that when the engine stops, and the nose of the machine is turned downwards, the aeroplane of its own accord takes up its gliding angle and glides to earth.
Gliding angles vary in different machines.If the angle is one in twelve, this would mean that if the glide wave commenced at a height of 1 mile, and continued in a straight line, the pilot would come to earth 12 miles distant.We are all familiar with the gradients shown on railways.There we see displayed on short sign-posts such notices as "1 in 50", with the opposite arms of the post pointing upwards and downwards.This, of course, means that the slope of the railway at that particular place is 1 foot in a distance of 50 feet.
One in twelve may be described as the natural gradient which the machine automatically makes when engine power is cut off.It will be evident why it is safer for a pilot to fly, say, at four or five thousand feet high than just over the tree-tops or the chimney-pots of towns.Suppose, for example, the machine has a gliding angle of one in twelve, and that when at an altitude of about a mile the engine should stop.We will assume that at the time of the stoppage the pilot is over a forest where it is quiteimpossible to land.Directly the engine stopped he would change the angle of the elevating plane, so that the aeroplane would naturally fall into its gliding angle.The craft would at once settle itself into a forward and slightly downward glide; and the airman, from his point of vantage, would be able to see the extent of the forest.We will assume that the aeroplane is gliding in a northerly direction, and that the country is almost as unfavourable for landing there as over the forest itself.In fact, we will imagine an extreme case, where the airman is over country quite unsuitable for landing except toward the south; that is, exactly opposite to the direction in which he starts to glide.Fortunately, there is no reason why he should not steer his machine right round in the air, even though the only power is that derived from the force of gravity.His descent would be in an immense slope, extending 10 or 12 miles from the place where the engine stopped working.He would therefore be able to choose a suitable landing-place and reach earth quite safely.
