
Why you can’t walk on the wing at the edge and angle of attack
This incident was told by my father. He was an aircraft engineer at the factory and was responsible for the final delivery of the product to the customer. A fighter was landing, which had just recently been rolled out of the final assembly workshop. Soft touch, full-time landing. In general, a normal test flight. Nothing new. But the pilot does not smile, as usual.
- What is it, Zhenya? - My father asks the pilot.
- Everything is fine, Valera, but so far “unsuccessful”: the angle of attack is lying, and it is lying much. I will not sign the acceptance certificate.
- How much?
“Right much.”
- Hm ... We’ll see.
How could he feel it? Some 5-7 degrees. Does he feel so good about the car? At the beginning of my flight career, this question touched me on a lively note, so I listened to my father’s story with particular interest.
It was believed that a pilot is more humanitarian than an engineer. Among engineers, of course. Therefore, the words of the pilots were not always trusted and tried to check them very carefully. However, close work with the pilots suggested that if they are not sure and say that "something is wrong," the fact deserves attention. In addition, it was among the test pilots that many pilots knew the materiel not simplistically, but quite comprehensively right down to units and circuit diagrams. And if the engineer was responsible only for his direction, for example, the radio equipment engineer knew only the radio equipment, the SD engineer (an airplane and engine glider specialist) knew only the engine, then the pilot knew everything.
Before telling further, let's figure out what the angle of attack is by definition. This is the angle between the projection of the velocity vector on the axis of asymmetry of the aircraft and the longitudinal axis of the aircraft.

An important parameter by which pilots determine how stable the aircraft is in the air. That is, the wing, being in a certain position at a certain speed and with a certain weight, creates a certain lifting force on the wing.
But only until a certain moment, until the flow is disrupted from the wing. In the cockpit, it feels like this: at first - the steering wheel is shaking (or the plane in another way signals approaching the critical angle), then when the critical angle of attack is exceeded, the air flow on the wing further breaks down, the lifting force is sharply lost, and finally the plane falls into a tailspin.
How to measure the angle of attack? Information about the angle of attack is read by pilots from UAAS. The automatic machine of angles of attack and signaling of overloads (AUASP) is an element of the flight-navigation complex in an airplane, designed to control the current angle of attack and notify the crew in case of reaching a critical or critical angle of attack. As we have already said, the danger of exceeding the permissible value of the angle of attack is a possible disruption of the flow and the subsequent dumping of the aircraft in a tailspin.
The principle of operation of AUASP is based on the continuous measurement of the current angle of attack, local critical and overload with built-in sensors and their comparison with the maximum allowable for this type of aircraft. In case of reaching a critical level, an audible alarm is triggered and the light panel lights up.
In other words, the flygun deviates from the incoming flow and, through a system of special sensors, supplies the value of the current angle of attack.
This is a very important device. Even the Wright brothers took him in flight. In general, he was the only device with them. There was no indicator of speed or altitude, there was no horizon or even a compass. The first AUASP looked like a twine tied to the front edge of the wing. She showed the first pilots the angle of attack of the aircraft, and already by it they judged the speed of flight!
So, now you understand why 5–7 degrees of the angle of attack is a “failure” in acceptance.
The first thing the factory did was double-check the logs of the test equipment. All parameters according to the records are normal.
The aircraft was rolled into the hangar and, like a sick patient in intensive care, was connected to the stand.
Verification occurred as follows. The plane was connected to the stand and the windshield was manually rejected. The stand did not record false information. Rejected by 5 degrees - 5 degrees was registered at the stand, rejected by 10 degrees - 10 was registered. All parameters were normal.
Hmm ... okay. Again the plane rolled out for testing. Again the flight. Again, the test pilot does not sign the verification certificate. The angle of attack is lying, and lying decently. This procedure was performed several times. Several times the plane was lifted into the air, and each time the pilot confirmed the defect, each time dozens of aviation specialists searched for a defect on the ground that was not confirmed. Fuel, aerodrome services, engine life, aircraft engineer’s hours — these are all the costs incurred by the plant when testing a newly manufactured machine, and if you think that in the Soviet Union no one considered such costs, then you are mistaken.
- Eugene, do not be foolish, the plane is serviceable, sign, - both father and factory superiors pressed on the pilot.
But Zhenya did not agree.
- I won’t sign them, I’d better break my arm myself ...
Time passed, the pilot did not sign, the plane on the ground was operational, production indicators fell, which portended problems already at the level of the Ministry of Aviation Industry. They decided to "increase the angle of attack" - to put pressure on the pilot with "heavy artillery", but at the crucial moment, when very authoritative people began to put pressure on him, he "son of a bitch", took and went to the hospital. An “alternative” test pilot was called from the capital of our motherland, Moscow, who again confirmed the defect!
We will omit disputes and abuse in our narrative, the methods of psychological pressure on the personality between the developer and the customer, we will also omit the methods of finding the cause, but the defect was nevertheless revealed! It was all simple: some technician who serviced the aircraft, while on a stepladder or in some other position, stepped on this windshield and simply deformed it a little.
