In general, the biplane consists of two large sustaining planes, one above the other. Between the planes is the motor which operates a propeller located in the rear of the planes. Projecting behind the planes, and held by a framework of bamboo rods, is a small horizontal plane, called the tail. The rudder which guides the aeroplane to the right or the left is partially bisected by the tail. This rudder is worked by wires which run to a steering wheel located in front of the pilot’s seat. This wheel is similar in size and appearance to the steering wheel of an automobile, and is used in the same way for guiding the aeroplane to the right or left. (See illustration of the Curtiss machine in Chapter V.) In front of the planes, supported on a shorter projecting framework, is the altitude rudder, a pair of planes hinged horizontally, so that their front edges may tip up or down. When they tilt up, the air through which the machine is passing catches on the under sides and lifts them up, thus elevating the front of the whole aeroplane and causing it to glide upward. The opposite action takes place when these altitude planes are tilted downward. This altitude rudder is controlled by a long rod which runs to the steering wheel. By pushing on the wheel the rod is shoved forward and turns the altitude planes upward. Pulling the wheel turns the rudder planes downward. This rod has a backward and forward thrust of over two feet, but the usual movement in ordinary wind currents is rarely more than an inch. In climbing to high levels or swooping down rapidly the extreme play of the rod is about four or five inches. Thus the steering wheel controls both the horizontal and vertical movements of the aeroplane. More than this, it is a feeler to the aviator, warning him of the condition of the air currents, and for this reason must not be grasped too firmly. It is to be held steady, yet loosely enough to transmit any wavering force in the air to the sensitive touch of the pilot, enabling him instinctively to rise or dip as the current compels. [Illustration: _Courtesy N. Y. Times._ View of the centre of the new Wright machine, showing method of operating. Archibald Hoxsey in the pilot’s seat. In his right hand he holds a lever with two handles, one operating the warping of the wing tips, and the other the rudder. Both handles may be grasped at once, operating both rudder and wing tips at the same moment. In his left hand Hoxsey grasps the lever operating the elevating plane--at the rear in this type. The passenger’s seat is shown at the pilot’s right.]