Why can not walk on the wing at the edge and angle of attack
This case is told by my father. He was an aeronautical engineer at the factory and was responsible for the final delivery of the product to the customer. A fighter landed, which just recently rolled out of the final assembly shop. Soft touch, full-time landing. In general, the usual test flight. Nothing new. But the pilot does not smile, as usual.
- What is it, Zhenya? - My father asks the pilot.
- All is well, Valer, but for now “not good”: the angle of attack is lying, and it lies much more. I will not sign the acceptance certificate.
- How much?
- Right much more.
- Hmm ... We will see.
How could he feel this? Some 5-7 degrees. Does he feel so good car? At the beginning of my flying career, this issue touched me to the quick, so I listened to my father’s story with particular interest.
')
It was believed that the pilot is more humanitarian than the 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 pilots suggested that if they are not sure and say that “something is wrong”, then the fact deserves attention. In addition, it was precisely among the test pilots that many pilots knew the hardware not in an oversimplified manner, but in quite a comprehensive way, up 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 (aircraft glider and engine specialist) knew only the engine, then the pilot knew everything.
Before we talk further, let's see 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 the 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 from the wing disrupts. In the cockpit, it feels like this: first, the shaking of the steering wheel (or the aircraft otherwise signals an approaching critical angle), then when the critical angle of attack is exceeded, the air flow on the wing is further disrupted, the lift is suddenly lost, and finally the plane collapses into a spin.
How to measure the angle of attack? Information about the angle of attack pilots read with UASP. The automatic angle of attack and signaling overloads (AUASP) is an element of the flight-navigation complex in the aircraft, designed to control the current angle of attack and alert the crew in case of reaching the critical or critical angle of attack. As we have said, the danger of exceeding the permissible value of the angle of attack is a possible disruption of the flow and the subsequent stalling of the aircraft into a tailspin.
The principle of operation of AUASP is based on the constant measurement of the current angle of attack, local critical and overload by the built-in sensors and their comparison with the maximum permissible on this type of aircraft. In the case of reaching the critical level, an audible alarm is triggered and a light panel lights up.
In other words, the wind vane deviates from the incident flow and gives the value of the current angle of attack through a system of special sensors.
This is a very important device. Even the Wright brothers took him flying. In general, they had it the only device. There was no speed or altitude indicator; there was no artificial horizon and even a compass. The first AUASP looked like a string tied to the front edge of the wing. She showed the first pilots the angle of attack of the aircraft, and already on it they judged the speed of flight!
So, now you understand why the 5–7 degree angle of attack is “not satisfactory” on acceptance.
First of all, the test equipment logs were checked at the factory. All parameters according to the records are normal.
The plane was rolled into a hangar and, like a sick patient in intensive care, hooked up to a stand.
The check was done in the following way. They connected a plane to the stand and manually rejected the fly-flap. The stand did not record false information. Rejected by 5 degrees - 5 degrees was prescribed on the stand, rejected by 10 degrees - 10 were registered. All parameters were normal.
Hmm ... okay. Again, the plane rolled out for testing. Again flight. Again the test pilot does not sign the act of verification. Angle of attack is lying, and lying is decent. This procedure was done 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 looked for a defect on the ground, which was not confirmed. Fuel, airfield services, engine resource, aviation engineer labor hours — these are all the expenses that the plant incurred in testing a machine that had just been produced, and if you think that nobody in the Soviet Union considered such costs, then you are mistaken.
“Zhenya, do not be fooled, the plane is in order, sign it,” the father and the factory bosses pressured the pilot.
But Zhenya did not agree.
- I will not sign, guys, I'd rather “break my arm” ...
As time went on, the pilot did not sign, the aircraft on the ground was in good condition, production figures fell, which foreshadowed problems already at the level of the Ministry of Aviation Industry. We decided to "increase the angle of attack" - to put pressure on the pilot with "heavy artillery," but at the crucial moment, when very reputable people began to crush, he was a "son of a bitch", took it and went to the hospital. An “alternative” test pilot was called from the capital of our homeland of Moscow, who again confirmed the defect!
We omit disputes and abuse in our narrative, methods of psychological pressure on the person between the developer and the customer, omit the ways of finding the cause, but the defect was still revealed! Everything was simple: some technician who serviced the plane, being on a stepladder or in some other position, stepped on this flyugarka and simply deformed it a little.