In general, of course, you can walk on the wing. It is very durable, it carries an entire aircraft and experiences enormous loads - much more than the weight of a couple of people trying to service it. But not everywhere! Zones where you cannot enter are marked with special symbols. Moreover, not because of strength indicators, but just because of the proximity to different sensors and for other reasons (although on some aircraft and because of strength).
The dent was invisible to the eye, but it still created a different profile for the air to flow around this flygar. That is, when it was rejected by the hand on the ground, everything was normal, but the angle of deviation in the air from the incoming flow was different - off-design. That is the whole answer. And test pilots “just felt” this difference!
How? I asked myself a question. Ass, the pilots answered. In fact, the answer is simple: in horizontal flight, the angle of attack equals the pitch. It is really simple.
Pitch is the angle between the horizon and the construction axis of the aircraft. Positive pitch with an increase in the angle (nose lift) - cabling, steering wheel toward you; negative with decreasing angle (lowering the nose) - dive, steering wheel away from you. Measured in degrees, induced at the checkpoint by a flight control device. They don’t feel it ... This value is quite physical, which is looked at at the checkpoint.
As time passed, I began to fly, the close connection between speed, angle of attack and pitch was felt more and more clearly already in practice. However, what was my surprise when I began to get acquainted with foreign technology! On foreign cars of the last generation there is no UAPP or its analogue. Until now, many pilots retraining from domestic technology, this fact is not something that surprises - it shakes them.
- Why? I asked.
- What for? - answered me. - There is speed, fly in speed.
- And if she is not?
- Who is absent?
- Speeds.
- How is that?
- Well, how? So: it doesn’t show speed for some reason.
There are memory actions for this. The same refusal is registered in a special book, which defines all the actions in this refusal, which we must remember by heart. We turn off the autopilot, turn off the traction machine (the machine that is responsible for the engine’s operating mode and, therefore, maintain the speed), turn off the director’s flight (these are straps on the flight pilot device that tell the pilot which pitch and roll to maintain in order to maintain the given flight mode ) and set certain engine speeds for a certain wing mechanization. And that's it - we fly.
Ohhhh ... But on Soviet technology, it seems to be self-evident. Next, I foresee heated debate on this topic. It is great that it is written in a special book, and not just written, but also included in the list of failures that you need to know by heart.
At first glance it seems: everything is simple. In fact, the simple question of the angle of attack causes a lot of controversy among engineers and pilots about whether it is needed.
Also our posts about aviation: why specifically pour the airplane before departure, and what will happen if it isn’t done , how business aviation works in Russia , the FBO Sheremetyevo infrastructure , cargo flight , flight preparation for pilots ,the history of on-board catering and our rating of the “tastiest” airlines , by what rules a plane flies in Russia , the safety of air travel .
- What is it, Zhenya? - My father asks the pilot.
- Everything is fine, Valera, but so far “unsuccessful”: the angle of attack is lying, and it is lying much. I will not sign the acceptance certificate.
- How much?
“Right much.”
- Hm ... We’ll see.
How could he feel it? Some 5-7 degrees. Does he feel so good about the car? At the beginning of my flight career, this question touched me on a lively note, so I listened to my father’s story with particular interest.
It was believed that a pilot is more humanitarian than an engineer. Among engineers, of course. Therefore, the words of the pilots were not always trusted and tried to check them very carefully. However, close work with the pilots suggested that if they are not sure and say that "something is wrong," the fact deserves attention. In addition, it was among the test pilots that many pilots knew the materiel not simplistically, but quite comprehensively right down to units and circuit diagrams. And if the engineer was responsible only for his direction, for example, the radio equipment engineer knew only the radio equipment, the SD engineer (an airplane and engine glider specialist) knew only the engine, then the pilot knew everything.
Before telling further, let's figure out what the angle of attack is by definition. This is the angle between the projection of the velocity vector on the axis of asymmetry of the aircraft and the longitudinal axis of the aircraft.

An important parameter by which pilots determine how stable the aircraft is in the air. That is, the wing, being in a certain position at a certain speed and with a certain weight, creates a certain lifting force on the wing.
But only until a certain moment, until the flow is disrupted from the wing. In the cockpit, it feels like this: at first - the steering wheel is shaking (or the plane in another way signals approaching the critical angle), then when the critical angle of attack is exceeded, the air flow on the wing further breaks down, the lifting force is sharply lost, and finally the plane falls into a tailspin.
How to measure the angle of attack? Information about the angle of attack is read by pilots from UAAS. The automatic machine of angles of attack and signaling of overloads (AUASP) is an element of the flight-navigation complex in an airplane, designed to control the current angle of attack and notify the crew in case of reaching a critical or critical angle of attack. As we have already said, the danger of exceeding the permissible value of the angle of attack is a possible disruption of the flow and the subsequent dumping of the aircraft in a tailspin.
The principle of operation of AUASP is based on the continuous measurement of the current angle of attack, local critical and overload with built-in sensors and their comparison with the maximum allowable for this type of aircraft. In case of reaching a critical level, an audible alarm is triggered and the light panel lights up.
