Skydiving refers to corrective activities - having passed the “point of no return” (jumping out of an airplane), we can influence the development of events only by our actions. Paratroopers are always forced to operate in conditions of severe shortage of time and altitude. The free fall speed of a parachutist is 170 - 200 km / h. The free fall time from a height of 4000 meters to the opening of the parachute is 50-60 seconds.
After separation from a horizontally flying aircraft, the body by inertia continues to move in the direction of the aircraft's flight, and tends downward under the influence of gravity. As a result, the body moves along a curve, gradually deviating from the horizontal direction of movement and approaching the vertical one. In this case, the horizontal component of the velocity, due to air resistance, will noticeably decrease, and the vertical component will increase. On average, if you do not apply special techniques to reduce or increase the resistance force of the oncoming flow, the horizontal component will drop to zero by 10 - 12 seconds of free fall and the body will fly 300 - 350 meters behind the aircraft. The vertical component, under the influence of gravity, increases, but again, due to air resistance, by 10 - 15 seconds it reaches an equilibrium value, which is determined by the weight and size (area) of the parachutist and is about 50 m / s.
In free fall, a parachutist, using the force of the oncoming air flow, can change his position, using his arms and legs as “rudders”, change the speed of vertical fall, move horizontally in any direction, rotate around vertical or horizontal axes. Accordingly, falling in a group of two, three or more skydivers, it is possible to move up and down relative to the group, approach any skydiver, move according to a pre-planned program. Many types of parachuting are built on this - individual and group acrobatics, freestyle and freefly. Free fall and evolution in free fall is what people come to skydiving for.
The main position of the body for free fall is the neutral posture, in which the skydiver falls vertically downwards, without displacements along the horizon and rotation. Skydivers call this body position "box position". In this position, the body is in a deflection position, the parachutist's center of gravity (CG) is on the same vertical axis as the center of pressure (CP) of the air flow.
The torso and hips lie in the same horizontal plane, the shins are bent at the knee joints at an angle of up to 90 degrees, the socks are pulled back. The angle between the hips up to 90 degrees. The arms at the elbows are bent 90 degrees. The angle between the body and the shoulder is 90 degrees. Shoulders and head are raised. The fingers are brought together. Fingertips and nose are on the same line. The muscles of the body are in a semi-relaxed state. The key points in taking a pose are deflection, symmetry and relaxation. This body position is “basic - neutral”, that is, all other body positions for maneuvers in free fall are made from it with the help of minimal body movements.
The speed of a parachutist's fall depends on the time of fall, the density of the air, the area of the falling body, and the drag coefficient. The mass of the falling body has little effect on the rate of fall.
A body falling in air is acted upon by two forces: the force of gravity, always directed downwards, and the force of air resistance, directed against the force of gravity. The rate of fall will increase until the force of gravity and the force of air resistance are balanced. At the beginning of the movement of the body in the air, the speed increases, then it becomes slower, and finally, at 11-12 seconds, the speed becomes almost constant. This state is called steady fall, and the corresponding speed is top speed.
In addition to the duration of the fall, the speed of the body is greatly influenced by the height of the jump, weight, size and position of the body.
Since the density of air changes with height, the rate of fall will also change. The farther from the ground, the faster the fall will be, because. air density decreases. Your fall speed will not exceed 35 m/sec. After separation from the aircraft, you will descend under the stabilizing dome.
Loads arising from the opening of the parachute.
The fit of the harness system is of great importance in relation to the load-bearing during the opening of the parachute. The more evenly and densely the straps lie, the more evenly it is distributed over the body. For the transfer of loads, the state of the body is essential - whether it is tense or relaxed. In anticipation of a breakthrough, the skydiver must group and tighten his muscles. In this case, the "blow" will be transferred much easier. The head must not be turned to the side or tilted, because. straps can cause bruising.
Parachute control in the air and its physical essence.
Under the control of a parachute is understood the possibility of changing its position in space by maneuvering in direction and speed. Horizontal movement can also be achieved on a round dome.
To create forward horizontal movement needs to be tightened front straps, creating a slide for the dome, and hold it in this position for the time necessary to move. In this case, the horizontal speed will be approximately = 1.5 - 2m/s.
In order to get horizontal movement back, left, right, you must respectively pull the rear, left or right straps.
When the lines are pulled up, the edge is lowered, the canopy is skewed, while the main part of the air begins to exit from the opposite side, a reactive force is created and the parachutist begins to move.
Decline of a parachutist on one and two domes.
