During aviation flight, when the aircraft takes off and lands,pilotIt is affected by+G and - G respectively.The action direction is perpendicular to the z-axis of the human bodyaccelerationIt is called lateral acceleration.According to acceleration andinertia forceThe lateral acceleration mainly includes forward acceleration (+Gx), backward acceleration (- Gx), right acceleration (+Gy) and left acceleration (- Gy).[1]
Chinese name
Lateral acceleration
English name
transverse acceleration
definition
The direction of overload action on human body is the linear acceleration from chest to back (or back to chest), which is usually expressed as - G x (or+G x).
Applied discipline
Aviation science and technology (first level discipline), aviation safety, life support system and aviation medicine (second level discipline)
In space flight, astronauts mainly bear sustained lateral acceleration.In order to achieve near orbitManned spaceflightIn flight, we must try to make the manned spacecraft reach a certain speed, and to obtain this necessary speed, we need to have a corresponding amount of acceleration and duration.In order to launch spacecraft into different orbits, multi-stage launch vehicles are generally used.Taking the three-stage rocket as an example, the whole launch process has formed three zigzag overweight curves.The duration of each stage is 100-200s, and the peak value varies from high to low. The total action time is 6-10min.In the early days of manned spaceflight,airshipThe maximum overweight value of the rising section can reach 6-8G.Later, with the improvement of carrier rocket technology, the maximum overweight value of the ascending segment of the spacecraft is about 5G, such as the Russian "Soyuz" series spacecraft and China's "Shenzhou" spacecraft.
After the mission is completed, the spacecraft will return to the ground from orbit.During the return phase, the overweight experienced by astronauts is related to whether the spacecraft uses lift when reentering the atmosphere and the size of reentry angle.[1]
Human impact
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Long term acceleration with the action direction at right angles to the long axis of the body rarely occurs in modern conventional flight.This acceleration only occurs during ejection takeoff, rocket or jet assisted takeoff, and landing on an aircraft carrier.However, the force generated by these flight movements is relatively small compared with human endurance, which will not cause problems.However, in the future combat aircraft, the pilot's seat may be tilted backward to increase the endurance of acceleration at right angles to the long axis of the aircraft. For the pilot, that is, from the tolerance of positive acceleration to the tolerance of lateral (forward) acceleration.In order to achieve the speed required for orbiting the earth, or the acceleration generated by breaking away from the earth's gravitational field, and then returning to the earth's surface, it can only be tolerated by astronauts when its inertial force acts laterally on the longitudinal axis of the body.For modern manned spacecraft, this acceleration effect lasts for several minutes, involving a peak value of 6-10G.In routine flight and space flight, the pilot is easier to observe the external environment, instruments, and control the controller when lying on his back than when lying prone in a recliner, so the long-term lateral acceleration that the human body often feels is almost all forward (ventral acceleration), that is, forward acceleration (+Gx), and rarely backward (dorsal acceleration), that is, backward acceleration (- Gx).Therefore, the effect of forward acceleration mentioned here is more detailed than that of backward acceleration.
Since the direction of inertia force is at right angles to the longitudinal axis of the body when the lateral acceleration acts, the body circulation will not change significantly.The major physiological obstacle caused by lateral acceleration occurs in the respiratory system.These obstacles limit the tolerance to this form of acceleration load.[2]
Generally speaking, for ordinary healthy people, with a back angle of 70 °~80 °, bent thighs and no other countermeasures, the human body's response to lateral acceleration is as follows:
1.+3~+6G, progressive chest tension and chest pain, breathing and speaking difficulties, peripheral vision reduction, blurred vision;Heart, lung, brain and other functions can be basically compensated, occasionallyArrhythmia；The ability of manipulation, judgment and reaction decreased slightly.
2．+6~+9G。Chest pain increases, breathing is difficult, shallow and fast, peripheral vision further decreases, blurred vision increases, and eyes shed tears;Important organs began to show signs of decline, which can be seenArrhythmia；The ability to manipulate, control, judge and respond is reduced+8~+9G。When the sound conduction and sound perception begin to decline and become disordered;There may be petechiae and ecchymosis on the back and other compressed areas, and occasionally there may be pathological damage such as emphysema and collapse of the lung.