In general, of course, you can walk on the wing. It is very durable, it carries a whole plane and suffers huge loads - far greater than the weight of a couple or three people trying to serve it. But not everywhere! Zones that cannot be stepped in are marked with special symbols. And not because of the strength indicators, but just because of the proximity to different sensors and for other reasons (although on some planes and because of the strength).
The dent was invisible to the eye, but it still created a different air flow profile around this flyugarka. That is, when it was deflected by the hand on the ground, everything was normal, but the deflection angle in the air from the incident flow was different — not calculated. That's the whole answer. And the test pilots "just felt" that difference!
How? - I asked myself a question. Ass, answered the pilots. In fact, the answer is simple: in horizontal flight the angle of attack equals the pitch. It is real simple.
Pitch is the angle between the horizon and the aircraft’s building axis. Positive pitch with increasing angle (elevation of the nose) - pitching, steering wheel; negative with decreasing angle (lowering the nose) - a dive, a steering wheel from oneself. Measured in degrees, induced at a checkpoint by a flight command device. He does not feel ... This is quite a physical value, which is looked at at the checkpoint.
As time passed, I began to fly, the close relationship between speed, angle of attack and pitch was felt more and more clearly 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 UASP or its equivalent. Until now, many pilots, retraining from domestic technology, this fact is not that surprising - it shocks them.
- Why? - I asked.
- What for? - answered me. - There is speed, piloting on speed.
- And if it is not?
- Who is absent?
- speeds.
- Is that how it is?
- Well, how? Here it is: it does not show speed for some reason.
For this there are memory actions. The same refusal is registered in a special book, where all the actions for this refusal are identified, which we must remember by heart. Turning off the autopilot, turning off the traction machine (machine, which is responsible for the engine's operating mode and, respectively, for maintaining the speed), turn off the director's flight (these are the slats on the flight-control device that tell the pilot how to withstand pitch and roll in order to maintain the specified flight mode ) and set a certain engine speed with a certain wing mechanization. And everything - we fly.
Opa-aaa ... And on the Soviet technology it seems to go without saying. Next, I foresee a heated debate on this topic. It's great that it is written in a special book, and not just spelled out, 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 many disputes among engineers and pilots whether it is needed.
Our aviation posts are also: why exactly do they pour a plane before departure, and what will happen if they don’t do this , how does business aviation in Russia work , Sheremetyevo’s FBO infrastructure , cargo flight , flight training for pilots , history of in-flight catering and our rating " the most delicious "airlines , according to what rules an airplane flies in Russia , the safety of air travel .
- What is it, Zhenya? - My father asks the pilot.
- All is well, Valer, but for now “not good”: the angle of attack is lying, and it lies much more. I will not sign the acceptance certificate.
- How much?
- Right much more.
- Hmm ... We will see.
How could he feel this? Some 5-7 degrees. Does he feel so good car? At the beginning of my flying career, this issue touched me to the quick, so I listened to my father’s story with particular interest.
')
It was believed that the pilot is more humanitarian than the 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 pilots suggested that if they are not sure and say that “something is wrong”, then the fact deserves attention. In addition, it was precisely among the test pilots that many pilots knew the hardware not in an oversimplified manner, but in quite a comprehensive way, up 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 (aircraft glider and engine specialist) knew only the engine, then the pilot knew everything.
Before we talk further, let's see 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 the 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 from the wing disrupts. In the cockpit, it feels like this: first, the shaking of the steering wheel (or the aircraft otherwise signals an approaching critical angle), then when the critical angle of attack is exceeded, the air flow on the wing is further disrupted, the lift is suddenly lost, and finally the plane collapses into a spin.
How to measure the angle of attack? Information about the angle of attack pilots read with UASP. The automatic angle of attack and signaling overloads (AUASP) is an element of the flight-navigation complex in the aircraft, designed to control the current angle of attack and alert the crew in case of reaching the critical or critical angle of attack. As we have said, the danger of exceeding the permissible value of the angle of attack is a possible disruption of the flow and the subsequent stalling of the aircraft into a tailspin.
The principle of operation of AUASP is based on the constant measurement of the current angle of attack, local critical and overload by the built-in sensors and their comparison with the maximum permissible on this type of aircraft. In the case of reaching the critical level, an audible alarm is triggered and a light panel lights up.
In other words, the wind vane deviates from the incident flow and gives the value of the current angle of attack through a system of special sensors.
This is a very important device. Even the Wright brothers took him flying. In general, they had it the only device. There was no speed or altitude indicator; there was no artificial horizon and even a compass. The first AUASP looked like a string tied to the front edge of the wing. She showed the first pilots the angle of attack of the aircraft, and already on it they judged the speed of flight!
