Thinking about ... connector resistance

In the paragliding world, we regularly use connectors to link our different supports: glider, harness, rescue risers, rescue, 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!

They exist for gliders, harnesses, spreaders and reserve parachutes, but in free flight there are currently none for connectors, which are the link between all these elements.

Let's take a 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 glider undergoes 2 tests: one involving a violent impact (1000 daN to 1200 daN) on the glider, which must emerge unscathed (it's the calibrated fuse that must break, not the glider or its components), and a structural resistance test which consists of a incremental load increase, with the glider inflated at the rear of a vehicle, up to a maximum of 8G, i.e. 8 times the maximum PTV. of the glider concerned. Once this value has been reached, the glider is released for analysis. No structural damage should be observed. This load is distributed over the entire canopy, from the fabric, seams and lines to the risers. And it's these that will receive the connectors that link the glider 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 wing's maximum PTV, divided by 2 (for each connector). For a wing with a maximum PTV of 145kg, this gives a minimum resistance of 5.8kN on each connector. (8xGx145)/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 PTV 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 PTV of 240kg on tandem wings, 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

When considering the rescue parachute and its connection to the harness, it is unfortunately not possible to refer to a strength value quoted in kN. This is because the structural test is not carried out in the same way as for canopies, with a load increase and a calibrated fuse. The reserve parachute and its test system are released from a height sufficient to reach a speed of 60m/s (at the most restrictive), then the opening is triggered. The parachute must withstand this test without any damage. Unfortunately, it's not possible to extract a kN value that would help us define the minimum strength of the connector to the reserve risers or harness (if the reserve risers are an integral part of the reserve parachute). We'll have to find another way of determining this value...

HARNESS: EN 1651 standard

The harness is the central piece of paragliding equipment. The glider and rescue system (parachute and risers) are attached to it, either directly or via various connectors. The reference standard will therefore be of prime importance when it comes to the expected structural strength of the connectors.

For all structural strength tests, the standard refers to a pilot mass of 100kg. For this reference, the highest load subjected during testing is 15000N (15kN), equivalent to an acceleration of 15G. As a reminder, the acceleration taken into account on canopies is 8G. If manufacturers wish to homologate the harness for a weight greater than 100kg, the test will be weighted by a correction factor corresponding to (Mc / Mref), where Mc is the tested weight and Mref 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'll have 15 x 1.2 = 18kN.

For the wing 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 one particularity in this standard concerning emergency risers. If these are supplied and permanently attached to the harness, the test value is 15kN. On the other hand, if they are detachable or supplied separately, the load value applied to the rescue risers rises to 24kN! This theoretically gives us a minimum resistance of 12kN on the connectors that will have to link 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 that in order to comply with the various minimum strengths required in the different standards, the values of the connectors must be as follows:

- Connection between harness and solo wing: 7.5kN for a harness approved for 100kg, and 9kN for 120kg.

- Connection between harness (pilot or passenger) and tandem seat spreaders: Idem, 7.5kN or 9 kN

- Connection between spreaders and tandem canopy: 10.8kN

- Connection between rescue and solo rescue risers: 15kN if harness approved to 100kg, and 18kN if 120kg: CAREFUL: only if the risers are delivered permanently mounted on the harness and cannot be removed!

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

- Connection between harness and rescue risers (if detachable): 7.5kN for a harness approved for 100kg, and 9kN for 120kg.

- Connection of spreaders / tandem rescue: 12kN

Connectors currently available on the market are generally rated from 18kN to 26kN, whether in 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 "Thoughts on ... Connectors" for more details.