Reflex profile
What is a reflex profile
Simply put, it is an aerofoil which – in case of decreased angle of attack – automatically tends to have it increased again. In other words, it always stays in neutral position regarding its load. On drawings it’s an aerofoil that has its tail turned upwards.)
One of the most distinct features of the paragliders equipped with reflex airfoil as opposed to classic paragliders is their substantially increased stability on high speeds.
As always in nature, nothing is for free. In case of longitudinal self-stability you pay for it with lesser lift coefficient. It means that in order to get good glide ratio you have to choose proper wing shape and aerofoil thickness. With paragliders there comes additional problem, namely big forces needed to steer it. These are main reasons why you don’t find full reflex aerofoils among free-flying paragliders. In our designs we solved these problems through carefully adjusted rigging as well as introducing several new solutions like ALC and TST systems.
With PPG or PPC canopies worse glide ratio is not that problematic, because there is always an engine to help, while self-stability means that even in turbulent air you can feel completely safe (and fly with hands in your pockets) Considering limited maneuverability of a glider burdened with paramotor this is an extremely desired feature. Last but not least, with such big margin of stability reflex canopies can be safely flown at much higher speeds than classic paragliders.
Differences between airfoils
In reflex-airfoil paragliders releasing trimmers and activating speed system results in shifting pilot’s weight towards leading edge, so that A and B rows carry almost all of it while C and D rows get relieved.
The opposite happens in classic paragliders – with increasing airspeed load on the A and B rows decreases, while more is carried by C and D lines. In some extreme cases full acceleration can lead to total unloading of the A risers, with subsequent frontal collapse (front stall).
The important question is, how to discern a reflex paraglider from a classic one? Currently there is quite a number of paraglider available claiming to be partially or semi-reflex, and no one knows for sure what does it exactly mean.
Sometimes such names are a mere marketing tricks, aimed to use established position of fully reflexed designs. However, there is a way to prove if there is a reflex attitude present or not.
In 2006 an idea was born within Dudek Paragliders concerning effective measurement of variable loads occurring at individual risers.The idea was brought to life by a Swiss test center Air Turquoise (http://www.para-test.com), while detailed technical solutions were prepared by École Polytechnique Fédérale de Lausanne.
