Overload- the ratio of the absolute value of linear acceleration caused by non-gravitational forces to the acceleration of gravity on the Earth's surface. Being a ratio of two forces, g-force is a dimensionless quantity, but g-force is often expressed in terms of gravitational acceleration g. Overload of 1 unit (that is, 1 g) is numerically equal to the weight of a body at rest in the Earth's gravity field. Overload at 0 g is tested by a body in a state of free fall under the influence of only gravitational forces, that is, in a state of weightlessness.
Overload is a vector quantity. For a living organism, the direction of the overload action is important. When overloaded, human organs tend to remain in the same state (uniform linear motion or rest). With a positive overload (head - legs), the blood moves from the head to the legs, the stomach goes down. With negative overload, blood flow to the head increases. The most favorable position of the human body, in which he can perceive the greatest overloads, is lying on his back, facing the direction of acceleration of movement, the most unfavorable for transferring overloads is in the longitudinal direction with his legs towards the direction of acceleration. When a car collides with a stationary obstacle, a person sitting in the car will experience back-chest overload. Such an overload can be tolerated without much difficulty. An ordinary person can withstand overloads of up to 15 g about 3 - 5 seconds without loss of consciousness. Overload from 20 - 30 g or more, a person can withstand no more than 1 - 2 seconds without losing consciousness, depending on the magnitude of the overload.
Symptoms and mechanism of action of overloads
General symptoms. A person’s reaction to overloads is determined by their magnitude, gradient of increase, duration of action, direction in relation to the main vessels of the body, as well as the initial functional state of the body. Depending on the nature, magnitude and combinations of these factors, changes in subtle functional shifts may occur in the body to extremely severe conditions, accompanied by complete loss of vision and consciousness in the presence of deep disorders of the functions of the cardiovascular, respiratory, nervous and other body systems.
General changes in a person’s condition under the influence of overloads are manifested by a feeling of heaviness throughout the body, at first difficulty, and with an increase in the magnitude of the overload and a complete lack of movement, especially in the limbs, in some cases, pain in the muscles of the back and neck [Babushkin V.P., 1959 ; de Graef P., 1983]. There is a clearly defined displacement of soft tissues and their deformation. During prolonged exposure to sufficiently large positive overloads, skin petechial hemorrhages in the form of dots or large spots, intensely colored but painless, which spontaneously disappear within a few days, may appear on areas of the legs, buttocks, and scrotum unprotected by backpressure. Sometimes swelling is observed in these places, and with negative overloads - swelling of the face. Visual disturbances occur early. With large values of overload, loss of consciousness develops, which lasts 9-21 s.
The mechanism of action of positive and negative overloads is complex and is determined by the primary effects caused by inertial forces. The most important of them are the following: redistribution of blood in the body to the lower (+G Z) or upper (-G z) half of the body, displacement of organs and deformation of tissues, which are sources of unusual impulses in the central nervous system, impaired circulation, breathing and stress reaction. Developing hypoxemia and hypoxia lead to dysfunction of the central nervous system, heart, and endocrine glands. The biochemistry of life processes is disrupted. Damage to cellular structures of a reversible or irreversible nature may occur, detected by cytochemical and histological methods.
One of the main requirements for military pilots and cosmonauts is the body’s ability to withstand overload. Trained pilots wearing anti-g suits can withstand g-forces from -3 ... -2 g up to +12 g. Resistance to negative, upward overloads is much lower. Usually at 7 - 8 g the eyes “turn red”, vision disappears, and the person gradually loses consciousness due to a rush of blood to the head. During takeoff, astronauts endure overload while lying down. In this position, the overload acts in the chest-back direction, which allows you to withstand an overload of several g units for several minutes. There are special anti-overload suits, the task of which is to alleviate the effects of overload. The suits are a corset with hoses that are inflated by an air system and hold the outer surface of the human body, slightly preventing the outflow of blood.
