The propellers revolved in opposite directions, and in order to gain this effect one chain, as will be seen from the sketch, had to be crossed in its tube. The Wrights preferred the use of two propellers, even though this necessitated gearing such as might have been avoided had a single propeller been coupled directly to the motor. They considered the thrust upon the aeroplane would be smoother with two screws. By using a couple of large propellers also, and running them rather slowly, they reckoned to obtain more efficiency than with a single high-speed screw. In illustration of this it may be mentioned that, whereas the single propellers upon some of the French machines made 1000 or 1500 revolutions a minute, the Wrights’ two screws made only 450 a minute. That their system was extremely efficient they were able to prove beyond question. Many critics condemned as clumsy the use of gearing chains, and pointed out the danger that existed should a chain break—causing one propeller to stop, while the other, by continuing its thrust, tended to throw the machine out of equilibrium. Such a system, indeed, never came into general use, but in fairness to the Wrights it should be said that very few accidents were ever attributed to the breaking of a chain.
Fig. 34.—The Wright Biplane.
A.A.—Main-planes; B. Double front elevator; C. Rudder (two narrow vertical planes); D. Motor; E. Propellers; F. Pilot’s lever; G. Skids upon which machine landed.
It is now possible to describe, as a completed craft, the Wright power-driven plane; [Fig. 34] shows its appearance; and in looking at it one is struck by the fact that, save for one or two modifications, and the fitting of motor and propellers, the machine is practically a glider, such as the Wrights used for soaring tests. Of the changes to be observed, the most interesting concern the elevator and rear-rudder. The former, it will be seen, has a double plane; it is, in fact, a smaller biplane on the principle of the main-planes. Needing to increase the surface of the elevator, the brothers fixed one plane above another so as to make the construction stronger and occupy less space. The rear-rudder, acting like that of a ship, worked upon the system described in [Fig. 14]. With this, as with the elevator, in order to economise space and obtain rigidity, two narrow planes were fitted side by side.
So now the practical aircraft stood complete—each part adapted and perfected; and, having traced its development step by step, we see how the pioneers had helped the Wrights to their conquest. Sustaining planes, propellers, controlling surfaces—all had been foreshadowed, all hinted at and sketched crudely; but what had been lacking was the skill which should put these theories into shape; and this skill, and also this patience, Wilbur and Orville Wright provided to the full.
Having discussed the construction of the machine, the method by which it was controlled when in the air may be described. In [Fig. 35] the operator is seen in the driving seat; and near him will be observed the motor which drives the craft. In his left hand—that is to say in the one nearest us—he grasps the lever which operates the elevating planes. The rod from lever to plane can be seen, and the motions the pilot makes are these: should he wish to rise, he draws the lever towards him and tilts up the elevating planes in the manner already described, increasing the lifting power of the main-planes and so causing the machine to ascend; by a reverse movement of the lever—by pushing it away from him, that is to say—he makes the craft glide downward.
