BackgroundĪircraft went through a period of rapid development and commercialization after World War I, with the development of airmail and regular passenger flights. Commercial use of high-speed aircraft has been limited primarily to the Concorde, but plans exist for hypersonic flight (Mach 5 or higher). Not only did he prove that the " sound barrier" could be broken, but he set in motion development that has led to the high-speed fighters that are critical to military defense. Thus, it literally appears as if the F-18 is pushing through the sound barrier at the instant the photo was taken.In 1947, Chuck Yeager (1923- ) became the first person to fly faster than the speed of sound. Ensign Gay snapped his photo at the moment he heard the boom, just before the cloud vanished. Then, just as the aircraft bursts through the sound barrier, the air is locally disturbed by the resulting shock wave and the condensation/vapor cloud disappears. As the aircraft continues to speed up, the vapor cloud will appear farther toward the rear of the aircraft. As the jet produces these pressure waves and propagates ahead of them, the regions of lower pressure are usually strongest behind the nose of the jet, on the wings and body. The lowered pressure condenses the water in the air, creating a vapor cloud. Because aircraft wings generate both low-pressure regions (because of lift) and amplified low-pressure disturbances, large low-pressure regions exist near the aircraft, especially under sonic flight conditions. He snapped a photo of an F/A-18 Hornet on a humid day from the weather deck of the USS Constellation in the Pacific Ocean ( see image). Navy Ensign John Gay captured one of the best images ever taken of a sonic boom (the breaking of the sound barrier) in 1999. The intensity of the boom is greatest directly below the flight path and decreases on either side of it. The region in which someone can hear the boom is called the boom carpet. ![]() When the object has passed over the observer, the pressure disturbance waves (Mach waves) radiate toward the ground, causing a sonic boom. ![]() These time periods are often referred to as the zone of silence and the zone of action. Only after the object has passed will the observer be able to hear the sound waves emitted from the object. The change in pressure as the object outruns all the pressure and sound waves in front of it is heard on the ground as an explosion, or sonic boom.Īt supersonic speeds (those greater than the local sound speed), there is no sound heard as an object approaches an observer because the object is traveling faster than the sound it produces. If the object has sufficient acceleration, it can burst through this barrier of sound waves and move ahead of the radiated sound. As the speed of the object increases to the sonic velocity (the local velocity of sound waves), these sound waves begin to pile up in front of the object. As the local temperature decreases, the sound speed also decreases, so for a plane flying at 35,000 feetwhere the ambient temperature is 54 Cthe local speed of sound is 295 meters per second (660 miles per hour).īecause the propagation speed of sound waves is finite, sources of sound that are moving can begin to catch up with the sound waves they emit. ![]() At sea level and standard atmospheric conditions of 22 degrees Celsius, sound waves travel at 345 meters per second (770 miles per hour). Anyone who has heard an echo (sound waves reflecting off a distant surface) or been far enough away from an event to see it first and then hear it is familiar with the relatively slow propagation of sound waves. AN F/A -18 HORNET BREAKS THE SOUND BARRIER in the skies over the Pacific Ocean.Īny discussion of what happens when an object breaks the sound barrier must begin with the physical description of sound as a wave with a finite propagation speed.
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