Overloading increases the stress on the machine structure and can lead to machine failure or destruction, as well as the movement of loose or poorly secured loads. The permissible overload value for civil aircraft is 2.5 g
For some special reason, much attention is paid in the world to the speed of acceleration of a car from 0 to 100 km/h (in the USA from 0 to 60 mph). Experts, engineers, fans of sports cars, as well as ordinary car enthusiasts, with some kind of obsession, constantly monitor the technical characteristics of cars, which usually reveal the dynamics of a car’s acceleration from 0 to 100 km/h. Moreover, all this interest is observed not only in sports cars for which the dynamics of acceleration from a standstill is very important, but also in completely ordinary economy class cars.
Nowadays, the greatest interest in acceleration dynamics is directed towards modern electric cars, which have begun to slowly displace sports supercars with their incredible acceleration speeds from the car niche. For example, just a few years ago it seemed simply fantastic that a car could accelerate to 100 km/h in just over 2 seconds. But today some modern ones have already come close to this indicator.
This naturally makes you wonder: What speed of acceleration of a car from 0 to 100 km/h is dangerous to human health? After all, the faster the car accelerates, the more load the driver who is (sitting) behind the wheel experiences.
Agree with us that the human body has its own certain limits and cannot withstand the endless increasing loads that act and have a certain impact on it during rapid acceleration of the vehicle. Let us find out together what the maximum acceleration of a car can theoretically and practically be withstood by a person.
Acceleration, as we all probably know, is a simple change in the speed of movement of a body per unit of time. The acceleration of any object on the ground depends, as a rule, on gravity. Gravity is a force acting on any material body that is close to the surface of the earth. The force of gravity on the surface of the earth consists of gravity and the centrifugal force of inertia, which arises due to the rotation of our planet.
If we want to be absolutely precise, then 1g human overload sitting behind the wheel of a car is formed when the car accelerates from 0 to 100 km/h in 2.83254504 seconds.
And so, we know that when overloaded in 1g the person does not experience any problems. For example, a production Tesla Model S car (an expensive special version) can accelerate from 0 to 100 km/h in 2.5 seconds (according to the specification). Accordingly, the driver behind the wheel of this car will experience an overload of 1.13g.
This, as we see, is more than the overload that a person experiences in ordinary life and which arises due to gravity and also due to the movement of the planet in space. But this is quite a bit and the overload does not pose any danger to humans. But, if we get behind the wheel of a powerful dragster (sports car), then the picture here is completely different, since we are already seeing different overload figures.
For example, the fastest one can accelerate from 0 to 100 km/h in just 0.4 seconds. As a result, it turns out that this acceleration causes overload inside the car in 7.08g. This is already, as you can see, a lot. Driving such a crazy vehicle you will not feel very comfortable, and all due to the fact that your weight will increase almost seven times compared to before. But despite this not very comfortable state with such acceleration dynamics, this (this) overload is not capable of killing you.
So how then does a car have to accelerate to kill a person (the driver)? In fact, it is impossible to answer this question unambiguously. The point here is the following. Each organism of any person is purely individual and it is natural that the consequences of exposure to certain forces on a person will also be completely different. Overload for some at 4-6g even for a few seconds it will already be (is) critical. Such an overload can lead to loss of consciousness and even death of that person. But usually such overload is not dangerous for many categories of people. There are known cases when overload in 100g allowed a person to survive. But the truth is, this is very rare.
Airplane. Overload is a dimensionless quantity, but is widely identified with the acceleration of gravity g. Normal overload 1 g means horizontal straight flight. If an airplane performs a horizontal coordinated turn with a bank of 60 degrees, its structure experiences a normal overload of 2 units (or 2g).
The permissible overload value for civil aircraft is 4.33 live. An ordinary person can withstand overloads of up to 5 g. Trained pilots wearing anti-g suits can withstand g-forces of up to 9 g. Resistance to negative, upward overloads is much lower. Usually at 2-3 g the eyes “turn red” and the person loses consciousness due to a rush of blood to the head.
| Man standing motionless | 1 g |
| Passenger on an airplane during takeoff | 1,5 g |
| Skydiver landing at a speed of 6 m/s | 1,8 g |
| A parachutist when opening a parachute (when the speed changes from 60 to 5 m/s) | 5,0 g |
| Cosmonauts during descent in the Soyuz spacecraft | up to 3.0-4.0 g |
| Pilot performing aerobatic maneuvers | up to 5 g |
| A pilot recovering an aircraft from a dive | 8,0-9 g |
| Overload (long-term), corresponding to the limit of human physiological capabilities | 8,0-10,0 g |
| The greatest (short-term) overload of a car in which a person managed to survive | 179,8 g |
Notes
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See what “Overload (aerodynamics)” is in other dictionaries:
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Overload is the ratio of the resultant of all forces (except weight) acting on the aircraft to the weight of the aircraft.
