Transportation in the Air 399 



Tilting to one side or the other may be controlled by several 

 methods. It may be partly met by the instinctive leaning of 

 the pilot to the side opposite the tilt ; but his weight is not 

 sufficient to balance the machine. The back of his seat is 

 often made movable, and to its top are attached wires connect- 

 ing with the rear tips of the planes. If the machine tips toward 

 the right, the aviator leans instinctively and automatically to 

 the left. This movement pulls the rear edge of the right planes 

 down so that they meet with more air resistance. The extra 

 lifting force thus secured under the right plane restores the 

 balance of the machine. Of course if the pilot wishes to turn 

 to the right, he leans a little in that direction just as a bicycle 

 rider does in turning a curve. 



Some machines are equipped with automatic stabilizers of 

 different sorts. These utilize the gyroscope, the pendulum, 

 or an apparatus controlled by the pendulum. Other machines 

 are designed and built in such a way as to secure what is known 

 as inherent stability, or " autostability." This is secured in some 

 measure by the arrangement of the central surfaces of the 

 machine, a deep vertical keel, and a low center of gravity. 



It is interesting to note that Professor Langley, the pioneer 

 in America in planning and constructing flying machines, 

 thought out carefully and described in his notes substantially 

 every method or system, which has since been tried, to secure 

 stability. He worked out the principles of the proportions of 

 parts of a machine, suggested and tried apparatus for control, 

 and succeeded in laying the foundation for the attainment of 

 inherent stability, although this has only lately been recognized. 



185. The motor. The engine by which motive power is 

 generated for the airplane has from the beginning been of utmost 

 importance. A satisfactory engine must combine dependability 

 and great power with speed and the least possible weight. A 

 steam engine on one of the modern transatlantic liners will 

 weigh, including the boilers, about 100 pounds for each horse 

 power produced. A gasoline engine such as is generally used 