The speed of a skydiver relative to the ground upon landing depends on: sink rate; wind speed; parachute control; the presence of swing.
The vertical speed of a parachute system depends on: the weight of a person with a parachute; drag coefficient of the parachute canopy, which depends on the area, the shape of the canopy and the breathability of the material; air density.
It is roughly considered that if the body weight is increased by 10%, then this causes an increase in the rate of descent by 5%.
For example: the weight of a paratrooper with a D-6 parachute is 100 kg - the rate of descent = 5.0 m / s, and with a weight of 110 kg, the vertical speed = 5.25 m / s.
Depending on the height of the terrain above sea level, the rate of descent is measured something like this: with an increase of 200m, the speed increases by 1%. In winter in frosty weather, when the air density increases slightly, the rate of decline can be considered 5% less than in summer in hot weather.
The descent of a parachutist on two canopies is slightly reduced compared to the rate of descent on one canopy. The reason for the slight decrease in vertical speed is the collapse of two canopies during the descent, which entails a decrease in the area of the canopies operating relative to the ground.
Where to aim? Maggie crashed onto the stone floor of the station, but his fall was halted when he crashed through the glass roof a moment before. It hurts, but it saves. A haystack would do too. Some lucky ones remained alive, having landed in a dense bush. The thicket is also not bad, although you can run into some branch. Snow? Just perfect. Swamp? A soft, vegetated bog is the most desirable option. Hamilton talks about the case when a skydiver with a parachute that did not open landed directly on high-voltage wires. The wires spring back and throw him up, saving his life. The most dangerous surface is water. Like concrete, it is practically incompressible. The result of falling on the ocean surface will be about the same as on the sidewalk. The only difference is that asphalt, alas! — will not open beneath you to forever devour the broken body.
Without losing sight of the intended goal, take care of the position of your body. To slow down your fall, act like a skydiver on a high jump. Spread your legs and arms wider, throw your head back, straighten your shoulders, and you yourself will turn your chest to the ground. Your frontal resistance will immediately increase, and there will be room for maneuver. The main thing is not to relax. In your, frankly, predicament, the question of how to prepare for a meeting with the earth, unfortunately, remains not completely resolved. An article on this subject was published in the journal War Medicine in 1942. It said: "In an attempt to avoid injuries, the distribution of loads and their compensation plays a large role." Hence the recommendation - you need to fall flat. On the other hand, a 1963 report published by the Federal Aviation Administration (FAA) states that the classic grouping adopted among skydivers will be optimal for saving life: legs together, knees higher, shins pressed to the hips. The same source notes that disaster survival is greatly facilitated by training in sports such as wrestling or acrobatics. When falling on hard surfaces, it would be especially useful to have some skills in martial arts.
Japanese skydiver Yasuhiro Kubo trains like this: he throws his parachute out of the plane, and then jumps out himself. Dragging the process to the limit, he catches up with his equipment, puts it on and then pulls the ring. In 2000, Kubo jumped at a height of 3 km and spent 50 seconds in free fall until he caught up with the satchel with his parachute. All these useful skills can be practiced in safer environments, such as free fall simulators - vertical wind tunnels. However, simulators will not allow you to work out the most crucial stage - a meeting with the ground.
If the water surface is waiting for you below, get ready for quick and decisive action. According to the surviving lovers of jumping from high bridges, we can conclude that the optimal entry into the water would be a “soldier”, that is, feet first. Then you will have at least some chance to get to the surface alive.
On the other hand, famous cliff divers who hone their skills near Acapulco believe that it is better to enter the water head first. At the same time, they put their hands with interlaced fingers in front of their heads, protecting it from a blow. You can choose any of these positions, but try to maintain a parachuting position until the very last second. Then, above the water itself, if you prefer to dive "soldier", we strongly recommend that you strain your buttocks with all your might. It would not be too decent to explain why, but you can probably guess for yourself.
Whatever surface awaits you below, in any case, do not land on your head. Researchers from the Institute for Road Safety concluded that in such situations, the main cause of death is a traumatic brain injury. If you're still being carried head first, it's best to land on your face. This is safer than hitting the back of the head or the top of the skull.
07:02:19 Altitude 300 meters
If, having fallen out of the plane, you started reading this article, then by now you have reached just these lines. You already have the initial course, and now it's time to pull yourself together and focus on the task ahead of you. However, here is some additional information.
