A falling parachute is subject to two influences:
Gravity (land attraction)
The resistance of the air
Basically, we can assume that the influence of gravity depends only on the mass of the parachute and its equipment. We will ignore the variation of the earth’s attraction as a function of altitude.
The resistance of the air is more complex to describe; It depends on many factors, and the resultant of its action is not always the same.
The factors that matter are in descending order:
The horizontal and / or vertical speed of the para: the greater the speed, the greater the resistance
The size (area) and the position of the parachute and its equipments:
The more exposed there is, the greater the resistance
The more the assembly has an aerodynamic profile (shape coefficient like Cx), the less resistance is great
To a lesser extent, the nature of the clothes he wears: the smoother the clothes (lycra instead of cotton), the less resistance is important; The more the garment is adjusted (as opposed to ample and “floating”), the less resistance is
Possibly, not very sensitive to the current altitudes (<4000), the density of the air; The air becoming scarce with altitude, the higher the altitude, the less resistance is important
For simplicity, the resistance of the air can be considered to be a force which applies to the exposed surfaces and which tends to oppose the movement (in this case the fall); In some cases, this force may also have non-vertical effects: horizontal rotations or displacements.
The points to remember are the following
If a given parachute maintains the same position for a long time (assuming that it succeeds, which is not always easy when it starts!), Its rate of fall will stabilize at such a rate that the resistance of the air Will exactly compensate for its weight.
At this point, the sensation of falling as you can know by jumping from a diving board to the pool (or a bridge attached to a bungy) disappears. The relative wind (the apparent wind created by the displacement of the para in the surrounding air mass) and the landscape aside, we feel as if we were resting on a soft surface, a kind of mattress. Just has the feeling of hovering!
The falling sensation itself – which gives the impression that the stomach and other normally immobile organs are moving – is not felt as a fall. This is also why the term “freefall” is improper: a truly free fall would be a fall in which the speed would increase continuously (uniformly accelerated motion), permanently giving the impression that the stomach ” Floats “inside!
Naturally, there are phases during which one feels the fall: these are all the phases of transition during which the speed will evolve in order to reach the equilibrium value:
Exit of the plane
Change of paratrooper position
It should be noted that the falling sensation does not occur by changing position unless the new position is more gathered or “contoured” (i.e. is such that the resistance of the air decreases); Otherwise, the falling speed will decrease, giving the impression of “braking”.
Image courtesy of Findadviser
“The following rules summarize:
If the velocity (of fall) is constant (zero, weak, or very great), the feeling of fall disappears (it does not necessarily thus feelings in general !!!).
If the velocity (of fall) increases, the feeling of fall is present, all the more clear that the variation of the speed is great
If the (falling) speed decreases, the feeling of fall does not appear (personal case); In fact, the sensation is not simple to describe, it must have lived it to realize well.
In short: the falling sensation depends on the variation of the speed, not on the speed itself.
Speaking of speed, we can give some orders of magnitude:
In stabilized speed, an average para, falling flat (belly to the ground, arms and legs spread) falls to 50m / s (180km / h).
Still in the same position, this speed can vary in a range of +/- 10% depending on the weight: 45-55m / s (162-198km / h).
In fast positions (standing, dive, or even sitting), the speed is much higher.
At the exit of the aircraft, it takes about 10 seconds for the speed to stabilize (assuming that the para leaves and looks for a flat position), and it is considered that it will have tumbled by 300 meters.
With regard to the aircraft precisely, an important element is the horizontal speed of the aircraft at the time of exit. Most jet aircraft (including helicopters) fly at a high (horizontal) speed, which can range from 120 to more than 180 km / h. So, as soon as one puts the nose out of the plane, one is placed in a relative horizontal wind corresponding to this speed. This has several effects:
For fast-flying aircraft, the loss of height for the first 10 seconds is slightly less than 300m.
The para has the feeling to have supports as soon as it leaves plane; In other words, jumping from an aircraft having a high jetting speed as the normally experienced drop sensation during the acceleration phase.
The last point explains in part the “sensational” character of the balloon jumps, for example: lack of initial horizontal speed, the para feels really falling during the first seconds, and in a perfectly unusual silence! (Honestly, engine, propeller and relative wind really make a hell of a row).
