STUDY ON SHOCKABSORBING DEVICES FOR PARAGLIDING HARNESSES TO PREVENT SPINE INJURIES

Tested on September 29, 1996

Article translated from French and summarised by Ulf Arndt.

Tests were based on 8m/s horizontal (X) and 6m/s vertical (Z) impact forces. Six meter per second vertical is what one can expect on a reserve. The 8m/s corresponds to a 30km/h wind. This results in a combined impact speed of 10m/s. 75 percent of all accidents happen with impacts below 36km/h (10m/s). A test dummy which allowed me asurements of accelerations in the brain, middle spine and lower spine was used in a slightly leaning back sitting position.

The following combinations were used:
1. Sup-Air harness (Profeel II) with 10+14 = 24 cm foam. Using Mousse Bag 10 and Mousse Bag 14. Called Mousse Bag 24. Not marketed. (Takeoff could be dangerous with this combination.)
2. Sup-Air harness (Profeel II) with 14 cm foam called Mousse Bag 14.
3. Sup-Air harness (Profeel II) with 10 cm foam called Mousse Bag 10.
4. Air-Wave harness with Rap-Air (called Rap-Air).
5. Air-Bulle harness with Back-Up-II (called Back-Up II).
6. Sup-Air harness (type montagne) with a zip on Air Bag from Keller (called Air Bag).
7. A prototype rigid harness with integrated composite components. Designed by Mr. Lemaire, called Scarabee.
8. Sup-Air harness (Profeel II) with a Kevlar backplate and a thin polystyrene cover plus a 15mm foam (Kevlar).
9. Scorpio harness without any protection, as a control reference. (The results with this is always not acceptable as protection.)

A. With Maximum Accelerations measured in X and Z:
Found acceptable as backprotection are:
1. Scarabee
2. Air Bag
3. Mousse Bag 24

Not sufficient are:
1. Kevlar Backplate only
2. Rap Air
3. Back-Up-II
4. Mousse Bag 14
5. Mousse Bag 10

B. How hard is the punch / shock on impact (jolt)?
Found to be within acceptable human tolerances in Z (vertical):
1. Air Bag
2. Scarabee
3. Mousse Bag 24
4. Mousse Bag 14
5. Mousse Bag 10

Acceptable in X (horizontal):
1. Air Bag
2. Mousse Bag 24
3. Scarabee
Considered insufficent are Rap-Air, Back-Up-II, Mousse Bag 14
Classed as dangerous are Mousse Bag 10, Kevlar

C. Exposure time to accelerations:
Found to be within human limits:
1. Scarabee
2. Air Bag
3. Mousse Bag 24

Not rated sufficient are Rap-Air, Back-Up-II, Mousse Bag 14, MousseBag 10, Kevlar

Conclusion
From 8 available devices tested, 3 proved quite satisfactory, 3 were useless and 2 dangerous. It is encouraging that 3 completely different designs were really efficient.

On the Air Bag
Vertical Impact: This form of impact with the Air Bag is surprising. The dummy hardly moves. The lower area goes flat under the pelvis, inflates the back which supports the neck and works its way to the head support. This movement keeps the pilot upright and settles the dummy on the ground, sitting upright. Horizontal Impact: It is also clear that the half brake distance (about 15 cm) is not good enough as the dummy tumbled over.
It is the most attractive protection, light, compact, and gives a good headrest once inflated. Video shows that the first 15 cm of impact are useless in shock absorbing. The test showed that it is effective in the test environment and similar real inciden ts. (The Air Bag was kept under 45mbar pressure until impact, which is not the case if it comes off or gets twisted). An Air Bag got torn loose on impact in an accident (which was to the benefit of the pilot in that specific case ).
A bad practise is to bounce on purpose at landing with the airbag, which could result in weakening it.

It gives excellent support of the back in the absence of shear and with low accelerations in X (horizontal). However, with the measured accelerations in Z much lower than with any other protection device, the voluntary limits are still exceeded, and the device still spreads lots of acceleration into the body in Z. Shock absorbing is too soft at the beginning. (Time is required to pressure up the Air Bag). Pressure reaches approximately 0.6 bar and could result in bursting the bag, resulting in a direct contact of the dummy with the ground. An improvement could be to put about 10cms of foam under the seat, in case the bag bursts.

Editorial Comment: It is generally agreed that the best backprotection available is a combination of good thick foam protection AND the airbag. It can happen that the airbag was not closed properly, causing the air to spill out too fast, or that it burst on an exceptionally hard landing in a specific position. It is therefore still advisable to have good foam or other protection in the harness. Backprotection of the hard type (such as the Kevlar backplate only) is now regarded as not good enough, because it does not offer enough shock absorption.

The airbag does not increase drag - its profile provides a more aerodynamic shape to the harness. Provided it is fitted with care, the reserve should deploy without difficulty, even when fitted below or on the back of the harness. Airbags can be attached with the straps provided or sewn on (fastened by zips).

In spite of the use of certain names in this article, it is not concidered that those harnesses are worse than any other with similar thickness foam protectors.


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