How many kilometers is Mach 1 equal to? Why do aircraft use Mach to describe speed and how fast it is

Tech 2023-11-10 10:04:52 Source: Network

One day, the animal kingdom held an all-around race, where in addition to rabbits and turtles, there were also animals of vastly different sizes, such as ants and elephants. At first, the competition went smoothly, but when everyone discussed which unit to use to display the speed of the animals, serious disagreements arose

One day, the animal kingdom held an all-around race, where in addition to rabbits and turtles, there were also animals of vastly different sizes, such as ants and elephants. At first, the competition went smoothly, but when everyone discussed which unit to use to display the speed of the animals, serious disagreements arose.

Because when the ants were panting and crawling rapidly, the elephant lifted its long legs and ran a few steps away, not to mention fish and shrimp swimming in the water, birds and bees flying in the air. There are differences in body shape, speed, and even environmental media, so it is understandable that it is difficult to unify units.

Seeing that animals were helpless, everyone turned to higher animals and humans for help. Humans say that they are actually worrying about how to measure different movement speeds every day, but fortunately, clever humans have invented conversion modes between different units.

(A plane breaking through the sound barrier)

For example, walking is calculated in meters; Vehicles, ships, civil aviation, and passenger planes are calculated in kilometers; Higher speed supersonic aircraft, such as supersonic fighter jets, rockets, missiles, etc., are calculated using Mach. In this way, the movement speed of different objects can be clearly displayed, and various measurement units can be accurately used for conversion.

After listening to the introduction of humans, the animals all sighed: the reason why this upright walking monkey can rule the earth is that there is real thing in its mind.

The next thing to talk about is the measurement unit of supersonic aircraft - Mach.

Why use Mach instead of kilometers for the speed unit of supersonic flight?

The term 'Mach' is both familiar and unfamiliar to most people. Familiarity is because it is often seen from various types of information that it is used to refer to the speed of a certain high-speed aircraft. Due to the fact that most people know very little about it, the speed at which it refers is often half understood.

(Concorde aircraft capable of supersonic flight)

From the perspective of habitual thinking, the speed of a certain object's movement can be accumulated. For example, the speed of an ordinary train is 120 kilometers per hour, the speed of a high-speed train can reach 300 to 600 kilometers per hour, and the speed of an airplane exceeds 800 kilometers per hour. Move faster by adding numbers before the original 'kilometer' unit. However, there is an upper limit to the increase in numbers, which is the propagation speed of sound.

Sound speed, also known as sound speed, can be summarized as the transmission rate of sound waves in environmental media. The speed of sound varies depending on the environmental medium. The daily term "sound speed" refers to the speed at which sound travels in an air medium, which is approximately 343.2 meters per second, or 1236 kilometers per hour.

It seems that the value of this unit can be fixed, but in reality, even in the air, the value of sound speed can change due to differences in height, density, humidity, and temperature.

(Sound explosion generated by aircraft at Mach 2.92)

For example, the speed of sound at an altitude of 10000 meters is approximately 295 meters per second, but if it is lowered to sea level, its speed becomes 331.5 meters per second; In addition to differences in height, for every degree Celsius increase in temperature in the air, the speed of sound also increases at a rate of approximately 0.6 meters per second.

At present, in human society, the only object that can move beyond the speed of sound is an aircraft. If measured in conventional speed units, it is not impossible, but on the one hand, such values will be large, and on the other hand, they cannot accurately express the specific situation of the environmental medium in which the aircraft is located. So in the field of professional expression, the unit Mach emerged.

Because the speed of sound propagation in the air changes with the environment, and Mach represents only a relative unit, the specific speed of "one Mach" is not fixed.

(Shock waves generated by supersonic flight are also known as shock waves)

In addition, once the aircraft flies in a supersonic attitude, the control performance and stability of the aircraft itself can change at any time, and the measured Mach number is precisely the precise expression that appears to respond to this change.

Therefore, strictly speaking, Mach can be converted into conventional speed units (one Mach is approximately 1225 kilometers per hour), but in the eyes of professionals, it is not just used to express speed.

Some people may still be puzzled. Isn't it just beyond the speed of sound? Why do we have to make the expression so complicated? This brings us to the question of whether it is difficult or not to exceed the speed of sound.

What is supersonic flight that exceeds?

A plane flies at a speed of 800 kilometers per hour, and when it flies behind, the sound generated by the engine rotation and the friction of the airflow will run to the front.

Once the aircraft flies at speeds exceeding the speed of sound, the body itself must catch up with the sound it had previously made. In the process of constantly catching up with the sound and producing new sounds, shock waves will be generated due to the intense friction with the air.

Shock waves, also known as shock waves or shock waves, form a transverse plane in the air that runs in front of the aircraft, and the resulting resistance is called a sound barrier. Simply put, supersonic flight itself also generates drag, and this drag is accompanied by an increase in speed.

To use an inappropriate metaphor, it's like alternately stepping on one's own feet and going to heaven. In reality, it is difficult for people to break through gravity and not go up, but in theory, as long as the speed of your feet alternating exceeds gravity, you can go up into the sky. Supersonic flight also requires breaking through the sound barrier generated by the body itself.

In the early 20th century, due to humans' limited understanding of aerodynamics, aircraft attempting supersonic flight either disintegrated due to drag and friction caused by sound barriers or crashed out of control.