Travel & Positions
It is true that to feel falling, then to hover is a sensation so wonderful (especially when it is accompanied by a view … impregnable on the clouds) that one could almost make it the very goal of a jump . But to enjoy it, it is better to control his position and his movements.
And then, in a certain way, to master position and movements in the air is precisely the essential difficulty of this sport.
You will find some common positions there.
It’s funny, but seeing falling images, many people imagine it’s simple: just drop it. The main difficulty they identify is the very fact of jumping from an airplane, that is, overcoming a fear of the void. But, according to them, fear apart, where is the difficulty?
Well, to say that to overcome fear and its little sisters stress and anguish is not an element that is easily set aside, at least for the first jumps. But that’s not all.
First of all, in general, given that the air flow is sufficient to balance the weight of a para, it can a priori:
Fall more or less quickly (vertically)
Be animated by horizontal movements (which means that the point of the ground on which it is situated can move), rectilinear or not.
Turn on itself, around any axis.
To control each element, you must:
Understand how air acts on oneself, and how to predict the effect of a position, a gesture
Be aware – and with sufficient precision! – its position in the air (not cambered, too cambered, arms too bent, asymmetrical legs, etc.),
Know how to dose his gestures, coordinate his movements, remain toned but not tense
And well, believe me, it’s not simple! The first point may seem simple, and can be explained quite easily with diagrams or photos. That said, paratroopers do not all have the same morphology (limb size, limb weight, general flexibility, etc.), and the effect of a displaced hand or a tense leg will be different depending on the individual.
The second point is already less obvious. Let us not forget that we are in a completely unusual environment, subject to stimuli different from those we know, in unusual positions, and that we have (almost) no return: no sound, No self-image (moving the head to “see” how it goes on the feet is not a solution). In short, the problem is called “constructing a body pattern in unusual circumstances”. It comes with the habit, practice (parachuting of course, but also other sports).
With regard to returns: students have three types of return:
The comments of a monitor who observed the fall from the ground, using glasses It is rudimentary, it costs not, it is not always very effective, but it is better than nothing.
A video film taken from the ground by a monitor It is much better: we see, the comments of the monitor are related to the situation (genre, freeze frame and “well then, what are you doing With your hands here? “). The limit: it follows the jump of an easy 1/2 hour (or even more), the images are often backlit, so difficult for an unusual eye to spot details,
The signs, gestures and other corrective actions made in fall by a monitor “P.A.C”, in the case of a learning of type P.A.C. P.A.C = Progress Accompanied in Fall.
C.f. over there.
Question back, probably the ideal.
As for knowing how to dose, coordinate, feel, anticipate … it is because it has nothing to say that parachuting is … sporting. When, in addition, one chronometer, one measures the precision or one judges according to video the aesthetic of the movements, one obtains a sport of competition.
Well, in general, you have to know what a folded parachute looks like; For that, go see on this page. For an opening sequence filmed and commented, it is here.
Naturally various systems of opening of the main sail exist.
However, the essential point is this:
To adopt a stable fall position, facing the relative wind (thus generally facing the ground), and without rotation
Grasp a handle, compensating the gesture of the hand by a suitable movement to remain stable
Pull the handle and, as the case may be, bring it at arm’s length and release it, or throw it immediately, or keep it in the hand (as long as it is within 50 F)
Return to the starting stable position and wait (2 or 3 seconds) for the deployment of the sail
Once fully developed, or even during blossoming, grasp the controls and remove the half-brakes, check that the whole is in working order (broken line, blocked control, torn sail, etc.) and that the track is free Para under sail on the trajectory).
A remark concerning the contactors: they leave the plane at 2000m and immediately open their parachute, the work being done sailing open. This has two consequences: first, their position at the opening is not horizontal, but almost vertical. Indeed, at the exit of the plane, the main aerodynamic supports do not come from the fall (still nonexistent), but from the speed of release of the airplane. As the latter is flying horizontally (in principle!), The air flow is horizontal, and the opening position is therefore (rather) vertical. The second consequence is that the sail must be opened as soon as possible (in particular so that the parasites are not too dispersed); The opening system is therefore a “pull-out” and not a “hand-deploy”. It does not matter at the moment.
