To steer to right or left in the air an aeroplane has a rudder of one or more small vertical planes, also placed in the tail, which acts in the same fashion as the rudder of a boat. To prevent an aeroplane from rolling over sideways—that is, to provide it with lateral stability—has proved a specially difficult task, and a variety of means have been tried. The early French constructors believed in having a number of upright surfaces which should offer resist-ance to the air when the machine tended to roll over. If we look at pictures of the first French biplanes that ever flew—the Santos Dumont and the Voisin (it is not ten years since they were built, but they look as out of date as the pterodactyl) we shall see that the planes were all boxed in and divided into compartments by these 'panels,' as they were called. But the cure proved worse than the disease, for the panels not only offered great resistance to turning, but, with a side wind, they caused the aeroplane to veer from her course and progress crab-wise through the sky. So panels went by the board.
Another method by which they endeavoured to get the same effect was by tilting the planes upwards from the middle so as to form a very shallow V with the body of the machine. This is called the 'dihedral angle,' and by its means an increased side area is afforded. It is used in modified form in many machines of to-day; sometimes the lower plane only is made V-shaped, sometimes the ends of the upper planes are turned slightly upwards. Large panels are no longer employed, but the question of 'side areas' is an all-important one. If there is a big rudder in the tail and no upright surface in the front, the machine may not steer properly, but will tend to spin round in a spiral. The aeroplane constructor has therefore to consider his side areas very carefully, and provide for them by such means as making the front of the body deep and covered-in; or by affixing small fins where they may be most effective. The old American Wright machines, for example, had tiny upright planes known as' blinkers' in the front elevator, and when the elevator was put at the back it was found that the blinkers had still to be retained, and so they were placed on the front of the skids.
Further to assist in its balancing every aeroplane is provided with one of two special means of control —'warping' or 'ailerons,' The Wright Brothers were the first to employ the warping device on their original gliders. They made the rear edges of their planes flexible, and connected them with a lever in such a manner that when the machine tilted down on one side the pilot was able to pull down or 'warp' the edges of the planes on the end that was depressed ; while the same movement twisted or warped upwards the edges of the end that tilted up. In this fashion more wind pressure was brought to bear on the falling end, tending to lift it, while less pressure was exerted on the rising end, causing it to descend, and so the machine was made to keep an even keel. It was in the carrying out of this warping action that the Wright Brothers claimed, and won, their famous patent, the subject of so much discussion and litigation. The fact that the same patent had been employed by the birds since time immemorial has had no legal bearing on the case.
The same effect as that produced by warping the wings may be obtained by providing them with 'ailerons,'—movable flaps fixed at the rear ends of the main planes. These flaps are hinged portions of the planes themselves which can be pulled downwards when needed, offering increased resistance at the end which requires it, and so causing the machine to right itself. The warping system of balancing has been mainly used on the monoplanes, and the ailerons on the biplanes; but latterly the tendency in aeroplane construction has been all in favour of aileron control, for the continual twisting and bending of the materials of the wings in warping is shown to have a bad effect upon them.
In technical slang they tend to become 'tired ' and 'sloppy,' and in some cases permanently distorted. In the future, therefore, it looks as if warping will disappear and the use of ailerons entirely take its place ; while in the perfected machines even now arriving in our midst, possessing ever more stability in the air, both warp and aileron will grow less and less necessary.
The battle-cry of the aeroplane designer of but a short while ago was ' Speed !' Later he altered it to 'Stability!' His aim and object was the production of the 'fool-proof' machine that shall fly itself in the air, not only without its pilot's guidance but actually in defiance of him by correcting his errors. Such a machine will rock to the winds and swing to the aerial waves even as a well-found boat; yet like the boat will never upset but return to an even keel. There are rival methods of achieving this end, some constructors (among them Orville Wright in America) seeking to attain it by 'automatic' and others by ' inherent' stability. The latter speak disrespectfully of the devices of the former ; they call them ' gadget' stabilizers. The word is a trifle obscure, inasmuch as ' gadget' is the sea term for any miscellaneous article which does not appear to have a definite name, or at least one which comes ready at the moment. I asked a famous expert the other day to define a ' gadget stabilizer,' and he did so promptly and forcibly as ' any old thing which you hang on,' Less picturesquely an automatic stabilizer is some means of giving stability, such as a gyroscope or a pendulum, which is put on to a machine, and is not in itself an essential part of its construction.
The inherent stability people maintain that by careful design and construction alone, by theorist and practical man working side by side, by scientific disposal of weights and surfaces, different tendencies may be made to balance and correct each other, one set of oscillations to damp out another, and so the perfect machine be evolved. Further they have proved their point by succeeding. The naturally stable machine is no dream of to-morrow but the realization of to-day; not sprung upon us in a moment by some fresh epoch-making discovery, but now arrived at as the consummation of the labours which began with the earliest pioneers.