Surely many have heard about the mysterious sound barrier that fighters and bombers overcome, as well as supersonic missiles. What is this barrier, can it be seen visually and what is the cause of the loud explosive sound?
What is a sound barrier?
Sound barrier in the field of aerodynamics - these are technical difficulties that arise as a result of phenomena associated with the movement of an aircraft at a speed equal to or greater than the speed of sound.
You need to understand that this is not a real obstacle that an airplane must overcome, like some kind of invisible wall, but rather an abstract concept. It arose at a time when aviation only thought about aircraft that can travel at high speed - supersonic. Many even insisted on the unattainability of such results.
What is the speed of sound?
The speed of sound is the speed with which elastic waves propagate in a particular medium. This indicator varies depending on the environment. For instance, the speed of sound in air - 331 m / s or 1191.6 km / h.
Overcoming the speed of sound
How is the sound barrier overcome? The plane takes off and gradually accelerates more and more. A supersonic air stream flows around it, as a result of which a bow is formed in the nose shock wave. There may be several, depending on the shape of the aircraft.
In this area, the pressure and density of the air rises sharply. At a time when the plane exceeds the speed of sound, it passes through this area and a loud pop sound appears, which looks like a shot. The pilot in the cockpit does not hear any sounds - he learns about overcoming the sound barrier only by special sensors. Changes in aircraft management are also noticeable.
A loud explosive pop is a sonic boom. It can be heard standing on the surface of the earth when the plane is flying at supersonic speeds nearby. The shock waves that it forms can be visually represented in the form of a cone accompanying the aircraft. The top of the cone is located in the bow. Waves propagate from it over long distances.
The rumor of a person standing on the ground picks up the boundaries of a given imaginary cone. A sharp jump in pressure is perceived as explosive cotton. From the moment of overcoming the barrier, an acoustic shock constantly accompanies the aircraft. However, cotton will be heard every time it flies over a fixed point on the surface.
Since the plane moves faster than sound, first the observer will hear a pop and only after that the engine noise.
Interesting fact: the overcoming of the sound barrier is often associated with the appearance of a white cloud in the tail section of the aircraft. However, it has nothing to do with the sound barrier. We are talking about the Prandtl-Glauert effect - moisture condensation immediately behind a moving airplane.
Supersonic Flight Issues
No matter how normal a plane accelerates, it will not be able to fly at supersonic speed for a long time. Subsonic aircraft are smoother and more rounded. And when flying at supersonic speeds, other aerodynamic conditions arise.
The air resistance sharply increases, the aircraft body heats up due to friction. As a result, an ordinary aircraft will lose stable control and may begin to collapse right in the air.
Actively developed supersonic aviation began in the 50-60s. The first supersonic aircraft to be mass-produced was the North American F-100 Super Saber fighter. This model first flew in 1953.
Created and passenger supersonic aircraft, which performed regular flights. But there were only 2 of them: the Soviet Tu-144 and the English-French Concorde.
The advantage of such aircraft is to overcome long distances in a short period of time. Also, a supersonic aircraft moves at a higher altitude than conventional ones. Accordingly, the airspace is not loaded. But their use was soon abandoned due to several shortcomings:
- shock wave;
- high fuel consumption;
- complexity of operation;
- noise over the airfield.
A loud bang is a sharp jump in pressure in front of the plane, which occurs when the plane begins to move at supersonic speed (it overcomes the sound barrier). The shock wave in front of the aircraft propagates cone-shaped. A person observing an airplane’s flight hears a pop when this wave reaches him, and only after that can the engine work. The shock wave constantly accompanies the plane at supersonic speed.However, pops will be heard only during the passage of the aircraft at a certain point - close to the observer.