Once the chute is deployed, the paratrooper has two controls: two handles, each connected to a group of lines. Pulling the left-hand control tilts the left rear edge of the sail, and triggers a left-hand turn, all the more sharp and marked as the control is pulled quickly and over a long length. Pull the right control … same thing right 😉
Pulling both controls at the same time allows you to slow down without changing direction; (At the right time and with the right amplitude), one can thus practically cancel its speed (horizontally and vertically) to a few tens of centimeters from the ground, which allows for soft landings.
I will probably never tell the ignorant enough: the rolled-up is no longer topical.
This does not mean that the landing is no longer a delicate moment; Simply put, the equipment now allows to control its approach, both in terms of landing point and in terms of speed.
This animated gif weighs 400KB and shows a landing; The speed of the sequence should be half the actual speed.
It is perfectly visible the para lower the 2 arms to brake its sail and round.
Yet the statistics indicate that most accidents (fatal or not) take place perfectly open sail, landing. The trick is that to land by making a “flare”, but that is used in French to say “land in overspeed and brush the ground as long and as quickly as possible before definitively Stopping “), it’s really cool. The trouble is, that it is necessary for this to put its sail in overspeed; For this, it is necessary to “send” a turn just before the final. The problem is that the turns not only accelerate the sail, they are also accompanied by a significant loss of height. Thus, it is crucial to determine its turn according to its height; And this dosage, there are not many who have done wrong: turn too strong, sent too late, too low: impact with the ground at high speed, and voila.
If something goes wrong …
We must act quickly; Depending on the problem, we will try to resorb it once (usually by pulling the controls clearly), otherwise we will perform the backup procedure:
Release the main sail (“pull” on a handle on the chest, right)
Open the rescue parachute (by pulling a handle on the chest, left)
This procedure is not complicated, but one must be able to do it quickly and well; This is why it is advisable to repeat it often (on the ground or harness of libé!).
Examples of “things” that may be wrong:
At the moment of opening, the para seeks the handle of the extractor, and does not find it (example: it “unblocks”, and looks for it where it is not – perhaps because it jumps with A material different from the one he is used to–) or finds it but can not pull the extractor out of its pouch (extractor badly folded, or the para has grasped anything other than the handle of the extractor. .); The handle action is generally about 900m, ie 18sec before impact; Insisting and groping to get out this fucking extractor is the best way to go straight on the ground.
An error is made to the folding; The para finds the extractor, the spell, the coward and … nothing, it continues to fall to 180km / h; The para realizes that nothing happens, and turns his head to see what makes his extractor: the latter has taken the air, the halyard is stretched, but that’s all: the bag is blocked.
The POD opens, the POD comes out, goes up by unfastening the lines, the POD opens, the elevators stretch, the sail takes the air and begins to blossom; Instead of opening normally, it opens badly and starts in “autorotation”: the para is no longer really in free fall, but its sail does not slow it down enough, and is uncontrollable.
Broken line (s) or styling (s), torn sail, or broken drive (s)
…. it does not happen happily often, but when it happens: Procedure Relief!
A rescue parachute is smaller than a main chute it ‘s “sturdy”, it’ s boring, long and difficult to fold, it uses somewhat special techniques (POD perdable, Extractor, loop with elastic sewn, loop passing through the extractor, etc.), but it is designed to open, and open quickly.
Various systems exist that can complement an equipment:
LOR or RSL: it is a system of strap that triggers the opening of the rescue by the simple act of releasing; In all rigor, it is enough to release. However, since not all parachutes are equipped with it, it is better not to get used to counting on it and pull the rescue handle yourself (even if it’s useless).
Why do not all parachutes have this system: in VR it happens that at separation 2 paras are not sufficiently distant from each other and “hook” after opening, so sails open (Or rather veils). It is then interesting to be able to release, to wait in a short time (starting again to fall, or even to drift) to move away from the other, then to open the rescue.
Trigger: a mechanical, electronic or other device opens the rescue if the para reaches a limit altitude (eg 300m) with a fall rate too high to be normal.