Increasing performance and safety on a Glider has many aspects and variables. One of them is the reduction of tolerance within the line set. In this feature, I’ll explain in detail how and why so much effort is required in achieving the perfect bridle.


You might ask why are we talking about Performance and Safety when the topic is about lines. The answer is simple...Because lines are the most important variable in both aspects. The key word here is accuracy. Only if the calculated line length from the 3D model is matching with the resulting Line Set will the Glider perform as intended - especially on high performance wings such as the BUTEO XC. The explanation therefore is quite simple: The more ribs a Glider has, the less ballooning will accrue. This means, that the glider will generally be more solid in terms of structural stiffness, as well as more sensitive to mistakes and variations within the lines. In terms of safety, an accurate Line Set ensures that the tested and certified Glider will remain in their specified parameters.

Looking into this line matter is key for every designer in order to enhance overall flight characteristics. Well, let’s have a look together:


Never heard about Loop Compensation before? Lucky you, because this topic has a frustrating side. Let’s take the BUTEO XC as an example: each line type has different diameters. If I want to connect two different lines together, I first need to calculate how much longer each connection needs to be be to reach the calculated 3D length from the DESIGN software. Just imagine that you have various line types connected together, including various lines attached to the Tree of lines. It will result in a Line Sheet like the one below, where each and every line connection has its own Loop Compensation. .

Without this compensation for each position, you will never be able to achieve a perfect result. If you make a mistake at one position in the Tree Line , this error will be forwarded to the Riser.


The Line Assembling is the second most essential part of the process to perfection. The way the lines are attached to each other, has to be defined prior to the Loop Compensation, allowing me to calculate the correct additions. In regards of the BUTEO XC, we start from the A-lines towards the Brake Lines, s and from the center of the Glider towards the tips.

The YELLOW marked circle explains which line has to be on TOP within a connection. The RED marked circle shows the hierarchy of how to assemble a TREE of lines.


As you know, all ICARO gliders are manufactured in Sri Lanka by AERO-DYNAMICS, and so far we’ve looked at this topic from a design perspective. So what about production? When looking for perfection, all production steps have to be tweaked as well. Every single line will be measured and marked under a specific load. After cutting, both sides are sewn to create the required loop. Now, each and every line is checked again. The tolerance herin cannot be greater than 1mm! Just imagine, if a single line would be 2mm too long and we have to connect 3 line levels together, this would result in a 6mm longer overall length. If we are adding a wrongly calculated Loop Compensation from another 2mm to each line connection, the overall error would be 12mm. These 12mm difference from the calculated 3D trim would be enough influence to change the Glider’s behaviours negatively.


So what’s the point? By tweaking and optimising all these aspects, we’ve been able to achieve and overall reduction in tolerance, from 10mm to 5mm within a tree of lines from the Glider down to the riser. This accomplishment has allowed me to develop the BUTEO XC with much higher precision than before, resulting in superior performance and safety.


Ralf Grösel

Ralf Grösel

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