HARNESS SAFETY
My name is Simone Caldana
I am one of the owners of the Woody Valley Company.
I am writing this article in my role as design supervisor and paragliding harness designer.
Pilots often ask us about safety and with this article I hope to satisfy at least in part their curiosity.
These are some of the most frequently asked questions:
What is the DHV and how do we perform the tests?
Is the emergency parachute holder positioned ina safe place?
How high isthe hook-in point of the harness?
There is no need to say that we pay particular attention in safety, both for the responsibility we take on for our clients and to ensure a certain continuity of our company.
Not always the sense of responsibility is enough to guarantee safe products and for this reason our harnesses are made and tested according to the standards provided by the DHV homologation.
DHV (Deutscher Hängegleiter Verband)
The DHV is a body legally authorized by Germany and Austria. The DHV deals with the safety control of free flight products(paraglider and hang-glider) and sets the test standards on the products and the parameters that must be met by the manufacturers.In Germany and Austria flying can be forbiddenif the products do not bear this homologation. This homologation is not mandatory in any other country, but it is commercially accepted and very often it is requested also in other countries, thus proving its validity as a control means.With regards to the harnesses there are threekinds of tests to be performed:
breaking load
crash test
FLYING TEST
The BREAKING LOAD comprises four different tests with various loads. Once these are reached, they must be kept for 10seconds without showing any substantial breaks in the tested product.Initially, the maximum load for which the homologation is required is specified, for example 100 kg.The hook-in point of the main karabiner is tested with 9 positive G only on one side, (that is to say while flying). In our case a 9-G load will be applied(equal to 9000 N) to homologate a harness with maximum load of 100 kg. Do notbe deceived by the position in the picture. In truth the dummy is pulled from below. The test is performed upside-down so that the karabiner loop is notalready loaded with the dummy weight (ca. 40 kg) before starting the tension ingtest.
Both karabiner loops are tested with 6 negative G simulating the pilot’s positionupside-down. In this case, the buckles hardly do any work while the seams aretensioned in the opposite direction compared with the normal use.
The bridle to which the emergency parachute will be hooked is tested with 9 G. Asyou can see in the picture, since it is possible to connect both to the V-shapethat starts from the shoulders and to the single loop near the shoulder, the test is performed in the hypothetically most unfavourable condition, that is to say only in one point.
The last breaking load test is performed on the loops that are used when towing. Onboth towing loops a 3-G load is applied. In this case we do not have the photo of the test performed at the DHV. We took this picture before executing the official tests at the DHV. The unusual cross of the straps simulates thesupporting strap of our "Velvet" harness. All the details used in thevarious harnesses were tested with a dynamometer. This is to avoid any possible failure during the official tests at the DHV that would result in a waste of energies.
Once the loading test is over we proceed withthe CRASH TEST or impact test for the back protections.
Research on the ejector seats for military air planes suggests that a medium-built man can withstand up to 20 negative G(“negative” means during deceleration) on his spine for a few split second ssuch as during an impact.
This is the data accepted by the DHV.
Thus during the test the harness is fixed on a moving structure with a global weight of 44 kg that simulates the pilot’s lower back.
The weight of the test is so low because it is thought that, when falling down, a person’s feet, legs and arms fall down atthe same time in the attempt to safeguard the lower back. Thus part of the body weight is not loaded on the spine.
The harness is fixed in this way and let falldown from a height of 1.5 m. An electronic sensor on the cart reads the deceleration exercised on the spine and is measured in negative G. If the value is lower than 20 negative G, then the protection passes the test.
1.5 m may seem a small height, but if you letthis cart fall from 20 cm without any protection, you reach nearly 100 G. This happens because it is a rigid structure.
But the reality is a little more reassuring: a protection that barely remains within 20 G when falling down from 1.5 m in truth will save your life from 4 metres or more. First of all because it isvery unlikely to fall down on a steel plate like in the test. Second becausethe body is also made of soft tissues and flexible bones that help dampen smalland medium impacts.
Third because it rarely happens to fall down vertically on the spine. There is often a movement that slows down the vertical falling speed compared with the appearances or to the free fall.
Also for the crash tests, going to Munich(Germany) where they perform all the DHV tests implies remarkable efforts in terms of time, energy and also money.
We decided to build our own crash test machine ,so as to avoid failures and numerous transfers. Our aim is to obtain the best protection before executing the official test at the DHV.
So far our results are truly excellent: you only have to consider our latest homologated harness, the “MIX-AIRBAG”. Were ached only 8.4 negative G, greatly lower than the 20 negative G required by the test.