Statistics show that in the event of a disaster, it is more profitable to be a crew member or a child, and if there is a choice, it is better to crash on a military aircraft. Over the past 40 years, at least 12 plane crashes have been recorded in which only one person survived. On that list, four were crew members and seven were passengers under the age of 18. Survivors include Mohammed el-Fateh Osman, a two-year-old child who survived a Boeing crash in Sudan in 2003, landing in the wreckage. Last June, when a Yemenia Airways liner crashed near the Comoros, only 14-year-old Bahia Bakari survived.
The survival of crew members can be associated with more reliable passive safety systems, but why children are more likely to survive is not yet clear. FAA studies note that children, especially those under the age of four, have more flexible bones, more relaxed muscles and a higher percentage of subcutaneous fat, which effectively protects internal organs. People of small stature - if their head does not stick out from behind the backs of aircraft seats - are well protected from flying debris. With a small body weight, the steady rate of fall will also be lower, and a smaller frontal section reduces the chance of running into a sharp object when landing.
07:02:25 Altitude 0 meters
So, we've arrived. Hit. Are you still alive? And what are your actions? If you escaped with minor injuries, you can stand up and smoke, as did the British Nicholas Alkemade, the tail gunner, who in 1944, after falling from a six-kilometer height, landed in a snow-covered thicket. If no jokes, then there is still a lot of trouble ahead of you.
Consider the case of Juliana Kopke. She flew a Lockheed Electra on Christmas Eve in 1971. The liner exploded somewhere over the Amazon. The 17-year-old German woman woke up the next morning under the jungle canopy. She was strapped into her seat, and there were piles of Christmas presents all around. Wounded, all alone, she forced herself not to think about her dead mother. Instead, she focused on the advice of her biologist father: "Lost in the jungle, you will go out to people, following the flow of water." Kopke walked along forest streams, which gradually merged into rivers. She avoided the crocodiles and pounded the shallow water with a stick to scare away the stingrays. Somewhere, having stumbled, she lost a shoe, only a torn miniskirt remained from her clothes. Of the food, she had only a bag of sweets with her, and she had to drink dark, dirty water. She ignored her broken collarbone and the inflamed open wounds.
After separation from the aircraft, the parachutist flies for some time in a horizontal direction at a speed equal to the speed of the aircraft. But as a result of air resistance, the horizontal speed gradually decreases. At the same time, under the influence of the force of gravity, the parachutist acquires an increasing vertical speed every second and makes an accelerated downward movement. However, as the vertical speed increases, the air resistance also increases, and in the end, there comes a moment when the parachutist's falling speed reaches a certain limit and no longer increases. This speed is called the critical (limiting) speed.
Consequently, the critical speed (V, m/s) depends on the weight of the skydiver (W, kg), the average drag area of the skydiver (S, m2), mass air density (p), and drag coefficient (Cx).
If the globe were not surrounded by an air shell, the speed of the fall of a parachutist would increase by 9.81 m every second (acceleration of gravity. g). It is not difficult to imagine what would have happened to him at the moment of landing. However, fortunately, the globe is surrounded by an atmosphere and its air layers resist the body moving in it. Therefore, after a certain time, the speed of a freely falling body stabilizes. After how much time will this moment come in the free fall of a parachutist and what value will the speed reach? I have not had to make long jumps, and therefore, to answer this question, I will use the data contained in the literature. When jumping from a height of 2000 m, the specified moment will come in 12 seconds. free fall, and the speed will reach 53 m / s. If the jump is made from heights of 4000, 10000 and 16000 m, this moment will occur in 14, 18 and 23 seconds, respectively. free fall, and the speed will be 59 (over 200 km/h), 80 (about 300 km/h) and 115 m/s (over 400 km/h).
As I mentioned above, high-altitude long jumps were made in the Soviet Union and other countries. Paratroopers during such jumps separated from the aircraft at high altitude and opened the parachute 200-300 m from the ground. Below I give, however, rather outdated data regarding the records that were set at one time.
An ordinary parachute is designed to open after 40-50 m of free fall of a parachutist, that is, after about 4 seconds. after separation from the aircraft. In other words, the opening occurs when the inertial speed is almost gone. So, when we made jumps, the parachute opened approximately after
55 m free fall, or after 4 sec. from the moment of separation from the aircraft.
In conclusion, I will give the formulas by which the critical velocity V and the air resistance force R are determined:
where S is the average resistance area (parachutist - 05-0.9 m2, parachute - 50 m2); p - air mass density (near the ground - 0.125, at an altitude of 6700 m - half as much, at an altitude of 500 m and below - an average of 012) - Cx - drag coefficient (parachutist - 0.04, parachute - 0.6-0.8 , a well-streamlined physical body (in the fall) - 0.025-0.03).