Thinking about ... connector resistance

In the world of paragliding, we regularly use connectors to link our various pieces of equipment: wing, harness, reserve risers, reserve parachute, and spreaders.

They come in different shapes: square, trapezoid, oval, triangular, etc., in different materials: metal, textile (Dyneema), etc., and with different operating modes: self-locking, anti-reverse, etc.

Each has its own advantages/disadvantages, which will offer more or less optimal use depending on the area in which they are to be used. But if there's one aspect we all have in mind when talking about connectors, and which "worries" some people, it's their breaking strength. Basically, is this connector I'm using here strong enough?

How can you be sure that the model you've chosen is strong enough to withstand the various loads it will be subjected to? There are standards, of course!

There are standards for sails, harness, spreaders, and reserve parachutes, but in free flight there are currently no standards for connectors, which are the link between all these elements.

Let's look at each of the existing standards, to see what we can find as recommended resistance values at the various points where connectors could be found.

PARAGLIDING: Standard EN 926-1&2

Part 1 deals with structural strength, and Part 2 with flight behavior. We will therefore focus solely on EN 926-1.

As part of this certification process, the wing undergoes two tests: one involves subjecting the wing to a violent impact (1000 DaN to 1200 DaN), which it must withstand without damage (it is the calibrated fuse that must fail, not the wing or its components), and a structural strength test consisting of a load increase, with the wing inflated at the rear of a vehicle, up to a maximum of 8G, i.e., 8 times the maximum PTV of the wing in question. Once this value is reached, the wing is released for analysis. No structural damage must be observed. This load is distributed over the entire wing, the fabric, the seams, the lines, but also over the risers. And it is the risers that will receive the connectors used to connect the wing to the harness.

From this test, we can deduce that the minimum strength required on each riser (and therefore on the associated connector) must be 8 times the sail's maximum weight, divided by 2 (for each connector). For a sail with a maximum GVW of 145kg, this gives a minimum resistance of 5.8KN on each connector. (8x G x 145)/2 = 5.8KN (with G rounded to 10m/s²)

In the case of a wing designed for tandem flight, each connector linking the spreaders to the wing must have a minimum strength of 9.6KN. With a 240kg GVW loaded at 8G.

SPACERS: LTF NfL II 91/09 standard

A load corresponding to 9G of max PTV is applied to the canopy connection, using the pilot and passenger connections as anchor points (high and low points successively). The same tests are carried out with the reserve parachute anchor point. For a maximum GVW of 240kg on two-seaters, we obtain a load value of 21.6KN (with G rounded off to 10m/s²). Or 10.8KN on each spreader.

EMERGENCY PARACHUTE: Standard EN 12491

Considering the emergency parachute and its connection to the harness, it is unfortunately not possible to refer to a resistance value expressed in KN. This is because the structural test is not carried out in the same way as for wings, with a load increase and a calibrated fuse. The reserve parachute and its testing system are dropped from a height sufficient to reach a speed of 60 m/s (at the most demanding), then the opening is triggered. The parachute must withstand this test without any damage. Unfortunately, it is not possible to extract a value in KN that would help us define the minimum strength of the connector linking the emergency risers or the harness if the emergency risers are an integral part of the emergency parachute). We will have to find another way to determine this value...

harness EN 1651 standard

The harness the central component of a paraglider's equipment. It is to the harness that the wing and the reserve system (parachute and risers) are attached, either directly or via various connectors. The reference standard will therefore be essential in terms of the structural strength expected of the connectors.

For all structural strength tests, the standard uses a pilot mass of 100 kg as a reference. For this reference, the highest load applied during testing is 15,000 N (15 kN), which is equivalent to an acceleration of 15 G. As a reminder, the acceleration taken into account for wings is 8G. If manufacturers wish to certify the harness a weight greater than 100kg, the test will be weighted using a correction factor corresponding to (Mc / Mref), where Mc is the tested weight and Mref is the reference weight of 100kg. For a test at 120kg, we therefore have a factor of (120/100)=1.2, which will update all the load values. For the maximum value of 15KN, we will have 15 x 1.2 = 18KN.

For the sail connection, we have a test that applies 15KN symmetrically, and therefore applies 7.5KN to each of the anchor points. The same applies to the emergency riser anchors at the shoulders. In the event of a higher pilot weight (120kg), the minimum value on each anchor is increased to 9KN.

There is a special feature in this standard concerning emergency lifts. If these are supplied and permanently attached to the harness, the test value is 15 kN. However, if they are detachable or supplied separately, the load value applied to the emergency lifts increases to 24 kN! This theoretically gives us a minimum resistance of 12 kN on the connectors that will be used to connect them to the harness.

It's not easy to find your way around, is it?

The following drawings will enable us to relate these different values, and help us to see things a little more clearly. For each standard, a color and the associated minimum resistance value.

Rescue standard: EN 12491

CONCLUSION

Our previous analysis has shown us that in order to comply with the various minimum resistances required in the different standards, the values of the connectors must be as follows:

– harness solo wing connection: 7.5 kN for a harness for 100 kg, and 9 kN for 120 kg.

– harness connection harness pilot or passenger) / spreaders in two-seater: Same, 7.5 kN or 9 kN

- Connection between spreaders and tandem canopy: 10.8KN

– Connection of emergency lifts/solo emergency lifts: 15 kN if harness for 100 kg, and 18 kN if certified for 120 kg: CAUTION: only if the lifts are delivered permanently attached to the harness cannot be removed!

- Rescue/rescue riser connection, if risers are supplied separately and removable: 24KN. Valid for solo or tandem flights.

– Connection harness emergency lifts (if removable): 7.5 kN for a harness for 100 kg, and 9 kN for 120 kg.

- Connection of spreaders / tandem rescue: 12KN

Connectors currently available on the market are generally rated from 18KN to 26KN, whether made of Zicral or textile. Steel connectors are rated up to 28KN, and some textile connectors up to 30KN!

Resistance values are normally marked directly on the connectors, where possible.

So, in most cases, they're strong enough, provided you choose them wisely and use them in the right position. But as you've seen, this isn't always easy, since the various standards are not in phase with each other! The best way to be on the safe side is to use only connectors that are suitable for any purpose, and therefore have a resistance value greater than 24 KN, which is the most important minimum value in all these standards (in EN 1651 for independent emergency risers). You'll find this value on every connector. If in doubt, contact the manufacturer directly for further information.

Be careful, however, to take into account the other characteristics (locking, multi-axis work, fatigue work, dimensions) of each connector before assigning them a role.

We invite you to take a look at "Reflections on ... Connectors" for more details.