What is a sound barrier. Breaking the sound barrier. Who was the first to break the sound barrier? Sound barrier speed
The first pilot to break the sound barrier was Charles Yeager, who flew a Bell X-1 in the fall of 1947. In the Soviet Union, this feat was repeated by pilots Fedorov and Sokolovsky, who piloted an LA-176 fighter at an altitude of more than 15 thousand meters. The supersonic speed of the vessel was 1104 km / h, at which it could cover about a thousand kilometers without refueling. Mach number is the ratio of the speed of sound to the speed at which the aircraft is traveling. Named after the famous Austrian physicist Ernst Maievsky, who studied the causes of shock waves and aerodynamic processes during the supersonic movement of bodies.
What is a sound barrier?
The sound barrier in aerodynamics refers to a number of phenomena that accompany the movement of an aircraft at the speed of sound (340 m / s) or higher. A sonic boom occurs due to pressure surges and is accompanied by a “bang”, which is perceived by the observer as the sound of an explosion. As a result of the wave crisis, the nature of the airplane flow changes, vibrations appear, lift and the frontal resistance is growing.
The need to overcome the sound barrier arose during the Second World War, when many pilots noticed that an increase in the speed of a fighter worsened its controllability and a number of other important characteristics, such as adjusting ailerons and air rudders. Pilots of piston-type aircraft, attempting to reach maximum speeds, inevitably faced a wave crisis, from which it was not possible to get out without a dive.
A significant role in the problem of explaining and overcoming the sound barrier was played by scientific work dedicated to the study of supersonic gas motion.
While the plane is moving at a low speed (up to 420 km / h) at an altitude of up to 3 thousand meters, it is quite simple to calculate the exact flight parameters. However, in the case of overcoming the sound barrier by an aircraft, not only the temperature overboard drops, but also the density of the air environment. When the instruments show equivalent speed readings at an altitude of 2,000 meters and 10,000 meters, the actual speed will be greater in thin air.
The value of the supersonic flight speed
At the speed of sound, the airspace ceases to be homogeneous and greatly impedes the movement of low-speed aircraft. An environment is created in which shock waves and changes in the nature of the flow around the aircraft appear, which creates the prerequisites for a wave crisis. A shock wave increases the entropy of the gas, which decreases as the sound barrier passes.
Features of supersonic flight
The transition to supersonic speed is accompanied by a shock wave arising from the pressure difference. If it lasts more than a second, the fuselage of the vessel may not withstand such loads, which will lead to its wreck. If you look at the airplane overcoming the sound barrier in the video, you will notice that almost all the glass of residential buildings located on the earth's surface are destroyed by the shock wave.
After the American pilot Charles Yeager managed to overcome the sound barrier for the first time, he was struck by the "divine silence" that reigned in the cockpit. At the moment when the arrow of the makhmeter manages to pass the mark 1.0, the sound pressure inside the vessel decreases noticeably. However, the risk of deformation of the fuselage and other parts of the aircraft increases.
The energy indicators (intensity) of the shock are influenced by environmental conditions, design features the aircraft and the speed of its movement. The pilots of the Concorde and TU-144 hypersonic passenger airliners were allowed to overcome the sound barrier exclusively over the ocean surface in an air space several thousand meters higher than the height of movement of standard civil aircraft.
Have you ever heard the pop from an airplane crossing a supersonic barrier?
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What happens to the plane when it crosses the sound barrier?
What happens to an aircraft when it reaches the speed of sound? The formation of shock waves begins, which appear in the tail of the aircraft, in the rear and front edges, as well as on the tip of the fuselage. The shock wave has a very small thickness, and the shock front is characterized by dramatic changes in the flow properties. Its speed indicators decrease in relation to the body, and the speed acquires subsonic properties. Kinetic energy is partially converted into gas (internal) energy.
The clap of a supersonic aircraft is a “sonic boom” that occurs due to surges in air pressure. The clap appears as a result of the passage of the main wave and is perceived by the listener every time the plane flies over his head.
The scale of such changes is directly proportional to the speed of the hypersonic flow. The Mach number in this case exceeds 5, and the temperature readings increase significantly, which causes a number of problems for aircraft moving at supersonic speeds. Damage to the thermal shields triggered the crash of NASA's reusable space shuttle Columbia in 2003. The shuttle entered the Earth's atmosphere to land and was damaged by a high force shock wave.
Russian supersonic passenger aircraft
The first passenger plane to break the sound barrier was the Tu-144, created by engineers from the Tupolev design bureau. To overcome the sound barrier, the liner was made in the form of a tailless low-wing aircraft, equipped with additional power plants... The TU-144 was deprived of the flaps and slats customary for aircraft of the previous generation, and the transition to the hypersonic mode was carried out thanks to a complex procedure for redistributing fuel to the rear centering tanks.
Valkyrie supersonic high-altitude bomber
The Valkyrie XB-70 high-altitude bomber, which develops a speed of over three Machs (3673 km / h) and rises to an altitude of over 20 thousand meters, easily overcomes the sound barrier. To travel at hypersonic speed, the designers were forced to reduce the take-off weight, and also to transfer the aircraft to a pentaboran (borohydrogen fuel mixture) with increased combustion energy. The bomber is a tailless bomber made of high-strength tool steel.