Overloads are defined in the associated coordinate system:
nx- longitudinal overload; nу- normal overload; nz- lateral overload.
Full overload is determined by the formula
Longitudinal overload nх occurs when engine thrust and drag change.
If the engine thrust is greater than the drag, then the overload is positive. If the magnitude of the drag is greater than the engine thrust, then the overload is negative.
Longitudinal overload is determined by the formula
Lateral overload nz occurs when the aircraft is flying in a sliding state. But in terms of magnitude, the lateral aerodynamic force Z is very small. Therefore, in calculations, the lateral overload is taken equal to zero. Lateral overload is determined by the formula
The performance of aerobatic maneuvers is mainly accompanied by the occurrence of large normal overloads.
Normal overload nу is called the ratio of lift to the weight of the aircraft and is determined by the formula
Normal overload, as can be seen from formula (11.5), is created by lifting force. In horizontal flight in a calm atmosphere, the lift force is equal to the weight of the aircraft, therefore, the overload will be equal to unity:
Rice. 6 The effect of centrifugal inertial force on the pilot a - with a sharp increase in the angle of attack, b - with a sharp decrease in the angle of attack
In curved flight, when the lift force becomes greater than the weight of the aircraft, the overload will be greater than one.
When an airplane moves along a curved path, the centripetal force is, as already mentioned, lift, i.e., air pressure on the wings. In this case, the magnitude of the centripetal force is always accompanied by an equal, but opposite in direction, centrifugal force of inertia, which is expressed by the force of pressure of the wings on the air. Moreover, the centrifugal force acts like weight (mass), and since it is always equal to the centripetal force, when the latter increases, it increases by the same amount. Thus, aerodynamic overload is similar to an increase in the weight of the aircraft (pilot).
When overload occurs, the pilot feels as if his body has become heavier.
Normal overload is divided into positive and negative. When the overload presses the pilot into the seat, then this overload positive, if he separates him from the seat and holds him on the seat belts - negative (Fig. 6).
In the first case, the blood will flow from the head to the feet, in the second case, it will flow to the head.
As already mentioned, an increase in lift in curvilinear motion is equivalent to an increase in the weight of the aircraft by the same amount, then
(11.6)
(11.7)
Where n level - available overload.
From formula (11.7) it is clear that the amount of available overload is determined by the reserve of lift coefficients (margin of angles of attack) from those required for horizontal flight to its safe value (Su TR or Su CR).
The maximum possible normal overload can be obtained when, in flight at a given speed and flight altitude, the aircraft's ability to create lift is fully utilized. This overload can be obtained in the case when the aircraft is sharply (without a noticeable decrease in flight speed) brought to C y = C y max:
(11.8)
However, it is undesirable to bring the aircraft to such an overload, as there will be a loss of stability and a stall into a tailspin or spin rotation. For this reason, it is not recommended to sharply tilt the control stick toward you at high flight speeds, especially when exiting a dive. Therefore, the maximum possible or available overload is taken to be smaller in value in order to prevent the aircraft from entering the shaking mode. The formula for determining this overload has the form
(11.9)
For the Yak-52 and Yak-55 aircraft, graphical dependences of available overloads on flight speed are shown in Fig. 7, Fig. 8. When performing flights on Yak-52 and Yak-55 aircraft, the available normal overload is mainly limited by the strength characteristics of the aircraft.
Maximum permissible operational overload for the Yak-52 aircraft:
with wheeled chassis:
positive +7;
negative -5;
with ski chassis:
positive +5;
negative -3.
Maximum permissible operational overload for the Yak-55 aircraft:
in the training version:
positive +9;
negative -6;
in distillation version:
positive +5;
negative -3.
Exceeding these overloads in flight is prohibited, since residual deformations may appear in the aircraft structure.
