If we need extra sails for stability and ascent or descent, we need them also for changes of horizontal direction. Let _ab_ be the top view of the main plane of a machine, following the course _xy_. At _rs_ is a vertical plane called the _steering rudder_. This is pivoted, and controlled by the operator by means of the wires _t_, _u_. Let the rudder be suddenly shifted to the position _r´s´_. It will then be subjected to a pressure _P´_ which will swing the whole machine into the new position shown by the dotted lines, its course becoming _x´y´_. The steering rudder may of course be double, forming a vertical biplane, as in the Wright machine shown below. [Illustration: ACTION OF THE STEERING RUDDER] Successful steering necessitates lateral resistance to drift, _i.e._, a fulcrum. This is provided, to some extent, by the stays and frame of the machine; and in a much more ample way by the vertical planes of the original Voisin cellular biplane. A recent Wright machine had vertical planes forward probably intended for this purpose. [Illustration: RECENT TYPE OF WRIGHT BIPLANE] It now begins to appear that the aviator has a great many things to look after. There are many more things requiring his attention than have yet been suggested. No one has any business to attempt flying unless he is superlatively cool-headed and has the happy faculty of instinctively doing the right thing in an emergency. Give a chauffeur a high power automobile running at maximum speed on a rough and unfamiliar road, and you have some conception of the position of the operator of an aeroplane. It is perhaps not too much to say that to make the two positions fairly comparable we should _blindfold_ the chauffeur. Broadly speaking, designers may be classed in one of two groups--those who, like the Wrights, believe in training the aviator so as to qualify him to properly handle his complicated machine; and those who aim to simplify the whole question of control so that to acquire the necessary ability will not be impossible for the average man. If aviation is to become a popular sport, the latter ideal must prevail. The machines must be more automatic and the aviator must have time to enjoy the scenery. In France, where amateur aviation is of some importance, progress has already been made in this direction. The universal steering head, for example, which not only revolves like that of an automobile, but is hinged to permit of additional movements, provides for simultaneous control of the steering rudder and the main plane warping, while scarcely demanding the conscious thought of the operator. TURNING CORNERS