It was not until the morning of October 14, 1947, that the United States successfully conducted supersonic flight tests. The X-1 plane piloted by pilot Yeger reached 1066 kilometers per hour, making him the first person to break through the sound barrier. From then on, humans mastered supersonic flight technology.

(During the flight test of the first supersonic aircraft X-1)

So, in supersonic flight, the first thing to surpass is the sound barrier. I just don't know if anyone on the ground heard any terrifying noise during the first test flight.

How powerful is the sonic boom?

In recent years, people have often discussed online that a thunderous explosion suddenly sounded in a clear sky. In the past, people didn't know what that was, but now everyone has heard of the word 'sonic boom'.

Sound boom and sound barrier are inseparable. Simply put, once the speed of the aircraft exceeds the critical point of sound barrier, the shock wave will produce a sound like an explosion, which is called a sound boom. This deafening sound can easily break glass and even cause cracks in buildings.

(X-1 aircraft disengages from the motherplane before test flight)

Because of the enormous power of the sonic boom, at least in terms of sound, countries with modern advanced fighter jets often use the airplane's sonic boom to intimidate their opponents. This is something that the Israeli military has excelled in using.

Palestinians living in the Gaza Strip often complain that their window glass is constantly broken, and sometimes their houses are cracked due to the loud thunder. This sound is precisely produced by Israeli Air Force fighter jets flying at low altitude supersonic speeds.

Due to the loud and destructive sound, some countries' counter-terrorism departments even want to try to use sound booms to deter terrorists. Alternatively, in the operation of rescuing hostages, sonic booms can be used to shatter the glass of their location, facilitating ground troops' operations.

(F-18 sonic boom moment, it is said that it took photographers 5 years to capture)

In addition to its lethality, under specific environmental conditions, sonic booms can also generate some visual feast, the most common being sonic boom clouds. Because the pressure of the shock wave causes a decrease in temperature, rapidly condensing water vapor will gather at the rear of the aircraft, forming a huge halo at the moment of the sonic boom.

In reality, what has been troubling the sonic boom for many years is the development of supersonic aircraft in the field of civil aviation.

Without eliminating the sonic boom, it is difficult for civil aviation to achieve supersonic flight

In fact, in the 20th century, Britain, France, and the Soviet Union, which were the first to resist the problem of sonic booms, developed and operated supersonic civil aircraft.

In the 1960s, Britain and France jointly developed the Concorde aircraft, while the Soviet Union developed the Tu-144 aircraft. Afterwards, the commercial operation of Soviet aircraft continued until 1978, while Concorde aircraft continued to operate until 2003. After the retirement of two aircraft, there are no more supersonic aircraft in the world.

(Figure 144 and Concorde)

The reason why countries no longer launch supersonic airliners is precisely because there is no technology to eliminate sonic booms. The huge noise during the takeoff and landing process of the aircraft can seriously disturb the residents around the airport. Moreover, supersonic flight inherently requires greater power, and fuel consumption and high costs have become a pain for many airlines, especially in line with the current concept of low-carbon and environmental protection.

Despite many difficulties, countries have not given up on technological breakthroughs for many years. In 2018, Lockheed Martin was developing a low-frequency explosive aircraft, which is said to produce a sound similar to closing a car door at a flight speed of 1.42 Mach.

(NASA Bass Burst Jet Design Drawing)

United Airlines, on the other hand, announced in a high-profile manner in 2021 that the company will resume high-speed air passenger services by 2029 at the latest. Once the supersonic airliner resumes operation, it is said that flying from Europe to North America will only take three and a half hours.

At that time, a large number of wealthy individuals will try to order small supersonic private jets. Rich people need speed, and airlines can also find new profit points. In terms of the current flight technology possessed by humans, the development of supersonic aircraft is the optimal solution.

(Boeing envisions a future airliner that can reach five times the speed of sound)

Conclusion: Can light speed flight be achieved?

Of course, for many years, humans have also been imagining flying at the speed of light or beyond, but many methods and theories have been proposed, and none of them have yet been implemented.

In 2019, NASA researcher David Burns published a new theory that uses near light speed particles to accelerate a relativistic spiral engine, which can then allow spacecraft to operate close to the speed of light. Although the theory sounds good, many scientists currently do not have the support of physical theorems.

In addition to this theory, Hawking proposed the principle of laser propulsion a year before his death, while Russian scientists are studying the use of sunlight to achieve speed increase.

Some researchers have also attempted to use nuclear powered rockets to complete interstellar navigation. In 2019, it was reported that a private company founded by a former astronaut in the United States was developing nuclear powered rockets. It is said that the rocket can fly to Mars in a month.

At present, both in theory and practice, there have been no achievements in achieving light speed flight. However, since humans can overcome the obstacle of sound speed, the speed of light can also be overcome. But the path of scientific research is long and arduous.

References:

Incredible Moments: How Supersonic Aircraft Achieve "Sound Bomb", People's Liberation Army Daily, May 28, 2016
How Warplanes Break Through the "Sound Barrier", People's Liberation Army Daily, April 17, 2020
The Moment of Fighter Breaking through the Sound Barrier: Blooming Strange Beauty "Science Popularization China August 29, 2017
The "Sound Explosion" Does Not Solve the Difficulty of Civil Aviation in Realizing Supersonic Flight "BBC, July 24, 2018

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