Overview of a Sonic Boom

A Sonic boom is an impulsive noise similar to thunder. It is caused by an object moving faster than sound, about 750 miles per hour at sea level. An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to the water waves caused by a ship’s bow. When the aircraft exceeds the speed of sound, these pressure waves combine and form shock waves, which travel forward from the generation or “release” point.
As an aircraft flies at supersonic speeds it is continually generating shock waves, dropping sonic boom along its flight path, similar to someone dropping objects from a moving vehicle. From the perspective of the aircraft, the boom appears to be swept backwards as it travels away from the aircraft. If the plane makes a sharp turn or pulls up, the boom will hit the ground in front of the aircraft.
The sound heard on the ground as a “sonic boom” is the sudden onset and release of pressure after the buildup by the shock wave or “peak overpressure.” The change in pressure caused by sonic boom is only a few pounds per square foot, about the same pressure change we experience on an elevator as it descends two or three floors, in a much shorter time. It is the magnitude of this peak overpressure that describes a sonic boom.
There are two types of booms: N-waves and U-waves. The N-wave is generated from steady flight conditions, and its pressure wave is shaped like the letter “N.” N-waves have a front shock to a positive peak overpressure, which is followed by a linear decrease in the pressure until the rear shock returns to ambient pressure. The U-wave, or focused boom, is generated from maneuvering flights, and its pressure wave is shaped like the letter “U.” U-waves have positive shocks at the front and rear of the boom in which the peak overpressures are increased compared to the N-wave.

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Unusual Sonic Boom heard in Three Countries

An unusual sonic boom which was heard in three countries at the same time prompted a delude of emergency calls. Ministry of Defense says it was caused when jets responding to another aircraft lost communication. According to reports, several windows of homes and buildings were broken.
Aircraft breaking the sound barrier causes a sonic boom and this was identified to be the cause of broken windows in Cambridgeshire on Saturday June 15 2013. According to reports, the incredible noise could be heard in Hertfordshire and Essex, which occurred at around 11.30 am. The ministry of defense confirmed after the event that the damages was caused by a typhoon fighter jet from the RAF Coningsby in Lincolnshire which was responding to a loos of communication from a passenger plane that was on its way to Heathrow airport.
As with all commercial flights, air traffic controllers became worried when they lost communication with a plane travelling from the United States, to the airport and failed in responding to any radio communications. Communication was only re-established late after the jet took off and the plane in question landed safely without incident.
However the take off off the jet caused wide spread panic with reports of windows being smashed. Many people phoned in with reports that objects have hit their roofs as their houses shook. Other people actually thought that their neighbor’s homes were being blown up, that is how loud the noise from the sonic boom was.
Apparently it was the loudest noise anyone has ever heard is the report as many people have never heard the sound of a severe sonic boom before. Many people thought it was a plane crash close by that shook their homes and this phenomenon is something that does not happen very often.

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How a Sonic Boom is created

Explaining how a sonic boom is caused in simple and easy to understand terms, is by looking at wakes left by boats in the water. When you toss a pebble into the water or into a pond, little waves are formed in concentric circles and then propagate away from the point of impact. If a boat for example travels through the water at 3 to 5 miles per hour, little waves will propagate in the same way both behind and ahead of the boat. The boat will travel through the waves.
If the boat travels faster through the water than the waves can propagate, the waves cannot get out of the way of the boat fast enough and this is how a wake is formed. The wake is a larger single wave caus3ed by the boat travelling faster. This wake is formed by the smaller waves initially formed when the boat was travelling slower. These little waves would have propagated in front of the boat but now it cannot because of the speed the boat travels at.
Now, when an airplane travels through the air, it produces sound waves instead of water waves. When an airplane travel at a speed slower than the speed of sound, the sound waves can propagate in front of the airplane. Speed of sound varies but is normally measured at 7oo miles per hour through air.
When a plane travels faster and breaks the sound barrier then the sonic boom is generated. The shock waves are formed which cannot stay ahead of the airplane. The sonic boom is the wake described earlier compared to a boat. The shock waves, which would have propagated in front of the airplane normally, are now combined together. At first, you will not be able to hear anything then you will hear the sonic boom the shock waves create.

