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Karma II

Friday 5 August 2011

The Karma II is now in production. We would like to briefly go over the various stages of its design.

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The Karma I was comfortable but the 17cm mousse bag made it bulky and difficult to pack into a standard backpack.
So our objective was to reduce the weight and the volume of the harness whilst maintaining the levels of durability, comfort and piloting precision.

1- Comfort:

The comfort of a harness depends directly on the way in which the pilot’s mass is supported by the material of the harness itself.
The mass must be optimally distributed, with no zones of discomfort, in a straight seated position as well as inclined in turns.
Up to 60% of a cross country pilot’s flight time is spent in thermals and for a leisure pilot flying locally the amount of time spent thermalling can reach 80%.
It is clear that the pressure points are very different in these two positions and that the comfort of a harness should also be judged in a thermalling position.

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pression assis-incliné

Thus the level of comfort provided by the lateral support should be consistent with that found in a straight seated position.
So we have been particularly careful to ensure that the harness is completely adapted to the pilot’s morphology in any position .
The level of comfort also depends on the level of roll damping and the capacity of the harness to filter certain movements.
Two systems do exist:

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ABS vs V
  • The two buckle V clip-in system used in the Karma I, which is adjustable in-flight, has the advantage of providing a very high level of damping which is independent of the waist strap setting. The inconvenience of this system is that it is not very progressive, it has a very on/off effect.
  • ABS has the advantage of being very progressive but is directly dependant on the waist strap setting (when stability is increased the risk of a riser twist is also increased) and the maximum level of damping is quite low compared with that of the V system.

For the Karma II we have succeeded in making the V system much more progressive. This makes the system easier to use and renders piloting in turns more progressive thus greatly improving the precision of the feedback to the pilot.

2- Active Security

Another aspect of the design effort concentrated on the ease of the transition from an upright to a seated position after take-off. The placement of the main strap (which acts as the centre of rotation for the transition to a seated position) was also improved as well as the shape of the seat board.
By improving the transition from an upright to a seated position we avoid the need for the pilot to use his hands to get correctly seated in the harness.
But just as importantly in the case of an in-flight incident the pilot will also be able to assume an upright position more easily in order to absorb the shock of a forced landing with his legs. (Legs are still a paraglider pilot’s best back protector!)

The reserve parachute pocket has also been redesigned, all types of reserve parachute, old or modern, compact or bulky, can be installed without risk of the parachute moving around in the pocket.
The reserve parachute handle still allows the reserve pocket to be opened even if the pod is installed inverted, and can now be operated by the left hand if the right hand becomes immobilized (a twist in the risers trapping the wrist or a tangle resulting from a collision etc.).

3- Passive Security

The Karma II is designed to be used as a main harness for intensive use.
In order to reduce the volume an airbag seemed to be the best solution. However an ordinary airbag has the disadvantage of providing little or no protection during the take-off phase. So we worked on a permanent airbag system, the Krash Box. As soon as the harness is unpacked the protector is effective thanks to a foam structure which gives the protector its shape and volume.
The shape of the side walls has been designed to optimize back protection. An airbag only starts to function when its internal pressure increases which only happens once the side walls have rounded out.

crash airbag

So for the same thickness an airbag with rounded side walls will be more efficient than an airbag with straight side walls.
What’s more the Krash Box will, up to a certain point, limit the sideways displacement of the airbag in the case of a shock in a non-vertical axis.

The Karma II equipped with its Krash Box satisfies the criteria of the LTF standard without having to be inflated. The second phase of inflation which occurs via the side air intake leads to a further increase in the protector’s performance.
However the certification crash test has led to certain pernicious developments recently.

Test LTF web

As the crash test protocol only tests the case of a direct vertical impact there are more and more back protectors on the market that are designed specifically to pass the certification but which do not take into account the behavior of the pilot and the harness during a real crash.
These protectors are thus of the most basic design positioned at the point of impact but do not protect the pilot’s back at all.

Real crash

We have chosen to give the Karma II back protector a maximum of volume by incorporating into the Krash Box an inflated segment which specifically protects the back.
Once the protector is inflated the harness satisfies the LTF standard even in a horizontal position.

However a reversible backpack-airbag solution has not been used. This option seems to us to be incompatible with a harness designed for intensive use. In the backpack mode the back protector can be damaged by the combined effects of friction, dust and UV. There is thus a risk that the airbag could fail in the case of a real crash because of premature wear.

4- Weight Reduction

Reducing the weight of the harness was also an objective.
This was achieved in part by replacing the large mousse bag, which weighed nearly 1kg, by the Krash Box.
But significant reductions were also made by using new stronger lighter materials.

  • Dyneema straps, three times lighter than the classic polyester straps.
  • High performance EVA foam with closed cells, in the place of traditional foam.
  • An improved understanding of the zones under constraint leading to an optimization of the placement of different materials allowing the weight of certain parts of the harness to be reduced without compromising its global durability.
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