In a straight horizontal flight, the angle of attack of the aircraft increases with increasing speed, adding to the aircraft the lifting force that the wing creates. However, inductive resistance is also growing. The angle of attack of the aircraft is indicated by the Greek letter "alpha" and means the angle that is located between the chord of the wing and the direction of air flow.
Wing and stream
As long as there is aviation in the world, so much does one of the most frequent and terrible dangers threaten aircraft — dumping in a tailspin, because the angle of attack of the aircraft becomes above a critical value. Then the smoothness of the flow of air around the wing is violated, and the lifting force decreases sharply. Disruption usually occurs on the same wing, as flow is almost never symmetrical. It is on this wing that the plane falls off, and it is good if the stall does not go into a tailspin.
Why such situations occur when the angle of attack of an aircraft increases to its critical value? Either speed was lost, or maneuvering overloaded the aircraft too much. Still, this can happen if the height is too high and is close to the "ceiling" of opportunities. Most often, the latter occurs when going overhead from thunderstorm clouds. The high-pressure head at high altitudes is small, the ship becomes more and more unstable, and the critical angle of attack of the aircraft can increase spontaneously.
Military and civil aviation
The situation described above is very familiar to pilots of maneuverable aircraft, especially fighters, who have theoretical knowledge and sufficient experience to get out of any situation of this kind. But the essence of this phenomenon is purely physical, and therefore it is characteristic of all aircraft, of all types, of all sizes and for any purpose. Passenger aircraft do not fly at extremely low speeds, and vigorous maneuvers are also not provided for them. Civilian pilots most often fail to cope with a situation where the angle of attack of an aircraft wing becomes critical.
It is considered an unusual situation if a passenger ship suddenly loses speed, moreover, many believe that this is generally excluded. But no. Both domestic and foreign practice shows that this does not even happen very rarely when stalling ends in disaster and the death of many people. Civilian pilots are not well trained to overcome this position of the aircraft. But the transition to a tailspin can be prevented if the angle of attack of the aircraft during takeoff does not become critical. At low altitude, it is practically impossible to do anything.
Examples
This happened in catastrophes that occurred with TU-154 aircraft at different times. For example, in Kazakhstan, when a ship sank in a stall mode, the pilot did not stop pulling the helm toward himself, trying to stop the descent. But the ship had to be given the opposite! Lower your nose to gain speed. But until the fall to the ground, the pilot did not understand this. Roughly the same thing happened both near Irkutsk and near Donetsk. Also, the A-310 near Kremenchug tried to gain altitude when it was necessary to gain speed and to observe the angle of attack sensor in an airplane all the time.
The lifting force is formed as a result of an increase in the flow velocity that flows around the wing from above as compared to the flow velocity under the wing. The greater the speed the flow has gained, the lower the pressure in it. The pressure difference on the wing and under the wing - here it is, the lifting force. The angle of attack of an aircraft is an indicator of normal flight.
What do we have to do
If the ship suddenly goes into a roll to the right, the pilot deflects the helm to the left, against the roll. At the same time, the aileron on the wing console deviates downward and increases the angle of attack, slowing the air stream and increasing pressure. At the same time, flow from above on the wing accelerates and lowers pressure on the wing. And on the right wing at the same moment, the opposite effect occurs. Aileron - up, angle of attack and lift decreases. And the ship leaves the bank.
But if the angle of attack of the aircraft (during landing, for example) is close to critical, that is, too large, the aileron cannot be turned down, then the smoothness of the air stream is violated, starting to swirl. And now this is a flow stall, sharply removing the speed of the air flow and also sharply increasing the pressure on the wing. The lift quickly fades away, while on the other wing everything is fine. The difference in lift force roll only increases. But the pilot wanted the best ... But the ship begins to decline, go into rotation, into a tailspin and fall.
How to proceed
Many practicing pilots talk about the angle of attack of the aircraft "for dummies", even Mikoyan wrote a lot about it. In principle, everything is simple: there is practically no complete symmetry in the air flow, and therefore, even without a roll, a breakdown of the air flow can occur, and also only on one wing. People who are very far from piloting, but knowing the laws of physics, will be able to realize that this is the angle of attack of the aircraft has become critical.
