ed of sound is varied at different altitudes due to the density of air, and how much air sound has to displace. At sea level the speed of sound is approximately 761 mph. In the early 1940s the sound barrier seemed almost impossible until the X wing class experimental aircraft had been developed. The speed of sound was unattainable by a conventional propeller; therefore new kinds of thrust had to be developed known as the jet engine. The jet engine carried aircraft into a new age of flight. The first aircraft to reach the speed of sound was the X-1 flown by the famous Chuck Yeager on October 14, 1947. The X-1 was shaped like a bullet because at the time it was believed to be the most aerodynamic design. The X-1 found out several important changes in flight during, before, and after an aircraft reaches the speed of sound. The X-1 found out that when an aircraft reaches the speed of sound it is at a very unstable point of flight, but before or after the speed of sound the flight was more stable. They also found out about shock waves and how they affect flight. In order to understand how high speed affects the compressibility of the air, let us consider an example of wave motion. Suppose we drop pebbles into a pool of water and observe the waves resulting from these disturbances. If we drop all pebbles at the same spot, but placed at equal time intervals, the waves would all spread out from a single point. The outermost wave would be from the first pebble, the next wave from the second, and so on. Now suppose that we drop the pebbles at the same time interval but slowly move to the right as we drop them. Notice that the waves are moving faster than our forward speed. Finally, we proceed at a rate faster than the waves are able to move. Each pebble hits outside of the wave made by the previous pebble. Just as we drop the fourth pebble, the waves pile up at the forefront of our motion and tend to reinforce each other (Smith 1...
