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.