When performing steady-state curved maneuvers, the overload depends on the thrust reserve of the power plant. The thrust reserve is determined from the condition of maintaining a given speed throughout the entire maneuver.
Maximum overload for available thrust PR is called the greatest overload at which the thrust of the power plant still balances the drag. It is determined by the formula
(11.10)
The maximum overload for the available thrust depends on the speed and altitude of the flight, since the above factors affect the available thrust Рр and the aerodynamic quality K on the speed. To calculate the dependence of n at PREV it is necessary to have curves Рр (V) for different altitudes and a grid of polars.
For each speed value, the values of the available thrust are taken from the curve Pp (V), the value of the coefficient Cy is determined from the polar for the corresponding speed V, and calculated using formula (11.10).
When maneuvering in a horizontal plane with an overload less than available, but more than the maximum thrust, the aircraft will lose speed or flight altitude.
Earthly Overloads
When a car collides with a stationary obstacle, a person sitting in the car will experience back-chest overload. Such an overload can be tolerated without much difficulty. An ordinary person can withstand overloads of up to 15 g about 3 - 5 seconds without loss of consciousness. Overload from 20 - 30 g or more, a person can withstand no more than 1 - 2 seconds without losing consciousness, depending on the magnitude of the overload.
Overloads applied to humans:
1 - 1 g .
3 - 15 g for 0.6 sec.
5 - 22 g .
One of the main requirements for military pilots and cosmonauts is the body’s ability to withstand overload. Trained pilots in anti-g suits can withstand g-forces from -3 ... -2 g up to +12 g . Resistance to negative, upward overloads is much lower. Usually at 7 - 8 g the eyes “turn red”, vision disappears, and the person gradually loses consciousness due to a rush of blood to the head. During takeoff, astronauts endure overload while lying down. In this position, the overload acts in the chest-back direction, which allows you to withstand an overload of several g units for several minutes. There are special anti-overload suits, the task of which is to alleviate the effects of overload. The suits are a corset with hoses that are inflated by an air system and hold the outer surface of the human body, slightly impeding the outflow of blood.
Space overload
During launch, the astronaut is subject to acceleration, the value of which varies from 1 to 7 g.
Overloads associated with acceleration cause a significant deterioration in the functional state of the human body: blood flow in the circulatory system slows down, visual acuity and muscle activity decrease.
With the onset of weightlessness, the astronaut may experience vestibular disorders; a feeling of heaviness in the head area persists for a long time (due to increased blood flow to it). At the same time, adaptation to weightlessness occurs, as a rule, without serious complications: a person maintains working capacity and successfully performs various work operations, including those that require fine coordination or large expenditures of energy. Motor activity in a state of weightlessness requires much less energy expenditure than similar movements in conditions of weight.
During longitudinal acceleration, the astronaut experiences visual illusions. It seems to him that the object he is looking at is moving in the direction of the resulting vector of acceleration and gravity.
With angular accelerations, an apparent movement of the object of vision occurs in the plane of rotation. This so-called circumgyral illusion is a consequence of the effects of overload on the semicircular canals (organs of the inner ear).
Conclusion:
If the blood flow in a state of weightlessness is an order of magnitude greater than on Earth, then loss of consciousness due to excessive blood flow to the head will occur both at a lower g and in the amount of seconds that an astronaut can withstand.. But there is one + Because we are in In the distant future, our anti-G suits, for example, which come with 350 rubles, will be an order of magnitude better at preserving consciousness during strong and prolonged overloads + should be saved by artificial gravity, which should create a counterbalance to the overloads in 2-5 seconds.
According to doctors, the human brain can withstand overloads of about 150 g, if they act on the brain for no more than 1–2 ms; with a decrease in overloads, the time during which a person can experience them increases, and an overload of 40 g, even with prolonged exposure, is considered relatively safe for the head.
An overload of up to 72 g is considered safe, overloads from 72 to 88 g fall into the intermediate “red” zone, and when exceeding 88 g, a head injury is considered highly probable. An important aspect of the EuroNCAP method is the assessment of the pressure acting on a person’s chest: chest compression of 22 mm is considered safe, compression of 50 mm is considered the maximum.
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