In other words, the flygun deviates from the incoming flow and, through a system of special sensors, supplies the value of the current angle of attack.
This is a very important device. Even the Wright brothers took him in flight. In general, he was the only device with them. There was no indicator of speed or altitude, there was no horizon or even a compass. The first AUASP looked like a twine tied to the front edge of the wing. She showed the first pilots the angle of attack of the aircraft, and already by it they judged the speed of flight!
So, now you understand why 5–7 degrees of the angle of attack is a “failure” in acceptance.
The first thing the factory did was double-check the logs of the test equipment. All parameters according to the records are normal.
The aircraft was rolled into the hangar and, like a sick patient in intensive care, was connected to the stand.
Verification occurred as follows. The plane was connected to the stand and the windshield was manually rejected. The stand did not record false information. Rejected by 5 degrees - 5 degrees was registered at the stand, rejected by 10 degrees - 10 was registered. All parameters were normal.
Hmm ... okay. Again the plane rolled out for testing. Again the flight. Again, the test pilot does not sign the verification certificate. The angle of attack is lying, and lying decently. This procedure was performed several times. Several times the plane was lifted into the air, and each time the pilot confirmed the defect, each time dozens of aviation specialists searched for a defect on the ground that was not confirmed. Fuel, aerodrome services, engine life, aircraft engineer’s hours — these are all the costs incurred by the plant when testing a newly manufactured machine, and if you think that in the Soviet Union no one considered such costs, then you are mistaken.
- Eugene, do not be foolish, the plane is serviceable, sign, - both father and factory superiors pressed on the pilot.
But Zhenya did not agree.
- I won’t sign them, I’d better break my arm myself ...
Time passed, the pilot did not sign, the plane on the ground was operational, production indicators fell, which portended problems already at the level of the Ministry of Aviation Industry. They decided to "increase the angle of attack" - to put pressure on the pilot with "heavy artillery", but at the crucial moment, when very authoritative people began to put pressure on him, he "son of a bitch", took and went to the hospital. An “alternative” test pilot was called from the capital of our motherland, Moscow, who again confirmed the defect!
We will omit disputes and abuse in our narrative, the methods of psychological pressure on the personality between the developer and the customer, we will also omit the methods of finding the cause, but the defect was nevertheless revealed! It was all simple: some technician who serviced the aircraft, while on a stepladder or in some other position, stepped on this windshield and simply deformed it a little.
In general, of course, you can walk on the wing. It is very durable, it carries an entire aircraft and experiences enormous loads - much more than the weight of a couple of people trying to service it. But not everywhere! Zones where you cannot enter are marked with special symbols. Moreover, not because of strength indicators, but just because of the proximity to different sensors and for other reasons (although on some aircraft and because of strength).
The dent was invisible to the eye, but it still created a different profile for the air to flow around this flygar. That is, when it was rejected by the hand on the ground, everything was normal, but the angle of deviation in the air from the incoming flow was different - off-design. That is the whole answer. And test pilots “just felt” this difference!
How? I asked myself a question. Ass, the pilots answered. In fact, the answer is simple: in horizontal flight, the angle of attack equals the pitch. It is really simple.
Pitch is the angle between the horizon and the construction axis of the aircraft. Positive pitch with an increase in the angle (nose lift) - cabling, steering wheel toward you; negative with decreasing angle (lowering the nose) - dive, steering wheel away from you. Measured in degrees, induced at the checkpoint by a flight control device. They don’t feel it ... This value is quite physical, which is looked at at the checkpoint.
As time passed, I began to fly, the close connection between speed, angle of attack and pitch was felt more and more clearly already in practice. However, what was my surprise when I began to get acquainted with foreign technology! On foreign cars of the last generation there is no UAPP or its analogue. Until now, many pilots retraining from domestic technology, this fact is not something that surprises - it shakes them.
- Why? I asked.
- What for? - answered me. - There is speed, fly in speed.
- And if she is not?
- Who is absent?
- Speeds.
- How is that?
- Well, how? So: it doesn’t show speed for some reason.
There are memory actions for this. The same refusal is registered in a special book, which defines all the actions in this refusal, which we must remember by heart. We turn off the autopilot, turn off the traction machine (the machine that is responsible for the engine’s operating mode and, therefore, maintain the speed), turn off the director’s flight (these are straps on the flight pilot device that tell the pilot which pitch and roll to maintain in order to maintain the given flight mode ) and set certain engine speeds for a certain wing mechanization. And that's it - we fly.
Ohhhh ... But on Soviet technology, it seems to be self-evident. Next, I foresee heated debate on this topic. It is great that it is written in a special book, and not just written, but also included in the list of failures that you need to know by heart.
At first glance it seems: everything is simple. In fact, the simple question of the angle of attack causes a lot of controversy among engineers and pilots about whether it is needed.
Also our posts about aviation: why specifically pour the airplane before departure, and what will happen if it isn’t done , how business aviation works in Russia , the FBO Sheremetyevo infrastructure , cargo flight , flight preparation for pilots ,the history of on-board catering and our rating of the “tastiest” airlines , by what rules a plane flies in Russia , the safety of air travel .