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Atmospheric Effect of Sonic Boom Propagation

When the actual temperature variations and wind variations occur in the atmosphere are taken into consideration, the cone pattern of the front shock wave can become significantly distorted. This is way when it is a propagating shock wave descending towards the earth, the different portions of the shock wave travels at different speeds. The wave closest to the ground will move much faster than the rest of the portions of the same shock wave.
When the sound speed also decrease much faster with altitude, the shock wane front can possible become perpendicular to the ground. When this occur it means the shock wave will never reach the ground as it will start travelling parallel to the ground, before it reaches the ground. The physical requirements for this type of effect are very unlikely, regardless of any or extreme and abnormal atmospheric conditions. Inevitably will a sonic boom be created if any object or aircraft move through the earth’s atmosphere at parallel level while travelling faster than the speed of light.
The sound speed’s decrease with altitude will also affect the portion of the front part of the wave spreading out to sides of a plane. Investigations of this effect during conditions where no wind is present showed that the lateral part of the sonic boom measured at ground level will range from approximately ten to thirty-five miles on either side of the ground track left by the plane.
It is also determined that the shock wave’s intensity will significantly diminish as it is spreading out. This will also result on the sonic boom to be less intense on the sides of the flight track created. If the wind is present on the other hand, the front of the shock wave will progress at rates which are the sum of the wind speed and the sound of speed.

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Overview of a Sonic Boom

A sonic boom sound is very similar to very loud thunder and caused by an object like an aircraft that moves faster than the speed of sound at approximately 750 or more miles per hour when at sea level. When an aircraft travel through air it continuously makes air-pressure wave which are more or less the same as the waves caused by a ship going through the waves. When aircrafts exceed speed of sound, pressure wave combine and the shock waves are formed.
When continues shock waves are formed it will drop a sonic boom along the flight path of the aircraft when it flies at supersonic speeds. From the aircraft’s perspective it will appear that the boom is swept backwards. The sound that we hear from the ground is what is called the sonic boom and it is the sudden onset and then pressure released after initial build-up of peak overpressure. The pressure change is a few pounds per square foot only, similar to the pressure change of a lift descending two or three floors. The sonic boom’s pressure just happens in a very shorter time frame and it is this magnitude of overpressure that perfectly describes a sonic boom.
A sonic boom comes in two different types of shock waves, namely, a U-wave and N-wave. U-wave is called a focused boom and generated by manoeuvred flights and the actual pressure wave has a U shape and they have positive shocks in front and back of the boom. The N-wave on the other hand is shaped like the letter N and is generated during steady flights from the aircraft. A N-wave starts with a front shock and peak overpressure is reached after linear decrease in pressure and rear shock turns to ambient pressure.

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History of the Concorde

The concept of developing supersonic aircraft started during the 1950 already, between Soviet union, United States, United Kingdom and France. After careful planning for years between the French Aviation and the British Bristol Aeroplane Company, the Concord entered the supersonic transport service in March 1969 and was introduced a supersonic turbojet-powered passenger airliner in January 1996. After 27 year and only 20 Concord’s built it was retired in November 2003.
A sonic boom of magnitude is inseparable from any supersonic aircraft’s flight and this was also the case in the Concord. Shock waves will start reaching the ground from Mach 1.15 which is about 850 mph and the sonic boom is created. This sound is heard across a width of 50 miles and the intensity of the sound will be highest directly under the aircraft’s flight path and dying away towards the edges.
It is because of the suddenness that a sonic boom has such a startling effect and worse for those who have never heard a sonic boom before. The Concorde’s sonic boom never caused any harm with its overpressure of approximately 161 pounds per square foot, neither to animals, humans or buildings in good state of repair. Researchers have proven that shock waves do not have any negative effect on any marine lives.
With the Concorde being a supersonic aircraft it never caused a sonic boom in vicinities of airports, but only after reaching approximately 100 miles from take-off point it will reach the speed needed to start creating a sonic boom. At the end of the Concorde’s journey it will start deceleration approximately 100 miles from its landing point also in order to eliminate shock waves in vicinity of the airport. Careful flight plans were drawn to place the sonic boom in very sparsely populated areas or over the oceans.