So, now you understand why the 5–7 degree angle of attack is “not satisfactory” on acceptance.
First of all, the test equipment logs were checked at the factory. All parameters according to the records are normal.
The plane was rolled into a hangar and, like a sick patient in intensive care, hooked up to a stand.
The check was done in the following way. They connected a plane to the stand and manually rejected the fly-flap. The stand did not record false information. Rejected by 5 degrees - 5 degrees was prescribed on the stand, rejected by 10 degrees - 10 were registered. All parameters were normal.
Hmm ... okay. Again, the plane rolled out for testing. Again flight. Again the test pilot does not sign the act of verification. Angle of attack is lying, and lying is decent. This procedure was done 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 looked for a defect on the ground, which was not confirmed. Fuel, airfield services, engine resource, aviation engineer labor hours — these are all the expenses that the plant incurred in testing a machine that had just been produced, and if you think that nobody in the Soviet Union considered such costs, then you are mistaken.
“Zhenya, do not be fooled, the plane is in order, sign it,” the father and the factory bosses pressured the pilot.
But Zhenya did not agree.
- I will not sign, guys, I'd rather “break my arm” ...
As time went on, the pilot did not sign, the aircraft on the ground was in good condition, production figures fell, which foreshadowed problems already at the level of the Ministry of Aviation Industry. We decided to "increase the angle of attack" - to put pressure on the pilot with "heavy artillery," but at the crucial moment, when very reputable people began to crush, he was a "son of a bitch", took it and went to the hospital. An “alternative” test pilot was called from the capital of our homeland of Moscow, who again confirmed the defect!
We omit disputes and abuse in our narrative, methods of psychological pressure on the person between the developer and the customer, omit the ways of finding the cause, but the defect was still revealed! Everything was simple: some technician who serviced the plane, being on a stepladder or in some other position, stepped on this flyugarka and simply deformed it a little.
In general, of course, you can walk on the wing. It is very durable, it carries a whole plane and suffers huge loads - far greater than the weight of a couple or three people trying to serve it. But not everywhere! Zones that cannot be stepped in are marked with special symbols. And not because of the strength indicators, but just because of the proximity to different sensors and for other reasons (although on some planes and because of the strength).
The dent was invisible to the eye, but it still created a different air flow profile around this flyugarka. That is, when it was deflected by the hand on the ground, everything was normal, but the deflection angle in the air from the incident flow was different — not calculated. That's the whole answer. And the test pilots "just felt" that difference!
How? - I asked myself a question. Ass, answered the pilots. In fact, the answer is simple: in horizontal flight the angle of attack equals the pitch. It is real simple.
Pitch is the angle between the horizon and the aircraft’s building axis. Positive pitch with increasing angle (elevation of the nose) - pitching, steering wheel; negative with decreasing angle (lowering the nose) - a dive, a steering wheel from oneself. Measured in degrees, induced at a checkpoint by a flight command device. He does not feel ... This is quite a physical value, which is looked at at the checkpoint.
As time passed, I began to fly, the close relationship between speed, angle of attack and pitch was felt more and more clearly 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 UASP or its equivalent. Until now, many pilots, retraining from domestic technology, this fact is not that surprising - it shocks them.
- Why? - I asked.
- What for? - answered me. - There is speed, piloting on speed.
- And if it is not?
- Who is absent?
- speeds.
- Is that how it is?
- Well, how? Here it is: it does not show speed for some reason.
For this there are memory actions. The same refusal is registered in a special book, where all the actions for this refusal are identified, which we must remember by heart. Turning off the autopilot, turning off the traction machine (machine, which is responsible for the engine's operating mode and, respectively, for maintaining the speed), turn off the director's flight (these are the slats on the flight-control device that tell the pilot how to withstand pitch and roll in order to maintain the specified flight mode ) and set a certain engine speed with a certain wing mechanization. And everything - we fly.
Opa-aaa ... And on the Soviet technology it seems to go without saying. Next, I foresee a heated debate on this topic. It's great that it is written in a special book, and not just spelled out, 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 many disputes among engineers and pilots whether it is needed.
Our aviation posts are also: why exactly do they pour a plane before departure, and what will happen if they don’t do this , how does business aviation in Russia work , Sheremetyevo’s FBO infrastructure , cargo flight , flight training for pilots , history of in-flight catering and our rating " the most delicious "airlines , according to what rules an airplane flies in Russia , the safety of air travel .
Source: https://habr.com/ru/post/449194/
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