CHAPTER XLVIII. Some Technical Terms used by Aviators
Though this book cannot pretend to go deeply into the technical side of aviation, there are certain terms and expressions in everyday use by aviators that it is well to know and understand.
First, as to the machines themselves. You are now able to distinguish a monoplane from a biplane, and you have been told the difference between a TRACTOR biplane and a PROPELLER biplane. In the former type the screw is in front of the pilot; in the latter it is to the rear of the pilot's seat.
Reference has been previously made to the FUSELAGE, SKIDS, AILERONS, WARPING CONTROLS, ELEVATING PLANES, and RUDDER of the various forms of air-craft. We have also spoken of the GLIDING ANGLE of a machine. Frequently a pilot makes his machine dive at a much steeper gradient than is given by its natural gliding angle. When the fall is about one in six the glide is known as a VOL PLANE; if the descent is made almost vertically it is called a VOL PIQUE.
In some cases a PANCAKE descent is made. This is caused by such a decrease of speed that the aeroplane, though still moving forward, begins to drop downwards. When the pilot finds that this is taking place, he points the nose of his machine at a much steeper angle, and so reaches his normal flying speed, and is able to effect a safe landing. If he were too near the earth he would not be able to make this sharp dive, and the probability is that the aeroplane would come down flat, with the possibility of a damaged chassis. It is considered faulty piloting to make a pancake descent where there is ample landing space; in certain restricted areas, however, it is quite necessary to land in this way.
A far more dangerous occurrence is the SIDE-SLIP. Watch a pilot vol-planing to earth from a great height with his engine shut off. The propeller rotates in an irregular manner, sometimes stopping altogether. When this happens, the skilful pilot forces the nose of his machine down, and so regains his normal flying speed; but if he allowed the propeller to stop and at the same time his forward speed through the air to be considerably diminished, his machine would probably slip sideways through the air and crash to earth. In many cases side-slips have taken place at aerodromes when the pilot has been rounding a pylon with the nose of his machine pointing upwards.
When a machine flies round a corner very quickly the pilot tilts it to one side. Such action as this is known as BANKING. This operation can be witnessed at any aerodrome when speed handicaps are taking place.
Since upside-down flying came into vogue we have heard a great deal about NOSE DIVING. This is a headlong dive towards earth with the nose of the machine pointing vertically downwards. As a rule the pilot makes a sharp nose dive before he loops the loop.
Sometimes an aeroplane enters a tract of air where there seems to be no supporting power for the planes; in short, there appears to be, as it were, a HOLE in the air. Scientifically there is no such thing as a hole in the air, but airmen are more concerned with practice than with theory, and they have, for their own purposes, designated this curious phenomenon an AIR POCKET. In the early days of aviation, when machines were far less stable and pilots more quickly lost control of their craft, the air pocket was greatly dreaded, but nowadays little notice is taken of it.
A violent disturbance in the air is known as a REMOUS. This is somewhat similar to an eddy in a stream, and it has the effect of making the machine fly very unsteadily. Remous are probably caused by electrical disturbances of the atmosphere, which cause the air streams to meet and mingle, breaking up into filaments or banding rills of air. The wind - that is, air in motion - far from being of approximate uniformity, is, under most ordinary conditions, irregular almost beyond conception, and it is with such great irregularities in the force of the air streams that airmen have constantly to contend.