Why is it accompanied by an explosive bang when the plane crosses the sound barrier? And what is a "sound barrier"?
There is a misunderstanding with “clap”, caused by a misunderstanding of the term “sound barrier”. This "clap" is correctly called "sonic boom". An airplane moving at supersonic speed creates shock waves in the surrounding air, jumps in air pressure. Simplified, these waves can be imagined in the form of a cone accompanying the flight of the aircraft, with the top, as it were, tied to the nose of the fuselage, and generatrices directed against the movement of the aircraft and propagating quite far, for example, to the surface of the earth.
When the boundary of this imaginary cone, denoting the front of the main sound wave, reaches the human ear, then a sharp jump in pressure is perceived by ear as a clap. A sonic boom, like a tethered one, accompanies the entire flight of the aircraft, provided that the aircraft is moving fast enough, albeit at a constant speed. A clap, on the other hand, seems to be the passage of the main wave of a sound boom over a fixed point on the earth's surface, where, for example, the listener is.
In other words, if a supersonic plane with a constant, but supersonic speed began to fly back and forth over the listener, the pop would be heard every time, some time after the plane had flown over the listener at a fairly close distance.
A "sound barrier" in aerodynamics is a sharp jump in air resistance that occurs when the aircraft reaches a certain boundary speed close to the speed of sound. When this speed is reached, the nature of the air flow around the aircraft changes dramatically, which at one time made it very difficult to achieve supersonic speeds. An ordinary, subsonic plane is not able to steadily fly faster than sound, no matter how it is accelerated - it will simply lose control and fall apart.
To overcome the sound barrier, scientists had to develop a wing with a special aerodynamic profile and come up with other tricks. It is interesting that the pilot of a modern supersonic aircraft feels well the "overcoming" of the sound barrier by his aircraft: when switching to supersonic flow, an "aerodynamic impact" and characteristic "jumps" in controllability are felt. But these processes are not directly related to the “pops” on the ground.
Before the plane breaks the sound barrier, an unusual cloud may form, the origin of which is still not clear. According to the most popular hypothesis, a pressure drop occurs near the plane and a so-called Prandtl-Glauert singularity followed by condensation of water droplets from humid air. Actually, you see the condensation in the pictures below ...
Click on the picture to enlarge it.
A sound barrier is a phenomenon that occurs during the flight of an airplane or rocket at the moment of transition from subsonic to supersonic flight speed in the atmosphere. When the speed of the aircraft approaches the speed of sound (1200 km / h) in the air, a thin area appears in front of it, in which there is a sharp increase in the pressure and density of the air environment. This compaction of the air in front of an airplane in flight is called a shock wave. On the ground, the passage of a shock wave is perceived as a pop, similar to the sound of a shot. Having exceeded the speed of sound, the plane passes through this area of increased air density, as if piercing it - it overcomes the sound barrier. For a long time, overcoming the sound barrier seemed to be a serious problem in the development of aviation. To solve it, it was necessary to change the profile and shape of the aircraft wing (it became thinner and swept), to make the front part of the fuselage more pointed and to supply the aircraft with jet engines. For the first time, the speed of sound was exceeded in 1947 by C. Yeager on a Bell X-1 (USA) liquid-propellant rocket engine launched from a Boeing B-29 aircraft. In Russia, the first to overcome the sound barrier in 1948 was the pilot O. V. Sokolovsky on an experimental La-176 aircraft with a turbojet engine.
Video.
Sound speed.
The speed of propagation (relative to the medium) of small pressure perturbations. In a perfect gas (for example, in air at moderate temperatures and pressures) C. h. does not depend on the nature of the propagating small perturbation and is the same both for monochromatic oscillations of different frequencies () and for weak shock waves. In a perfect gas at the point in space under consideration, C. z. but depends only on the composition of the gas and its absolute temperature T:
a = (dp / d (()) 1/2 = ((() p / (()) 1/2 = ((() RT / (()) 1/2,
where dp / d (() is the derivative of pressure with respect to density for the isentropic process, (-) is the adiabatic exponent, R is the universal gas constant, (-) is the molecular weight (in air a 20.1T1 / 2 m / s. at 0 (°) C a = 332 m / s).
In a gas with physicochemical transformations, for example, in a dissociating gas, C. z. will depend on how - in equilibrium or non-equilibrium - these processes proceed in the wave of disturbance. At thermodynamic equilibrium S. z. depends only on the composition of the gas, its temperature and pressure. With a non-equilibrium course of physical and chemical processes, dispersion of sound takes place, that is, S. z. depends not only on the state of the medium, but also on the vibration frequency (). High-frequency oscillations ((tm), ()) - relaxation time) propagate from the frozen S. z. aj, low-frequency ((,) 0) - with equilibrium S. z. ae, and aj> ae. The difference between aj and ai is usually small (in air at T = 6000 (°) C and p = 105 Pa, it is about 15%). In S.'s liquids z. much higher than in gas (in water a 1500 m / s)
