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To Reflex or not to Reflex


5n1gel
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Gentlemen (and Ladies)

I am a newbe at early stages of investigation not wanting to get into any kit either for initial training or even initial purchase which will deter me from the sport - I am aware of some quarters intense dislike for Reflex wings while others are very pro etc etc ...however, the following is extracted from a manufacturer web site!

Please comment !

Regards Nigel

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A Specific airfoil for PPG:

Because of what I have explained above, performance in glide and sink rate for free flying and speed for the motor, it is obvious that wings need developing specially for each category.

Everybody in PPG today has heard about “auto-stable” or “reflex” airfoils. Here is the simple explanation of the benefits of this type of airfoil:

As I’ve said earlier, pilots want to fly fast to cover long distances, so needed in the concept is everything to make a paraglider fly at low angle of attack (to go fast) with maximum stability. The “reflex” airfoil acts as an automatic system that helps the wing to handle turbulence by delaying the point of break (collapse) by positioning the lift forces quite far forward on the profile.

In effect, the more you accelerate, the more effective the reflex is and the more solid your wing becomes: This means it’s more solid, but as I’ll explain bellow, that doesn’t mean it’s safer!

Also, a reflex profile is usually associated with poor aerodynamic performance. In order to achieve maximum speed, a competition reflex wing my require 100% thrust in order to maintain level flight in trimmers out / fully accelerated position. This is the case with the Viper, for instance, which is designed with an emphasis on speed.

So to summarize, reflex profiles have been developed for speed in paramotoring and is the best known solution for speed with a certain amount of solidity and comfort in flight.

The negative sides of reflex airfoils are less often discussed, but are just as important:

The reality of a soft canopy concept, rigged with lines, is that the pilot is always vulnerable to the possibility of canopy collapse. Reflex in the canopy profile delays the point where the collapse occurs, but the risk is ever present.

Additionally, another rule of soft canopy aerodynamics is that the faster the airspeed and the lower the angle of attack at the time of collapse, the more dynamic will be the reaction of the glider to the collapse. Because a reflex wing will not deform at the leading edge in turbulence, collapses are generally larger in surface and volume than in a free flight profile, and as a result of this tend to be more aggressive in dive and surge during collapse.

The forces described earlier are - “in a simple way” of explanation – naturally making the airfoil to increase its Angle Of Attack (AOA), even when outside influences are pushing it down, and there are other direct consequences from that :

The altered point of lift on a reflex profile (put simply) naturally encourages the wing to increase its Angle of Attack (AOA), even when outside forces are encouraging it to decrease. There are other direct consequences of this, such as:

Slower inflation / poorer launching. The glider is reluctant to rise and needs to be held with the A’s until overhead otherwise the glider tends to drop back.

Poor flying characteristics at high AOA (slower speeds). Delayed recovery from stall and a short brake range (spin tendency), and poor handling are symptoms of a reflex profile.

Inefficiency: Fuel consumption is noticeably higher.

In pure theory, reflex is actually not the ideal solution for reaching higher speeds. Ideally, a symmetrical airfoil with a Moment as close as possible to zero would offer the highest possible airspeed. In comparison to a symmetrical airfoil reflex is actually slower. Reflex is the solution that fits the needs of our soft canopies when flying at low AOA (high speeds).

Speed is the most popular measure or performance in PPG, and Reflex is the technology currently ‘in fashion’.

There are other answers to increase speed, for example reducing the surface area of the wing dramatically. But like everything else, this must be paid for with higher take off and landing speed, and poor passive safety, which makes it a less than ideal solution for most pilots.

In the future, PPG designers will continue to focus on reduction of energy consumption and performance will center more on glide and sink (efficiency) as well as speed. This is where the limits of reflex become painfully apparent and designer’s skills will be tested when trying to achieve this delicate balance.

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Not sure there is much to add to the Ozone quote or what you will find on other threads on here.

For learning or flying in calm air you will have just as much fun on a non reflex wing and may find it easier to launch & land. Reflex is useful in stronger winds and covering longer distances with other people on fast wings. Lots of wings are standard with trimmers closed, and only become reflex when trimmers are released - so the best of both worlds and 2 wings in one. :)

Best thing is to do some training on school kit and make a purchase decision when you've got a bit of experience.

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