The woodwork of these aeroplanes is entirely of selected spruce and ash, all the posts, beams, and ribs being laminated. The propeller is a particularly difficult piece of laminated work, being built up of from twelve to eighteen layers of thinly cut wood, while the upright posts of the central section are made up of ash and spruce, the heavier and more flexible wood forming the core. A feature of strength is to be found in the double trussing which is placed in all of the vital parts of the aeroplane, where the greatest strength is required. All this trussing is made with a cable of galvanised steel wire tested to withstand a pulling strain of nearly half a ton.
Transportation and military use have been especially considered in the construction of the planes. The upper and lower planes are made up of interchangeable panels, which are so joined together that the machine is easily assembled and taken apart and may be transported compactly in two flat boxes which scarcely make one full wagon load, as indicated in an illustration in this book.
The wing-panels are made up with a light and strong wooden framework covered with cloth especially made and treated with a rubber coating for the purpose. The curved ribs are laminated also and the panels held together by a system of trussing which gives them great strength. These panels are covered both top and bottom.
Light and strong bamboo rods extend to the front of the main planes, supporting the elevator or forward horizontal surface, which acts as a rudder to steer upward and downward. Similar bamboo rods at the rear support the vertical rudder and rear elevators and stabilising plane. Front and rear elevators work in conjunction with each other so that as the front of the machine is directed up, the rear of the machine is depressed by the two rear elevators, called "flippers" from their resemblance to these appendages of a seal or a turtle, each of which is controlled by an individual set of cables, so that if one should break or get out of order the other may be used independently. The front or rear elevators are sufficient to maintain the fore and aft balance of the machine in flight, so if anything happens to one the other will enable a safe landing to be made. Some aviators take off the front elevating plane entirely, relying solely upon the two rear ones for horizontal control.
The elevators and the vertical rudder are manipulated by a single steering post at the top of which is the steering wheel. Turning the wheel to the right or left steers the aeroplane to the left or to the right as a boat or an automobile is steered, while pushing the wheel forward directs the machine downward and pulling the wheel causes it to rise, a system of control in accord with the natural impulse of the operator.
To maintain the lateral balance of the aeroplane, there are small movable planes, or "ailerons," attached at the ends of the main framework, midway between the upper and lower planes, at the rear. These ailerons are so arranged that the front edge remains in the same position; while one swings upward, the other swings downward, at the back, thus giving an upward pressure of air on the under side of the one, while the other is depressed by the air which strikes it on top. This movement is controlled by a movable back to the aviator's seat or a frame or yoke which fits around the shoulders of the aviator in such a way that he moves the ailerons to the proper position when he leans to the high side of the aeroplane as it tilts and is thus able automatically to correct its balance.
The motors with which the military and cross-country models are equipped are of the eight-cylinder "V-shaped" type, developing sixty and eighty horse-power. The propeller is attached directly to the motor shaft, thus doing away with any necessity of gearing, which consumes power, increases the risk of breakage, and decreases reliability. The speed of the motor is controlled by a throttle opened and closed by a movement of the left foot.
The seat for the aviator is placed well forward of the main planes, giving him a clear view not only ahead, but also straight downward. On the military model, a passenger-seat is provided immediately beside that of the aviator, and a dual system of control makes it possible for either passenger to operate the machine independently of the other.
DIAGRAM OF CURTISS AEROPLANE, SIDE VIEW