3. +10~+15G。 Severe or extreme dyspnea and speech difficulties, severe chest pain, unbearable, obvious fatigue and exhaustion, complete loss of peripheral vision or vision, loss of touch, dizziness;The function of heart, lung, brain and other organs is decompensated, and there is a risk of "black vision" and loss of consciousness;Arrhythmias are common (especially sinoatrial block, atrioventricular separation, and ventricular arrest)TachycardiaIs the most dangerous);If you stay awake, your ability to manipulate, control, judge and respond will be greatly reduced+The decrease and disorder of sound conduction and sound perception reached the maximum at 14G;There may be petechiae and ecchymosis at the back and other compressed places, and the probability of pneumothorax, emphysema, lung collapse and other pathological injuries increases.[1]
Protective measures
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Use shaped seats
When the human body bears the+Gx effect, because all the weight of the human body is borne by the backrest of the seat, the seat design has a great impact on the+Gx endurance of the human body.In order to minimize the stress concentration in some protruding parts of the back of the human body and limit the deformation of the human body under the action of gravity, the seat cushion should be designed to fit the back of the human body, so as to limit the obvious deformation of the human body, and ensure mobility and comfort.The nylon rope net stretched on the metal frame was designed in foreign countries in the early stage, which can automatically fit with the human body and ensure the mobility and comfort of the body. However, the biological effect and protective effect of sustained lateral acceleration were not used because of poor stability under+Gx.Later, it was usedRigid foam plasticThe molded cushion is covered with soft foam foam thin layer and fabric skin, which has good protective performance and has been applied in aerospace practice.[1]
Selection of reasonable posture
The impact of the acceleration generated in the process of space launch and return on the human body varies with the seat back angle.When the dorsal angle increases, the+Gx component increases, which has a greater impact on the blood supply of the head and is prone to visual changes;When the back angle decreases, the+Gx component increases, which is easy to occurArrhythmia、dyspneaPain associated with the heart pit.Therefore, it is very important to choose a reasonable posture.Astronauts generally take a supine posture with slightly raised legs in the spaceship. The back of the seat is at a certain angle (a) to the bilge plane, and the longitudinal axis of the bilge is at a certain angle (p) to the force direction. The difference between the two is the actual physiological dorsal angle.It determines the vertical and horizontal force of the human body.It is generally believed that the effective physiological back angle is around 15 ° (the seat back angle is 75 °), which is ideal.
Use space anti-G suit
Long term flight affects cardiovascular system, respiratory system, visual functioncentral nervous systemIt has a wide range of effects and can reduce the overweight tolerance of the human body.In order to improve the overweight tolerance of astronauts returning after long-term flight, Russia (including the Soviet Union) tried to use anti-G clothes when astronauts returned, which proved to be effective against visual disorder and other discomfort caused by+Gx overweight effect.When returning from space flight for more than one month, it has become a routine for Russian astronauts to wear anti-G suits.This space anti-G suit is a kind of anti-G suit with elastic band. By applying external pressure to the soft tissues of the leg, thigh and abdomen organs, it limits the blood flow during the gravity load period, reduces the amount of blood accumulated in the blood vessels of the lower limbs and abdomen, improves blood pressure, increases blood supply to the head, and fights against the occurrence of decreased orthostatic tolerance.During the launch and return phase of the space shuttle in the United States, there is a very important equipment that can adjust the pressure of the anti-G suit.During the launch and landing of the aircraft, all astronauts wear anti-G clothing. When accelerating and decelerating, it can pressurize the abdomen, buttocks and calves by about 6895kPa。The difference between the Russian and American space anti-G suits is that the former adopts the rope tension type for regulating pressure, and the latter adopts the inflatable type for regulating pressure.
Adopt anti+Gx breathing action
CentrifugeThe experiment shows that anti+Gx breathing action is very effective in preventing dyspnea and chest pain when+Gx acts.The main action points are: when inhaling, actively force the abdomen to bulge, so that the diaphragm sinks to prevent the abdominal organs from moving up due to the squeezing effect of gravity; when exhaling, the abdomen retains a certain tension, and the diaphragm moves up slightly, so repeatedly, use the chest movement to maintain rhythmic breathing.These movements can be basically mastered after 3-5 times of training, and then combined with centrifuge overweight endurance training for application and consolidation.
Carry out overweight endurance selection and training
This is one of the most effective ways to protect against space overload, and has always been valued by Russia (including the Soviet Union) and China.Considering that in manned space flight, astronauts bear the overweight effect of+Gx and+Gz at the same time, and the individual difference of overweight tolerance is large, therefore, the selection of+Gz and+Gx overweight tolerance must be carried out.After astronauts are selected, they need to be trained to further improve and maintain their tolerance and adaptability to space overweight.The training methods mainly include the following.
(1) Through proper physical training, physical training can improve the rapid compensatory regulation ability of the human heart and lung system, increase the tension of the sympathetic nerve, and enhance the endurance of the respiratory muscles, thus non-specific improving the+Gx and+Gz endurance of the human body.
(2) It is reported that after hypoxic adaptation,+Gx endurance can be improved by (2.4 ± 0.2) G.
(3) Anti+Gx breathing movement training enables astronauts to master the techniques and skills to fight against overweight, and establish conditioned reflex so that they can freely use the+Gx effect.
(4) Centrifuge training: after centrifuge training, the+Gz endurance of human can be increased by 2-2.5G, and the+Gx endurance can be increased by 1.6-58G。The training effect of the latter can last for 6 months.However, improper repeated centrifuge training may also bring adverse cumulative risks to the body, which should be avoided.[1]