We designed the mechanical components of thecrash test machine with a simple and cheap, yet functional structure. Thanks tothe experience gained with the past DHV tests performed on our protections, weimproved the system of hooking the harness to the structure.The partially visible wooden part has the sameshape as the DHV’s. The weight of the moving mass is the same. Everything ismounted on carts with bearings sliding on a track that is normally used to movethe blocks on sailing boats.Our results are very similar to those obtainedat the DHV (+/-5%).We obviously had to buy the decelerometer andthe software to analyse the data collected. This device can measuredecelerations up to 60 G and is normally employed to analyse the stress onvaluable goods during plane transport.During the third and last test the harness istested during flight to check that there are no remarkable manufacturingmistakes that can hamper the flying procedures and that cannot be observedduring the previous structural tests.In the past, the holder of the homologationcould only be resident in Germany and Austria, but this regulation was modifiedthree years ago so that we now hold the licence for the DHV.To do this we had to submit quite a complexdocumentation showing the manufacturing procedures and above all the safety andquality controls that we carry out.Then a DHV representative came to check thatwhat we declared with respect to the production stages and the quality controlwas truly fulfilled.
THE EMERGENCY PARACHUTE
When talking about safety, the position of theemergency parachute holder and how the parachute is inserted in the holder isanother issue of the utmost importance.
The requirements are:
* the easy extraction with a visible handle.
* a short as possible connection between the parachute and the extractionhandle.
* a central position that does not hamper the take-off.
* Some years ago all manufacturers mounted the emergency parachute holder on the back. Today, this position is no longer used as it does not meet all the requirements and since it can provoke anon-homogeneous impact surface compared with the linearity of the spine in case of a backwards fall.
Today the preferred positions are under the knees, on the side or at the front.The lateral or front positions best respect thesafety standards required. While the position under the knees keeps the frontfree for use of the ballast (when necessary). This is fixed to the mainkarabiners and does not affect the pilot's centre of gravity.How the parachute is inserted is of utmostimportance. The handle must be as close as possible to the parachute casing,thus giving a more effective release action.A free bridle of about one metre inserted in theholder permits the extraction and release of the parachute without itstensioning. In this way the inner container is opened in advance, thushampering the dropping phase. In this case the parachute will not have arelease thrust and so will take longer to fully open.The operations to fold and insert the parachuteare carried out every six months or once a year at most, so it is impossible toforget the correct procedures.The best thing to do is to ask an expert to dothis, but be sure that they do have a specific experience in this field.If you do it by yourself, you had better hangon to a simulator and check the functioning of the extraction and drop.It is well-known that the paraglider is theflying equipment where a wrong judgement can most seriously affect the chanceof an accident.So try at least to carry out carefully thepre-flying controls that can greatly reduce the accident rate.
ADJUSTMENTS AND STRAPS
The first adjustment changes the seat depth (not available on all models) by adjusting the side trimmers. With this adjustment the entrance into the harness after the take-off is even more difficult.
When adjusting the back (sidebuckles), you must choose the torso inclination with respect to the verticalaxis while flying. Taking on a too vertical position with the head between theparaglider straps can increase the perception of turbulence during flight. Thebest position is with the face at 15 cm. This allows the pelvis and the lowerpart of the body to follow the movements caused by turbulence, while the upperpart of the torso and the head stay still in a central position. This reducesthe perception of turbulence and the overcorrections produced by the possiblemovements of the shoulders and arms.
The shoulder-strap adjustmentoffsets the variations in the pilot's height. For a greater comfort, theshoulder-straps also support part of the torso weight.
The chest strap regulates thedistance between the two karabiners. The best adjustment can vary between 40and 44 cm. A wider opening does not allow a better manoeuvrability, while witha tighter closure we increase the chance of twist in case of asymmetric closingof the sail.A high positioning of the leg strap bucklesallows a more ample movement of the pilot’s thighs. It is important to find theideal sitting position during take-off without using your hands trying itbefore with the simulator. If you find it impossible not to use your hands,check again the sitting angle and then adjust the leg straps. When you can reachthe sitting position without your hands, the adjustment is correct.I would like to point out a few aspects aboutthe straps and hook-in points.It is not true that the harness can be moreeasily manoeuvred when the hook-in point is lower and vice versa.And, as said before, it is not true thatclosing the chest strap in case of turbulence can solve the problem.The harness stability or instability depends onmany factors:
the seat width
the chest strap width
therigidity of the resting structure
the deformability of the ABS triangulation
the height of the hook-in point
the height of the chest strap compared with the hook-in point
supplementary features (front protections, positioning of the emergency and of the ballast)With a compromise between all these factors, we can obtain the right manoeuvrability for the pilots to which the harness is destined.In conclusion, I would like to say that I do not paraglide; I only tried three times about ten years ago. But I have hang-glided for many years. This just shows that you do not need to fly to produce good harnesses and our results are confirmation of this. In fact, itcan often be a limit because the design can be strongly affected by the way youfly, which may not necessarily be correct or approved by the majority of pilots.No doubt the help of many people who fly is fundamental. Listening to them all and collecting each one’s useful tips. And all this with the awareness that what we produce is always a sort of compromise that can be considered excellent by many, but at the same time, inadequate by others.