Conclusion
Now it is easy to draw a simple and fundamental conclusion: if the angle of attack is large at low speed, it is impossible, categorically it is impossible to counteract the roll of ailerons. He cleans the steering wheel (pedals). Otherwise, it is easy to provoke a corkscrew. If the stall still happened, only military pilots can get the ship out of this situation, civilians are not taught this, they fly according to very strict restrictive rules.
But you need to learn! After air crashes, the records of conversations from the "black boxes" are always carefully analyzed . And never in the cockpit of a plane crashed in a tailspin did the sound “Steering wheel from me!” Sound, although this is the only possibility of salvation. And "The leg against the roll!" didn't sound either. Civil aviation pilots are not ready for such situations.
Why it happens
Passenger aircraft are almost completely automated, which, of course, facilitates the actions of the pilot. Especially it concerns difficult weather conditions and night flights. However, this is where the great danger lies. If it is impossible to use the ground-based system, if at least one node in the automatic system fails, then you need to use manual control. But pilots get used to automation, gradually losing piloting skills "the old fashioned way", especially in difficult conditions. After all, even the simulators for them are set to automatic mode.
So there are plane crashes. For example, in Zurich, a passenger plane could not land normally on drives. The weather was minimal, and the pilot did not taxi, collided with trees. Everyone died. It often happens that it is automation that causes stall. The autopilot always uses ailerons against spontaneous roll, that is, it does what should not be done with the threat of stall. At high angles of attack, the autopilot should be immediately turned off.
Autopilot Action Example
The autopilot harms not only at the beginning of the stall, but also when taking the plane out of a tailspin. An example of this is the case in Akhtubinsk, when the excellent military test pilot Alexander Kuznetsov was forced to eject, and realizing what was the matter. He attacked the target with the autopilot turned on, when he broke into a tailspin. Twice he managed to stop the rotation of the aircraft, but the autopilot stubbornly manipulated the ailerons, and the rotation returned.
Such problems, which constantly arise in connection with the widest distribution of programmed automatic control of aircraft, are extremely worrying not only for domestic specialists, but also for foreign civil aviation. International seminars and meetings are held on flight safety, where it is certainly noted that the crews are poorly trained in aircraft control with a high degree of automation. They come out of deplorable situations only if the pilot has personal inventiveness and good manual piloting techniques.
The most common mistakes
Even the automation that the ship is equipped with, pilots often do not understand enough. In 40% of flight accidents, this played a role (of which 30% ended in disaster). In the USA, they began to draw up evidence of disharmony among pilots with a highly automated aircraft, and their entire catalog has already accumulated. Very often, pilots do not even notice the failure of the automatic traction machine and autopilot in general.
They also poorly control the state of speed and energy, because this state is not saved. Some pilots do not realize that the deviation of the rudders is no longer correct. It is necessary to control the flight path, and the pilot is distracted by the programming of the automatic system. And many more such errors occur. The human factor is 62% of all serious accidents.
Fingers Explanation
Probably everyone already knows what the angle of attack of an airplane is, and even people who are not related to aviation are aware of the importance of this concept. However, are there any? If there is, then there are very few of them on Earth. Almost everyone flies with airplanes! And almost all flights are afraid. Someone is internally worried, and someone directly on board falls into hysteria at the slightest turbulence.
Probably, it would be necessary to tell passengers about the most basic concepts relating to an aircraft. Indeed, the critical angle of attack of an airplane is not at all what they are experiencing now, and it is better if they understand this. You can instruct the flight attendants to convey such information, to prepare relevant illustrations. For example, to tell that there is no such independent value as lifting force. It just doesn’t exist. Everything flies thanks to the aerodynamic force of air resistance! Such excursions to the basics of science can not only distract from the fear of flying, but also interest.
Angle of attack sensor
An airplane must have a device that can determine the angle of the wing and the horizontal air flow. That is, such a device, on which the well-being of the flight depends, is worth demonstrating to passengers at least in the picture. Using this sensor, you can judge how far the nose of the aircraft looks up or down. If the angle of attack is critical, the engines do not have enough power to continue the flight, and therefore there is a stall on one wing.
One can explain quite simply: thanks to this sensor, one can see the angle between the plane and the ground. The lines should be parallel in flight at an already gained altitude, when there is still time before the decline. And if the line running along the earth tends to the line mentally drawn along the plane, an angle is obtained, which is called the angle of attack. You won’t be able to do without it either, because the plane takes off at an angle and lands. But he cannot be critical. That's what you need to tell. And this is not all that passengers need to know about flights.