Reflections on the aerodynamics of harnesses

Improving airfoil performance by improving the lift/drag ratio

Reduced wingtip vortex

Reduced line yardage (4 -> 3 -> 2 lines)

Reduction in pilot drag by switching from a seated to a lying position, harnesses , and harnesses profiling.

But what is the influence of these different parameters?

At maximum glide speed, drag is roughly divided as follows:

50% induced drag (linked to profile lift)

50% of friction drag is distributed roughly equally between the friction drag of the sail fabric, the lines, and the pilot. (The surface area of 250 m of line with an average diameter of 0.8 mm is equal to 0.^{2 m²}, which is approximately equivalent to a modern harness as measured in a wind tunnel.)
At higher speeds, induced drag will decrease (as lift decreases), while other types of drag will increase with the square of the speed, but without knowing exactly what their proportions are.

Thus, pilot drag represents around 20-25% of a paraglider's total drag.
Assuming that it is still possible to reduce this drag by 50% (i.e. a drag equivalent to a surface area of 0.^1m2), we could theoretically gain 1 point of glide on a glider of glide ratio 10.

But in reality, the switch from a seated to a reclining position (theoretically from an estimated 0.^35m2 to 0.^2m2), which represents a theoretical gain in drag of 40%, has not resulted in the equivalent theoretical gain in glide ratio.
Similarly, since the appearance of certain rear-profiled models, there has been no clear impact on performance gains, even though bottom drag is clearly the penalizing element in aerodynamics.

We wanted to find out more, but lacking the resources to launch a large-scale wind-tunnel test campaign, we went down the road of digital simulation, without any illusions about the actual value of the results obtained, but more betting on their comparative qualities.

Several profile shapes were designed. The results were intended both to study the drag generated by these shapes, at the global level, and to break this down into lift/induced drag.
But another avenue soon emerged: the polarization of these shapes. Indeed, there's no point in having the most aerodynamic shape possible, if you can't keep it in its optimum position. In paragliding, the angle of incidence varies by more than 5° as a function of flight regime, and there's no way of controlling our attitude in the air precisely and accurately.

Comparisons between photos of wires laid on a current Kanibal Race and the flows obtained in simulation show that the latter are clearly too clean, but not completely far-fetched.

The various shapes modelled are as follows:

Kanibal Current race.

Cutting-edge profiling like we're seeing these days.

Bow profiling to avoid a downward-sloping profile.

Head and shoulder profiling, with different shapes

Without giving you the details of the results, compared with a current Kanibal Race, it's clear that current tip profiles don't help, partly because they don't address the problem, but also because the scoops needed to shape them compensate for their low gain.
Surprisingly, it seems that with these current geometries, it's much more interesting to have the airflow coming from the bottom (by about ten degrees, i.e. a very flat attitude), and not to have the cocoon well aligned in the airflow.
In fact, since the clearly penalizing zone is the upper body, neck, head and arms, by having the flow arrive from below, the body of the cocoon "masks" this penalizing zone and improves the flow. Having feet that point slightly downwards is clearly catastrophic.
So stop making fun of your buddies who have their feet in the sky - they're the ones who've got it right!

It's also clear that clean shaping of the shoulders, head and neck helps a lot.

The bow profiles are good, but not very tolerant of the angle of attack of air streams.

There's not much to be gained by unduly extending the length of the profile. What is gained may be lost in part through the increase in wetted surface?

Some geometries are more tolerant of airflow orientation than others.

Ultimately, the maximum potential gains are around 20% with the optimal base, on the 20% drag allocated to the harness. That's 4-5%, so probably even less in reality. We are therefore talking about an improvement in glide ratio of a few tenths of a point. This remains a significant factor in competition.