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Supersonic Boom Speed

By Unknown - February 17, 2018

Before we discuss Supersonic Boom Speed, let's first discuss about Supersonic. Supersonic travel is a rate of travel of the object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 ° C (68 ° F) at sea level, this speed is approximately 343 m / s, 1,125 ft / s, 768 mph, 667 knots, or 1,235 km / h. Speeds greater than five times the speed of sound (Mach 5) are often referred to as hypersonic. Flights in the air of an object, such as the ends of rotor blades, reach supersonic speeds are called transonic. This occurs typically somewhere between Mach 0.8 and Mach 1.23.

Sounds are traveling vibrations in the form of pressure waves in an elastic medium. In gases, sound travels longitudinally at different speeds, mostly depending on the molecular mass and temperature of the gas, and pressure has little effect. Since air temperature and composition varies significantly with altitude, Mach numbers for aircraft may change despite a constant travel speed. In water at room temperature supersonic speed can be considered as any speed greater than 1,440 m / s (4,724 ft / s). In solids, sound waves can be polarized longitudinally or transversely and have even higher velocities.

Supersonic fracture is crack motion faster than the speed of sound in a brittle material.

Supersonic fragments are cracking movements faster than the speed of light in fragile materials. This phenomenon was first discovered by scientists from the Max Planck Institute for Metal Research in Stuttgart (Markus J. Buehler and Huajian Gao) and the IBM Almaden Research Center in San Jose, California (Farid F. Abraham).

In 1942 the British Aviation Minister initiated a highly confidential project with Miles Aircraft to develop the first aircraft to penetrate the sound barrier. The project produced a prototype Miles M.52 aircraft, designed to reach 1000 mph (1600 km / h) at 36,000 feet (11 km) in 1 minute 30 seconds.

The design of the aircraft is very revolutionary introducing many innovations that are still used by supersonic aircraft today. The most important main development is the whole-tailed plane tail that allows control in supersonic speeds. The project was canceled by the Director of Scientific Research, Sir Ben Lockspeiser, before the manned flight. After that, on government orders, all the design and research data on Miles M.52 was sent to Bell Aircraft Corporation in the United States. There was an agreement on the exchange of data by both parties, "allegedly", after receiving the British data, the American government blocked the agreement. Subsequent experiments prove that the Miles M.52 design can penetrate sound barriers, using an unmanned 3/10 scale replica of this plane capable of reaching Mach 1.5 in October 1948.

Chuck Yeager was the first to break through the obstacles in flight on October 14, 1947, flying a Bell X-1 experimental aircraft on Mach 1 with a height of 45,000 feet (13.7 km).

Sonic Boom
A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate significant amounts of sound energy, sounding much like an explosion to the human ear. The crack of a supersonic bullet passing overhead or the crack of a bullwhip are examples of a sonic boom in miniature.

The sound source is travelling at 1.4 times
 the speed of sound (Mach 1.4). 
Since the source is moving faster than the sound waves it creates,
 it leads the advancing wavefront.

Below let us consider the slow motion of a fighter that performs Supersonic Boom Speed :

Contrary to popular belief, a sonic boom does not occur only at the moment an object crosses the speed of sound; and neither is it heard in all directions emanating from the speeding object. Rather the boom is a continuous effect that occurs while the object is traveling at supersonic speeds. But it only affects observers that intersects an imaginary geometrical cone behind the object. As the object moves, this imaginary cone also moves behind it and when the cone passes over the observer, they will briefly experience the boom. [more...]

When an aircraft passes through the air it creates a series of pressure waves in front of it and likes it. These waves travel at the speed of sound and, as the speed of the object increases, the waves are forced together, or compressed, because they can not get out of the way of each other. Eventually they merge into a single shock wave, which travels at the speed of sound, a critical speed known as Mach 1, and is approximately 1,235 km / h (767 mph) at sea level and 20 ° C (68 ° F).

In smooth flight, the shock wave starts at the nose of the aircraft and ends at the tail. Since the different radial directions around the aircraft's direction are equivalent (given the "smooth flight" condition), the shock wave forms a Mach cone, similar to a vapor cone, with the aircraft at its tip.

Perception & Noise
The sound of a sonic boom depends largely on the distance between the observer and the aircraft shape producing the sonic boom. A sonic boom is usually heard as a deep double "boom" as the aircraft is usually some distance away. However, as the aircraft is nearby the sonic boom is a sharper "bang" or "crack". The sound is much like that of mortar bombs, commonly used in firework displays. It is a common misconception that only one boom is generated during the subsonic to supersonic transition; rather, the boom is continuous along the boom carpet for the supersonic flight. As a former Concorde pilot puts it, "You do not actually hear anything on board We know that's what we see on Mach 1. But we do not hear the sonic boom or anything like that. "

In 1964, NASA and the Federal Aviation Administration began the Oklahoma City sonic boom tests, which caused eight sonic booms per day over a period of six months. Valuable data was gathered from the experiment, but 15,000 complaints were generated and ultimately entangled the government in a class action lawsuit, which was lost on appeal in 1969.

Sonic booms were also a nuisance in North Cornwall and North Devon as these areas were underneath the flight path of Concorde. Windows would rattle and in some cases the "torching" (pointing underneath roof slates) would be dislodged with the vibration.

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