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Paraglider Acceleration
via your Speed System

by Jorg Fedler

Pilots who are acquainted with paragliders know what a speed system is. But how many pilots do use it for maximum efficiency in flight? How many pilots do use it at all, except in situations where they have to because of strong winds?... Do we all know how to expertly trim this accelerator to bring everything into harmony? This article tries to explain the correct and safe usage of the “gas pedal”.

The “Gütesiegel” (AFNOR and DHV) have strict safety requirements.

This is one of the reasons why hand trimmers have generally disappeared on paragliders. In my opinion trimmers can be outright dangerous.

When you fly for maximum speed and get a collapse, then the last thing you want to do is to take your hands off the brakes; not even for a short moment.

For safety reasons your hands should be “glued” to the brake handles. They are the main controls to counter unevenness in your flight and should be treated with uppermost respect.

In comparison your speed system controls your glider speed much better than hand trimmers because it is dynamic whereas the hand trimmers are more or less static. In regard to versatility, a speed system always wins out against hand trimmers.

Different Systems

Older speed systems often pull down the B-risers first. This has stabilizing effect on the canopy, but you lose performance.
Others pull down the A- and B- risers simultaneously and the C- risers which are pulled down only half way.
Consequently the profile turns around the D- level and the trailing edge is slightly lifted. With that kind of system the leading edge is stabilized also because the A- and B- level are pulled together.
The profile become flatter the more you accelerate. Many speed systems on performance and intermediate wings pull down the A- risers a bit more than the B- risers. This gives you a better penetration or speed but can be a bit more tricky in rough conditions.

The Correct Fitting

We expect a speed system to be wise in construction and comfortable in its application.
Most speed systems are equipped with a 2:1 gear-ratio, meaning two pulleys are fitted onto each riser.

However, a 3:1 or 4:1 gear ratio would be more convenient to have. It consumes less strength and the angle of attack can be fine tuned much easier as there is a longer travel distance for your legs.
You may have to use a 2-step system to be able to fully extend your legs with a 4:1 ratio speed system.

On account of increased travel distance you will increase canopy control and the safety margin is widened as you cannot overreact that easily during sudden changes in flying conditions.

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It is important, that the first pulley on the harness is fitted approximately in the pilot's center of gravity. Otherwise you will tip back or forward while accelerating.
The result would be a loss in comfort and control, but more importantly: with a greater gear ratio you increase the travel distance of the speed system and reduce the strain on your legs. The picture (right), shows a system with a 4:1 ratio.

While accelerating the angle of attack is reduced and the profile is flattened.

When and how much to accelerate?

Most manufacturers trim their canopies for a maximum glide with “brakes off”. But most wings glide best when slightly accelerated. This becomes more and more true for performance gliders. Therefore designers develop a canopy for best glide combined with high speed.

The result is an increase in performance. Furthermore: with brakes off (neutral, un accelerated), the sink rate and the handling are optimized (best sink rate with brakes off and best glide when the speed bar is slightly pushed).

In headwind the best glide improves when you accelerate slightly. If you want to fly distances with the best average speed, you have to use your speed bar and change its position accordingly to the wind and lift conditions. The stronger the lift the more you can accelerate and the more headwind you encounter , the more you have to push the bar.

As soon as the thermals "work", 1 to 2 m/s (200-400 feet/min), you should fly slightly accelerated to maximize your flight performance. Flying with the throttle pinned to the floor can be outright dangerous. This should only be done when you encounter strong sink or strong headwind.

Dangers of acceleration

Pilots who use their speed system only to penetrate strong winds to reach the landing field are flying unsafe as any acceleration, reduces the angle of attack and your canopy's profile changes its shape. As a result the canopy is more prone to a collapse than it would be in a neutral shape.

As an example: when you encounter an asymmetric collapse during full acceleration, the loss of the laminar airflow and drag, associated with the deformation of the canopy on the collapsed side can get you into a negative spin.
The AFNOR-Gütesiegel does not include this test and the DHV-Gütesiegel will test this situation only up to the reproducibility as a standardized collapse in turbulent conditions is not possible. .

Accelerated flying during the landing approach can be dangerous as there is a higher risk that you may get into turbulence near the ground. If you find yourself in a situation where you have to use the speed system near the ground, it is important to know how much acceleration your wing “can take” before it gets too unstable.

Speed System with 4:1 ratio

ratio Note: “full throttle” near the ground can be outright dangerous.To find out the limits you best practice often with sufficient height.

Summary

Before you know exactly how much acceleration your wing can take, you need to practice at safe heights where you have a sufficient safety margin. Safety should always prevail before and while you are pressing your speed bar.




eagleRemember: Turbulence near the ground is more likely to be expected and the margin for recovery can be fine cut.
When you are not sure whether to press your speed bar or not, you should always decide against accelerating.

Flying is a challenge. Enjoy this challenge within the boundaries of your skills.

Jorg Fedler can be reached under jfe@bigpond.net.au or visit the web site http://www.clip1080.com



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