TRAVEL IN THE AIR 



311 



began to read the few books dealing with the sub- 

 ject. After long planning and much careful observa- 

 tion of birds, they built a series of gliders which 

 taught them many things about flying. At the close 

 of 1901, although they had made progress, they were 

 discouraged and ready to go back to their bicycle 

 business in Dayton. During the winter, however, their 

 interest revived and they built the first wind tunnel 

 to carry on experiments with model planes and glid- 

 ers. These experiments resulted in another glider 

 which had wings thirty feet long and five feet wide. 

 This proved a marked success and led them to plan 

 a machine which would carry an engine. This plane 

 was ready late in 1903 and was assembled at Kitty 

 Hawk, North Carolina. On December 17, 1903, Or- 



International News Photos 



FIG. 520. FIRST WRIGHT PLANE 



ville Wright made the first airplane flight lasting 

 only twelve seconds and covering a distance of about 

 120 feet. This plane was destroyed a few days later 

 by a strong wind, but other planes were built by the 

 Wright brothers, each improving on the one before. 

 Figure 520 shows the first Wright plane in flight at 

 Kitty Hawk, N.C. 



Why does the airplane stay up? If you have ever 

 held your hand or a piece of cardboard out of the. 

 window of a rapidly moving automobile you know 

 that air can exert a great force against a surface mov- 

 ing through it. By studying the forces which act upon 

 a kite we can clearly understand how the airplane 

 can fly even though it is heavier than air. 



When a kite is flown into the wind the surface of 

 the kite deflects the wind downward as shown in Fig- 

 ure 521. This tends to create a push against the kite 

 surface which with the force exerted on the string 

 offsets the weight of the kite. This keeps the kite in 

 the air. 



Have you ever observed the shape of an airplane 

 wing? One is as shown in Figure 522. As the plane is 

 pulled through the air by the rapidly turning pro- 

 peller the air currents act on the wing as shown in the 

 diagram. The downward curve of the wing tends to 

 deflect the air currents in the same manner as the 

 kite does. This creates a push against the bottom of 

 the wing. The air currents which pass over the top 



FIG. 521. DEFLECTION OF WIND BY A KITE 



of the wing are not able to follow its curve so readily 

 as those which go under the wing. This causes a low 

 pressure or suction above the wing which tends to 

 draw the wing upward. Under these two forces and 

 by the aid of the rear elevators the plane is able 

 to rise from the ground. All parts of the plane are 

 constructed to offer the least resistance to air. This 

 is called streamlining. 



How is the airplane controlled? Controlling the air- 

 plane involves taking off from the field, steering, turn- 

 ing, and landing. Figure 523 shows a view of the con- 



FIG. 522. AIR FLOW ACROSS AN AIRPLANE WING 



trolling devices on an airplane and what each part 

 does. Steering is controlled by the vertical fin and 

 rudder. The plane is moved to the left or right by 

 moving the rudder-bar with the feet and is nosed up 

 or down by the elevators, which are moved from the 

 control stick. The ailerons, one in either wing, are con- 

 trolled from the control stick and prevent sideslip- 

 ping when the plane is bank turning at high speeds. 