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The Two Types of Sonic Booms and Strengths

Two types of sonic booms are identified by the US Military, namely the U-wave and the N-wave. The U-wave is a focused sonic boom which created by maneuvering flights and the shock waves are shaped like a “U”. It has positive shock waves, both at the front and the tail of a boom during which peak overpressures increases.
The N-wave is created by steady flying conditions, with N-shaped pressure waves. The N-wave has front shock waves to peak over pressure and follows with a decrease in pressure towards the tail end to return to ambient pressure.
The peak overpressure in an N-wave can vary from under one pound to over ten pounds per square foot, during normal operating conditions. A U-wave’s peak overpressures is double and sometimes up to five times the amount, with the amplified overpressure impacting a small area when you compare it to the exposed area left by the sonic boom.
Realistic flight conditions recently recorded a sonic boom of twenty one pounds per square footage. If a building is in good condition it may still be damaged if flight altitude is low. Buildings in worse condition will suffer some serious damage from a sonic boom of that magnitude. Good buildings can even sustain damage from sonic booms with sixteen pound shock wave overpressure and generally less than sixteen pounds are acceptable to cause little or no damage.
Researchers tested the ultimate strength of sonic boom and without sustaining any injury they measured a massive boom of one hundred and forty –four pounds per square foot. An F-4 aircraft was used during this experiment, travelling at low altitude of hundred feet with speed just higher than the speed of light. Ground motion from sonic boom is generally below two pounds and the U.S. Bureau of Mines finds that well within the accepted structural damage threshold.

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Sonic Boom Overview

The sound associated with shock waves caused by objects travelling faster than speed of sound is called a sonic boom. The amount of sound energy generated is so enormous that it can in fact sound like a massive explosion.
Pressure waves are created when an object travels fast through air, both in front and behind and capable of speed of sound travelling normally. Now when an object travels faster than the speed of light, the pressure waves interlock and compress and causes the shock waves.
The speed of an airplane travelling at speed of light causes a shock wave at the nose and ending at the tail end, causing a Mach cone, which will go pointier the faster the airplane goes. An N-wave is formed after the pressure decreases from the nose to the tail and the sonic boom happens then by the changing in pressure. A supersonic aircraft causes a clearly distinctive double boom as an N-wave causes two booms.
A supersonic aircraft will therefore have a continuous sonic boom and the width depends on an aircraft’s altitude. The shape and size of an aircraft and the power it exudes with acceleration will determine the power of the shock wave generated. High altitudes and speeds a sonic boom will not be audible and the sound depends on distance. Pilots however are not aware of the amazing sonic boom created by the aircraft as it is behind them.
A sonic boom from a low flying aircraft can actually cause disruptions such as rattling windows and incredible noise, which can only be a problem when living in an area of continuous overhead aircraft noise. The altitude of the aircraft will determine how fast a person can hear the sonic boom, but approximately 2 seconds after flyover the sound is audible. Even the atmosphere has an effect on sonic boom sound as winds, temperature, atmospheric pollution and humidity causes sound to vary.

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Futuristic biplane design eliminates sonic boom

A throwback to early 20th Century aviation may hold the key to eliminating the sonic boom – at least according to researchers at MIT and Stanford University. Strongly reminiscent of biplanes still in use today, the researcher’s concept supersonic aircraft introduces a second wing which it is claimed cancels the shockwaves generated by objects near or beyond the sound barrier.

In fact the idea is not a new one. The idea of a biplane to negate the sonic boom was proposed in the 1930s by aviation pioneer Adolf Busemann, also responsible for the idea of swept-wing aircraft.

Read more

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You can learn a lot about sonic booms by looking at the wakes boats leave in the water.

If you toss a pebble in a pond, little waves will form in concentric circles and propagate away from the point of impact. If a boat travels through the pond at 3 to 5 miles per hour, little waves will propagate in the same way both ahead of and behind the boat, and the boat will travel through them.

If a boat travels faster than the waves can propagate through water, then the waves “can’t get out of the way” of the boat fast enough, and they form a wake. A wake is a larger single wave. It is formed out of all the little waves that would have propagated ahead of the boat but could not.

Read more

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