Definition
Trimming is the measurement of the total line lengths (from the base of the risers to the bottom surface fabric). The pitch defines the front view of the glider and the angles of each rib. It influences all flight characteristics!
Design and tuning
The trim is calculated at the time of design and then improved to meet all performance, handling, behaviour and certification criteria.
This is a long-term process. With each change to the trim, it is necessary to ensure that an improvement in one element does not adversely affect others…
Designers and test pilots often change a few lines by one cm when the result of a certification test is not what was expected!
The total lengths of the lines are indicated to the nearest millimetre in the tables found in the technical documentation: user manual, manufacturer’s website, certification test report…
Measuring instruments
The type of measuring tool is not important! The differences between these tools are not in the accuracy, but in the speed of the measurement.
It’s all the rest, i.e. the analysis and the various modifications that are complicated and very technical.
Respect of the product !
When the timing no longer corresponds to the original one, we believe that the performance and all the behaviours intended by the designer and validated by the homologation are not guaranteed.
And therefore it is no longer the product you chose !
Tolerances
The tolerance is ± 10 mm in relation to the dimensions of the certified paraglider.
Our adjustments
For our part, we find these tolerance values to be quite high for the magnificent performance wings we have today. It must be said that the values have not been changed for over 30 years!
We can adjust the trim of your paragliders more precisely, generally from -3 mm to + 3 mm on the B’s and 0 to + 5 mm on the C’s and + 5 mm to + 10 mm on the rear lines (reference 0 on the A’s).
Is this really necessary ?
Yes, because we have noticed some problems…
Slow speed
Most of the time the glider becomes slower. The more loaded A’s and B’s get longer while the rears can even get shorter! It is not uncommon to find differences of 15 to 25 mm which can reduce the speed by several km/h, which is a bigger difference in speed than if you fly a size S glider and the same model in size L !
Asymmetry
In other cases, it was the glider that was not flying straight. With the large lever arm, a small left/right difference at the wingtips is enough to make the glider go off course.
By correcting the stall, it is fixed !
Instability
Roll instability on a major EN-B model is caused by pitch differences of less than 10 mm (across the span)!!!
If you buy me a drink, I’ll show you the make and model! 🤣
Other behaviours
We believe that these examples are just the tip of the iceberg, as it is easy to notice that a wing swings from right to left with its arms up and it is much more difficult to notice the differences in other behaviours, such as spiral instability or stall. Yet it can be quite surprising and annoying…
To know the influence of a bad setting, you would have to put a poorly set wing through the whole battery of certification tests…
It’s more efficient to go back to the homologated setting!
When should the trimming be measured?
After the first 20 or 30 hours of flight, the setting may need to be corrected. It is often already out of certification!
This was not the case more than ten years ago, because the lines were much more numerous and also bigger.
Recent paragliders are much more efficient and lighter. While there is no problem with strength with the excellent materials we have today, the pruning of the lines and the use of thinner lines means that the lines move more.
At the same time, the effect on the beautiful, tight and smooth performance profiles is greater.
The trimming should be checked
• after a few dozen hours of flying
• and then at least every year.
More often for paragliders
• high-performance
• used intensively !
Thirsty to learn more?
There is cause for controversy!
Eric Laforge
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